package org.hl7.fhir.r5.conformance.profile;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import lombok.extern.slf4j.Slf4j;
import org.hl7.fhir.exceptions.DefinitionException;
import org.hl7.fhir.exceptions.FHIRException;
import org.hl7.fhir.r5.conformance.ElementRedirection;
import org.hl7.fhir.r5.model.Base;
import org.hl7.fhir.r5.model.CanonicalType;
import org.hl7.fhir.r5.model.ElementDefinition;
import org.hl7.fhir.r5.model.ElementDefinition.DiscriminatorType;
import org.hl7.fhir.r5.model.ElementDefinition.ElementDefinitionSlicingComponent;
import org.hl7.fhir.r5.model.ElementDefinition.SlicingRules;
import org.hl7.fhir.r5.model.ElementDefinition.TypeRefComponent;
import org.hl7.fhir.r5.model.StructureDefinition;
import org.hl7.fhir.r5.model.StructureDefinition.StructureDefinitionKind;
import org.hl7.fhir.r5.model.StructureDefinition.StructureDefinitionSnapshotComponent;
import org.hl7.fhir.r5.utils.ToolingExtensions;
import org.hl7.fhir.r5.utils.UserDataNames;
import org.hl7.fhir.utilities.CommaSeparatedStringBuilder;
import org.hl7.fhir.utilities.MarkedToMoveToAdjunctPackage;
import org.hl7.fhir.utilities.Utilities;
import org.hl7.fhir.utilities.VersionUtilities;
import org.hl7.fhir.utilities.i18n.I18nConstants;
import org.hl7.fhir.utilities.validation.ValidationMessage;
import org.hl7.fhir.utilities.validation.ValidationMessage.IssueSeverity;
import org.hl7.fhir.utilities.validation.ValidationMessage.Source;

import lombok.AccessLevel;
import lombok.AllArgsConstructor;
import lombok.Getter;
import lombok.With;

@AllArgsConstructor(access = AccessLevel.PRIVATE)
@MarkedToMoveToAdjunctPackage
@Slf4j
public class ProfilePathProcessor {

  /**
   * The code contains a fix for an issue that was reported where slices that are being defined don't inherit 
   * properties from the slice. This is a reference to this text in the profiling documentation:
   * 
   * > That is, the first element in a slice group must contain a slicing property that defines the discriminator 
   * > for all members of the group. It also contains the unconstrained definition of the element that is sliced, 
   * > potentially including children of the unconstrained element, if there are any
   * 
   * APPLY_PROPERTIES_FROM_SLICER = true will mean that this code works that way (though there is some interpretational questions 
   * around the meaning of this text)
   * 
   * But the community decided not to apply this fix in practice, and to change(/clarify) the text above, so the 
   * fix is not enabled. See discussion at 
   * https://chat.fhir.org/#narrow/channel/179252-IG-creation/topic/Slices.20not.20inheriting.20preferred.20bindings.20from.20root
   * 
   */
  private static final boolean APPLY_PROPERTIES_FROM_SLICER = false;
  

  @Getter
  protected final ProfileUtilities profileUtilities;

  @Getter
  @With
  final String debugIndent;

  @Getter
  @With
  final StructureDefinition.StructureDefinitionSnapshotComponent result;

  @Getter
  @With
  final StructureDefinition.StructureDefinitionDifferentialComponent differential;

  @Getter
  @With
  final int baseLimit;

  @Getter
  @With
  final int diffLimit;

  @Getter
  @With
  final String url;

  @Getter
  @With
  final String webUrl;

  @Getter
  @With
  final String profileName;

  @Getter
  @With
  final String contextPathSource;

  @Getter
  @With
  final String contextPathTarget;

  @Getter
  @With
  final boolean trimDifferential;

  @Getter
  @With
  final List<ElementRedirection> redirector;

  @Getter
  @With
  final StructureDefinition sourceStructureDefinition;

  @Getter
  @With
  final StructureDefinition derived;

  @Getter
  @With
  final PathSlicingParams slicing;


  private ProfilePathProcessor(
    ProfileUtilities profileUtilities
  ) {
    this.profileUtilities = profileUtilities;
    debugIndent = "";
    this.result = null;
    this.differential = null;
    this.baseLimit = 0;
    this.diffLimit = 0;
    this.url = null;
    this.webUrl = null;
    this.profileName = null;
    this.contextPathSource = null;
    this.contextPathTarget = null;
    this.trimDifferential = false;
    this.redirector = null;
    this.sourceStructureDefinition = null;
    this.derived = null;
    this.slicing = null;
  }

  public static ProfilePathProcessor getInstance( ProfileUtilities profileUtilities) {
    return new ProfilePathProcessor(profileUtilities);
  }

  public ProfilePathProcessor incrementDebugIndent() {
    return this.withDebugIndent(this.debugIndent + " ".repeat(2));
  }


  protected static void processPaths(ProfileUtilities profileUtilities, StructureDefinition base, StructureDefinition derived, String url, String webUrl, StructureDefinition.StructureDefinitionDifferentialComponent differential, StructureDefinition.StructureDefinitionSnapshotComponent baseSnapshot, MappingAssistant mapHelper) {

    ProfilePathProcessorState cursors = new ProfilePathProcessorState(
      base,
      baseSnapshot,
      0,
      0,
      base.getUrl(),
      null);


       getInstance(profileUtilities)
        .withResult(derived.getSnapshot())
        .withDifferential(differential)
        .withBaseLimit(baseSnapshot.getElement().size() - 1)
        .withDiffLimit(differential.hasElement() ? differential.getElement().size() - 1 : -1)
        .withUrl(url)
        .withWebUrl(webUrl)
        .withProfileName(derived.present())
        .withContextPathSource(null)
        .withContextPathTarget(null)
        .withTrimDifferential(false)
        .withRedirector(new ArrayList<ElementRedirection>())
        .withSourceStructureDefinition(base)
        .withDerived(derived)
        .withSlicing(new PathSlicingParams())
        .processPaths(cursors, mapHelper, null);

  }

  /**
   * @param cursors
   * @param mapHelper 
   * @throws DefinitionException, FHIRException
   * @throws Exception
   */
  private ElementDefinition processPaths(final ProfilePathProcessorState cursors, MappingAssistant mapHelper, ElementDefinition slicerElement) throws FHIRException {
    debugProcessPathsEntry(cursors);
    ElementDefinition res = null;
    List<TypeSlice> typeList = new ArrayList<>();
    boolean first = true;

    // just repeat processing entries until we run out of our allowed scope (1st entry, the allowed scope is all the entries)
    while (cursors.baseCursor <= getBaseLimit() && cursors.baseCursor < cursors.base.getElement().size()) {
      // get the current focus of the base, and decide what to do
      ElementDefinition currentBase = cursors.base.getElement().get(cursors.baseCursor);
      String currentBasePath = profileUtilities.fixedPathSource(getContextPathSource(), currentBase.getPath(), getRedirector());
      
      debugProcessPathsIteration(cursors, currentBasePath);
      checkDiffAssignedAndCursor(cursors);
      List<ElementDefinition> diffMatches = profileUtilities.getDiffMatches(getDifferential(), currentBasePath, cursors.diffCursor, getDiffLimit(), getProfileName()); // get a list of matching elements in scope

      // in the simple case, source is not sliced.
      if (!currentBase.hasSlicing() || currentBasePath.equals(getSlicing().getPath()))
      {
        ElementDefinition currentRes = processSimplePath(currentBase, currentBasePath, diffMatches, typeList, cursors, mapHelper, first ? slicerElement : null);
        if (res == null) {
          res = currentRes;
        }
      }
      else {
        processPathWithSlicedBase(currentBase, currentBasePath, diffMatches, typeList, cursors, mapHelper);
      }
      first = false;
    }

    int i = 0;
    for (ElementDefinition e : getResult().getElement()) {
      i++;
      if (e.hasMinElement() && e.getMinElement().getValue() == null)
        throw new Error(profileUtilities.getContext().formatMessage(I18nConstants.NULL_MIN));
    }
    return res;
  }

  private void checkDiffAssignedAndCursor(ProfilePathProcessorState cursors) {
//    int i = 0;
//    List<ElementDefinition> list = getDifferential().getElement();
//    for (ElementDefinition ed : list) {
//      boolean assigned = ed.hasUserData(UserDataNames.UD_DERIVATION_POINTER);
//      if (i < cursors.diffCursor) {
//        if (!assigned) {
//          throw new Error("what?");
//        }
//      } else if (i > cursors.diffCursor) {
//        if (assigned) {
//          throw new Error("what!?");
//        }
//      }
//      i++;
//    }
    
  }

  private void debugProcessPathsIteration(ProfilePathProcessorState cursors, String currentBasePath) {
    if (profileUtilities.isDebug()) {
      log.debug(getDebugIndent() + " - " + currentBasePath + ": "+
          "base = " + cursors.baseCursor + " (" + profileUtilities.descED(cursors.base.getElement(), cursors.baseCursor) + ") to " + getBaseLimit() +" (" + profileUtilities.descED(cursors.base.getElement(), getBaseLimit()) + "), "+
          "diff = " + cursors.diffCursor + " (" + profileUtilities.descED(getDifferential().getElement(), cursors.diffCursor) + ") to " + getDiffLimit() + " (" + profileUtilities.descED(getDifferential().getElement(), getDiffLimit()) + ") " +
        "(slicingDone = " + getSlicing().isDone() + ") (diffpath= " + (getDifferential().getElement().size() > cursors.diffCursor ? getDifferential().getElement().get(cursors.diffCursor).getPath() : "n/a") + ")");
      String path = cursors.diffCursor >=0 && cursors.diffCursor < getDifferential().getElement().size() ? getDifferential().getElement().get(cursors.diffCursor).present() : null;
    }

  }

  private void debugProcessPathsEntry(ProfilePathProcessorState cursors) {
    if (profileUtilities.isDebug()) {
      log.debug(getDebugIndent() + "PP @ " + cursors.resultPathBase + " / " + getContextPathSource() + " : base = " + cursors.baseCursor + " to " + getBaseLimit() + ", diff = " + cursors.diffCursor + " to " + getDiffLimit() + " (slicing = " + getSlicing().isDone() + ", k " + (getRedirector() == null ? "null" : getRedirector().toString()) + ")");
    }
  }


  public ElementDefinition processSimplePath(
    final ElementDefinition currentBase,
    final String currentBasePath,
    final List<ElementDefinition> diffMatches,
    final List<TypeSlice> typeList,
    final ProfilePathProcessorState cursors, MappingAssistant mapHelper, ElementDefinition slicerElement) throws FHIRException {
    ElementDefinition res = null;

      // the differential doesn't say anything about this item
      // so we just copy it in
      if (diffMatches.isEmpty())
        processSimplePathWithEmptyDiffMatches(currentBase, currentBasePath, diffMatches, cursors, mapHelper);
        // one matching element in the differential
      else if (oneMatchingElementInDifferential(getSlicing().isDone(), currentBasePath, diffMatches))
        res = processSimplePathWithOneMatchingElementInDifferential(currentBase, currentBasePath, diffMatches, cursors, mapHelper, slicerElement);
      else if (profileUtilities.diffsConstrainTypes(diffMatches, currentBasePath, typeList))
        processSimplePathWhereDiffsConstrainTypes(currentBasePath, diffMatches, typeList, cursors, mapHelper);
      else
        processSimplePathDefault(currentBase, currentBasePath, diffMatches, cursors, mapHelper);


    return res;
  }

  private void processSimplePathDefault(ElementDefinition currentBase, String currentBasePath, List<ElementDefinition> diffMatches, ProfilePathProcessorState cursors, MappingAssistant mapHelper) {
    // ok, the differential slices the item. Let's check our pre-conditions to ensure that this is correct
    if (!profileUtilities.unbounded(currentBase) && !(profileUtilities.isSlicedToOneOnly(diffMatches.get(0)) || profileUtilities.isTypeSlicing(diffMatches.get(0))))
      // you can only slice an element that doesn't repeat if the sum total of your slices is limited to 1
      // (but you might do that in order to split up constraints by type)
      throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ATTEMPT_TO_A_SLICE_AN_ELEMENT_THAT_DOES_NOT_REPEAT__FROM__IN_, currentBase.getPath(), currentBase.getPath(), cursors.contextName, diffMatches.get(0).getId(), profileUtilities.sliceNames(diffMatches)));
    if (!diffMatches.get(0).hasSlicing() && !profileUtilities.isExtension(currentBase)) // well, the diff has set up a slice, but hasn't defined it. this is an error
      throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.DIFFERENTIAL_DOES_NOT_HAVE_A_SLICE__B_OF_____IN_PROFILE_, currentBase.getPath(), cursors.baseCursor, getBaseLimit(), cursors.diffCursor, getDiffLimit(), getUrl(), currentBasePath));

    // well, if it passed those preconditions then we slice the dest.
    int start = 0;
    int newBaseLimit = profileUtilities.findEndOfElement(cursors.base, cursors.baseCursor);
//          if (diffMatches.size() > 1 && diffMatches.get(0).hasSlicing() && differential.getElement().indexOf(diffMatches.get(1)) > differential.getElement().indexOf(diffMatches.get(0))+1) {
    ElementDefinition slicerElement;
    StructureDefinition slicerSource;
    if (diffMatches.size() > 1 && diffMatches.get(0).hasSlicing() && (newBaseLimit > cursors.baseCursor || (diffMatches.size() > 1 ? getDifferential().getElement().indexOf(diffMatches.get(1)) : -1) > (diffMatches.size() > 0 ? getDifferential().getElement().indexOf(diffMatches.get(0)) : -1) + 1)) { // there's a default set before the slices
      int newDiffCursor = getDifferential().getElement().indexOf(diffMatches.get(0));
      int newDiffLimit = profileUtilities.findEndOfElement(getDifferential(), newDiffCursor);
      ProfilePathProcessorState ncursors = new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor, newDiffCursor, cursors.contextName, cursors.resultPathBase);
      ElementDefinition e = this
          .incrementDebugIndent()
          .withBaseLimit(newBaseLimit)
          .withDiffLimit(newDiffLimit)
          .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, 0)).withSlicing(new PathSlicingParams(true, null, null))
          .processPaths(ncursors, mapHelper, null);
      if (e == null)
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.DID_NOT_FIND_SINGLE_SLICE_, diffMatches.get(0).getPath()));
      e.setSlicing(diffMatches.get(0).getSlicing());
      slicerElement = setPath(e, currentBasePath);
      start++;
    } else {
      // we're just going to accept the differential slicing at face value
      ElementDefinition outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), currentBase.copy(), true);
      outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
      profileUtilities.updateFromBase(outcome, currentBase, getSourceStructureDefinition().getUrl());

      if (!diffMatches.get(0).hasSlicing()) {
        outcome.setSlicing(profileUtilities.makeExtensionSlicing());
        outcome.setUserData(UserDataNames.SNAPSHOT_auto_added_slicing, true);
      } else {
        outcome.setSlicing(diffMatches.get(0).getSlicing().copy());
        for (int i = 1; i < diffMatches.size(); i++) {
          if (diffMatches.get(i).hasSlicing()) {
            if (!slicingMatches(diffMatches.get(0).getSlicing(), diffMatches.get(i).getSlicing())) {
              profileUtilities.getMessages().add(new ValidationMessage(Source.InstanceValidator, ValidationMessage.IssueType.BUSINESSRULE, diffMatches.get(0).getPath(), 
                  profileUtilities.getContext().formatMessage(I18nConstants.ATTEMPT_TO_CHANGE_SLICING, diffMatches.get(0).getId(), slicingSummary(diffMatches.get(0).getSlicing()), diffMatches.get(i).getId(), slicingSummary(diffMatches.get(i).getSlicing())),
                      ValidationMessage.IssueSeverity.ERROR));
            } else {
              profileUtilities.getMessages().add(new ValidationMessage(Source.InstanceValidator, ValidationMessage.IssueType.BUSINESSRULE, diffMatches.get(0).getPath(), 
                  profileUtilities.getContext().formatMessage(I18nConstants.ATTEMPT_TO_CHANGE_SLICING, diffMatches.get(0).getId(), diffMatches.get(i).getId()),
                      IssueSeverity.INFORMATION));
              
            }
          }
        }
      }
      if (cursors.resultPathBase != null) {
        if (!outcome.getPath().startsWith(cursors.resultPathBase))
          throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ADDING_WRONG_PATH));
      }
      debugCheck(outcome);
      addToResult(outcome);
      slicerElement = setPath(outcome, currentBasePath);

      // differential - if the first one in the list has a name, we'll process it. Else we'll treat it as the base definition of the slice.
      if (!diffMatches.get(0).hasSliceName()) {
        profileUtilities.updateFromDefinition(outcome, diffMatches.get(0), getProfileName(), isTrimDifferential(), getUrl(),getSourceStructureDefinition(), getDerived(), diffPath(diffMatches.get(0)), mapHelper, false);
        if (!outcome.hasContentReference() && !outcome.hasType() && outcome.getPath().contains(".")) {
          throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.NOT_DONE_YET));
        }
        if (profileUtilities.hasInnerDiffMatches(getDifferential(), currentBasePath, cursors.diffCursor, getDiffLimit(), cursors.base.getElement(), false)) {
          if (baseHasChildren(cursors.base, currentBase)) { // not a new type here
            if (cursors.diffCursor == 0) {
              throw new DefinitionException("Error: The profile has slicing at the root ('"+currentBase.getPath()+"'), which is illegal");
            } else {
              throw new Error("This situation is not yet handled (constrain slicing to 1..1 and fix base slice for inline structure - please report issue to grahame@fhir.org along with a test case that reproduces this error (@ " + currentBasePath + " | " + currentBase.getPath() + ")");
            }
          } else {
            StructureDefinition dt = profileUtilities.getTypeForElement(getDifferential(), cursors.diffCursor, getProfileName(), diffMatches, outcome, getWebUrl(), getDerived());
            cursors.contextName = dt.getUrl();
            cursors.diffCursor++;
            start = cursors.diffCursor;
            while (getDifferential().getElement().size() > cursors.diffCursor && profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), currentBasePath + "."))
              cursors.diffCursor++;
            cursors.diffCursor--;

              this.incrementDebugIndent()
                .withBaseLimit( dt.getSnapshot().getElement().size() - 1)
                .withDiffLimit(cursors.diffCursor)
                .withWebUrl(profileUtilities.getWebUrl(dt, getWebUrl()))
                .withContextPathSource(currentBasePath)
                .withContextPathTarget(outcome.getPath()).withSlicing(new PathSlicingParams())     /* starting again on the data type, but skip the root */
            . processPaths(new ProfilePathProcessorState(dt, dt.getSnapshot(), 1 /* starting again on the data type, but skip the root */, start,
                cursors.contextName, cursors.resultPathBase), mapHelper, slicerElement);
          }
        } else {
          if (currentBase.hasContentReference() && !baseHasChildren(cursors.base, currentBase)) {
            // we have to dump the content of the redirect type inline here at this point.
            int bstart = resolveContentReference(cursors.base, currentBase);
            int bend = profileUtilities.findEndOfElementNoSlices(cursors.base, bstart);
            for (int i  = bstart + 1; i <= bend; i++) {
              ElementDefinition src = cursors.base.getElement().get(i);
              outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), src.copy(), true);
              outcome.setId(null);
              String path = outcome.getPath();
              path = fixForRedirect(path, currentBase.getIdOrPath(), currentBase.getContentReference().substring(currentBase.getContentReference().indexOf("#")+1));
              outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), path, getRedirector(), getContextPathSource()));
              profileUtilities.updateFromBase(outcome, src, getSourceStructureDefinition().getUrl());
              profileUtilities.markExtensions(outcome, false, cursors.baseSource);
              debugCheck(outcome);
              addToResult(outcome);
            }           
          }
        }
        start++;
        // result.getElement().remove(result.getElement().size()-1);
      } else
        profileUtilities.checkExtensionDoco(outcome);
    }
    // now, for each entry in the diff matches, we're going to process the base item
    // our processing scope for base is all the children of the current path
    int newDiffCursor = cursors.diffCursor;
    int newDiffLimit = cursors.diffCursor;
    for (int i = start; i < diffMatches.size(); i++) {
      // our processing scope for the differential is the item in the list, and all the items before the next one in the list
      newDiffCursor = getDifferential().getElement().indexOf(diffMatches.get(i));
      newDiffLimit = profileUtilities.findEndOfElement(getDifferential(), newDiffCursor);

      // now we process the base scope repeatedly for each instance of the item in the differential list

      ProfilePathProcessorState ncursors = new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor, newDiffCursor, cursors.contextName, cursors.resultPathBase);
      this.incrementDebugIndent()
          .withBaseLimit(newBaseLimit)
          .withDiffLimit(newDiffLimit)
          .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, i))
          .withSlicing(new PathSlicingParams(true, slicerElement, null))
          .processPaths(ncursors, mapHelper, slicerElement);
    }
    // ok, done with that - next in the base list
    cursors.baseCursor = newBaseLimit + 1;
    cursors.diffCursor = newDiffLimit + 1;
  }

  private ElementDefinition setPath(ElementDefinition ed, String path) {
    ed.setId(null);
    return ed;
  }

  private String fixForRedirect(String path, String rootPath, String redirect) {
    return path.replace(redirect, rootPath);
  }

  private int resolveContentReference(StructureDefinitionSnapshotComponent base, ElementDefinition currentBase) {
    String path = currentBase.getContentReference().substring(currentBase.getContentReference().indexOf("#")+1);

    // work backwards and find the nearest case
    int res = base.getElement().indexOf(currentBase) - 1;    
    while (res >= 0) {
      ElementDefinition ed = base.getElement().get(res);
      if (path.equals(ed.getPath())) {
        return res;
      }
      res--;
    }
    return -1;
  }

  private String diffPath(ElementDefinition ed) {
    return "StructureDefinition.differential.element["+differential.getElement().indexOf(ed)+"]"; 
  }

  private String slicingSummary(ElementDefinitionSlicingComponent s) {    
    return s.toString();
  }

  private boolean slicingMatches(ElementDefinitionSlicingComponent s1, ElementDefinitionSlicingComponent s2) {
    if ((!s1.hasOrdered() && s2.hasOrdered()) || (s1.hasOrdered() && s2.hasOrdered() && !Base.compareDeep(s1.getOrderedElement(), s2.getOrderedElement(), false))) { 
      return false;
    }
    if ((!s1.hasRules() && s2.hasRules()) || (s1.hasRules() && s2.hasRules() && !Base.compareDeep(s1.getRulesElement(), s2.getRulesElement(), false))) { 
      return false;
    }
    return Base.compareDeep(s1.getDiscriminator(), s2.getDiscriminator(), false);
  }

  private void processSimplePathWhereDiffsConstrainTypes(String currentBasePath, List<ElementDefinition> diffMatches, List<TypeSlice> typeList, ProfilePathProcessorState cursors, MappingAssistant mapHelper) {
    int start = 0;
    int newBaseLimit = profileUtilities.findEndOfElement(cursors.base, cursors.baseCursor);
    int newDiffCursor = getDifferential().getElement().indexOf(diffMatches.get(0));
    ElementDefinition elementToRemove = null;
    boolean shortCut = !typeList.isEmpty() && typeList.get(0).getType() != null;
    // we come here whether they are sliced in the diff, or whether the short cut is used.
    String path = diffMatches.get(0).getPath();
    if (shortCut) {
      // this is the short cut method, we've just dived in and specified a type slice.
      // in R3 (and unpatched R4, as a workaround right now...
      if (!VersionUtilities.isR4Plus(profileUtilities.getContext().getVersion()) || !profileUtilities.isNewSlicingProcessing()) { // newSlicingProcessing is a work around for editorial loop dependency
        // we insert a cloned element with the right types at the start of the diffMatches
        ElementDefinition ed = new ElementDefinition();
        ed.setPath(profileUtilities.determineTypeSlicePath(path, currentBasePath));
        for (TypeSlice ts : typeList)
          ed.addType().setCode(ts.getType());
        ed.setSlicing(new ElementDefinition.ElementDefinitionSlicingComponent());
        ed.getSlicing().addDiscriminator().setType(ElementDefinition.DiscriminatorType.TYPE).setPath("$this");
        ed.getSlicing().setRules(ElementDefinition.SlicingRules.CLOSED);
        ed.getSlicing().setOrdered(false);
        diffMatches.add(0, ed);
        getDifferential().getElement().add(newDiffCursor, ed);
        elementToRemove = ed;
      } else {
        // as of R4, this changed; if there's no slice, there's no constraint on the slice types, only one the type.
        // so the element we insert specifies no types (= all types) allowed in the base, not just the listed type.
        // see also discussion here: https://chat.fhir.org/#narrow/stream/179177-conformance/topic/Slicing.20a.20non-repeating.20element
        ElementDefinition ed = new ElementDefinition();
        ed.setPath(profileUtilities.determineTypeSlicePath(path, currentBasePath));
        ed.setSlicing(new ElementDefinition.ElementDefinitionSlicingComponent());
        ed.getSlicing().addDiscriminator().setType(ElementDefinition.DiscriminatorType.TYPE).setPath("$this");
        ed.getSlicing().setRules(ElementDefinition.SlicingRules.CLOSED);
        ed.getSlicing().setOrdered(false);
        diffMatches.add(0, ed);
        getDifferential().getElement().add(newDiffCursor, ed);
        elementToRemove = ed;
      }
    } else { // if it's not a short cut, then the path has to be correct
      String t1 = currentBasePath.substring(currentBasePath.lastIndexOf(".")+1);
      String t2 = path.substring(path.lastIndexOf(".")+1);
      if (!t1.equals(t2)) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ED_PATH_WRONG_TYPE_MATCH, path.replace(t2, t1), path));
      }
      
    }
    int newDiffLimit = profileUtilities.findEndOfElement(getDifferential(), newDiffCursor);
    // the first element is setting up the slicing

    if (diffMatches.get(0).getSlicing().hasOrdered()) {
      if (diffMatches.get(0).getSlicing().getOrdered()) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__IN__TYPE_SLICING_WITH_SLICINGORDERED__TRUE, currentBasePath, getUrl()));
      }
    }
    if (diffMatches.get(0).getSlicing().hasDiscriminator()) {
      if (diffMatches.get(0).getSlicing().getDiscriminator().size() != 1) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__IN__TYPE_SLICING_WITH_SLICINGDISCRIMINATORCOUNT__1, currentBasePath, getUrl()));
      }
      if (diffMatches.get(0).getSlicing().getDiscriminatorFirstRep().getType() != ElementDefinition.DiscriminatorType.TYPE) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__IN__TYPE_SLICING_WITH_SLICINGDISCRIMINATORTYPE__TYPE, currentBasePath, getUrl()));
      }
      if (!"$this".equals(diffMatches.get(0).getSlicing().getDiscriminatorFirstRep().getPath())) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__IN__TYPE_SLICING_WITH_SLICINGDISCRIMINATORPATH__THIS, currentBasePath, getUrl()));
      }
    }
    // check the slice names too while we're at it...
    for (TypeSlice ts : typeList) {
      if (ts.getType() != null) {
        String tn = profileUtilities.rootName(currentBasePath) + Utilities.capitalize(ts.getType());
        if (!ts.defn.hasSliceName()) {
          ts.defn.setSliceName(tn);
        } else if (!ts.defn.getSliceName().equals(tn)) {
          if (profileUtilities.isAutoFixSliceNames()) {
            ts.defn.setSliceName(tn);
          } else {
            throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__SLICE_NAME_MUST_BE__BUT_IS_, (!Utilities.noString(getContextPathSource()) ? getContextPathSource() : currentBasePath), tn, ts.defn.getSliceName()));
          }
        }
        if (!ts.defn.hasType()) {
          ts.defn.addType().setCode(ts.type);
        } else if (ts.defn.getType().size() > 1) {
          throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__SLICE_FOR_TYPE__HAS_MORE_THAN_ONE_TYPE_, (!Utilities.noString(getContextPathSource()) ? getContextPathSource() : currentBasePath), tn, ts.defn.typeSummary()));
        } else if (!ts.defn.getType().get(0).getCode().equals(ts.type)) {
          throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__SLICE_FOR_TYPE__HAS_WRONG_TYPE_, (!Utilities.noString(getContextPathSource()) ? getContextPathSource() : currentBasePath), tn, ts.defn.typeSummary()));
        }
      }
    }

    // ok passed the checks.
    // copy the root diff, and then process any children it has
    ProfilePathProcessorState ncursors = new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor, newDiffCursor, cursors.contextName, cursors.resultPathBase);
    ElementDefinition elementDefinition =
      this
        .incrementDebugIndent()
        .withBaseLimit(newBaseLimit)
        .withDiffLimit(newDiffLimit)
        .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, 0))
        .withSlicing(new PathSlicingParams(true, null, null))
        .processPaths(ncursors, mapHelper, null);
    if (elementDefinition == null)
      throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.DID_NOT_FIND_TYPE_ROOT_, path));
    // now set up slicing on the e (cause it was wiped by what we called.
    elementDefinition.setSlicing(new ElementDefinition.ElementDefinitionSlicingComponent());
    elementDefinition.getSlicing().addDiscriminator().setType(ElementDefinition.DiscriminatorType.TYPE).setPath("$this");
    elementDefinition.getSlicing().setRules(ElementDefinition.SlicingRules.CLOSED); // type slicing is always closed; the differential might call it open, but that just means it's not constraining the slices it doesn't mention
    elementDefinition.getSlicing().setOrdered(false);
    ElementDefinition slicerElement = elementDefinition.copy();
    if (elementDefinition.getType().size() > 1) {
      slicerElement.setMin(0);
    }
    
    start++;

    String fixedType = null;
    // now process the siblings, which should each be type constrained - and may also have their own children
    // now we process the base scope repeatedly for each instance of the item in the differential list
    for (int i = start; i < diffMatches.size(); i++) {
      // our processing scope for the differential is the item in the list, and all the items before the next one in the list
      if (diffMatches.get(i).getMin() > 0) {
        if (diffMatches.size() > i + 1) {
          throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.INVALID_SLICING__THERE_IS_MORE_THAN_ONE_TYPE_SLICE_AT__BUT_ONE_OF_THEM__HAS_MIN__1_SO_THE_OTHER_SLICES_CANNOT_EXIST, diffMatches.get(i).getPath(), diffMatches.get(i).getSliceName()));
        } else {
          elementDefinition.setMin(1);
        }
        fixedType = profileUtilities.determineFixedType(diffMatches, fixedType, i);
      }
      newDiffCursor = getDifferential().getElement().indexOf(diffMatches.get(i));
      newDiffLimit = profileUtilities.findEndOfElement(getDifferential(), newDiffCursor);
      ProfilePathProcessorState ncursors2 = new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor, newDiffCursor, cursors.contextName, cursors.resultPathBase);
      ElementDefinition typeSliceElement =
        this
         .incrementDebugIndent()
         .withBaseLimit(newBaseLimit)
         .withDiffLimit(newDiffLimit)
         .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, i))
         .withSlicing(new PathSlicingParams(true, elementDefinition, null))
         .processPaths(ncursors2, mapHelper, slicerElement);
      if (typeList.size() > start + 1) {
        typeSliceElement.setMin(0);
      }
    }
    if (elementToRemove != null) {
      getDifferential().getElement().remove(elementToRemove);
      newDiffLimit--;
    }
    if (fixedType != null) {
      for (Iterator<ElementDefinition.TypeRefComponent> iter = elementDefinition.getType().iterator(); iter.hasNext(); ) {
        ElementDefinition.TypeRefComponent tr = iter.next();
        if (!tr.getCode().equals(fixedType)) {
          iter.remove();
        }
      }
    }
    if (!"0".equals(elementDefinition.getMax())) {
      // check that there's a slice for each allowed types
      Set<String> allowedTypes = profileUtilities.getListOfTypes(elementDefinition);
      for (TypeSlice t : typeList) {
        if (t.type != null) {
          allowedTypes.remove(t.type);
        } else if (t.getDefn().hasSliceName() && t.getDefn().getType().size() == 1) {
          allowedTypes.remove(t.getDefn().getType().get(0).getCode());
        }
      }
      if (!allowedTypes.isEmpty()) {
        if (currentBasePath.contains("xtension.value") && shortCut) {
          for (Iterator<ElementDefinition.TypeRefComponent> iter = elementDefinition.getType().iterator(); iter.hasNext(); ) {
            ElementDefinition.TypeRefComponent tr = iter.next();
            if (allowedTypes.contains(tr.getCode())) {
              iter.remove();
            }
          }
        } else {
          elementDefinition.getSlicing().setRules(ElementDefinition.SlicingRules.OPEN);
        }
      }
    }
    // ok, done with that - next in the base list
    cursors.baseCursor = newBaseLimit + 1;
    cursors.diffCursor = newDiffLimit + 1;
  }

  private ElementDefinition processSimplePathWithOneMatchingElementInDifferential(ElementDefinition currentBase, String currentBasePath, List<ElementDefinition> diffMatches, ProfilePathProcessorState cursors, MappingAssistant mapHelper, ElementDefinition slicerElement) {
    boolean fromSlicer = slicerElement != null;
    ElementDefinition res;
    ElementDefinition template = null;
    StructureDefinition templateSD = null;
    if (diffMatches.get(0).hasType() && "Reference".equals(diffMatches.get(0).getType().get(0).getWorkingCode()) && !profileUtilities.isValidType(diffMatches.get(0).getType().get(0), currentBase)) {
      if (!ProfileUtilities.isSuppressIgnorableExceptions()) {
        throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.VALIDATION_VAL_ILLEGAL_TYPE_CONSTRAINT, getUrl(), diffMatches.get(0).getPath(), diffMatches.get(0).getType().get(0), currentBase.typeSummary()));
      }
    }
    String id = diffMatches.get(0).getId();
    String lid = profileUtilities.tail(id);
    if (lid.contains("/")) {
      // the template comes from the snapshot of the base
      profileUtilities.generateIds(getResult().getElement(), getUrl(), getSourceStructureDefinition().getType(), getSourceStructureDefinition());
      String baseId = id.substring(0, id.length() - lid.length()) + lid.substring(0, lid.indexOf("/")); // this is wrong if there's more than one reslice (todo: one thing at a time)
      template = profileUtilities.getById(getResult().getElement(), baseId);
      templateSD = getSourceStructureDefinition();
    } else if (diffMatches.get(0).hasType()
      && diffMatches.get(0).getType().size() == 1
      && diffMatches.get(0).getType().get(0).hasProfile()
      && !"Reference".equals(diffMatches.get(0).getType().get(0).getWorkingCode())
      && !(currentBase.getType().get(0).hasProfile() && currentBase.getType().get(0).getProfile().get(0).primitiveValue().equals(diffMatches.get(0).getType().get(0).getProfile().get(0).primitiveValue()))) {
      CanonicalType firstTypeProfile = diffMatches.get(0).getType().get(0).getProfile().get(0);
      StructureDefinition firstTypeStructureDefinition = profileUtilities.getContext().fetchResource(StructureDefinition.class, firstTypeProfile.getValue());
      if (firstTypeStructureDefinition == null && profileUtilities.getXver() != null && profileUtilities.getXver().matchingUrl(firstTypeProfile.getValue())) {
        switch (profileUtilities.getXver().status(firstTypeProfile.getValue())) {
          case BadVersion:
            throw new FHIRException("Reference to invalid version in extension url " + firstTypeProfile.getValue());
          case Invalid:
            throw new FHIRException("Reference to invalid extension " + firstTypeProfile.getValue());
          case Unknown:
            throw new FHIRException("Reference to unknown extension " + firstTypeProfile.getValue());
          case Valid:
            firstTypeStructureDefinition = profileUtilities.getXver().makeDefinition(firstTypeProfile.getValue());
            profileUtilities.generateSnapshot(profileUtilities.getContext().fetchTypeDefinition("Extension"), firstTypeStructureDefinition, firstTypeStructureDefinition.getUrl(), getWebUrl(), firstTypeStructureDefinition.getName());
        }
      }
      if (firstTypeStructureDefinition != null) {
        if (!firstTypeStructureDefinition.isGeneratingSnapshot()) { // can't do this check while generating
          if (!profileUtilities.isMatchingType(firstTypeStructureDefinition, diffMatches.get(0).getType(), firstTypeProfile.getExtensionString(ToolingExtensions.EXT_PROFILE_ELEMENT))) {
            throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.VALIDATION_VAL_PROFILE_WRONGTYPE2, firstTypeStructureDefinition.getUrl(), diffMatches.get(0).getPath(), firstTypeStructureDefinition.getType(), firstTypeProfile.getValue(), diffMatches.get(0).getType().get(0).getWorkingCode()));
          }
        }
        if (firstTypeStructureDefinition.isGeneratingSnapshot()) {
          // this is a special case, because we're only going to access the first element, and we can rely on the fact that it's already populated.
          // but we check anyway
          if (firstTypeStructureDefinition.getSnapshot().getElementFirstRep().isEmpty()) {
            throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ATTEMPT_TO_USE_A_SNAPSHOT_ON_PROFILE__AS__BEFORE_IT_IS_GENERATED, firstTypeStructureDefinition.getUrl(), "Source for first element"));
          }
        } else if (!firstTypeStructureDefinition.hasSnapshot()) {
          StructureDefinition sdb = profileUtilities.getContext().fetchResource(StructureDefinition.class, firstTypeStructureDefinition.getBaseDefinition());
          if (sdb == null)
            throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.UNABLE_TO_FIND_BASE__FOR_, firstTypeStructureDefinition.getBaseDefinition(), firstTypeStructureDefinition.getUrl()));
          profileUtilities.checkNotGenerating(sdb, "an extension base");
          profileUtilities.generateSnapshot(sdb, firstTypeStructureDefinition, firstTypeStructureDefinition.getUrl(), (sdb.hasWebPath()) ? Utilities.extractBaseUrl(sdb.getWebPath()) : getWebUrl(), firstTypeStructureDefinition.getName());
        }
        ElementDefinition src;
        StructureDefinition srcSD = null;;
        if (firstTypeProfile.hasExtension(ToolingExtensions.EXT_PROFILE_ELEMENT)) {
          src = null;          
          String eid = firstTypeProfile.getExtensionString(ToolingExtensions.EXT_PROFILE_ELEMENT);
          for (ElementDefinition t : firstTypeStructureDefinition.getSnapshot().getElement()) {
            if (eid.equals(t.getId())) {
              src = t;
              srcSD = firstTypeStructureDefinition;
            }
          }
          if (src == null) {
            if (firstTypeStructureDefinition.isGeneratingSnapshot()) {
              log.info("At this time the reference to "+eid+" cannot be handled - consult Grahame Grieve");
            } else if (Utilities.existsInList(currentBase.typeSummary(), "Extension", "Resource")) {
              throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.UNABLE_TO_FIND_ELEMENT__IN_, eid, firstTypeProfile.getValue()));
            }
          }
        } else {
          if (firstTypeStructureDefinition.getSnapshot().getElement().isEmpty()) {
            throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.SNAPSHOT_IS_EMPTY, firstTypeStructureDefinition.getVersionedUrl(), "Source for first element"));
          } else {
            src = firstTypeStructureDefinition.getSnapshot().getElement().get(0).copy();
            srcSD = firstTypeStructureDefinition;
            if (!src.getPath().contains(".") && firstTypeStructureDefinition.getKind() == StructureDefinitionKind.RESOURCE) {
              // we can't migrate the constraints in this case, because the sense of %resource changes when the root resource
              // is treated as an element. The validator will enforce the constraint
              src.getConstraint().clear(); // 
            }
          }
        }
        if (Utilities.existsInList(currentBase.typeSummary(), "Extension", "Resource")) {
          template = merge(src, slicerElement).setPath(currentBase.getPath());
          templateSD = srcSD;
          template.setSliceName(null);
          // temporary work around
          if (!"Extension".equals(diffMatches.get(0).getType().get(0).getCode())) {
            template.setMin(currentBase.getMin());
            template.setMax(currentBase.getMax());
          }
        } 
      }
    }
    if (template == null) {
      if (!APPLY_PROPERTIES_FROM_SLICER || slicerElement == null || currentBase.hasContentReference()) {
        template = currentBase.copy();
        templateSD = cursors.baseSource;
      } else {
        template = slicerElement.copy(); 
        templateSD = cursors.baseSource; 
        template.setPath(currentBase.getPath());
      }
    } else {
      // some of what's in currentBase overrides template
      template = profileUtilities.fillOutFromBase(template, APPLY_PROPERTIES_FROM_SLICER && slicerElement != null ? slicerElement : currentBase);
    }

    ElementDefinition outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), template, true);
    outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));

    res = outcome;
    profileUtilities.updateFromBase(outcome, currentBase, getSourceStructureDefinition().getUrl());
    if (diffMatches.get(0).hasSliceName()) {
      template = merge(currentBase, slicerElement);
      template = profileUtilities.updateURLs(getUrl(), getWebUrl(), template, true);
      template.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), template.getPath(), getRedirector(), getContextPathSource()));

      checkToSeeIfSlicingExists(diffMatches.get(0), template);
      outcome.setSliceName(diffMatches.get(0).getSliceName());
      if (!diffMatches.get(0).hasMin() && (diffMatches.size() > 1 || getSlicing().getElementDefinition()== null || getSlicing().getElementDefinition().getSlicing().getRules() != ElementDefinition.SlicingRules.CLOSED) && !currentBase.hasSliceName()) {
        if (!currentBasePath.endsWith("xtension.value[x]")) { // hack work around for problems with snapshots in official releases
          outcome.setMin(0);
        }
      }
    }
    profileUtilities.markExtensions(outcome, false, templateSD);
    profileUtilities.updateFromDefinition(outcome, diffMatches.get(0), getProfileName(), isTrimDifferential(), getUrl(), getSourceStructureDefinition(), getDerived(), diffPath(diffMatches.get(0)), mapHelper, fromSlicer);
//          if (outcome.getPath().endsWith("[x]") && outcome.getType().size() == 1 && !outcome.getType().get(0).getCode().equals("*") && !diffMatches.get(0).hasSlicing()) // if the base profile allows multiple types, but the profile only allows one, rename it
//            outcome.setPath(outcome.getPath().substring(0, outcome.getPath().length()-3)+Utilities.capitalize(outcome.getType().get(0).getCode()));
    if (!APPLY_PROPERTIES_FROM_SLICER && slicerElement != null && outcome.getMaxAsInt() > slicerElement.getMaxAsInt()) {
      outcome.setMaxElement(slicerElement.getMaxElement());
    }
    outcome.setSlicing(null);
    if (cursors.resultPathBase == null)
      cursors.resultPathBase = outcome.getPath();
    else if (!outcome.getPath().startsWith(cursors.resultPathBase))
      throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ADDING_WRONG_PATH));
    debugCheck(outcome);
    addToResult(outcome);
    cursors.baseCursor++;
    cursors.diffCursor = getDifferential().getElement().indexOf(diffMatches.get(0)) + 1;
    if (getDiffLimit() >= cursors.diffCursor && outcome.getPath().contains(".") && (profileUtilities.isDataType(outcome.getType()) || profileUtilities.isBaseResource(outcome.getType()) || outcome.hasContentReference())) {  // don't want to do this for the root, since that's base, and we're already processing it
      if (profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), diffMatches.get(0).getPath() + ".") && !profileUtilities.baseWalksInto(cursors.base.getElement(), cursors.baseCursor)) {
        if (outcome.getType().size() > 1) {
          if (outcome.getPath().endsWith("[x]") && !diffMatches.get(0).getPath().endsWith("[x]")) {
            String en = profileUtilities.tail(outcome.getPath());
            String tn = profileUtilities.tail(diffMatches.get(0).getPath());
            String t = tn.substring(en.length() - 3);
            if (profileUtilities.isPrimitive(Utilities.uncapitalize(t)))
              t = Utilities.uncapitalize(t);
            List<ElementDefinition.TypeRefComponent> ntr = profileUtilities.getByTypeName(outcome.getType(), t); // keep any additional information
            if (ntr.isEmpty())
              ntr.add(new ElementDefinition.TypeRefComponent().setCode(t));
            outcome.getType().clear();
            outcome.getType().addAll(ntr);
          }
          if (outcome.getType().size() > 1)
            for (ElementDefinition.TypeRefComponent t : outcome.getType()) {
              if (!t.getCode().equals("Reference")) {
                boolean nonExtension = false;
                for (ElementDefinition ed : diffMatches)
                  if (ed != diffMatches.get(0) && !ed.getPath().endsWith(".extension"))
                    nonExtension = true;
                if (nonExtension)
                  throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants._HAS_CHILDREN__AND_MULTIPLE_TYPES__IN_PROFILE_, diffMatches.get(0).getPath(), getDifferential().getElement().get(cursors.diffCursor).getPath(), profileUtilities.typeCode(outcome.getType()), getProfileName()));
              }
            }
        }
        int start = cursors.diffCursor;
        while (cursors.diffCursor <= getDiffLimit() && getDifferential().getElement().size() > cursors.diffCursor && profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), diffMatches.get(0).getPath() + "."))
          cursors.diffCursor++;
        if (outcome.hasContentReference()) {
          ProfileUtilities.ElementDefinitionResolution target = profileUtilities.getElementById(getSourceStructureDefinition(), cursors.base.getElement(), outcome.getContentReference());
          if (target == null)
            throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.UNABLE_TO_RESOLVE_REFERENCE_TO_, outcome.getContentReference()));
          profileUtilities.replaceFromContentReference(outcome, target.getElement());
          if (target.getSource() != getSourceStructureDefinition()) {
            cursors.base = target.getSource().getSnapshot();
            int newBaseCursor = cursors.base.getElement().indexOf(target.getElement()) + 1;
            int newBaseLimit = newBaseCursor;
            while (newBaseLimit < cursors.base.getElement().size() && cursors.base.getElement().get(newBaseLimit).getPath().startsWith(target.getElement().getPath() + "."))
              newBaseLimit++;

              ProfilePathProcessorState ncursors = new ProfilePathProcessorState(cursors.baseSource, cursors.base, newBaseCursor, start - 1, cursors.contextName, cursors.resultPathBase);
              this
                .incrementDebugIndent()
                .withBaseLimit(newBaseLimit - 1)
                .withDiffLimit(cursors.diffCursor - 1)
                .withContextPathSource(target.getElement().getPath())
                .withContextPathTarget(diffMatches.get(0).getPath()).withRedirector(profileUtilities.redirectorStack(getRedirector(), outcome, currentBasePath))
                .withSourceStructureDefinition(target.getSource())
                .withSlicing(new PathSlicingParams())
                .processPaths(ncursors, mapHelper, null);
          } else {
            final int newBaseCursor = cursors.base.getElement().indexOf(target.getElement()) + 1;
            int newBaseLimit = newBaseCursor;
            while (newBaseLimit < cursors.base.getElement().size() && cursors.base.getElement().get(newBaseLimit).getPath().startsWith(target.getElement().getPath() + "."))
              newBaseLimit++;

              ProfilePathProcessorState ncursors = new ProfilePathProcessorState(cursors.baseSource, cursors.base, newBaseCursor, start - 1, cursors.contextName, cursors.resultPathBase);
              this
                .incrementDebugIndent()
                .withBaseLimit(newBaseLimit - 1)
                .withDiffLimit(cursors.diffCursor - 1)
                .withContextPathSource(target.getElement().getPath())
                .withContextPathTarget(diffMatches.get(0).getPath())
                .withRedirector(profileUtilities.redirectorStack(getRedirector(), outcome, currentBasePath))
                .withSlicing(new PathSlicingParams())
                .processPaths(ncursors, mapHelper, null);
          }
        } else {
          StructureDefinition dt = null;
          TypeRefComponent tr = null;
          if (outcome.getType().size() > 1) {
            Set<String> types = new HashSet<>();
            for (TypeRefComponent t : outcome.getType()) {
              types.add(t.getCode());
            }
            if (types.size() == 1) {
              tr = outcome.getTypeFirstRep();
            } else {
               dt = profileUtilities.getProfileForDataType("Element");
            }
          } else {
            tr = outcome.getTypeFirstRep();
          }
          if (dt == null) {
            if (tr.getProfile().size() > 1) {
              dt  = profileUtilities.getContext().fetchTypeDefinition(tr.getWorkingCode());
            } else {
              dt  = profileUtilities.getProfileForDataType(tr, getWebUrl(), getDerived());
            }
          }
          if (dt == null)
            throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants._HAS_CHILDREN__FOR_TYPE__IN_PROFILE__BUT_CANT_FIND_TYPE, diffMatches.isEmpty() ? "??" : diffMatches.get(0).getPath(), getDifferential().getElement().get(cursors.diffCursor).getPath(), profileUtilities.typeCode(outcome.getType()), getProfileName()));
          cursors.contextName = dt.getUrl();

           this
              .incrementDebugIndent()
              .withBaseLimit(dt.getSnapshot().getElement().size() - 1)
              .withDiffLimit(cursors.diffCursor - 1)
              .withWebUrl( profileUtilities.getWebUrl(dt, getWebUrl()))
              .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, 0))
              .withContextPathSource(diffMatches.get(0).getPath()).withContextPathTarget(outcome.getPath()).withRedirector(new ArrayList<ElementRedirection>())
              .withSlicing(new PathSlicingParams()).  /* starting again on the data type, but skip the root */
            processPaths(new ProfilePathProcessorState(dt, dt.getSnapshot(), 1 /* starting again on the data type, but skip the root */, start,
              cursors.contextName, cursors.resultPathBase), mapHelper, null);
        }
      }
    }
    return res;
  }

  private ElementDefinition merge(ElementDefinition src, ElementDefinition slicer) {
    if (slicer != null && APPLY_PROPERTIES_FROM_SLICER) {
      ElementDefinition res = slicer.copy();
      if (src.getMin() > res.getMin()) {
        res.setMinElement(src.getMinElement().copy());        
      }      
      if (src.getMaxAsInt() < res.getMaxAsInt()) {
        res.setMaxElement(src.getMaxElement());
      }
      return res;
    } else {
      return src.copy();
    }
  }

  private void checkToSeeIfSlicingExists(ElementDefinition ed, ElementDefinition template) {
    List<ElementDefinition> ss = result.getElement();
    int i = ss.size() -1;
    ElementDefinition m = null;

    while (i >= 0) {
      ElementDefinition t = ss.get(i);
      if (pathsMatch(t.getPath(), ed.getPath())) {
        if (t.hasSlicing() || t.hasSliceName() || t.getPath().endsWith("[x]")) {
          m = t;
          break;
        }
      }
      if (t.getPath().length() < ed.getPath().length()) {
        break;
      }
      i--;
    }
    if (m == null) {
      if (template.getPath().endsWith(".extension")) {
        template.getSlicing().setRules(SlicingRules.OPEN);
        template.getSlicing().setOrdered(false);
        template.getSlicing().addDiscriminator().setType(DiscriminatorType.VALUE).setPath("url");
        addToResult(template);
      } else {
        log.error("checkToSeeIfSlicingExists: "+ed.getPath()+":"+ed.getSliceName()+" is not sliced");
      }
    }
  }

  private boolean pathsMatch(String path1, String path2) {
    String[] p1 = path1.split("\\.");
    String[] p2 = path2.split("\\.");
    if (p1.length != p2.length) {
      return false;
    }
    for (int i = 0; i < p1.length; i++) {
      String pp1 = p1[i];
      String pp2 = p2[i];
      if (!pp1.equals(pp2)) {
        if (pp1.endsWith("[x]")) {
          if (!pp2.startsWith(pp1.substring(0, pp1.length()-3))) {
            return false;
          }
        } else if (pp2.endsWith("[x]")) {
          if (!pp1.startsWith(pp2.substring(0, pp2.length()-3))) {
            return false;
          }
          
        } else {
          return false;
        }
      }
    }
    return true;
  }

  private int indexOfFirstNonChild(StructureDefinitionSnapshotComponent base, ElementDefinition currentBase, int i, int baseLimit) {
    return baseLimit+1;
  }

  private boolean baseHasChildren(StructureDefinitionSnapshotComponent base, ElementDefinition ed) {
    int index = base.getElement().indexOf(ed);
    if (index == -1 || index >= base.getElement().size()-1)
      return false;
    String p = base.getElement().get(index+1).getPath();
    return isChildOf(p, ed.getPath());
  }


  private boolean isChildOf(String sub, String focus) {
    if (focus.endsWith("[x]")) {
      focus = focus.substring(0, focus.length()-3);
      return sub.startsWith(focus);
    } else 
      return sub.startsWith(focus+".");
  }


  private void processSimplePathWithEmptyDiffMatches(ElementDefinition currentBase, String currentBasePath, List<ElementDefinition> diffMatches, ProfilePathProcessorState cursors, MappingAssistant mapHelper) {
    ElementDefinition outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), currentBase.copy(), true);
    outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
    profileUtilities.updateFromBase(outcome, currentBase, getSourceStructureDefinition().getUrl());
    profileUtilities.updateConstraintSources(outcome, getSourceStructureDefinition().getUrl());
    profileUtilities.checkExtensions(outcome);
    profileUtilities.markExtensions(outcome, false, cursors.baseSource);
    profileUtilities.updateFromObligationProfiles(outcome);
    profileUtilities.updateURLs(url, webUrl, outcome, true);
    profileUtilities.markDerived(outcome);
    if (cursors.resultPathBase == null)
      cursors.resultPathBase = outcome.getPath();
    else if (!outcome.getPath().startsWith(cursors.resultPathBase))
      throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ADDING_WRONG_PATH__OUTCOMEGETPATH___RESULTPATHBASE__, outcome.getPath(), cursors.resultPathBase));
    debugCheck(outcome);
    addToResult(outcome);
    if (profileUtilities.hasInnerDiffMatches(getDifferential(), currentBasePath, cursors.diffCursor, getDiffLimit(), cursors.base.getElement(), true)) {
      // well, the profile walks into this, so we need to as well
      // did we implicitly step into a new type?
      if (baseHasChildren(cursors.base, currentBase)) { // not a new type here

          this.incrementDebugIndent()
          .withSlicing(new PathSlicingParams())
          .processPaths(new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor + 1, cursors.diffCursor, cursors.contextName, cursors.resultPathBase), mapHelper, null);
        cursors.baseCursor = indexOfFirstNonChild(cursors.base, currentBase, cursors.baseCursor + 1, getBaseLimit());
      }
      else {
        if (outcome.getType().size() == 0 && !outcome.hasContentReference()) {
          throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants._HAS_NO_CHILDREN__AND_NO_TYPES_IN_PROFILE_, currentBasePath, getDifferential().getElement().get(cursors.diffCursor).getPath(), getProfileName()));
        }
        boolean nonExtension = false;
        if (outcome.getType().size() > 1) {
          for (ElementDefinition.TypeRefComponent t : outcome.getType()) {
            if (!t.getWorkingCode().equals("Reference")) {
              for (ElementDefinition ed : diffMatches) {
                if (ed != diffMatches.get(0) && !ed.getPath().endsWith(".extension")) {
                  nonExtension = true;
                }
              }
            }
          }
        }
        if (!profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), currentBasePath + ".")) {
          cursors.diffCursor++;
        }
        int start = cursors.diffCursor;
        while (getDifferential().getElement().size() > cursors.diffCursor && profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), currentBasePath + "."))
          cursors.diffCursor++;
        if (nonExtension) {
          throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants._HAS_CHILDREN__AND_MULTIPLE_TYPES__IN_PROFILE_, currentBasePath, getDifferential().getElement().get(cursors.diffCursor).getPath(), profileUtilities.typeCode(outcome.getType()), getProfileName()));
        }
        if (outcome.hasContentReference()) {
          ProfileUtilities.ElementDefinitionResolution tgt = profileUtilities.getElementById(getSourceStructureDefinition(), cursors.base.getElement(), outcome.getContentReference());
          if (tgt == null)
            throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.UNABLE_TO_RESOLVE_REFERENCE_TO_, outcome.getContentReference()));
          profileUtilities.replaceFromContentReference(outcome, tgt.getElement());
          if (tgt.getSource() != getSourceStructureDefinition()) {
            cursors.base = tgt.getSource().getSnapshot();
            int newBaseCursor = cursors.base.getElement().indexOf(tgt.getElement()) + 1;
            int newBaseLimit = newBaseCursor;
            while (newBaseLimit < cursors.base.getElement().size() && cursors.base.getElement().get(newBaseLimit).getPath().startsWith(tgt.getElement().getPath() + "."))
              newBaseLimit++;

              ProfilePathProcessorState ncursors = new ProfilePathProcessorState(cursors.baseSource, cursors.base, newBaseCursor, start - 1, cursors.contextName, cursors.resultPathBase);
              this
                .incrementDebugIndent()
                .withBaseLimit(newBaseLimit - 1)
                .withDiffLimit(cursors.diffCursor - 1)
                .withContextPathSource(tgt.getElement().getPath())
                .withContextPathTarget(diffMatches.get(0).getPath())
                .withRedirector(profileUtilities.redirectorStack(getRedirector(), outcome, currentBasePath))
                .withSourceStructureDefinition(tgt.getSource())
                .withSlicing(new PathSlicingParams())
                .processPaths(ncursors, mapHelper, null);
          } else {
            int newBaseCursor = cursors.base.getElement().indexOf(tgt.getElement()) + 1;
            int newBaseLimit = newBaseCursor;
            while (newBaseLimit < cursors.base.getElement().size() && cursors.base.getElement().get(newBaseLimit).getPath().startsWith(tgt.getElement().getPath() + "."))
              newBaseLimit++;

              ProfilePathProcessorState ncursors = new ProfilePathProcessorState(cursors.baseSource, cursors.base, newBaseCursor, start, cursors.contextName, cursors.resultPathBase);
              this
                .incrementDebugIndent()
                .withBaseLimit(newBaseLimit - 1)
                .withDiffLimit(cursors.diffCursor - 1)
                .withContextPathSource(tgt.getElement().getPath())
                .withContextPathTarget(outcome.getPath())
                .withRedirector(profileUtilities.redirectorStack(getRedirector(), outcome, currentBasePath)).withSlicing(new PathSlicingParams())
                .processPaths(ncursors, mapHelper, null);
          }
        } else {
          StructureDefinition dt = outcome.getType().size() > 1 ? profileUtilities.getContext().fetchTypeDefinition("Element") : profileUtilities.getProfileForDataType(outcome.getType().get(0), getWebUrl(), getDerived());
          if (dt == null) {
            throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.UNKNOWN_TYPE__AT_, outcome.getType().get(0), currentBasePath));
          }
          cursors.contextName = dt.getUrl();
          if (getRedirector() == null || getRedirector().isEmpty()) {
            /* starting again on the data type, but skip the root */
            ProfilePathProcessorState ncursors = new ProfilePathProcessorState(dt, dt.getSnapshot(), 1 /* starting again on the data type, but skip the root */, start,
                      cursors.contextName, cursors.resultPathBase);
              this
                .incrementDebugIndent()
                .withBaseLimit(dt.getSnapshot().getElement().size() - 1)
                .withDiffLimit(cursors.diffCursor - 1)
                .withWebUrl(profileUtilities.getWebUrl(dt, getWebUrl()))
                .withContextPathSource(currentBasePath)
                .withContextPathTarget(outcome.getPath())
                .withSlicing(new PathSlicingParams())
                .processPaths(ncursors, mapHelper, null);
          } else {
            ProfilePathProcessorState ncursors2 =    /* starting again on the data type, but skip the root */
                new ProfilePathProcessorState(dt, dt.getSnapshot(), 1 /* starting again on the data type, but skip the root */, start,
                    cursors.contextName, cursors.resultPathBase);
              this
                .incrementDebugIndent()
                .withBaseLimit(dt.getSnapshot().getElement().size() - 1)
                .withDiffLimit(cursors.diffCursor - 1)
                .withWebUrl(profileUtilities.getWebUrl(dt, getWebUrl()))
                .withContextPathSource(currentBasePath)
                .withContextPathTarget( outcome.getPath())
                .withRedirector(profileUtilities.redirectorStack(getRedirector(), currentBase, currentBasePath)).withSlicing(new PathSlicingParams())
                .processPaths(ncursors2, mapHelper, null);
          }
        }
      }
    }
    cursors.baseCursor++;
  }

  private void processPathWithSlicedBase(
    ElementDefinition currentBase,
    String currentBasePath,
    List<ElementDefinition> diffMatches, List<TypeSlice> typeList,
    final ProfilePathProcessorState cursors, MappingAssistant mapHelper
  ) {
    // the item is already sliced in the base profile.
    // here's the rules
    //  1. irrespective of whether the slicing is ordered or not, the definition order must be maintained
    //  2. slice element names have to match.
    //  3. new slices must be introduced at the end
    // corallory: you can't re-slice existing slices. is that ok?

    // we're going to need this:
    String path = currentBase.getPath();

    if (diffMatches.isEmpty()) {
      processPathWithSlicedBaseAndEmptyDiffMatches(currentBase, currentBasePath, diffMatches, cursors, path, mapHelper);
    }
    else if (profileUtilities.diffsConstrainTypes(diffMatches, currentBasePath, typeList))
    {
      processPathWithSlicedBaseWhereDiffsConstrainTypes(currentBasePath, diffMatches, typeList, cursors, mapHelper);
    }
    else
    {
      processPathWithSlicedBaseDefault(currentBase, currentBasePath, diffMatches, cursors, path, mapHelper);
    }
  }

  private void processPathWithSlicedBaseDefault(ElementDefinition currentBase, String currentBasePath, List<ElementDefinition> diffMatches, ProfilePathProcessorState cursors, String path, MappingAssistant mapHelper) {
    // first - check that the slicing is ok
    boolean closed = currentBase.getSlicing().getRules() == ElementDefinition.SlicingRules.CLOSED;
    int diffpos = 0;
    if (diffMatches.get(0).hasSlicing()) { // it might be null if the differential doesn't want to say anything about slicing
//            if (!isExtension)
//              diffpos++; // if there's a slice on the first, we'll ignore any content it has
      ElementDefinition.ElementDefinitionSlicingComponent dSlice = diffMatches.get(0).getSlicing();
      ElementDefinition.ElementDefinitionSlicingComponent bSlice = currentBase.getSlicing();
      if (dSlice.hasOrderedElement() && bSlice.hasOrderedElement() && !profileUtilities.orderMatches(dSlice.getOrderedElement(), bSlice.getOrderedElement()))
        throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.SLICING_RULES_ON_DIFFERENTIAL__DO_NOT_MATCH_THOSE_ON_BASE___ORDER___, profileUtilities.summarizeSlicing(dSlice), profileUtilities.summarizeSlicing(bSlice), path, cursors.contextName));
      if (!profileUtilities.discriminatorMatches(dSlice.getDiscriminator(), bSlice.getDiscriminator()))
        throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.SLICING_RULES_ON_DIFFERENTIAL__DO_NOT_MATCH_THOSE_ON_BASE___DISCIMINATOR___, profileUtilities.summarizeSlicing(dSlice), profileUtilities.summarizeSlicing(bSlice), path, url));
      if (!currentBase.isChoice() && !profileUtilities.ruleMatches(dSlice.getRules(), bSlice.getRules()))
        throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.SLICING_RULES_ON_DIFFERENTIAL__DO_NOT_MATCH_THOSE_ON_BASE___RULE___, profileUtilities.summarizeSlicing(dSlice), profileUtilities.summarizeSlicing(bSlice), path, cursors.contextName));
    }
    ElementDefinition outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), currentBase.copy(), true);
    outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
    profileUtilities.updateFromBase(outcome, currentBase, getSourceStructureDefinition().getUrl());
    if (diffMatches.get(0).hasSlicing() || !diffMatches.get(0).hasSliceName()) {
      profileUtilities.updateFromSlicing(outcome.getSlicing(), diffMatches.get(0).getSlicing());
      profileUtilities.updateFromDefinition(outcome, diffMatches.get(0), getProfileName(), closed, getUrl(), getSourceStructureDefinition(), getDerived(), diffPath(diffMatches.get(0)), mapHelper, false); // if there's no slice, we don't want to update the unsliced description
    } else if (!diffMatches.get(0).hasSliceName()) {
      diffMatches.get(0).setUserData(UserDataNames.SNAPSHOT_GENERATED_IN_SNAPSHOT, outcome); // because of updateFromDefinition isn't called
    } else {
      outcome.setUserData(UserDataNames.SNAPSHOT_auto_added_slicing, true);
    }
    
    ProfileUtilities.markExtensions(outcome, false, cursors.baseSource);
    debugCheck(outcome);
    addToResult(outcome);

    if (!diffMatches.get(0).hasSliceName()) { // it's not real content, just the slice
      diffpos++;
    }
    if (profileUtilities.hasInnerDiffMatches(getDifferential(), currentBasePath, cursors.diffCursor, getDiffLimit(), cursors.base.getElement(), false)) {
      int newBaseLimit = profileUtilities.findEndOfElement(cursors.base, cursors.baseCursor);
      int ndx = getDifferential().getElement().indexOf(diffMatches.get(0));
      int newDiffCursor = ndx + (diffMatches.get(0).hasSlicing() ? 1 : 0);
      int newDiffLimit = profileUtilities.findEndOfElement(getDifferential(), ndx);
      if (newBaseLimit == cursors.baseCursor) {
        if (cursors.base.getElement().get(cursors.baseCursor).getType().size() != 1) {
          throw new Error(profileUtilities.getContext().formatMessage(I18nConstants.DIFFERENTIAL_WALKS_INTO____BUT_THE_BASE_DOES_NOT_AND_THERE_IS_NOT_A_SINGLE_FIXED_TYPE_THE_TYPE_IS__THIS_IS_NOT_HANDLED_YET, currentBasePath, diffMatches.get(0).toString(), cursors.base.getElement().get(cursors.baseCursor).typeSummary()));
        }
        StructureDefinition dt = profileUtilities.getProfileForDataType(cursors.base.getElement().get(cursors.baseCursor).getType().get(0), getWebUrl(), getDerived());
        if (dt == null) {
          throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.UNKNOWN_TYPE__AT_, outcome.getType().get(0), diffMatches.get(0).getPath()));
        }
        cursors.contextName = dt.getUrl();
        while (getDifferential().getElement().size() > cursors.diffCursor && profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), currentBasePath + "."))
          cursors.diffCursor++;
          ProfilePathProcessorState nc = new ProfilePathProcessorState(dt, dt.getSnapshot(), 1, newDiffCursor, cursors.contextName, cursors.resultPathBase);
          this
            .incrementDebugIndent()
            .withBaseLimit(dt.getSnapshot().getElement().size() - 1)
            .withDiffLimit(newDiffLimit)
            .withWebUrl(profileUtilities.getWebUrl(dt, getWebUrl()))
            .withContextPathSource(currentBasePath).withContextPathTarget(outcome.getPath())
            .withSlicing(new PathSlicingParams())
            .processPaths(nc, mapHelper, null);
      } else {
        ProfilePathProcessorState nc = new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor + 1, newDiffCursor,
            cursors.contextName, cursors.resultPathBase);
          this
            .incrementDebugIndent()
            .withBaseLimit(newBaseLimit)
            .withDiffLimit(newDiffLimit)
            .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, 0))
            .withRedirector(null).withSlicing(new PathSlicingParams())
            .processPaths(nc, mapHelper, null);
      }
//            throw new Error("Not done yet");
//          } else if (currentBase.getType().get(0).getCode().equals("BackboneElement") && diffMatches.size() > 0 && diffMatches.get(0).hasSliceName()) {
    } else if (!currentBase.getType().isEmpty() && currentBase.getType().get(0).getCode().equals("BackboneElement")) {
      // We need to copy children of the backbone element before we start messing around with slices
      int newBaseLimit = profileUtilities.findEndOfElement(cursors.base, cursors.baseCursor);
      for (int i = cursors.baseCursor + 1; i <= newBaseLimit; i++) {
        outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), cursors.base.getElement().get(i).copy(), true);
        outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
        profileUtilities.markExtensions(outcome, false, sourceStructureDefinition);
        debugCheck(outcome);
        addToResult(outcome);
      }
    }

    // now, we have two lists, base and diff. we're going to work through base, looking for matches in diff.
    List<ElementDefinition> baseMatches = profileUtilities.getSiblings(cursors.base.getElement(), currentBase);
    for (ElementDefinition baseItem : baseMatches) {
      cursors.baseCursor = cursors.base.getElement().indexOf(baseItem);
      outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), baseItem.copy(), true);
      profileUtilities.updateFromBase(outcome, currentBase, getSourceStructureDefinition().getUrl());
      outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
      outcome.setSlicing(null);
      profileUtilities.markExtensions(outcome, false, sourceStructureDefinition);
      if (!outcome.getPath().startsWith(cursors.resultPathBase))
        throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ADDING_WRONG_PATH));
      if (diffpos < diffMatches.size() && diffMatches.get(diffpos).hasSliceName() && diffMatches.get(diffpos).getSliceName().equals(outcome.getSliceName())) {
        // if there's a diff, we update the outcome with diff
        // no? updateFromDefinition(outcome, diffMatches.get(diffpos), profileName, closed, url);
        //then process any children
        int newBaseLimit = profileUtilities.findEndOfElement(cursors.base, cursors.baseCursor);
        int newDiffCursor = getDifferential().getElement().indexOf(diffMatches.get(diffpos));
        int newDiffLimit = profileUtilities.findEndOfElement(getDifferential(), newDiffCursor);
        // now we process the base scope repeatedly for each instance of the item in the differential list
        ProfilePathProcessorState nc = new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor, newDiffCursor, cursors.contextName, cursors.resultPathBase);
          this
            .incrementDebugIndent()
            .withBaseLimit(newBaseLimit)
            .withDiffLimit(newDiffLimit)
            .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, diffpos))
            .withTrimDifferential(closed)
            .withSlicing(new PathSlicingParams(true, null, null))
            .processPaths(nc, mapHelper, null);
        // ok, done with that - now set the cursors for if this is the end
        cursors.baseCursor = newBaseLimit;
        cursors.diffCursor = newDiffLimit + 1;
        diffpos++;
      } else {
        debugCheck(outcome);
        addToResult(outcome);
        cursors.baseCursor++;
        // just copy any children on the base
        while (cursors.baseCursor < cursors.base.getElement().size() && cursors.base.getElement().get(cursors.baseCursor).getPath().startsWith(path) && !cursors.base.getElement().get(cursors.baseCursor).getPath().equals(path)) {
          outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), cursors.base.getElement().get(cursors.baseCursor).copy(), true);
          outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
          if (!outcome.getPath().startsWith(cursors.resultPathBase))
            throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ADDING_WRONG_PATH));
          outcome.setUserData(UserDataNames.SNAPSHOT_BASE_PATH, outcome.getPath());
          outcome.setUserData(UserDataNames.SNAPSHOT_BASE_MODEL, getSourceStructureDefinition().getUrl());
          profileUtilities.markExtensions(outcome, false, sourceStructureDefinition);
          debugCheck(outcome);
          addToResult(outcome);
          cursors.baseCursor++;
        }
        //Lloyd - add this for test T15
        cursors.baseCursor--;
      }
    }
    // finally, we process any remaining entries in diff, which are new (and which are only allowed if the base wasn't closed
    if (closed && diffpos < diffMatches.size()) {
      // this is a problem, unless we're on a polymorhpic type and we're going to constrain a slice that actually implicitly exists
      if (!currentBase.getPath().endsWith("[x]")) {
        throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.THE_BASE_SNAPSHOT_MARKS_A_SLICING_AS_CLOSED_BUT_THE_DIFFERENTIAL_TRIES_TO_EXTEND_IT_IN__AT__, getProfileName(), path, currentBasePath));
      }
    }
    if (diffpos != diffMatches.size()) {
      while (diffpos < diffMatches.size()) {
        ElementDefinition diffItem = diffMatches.get(diffpos);
        for (ElementDefinition baseItem : baseMatches)
          if (baseItem.getSliceName().equals(diffItem.getSliceName()))
            throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.NAMED_ITEMS_ARE_OUT_OF_ORDER_IN_THE_SLICE));

        String id = diffItem.getId();
        String lid = profileUtilities.tail(id);
        ElementDefinition template = currentBase;
        if (lid.contains("/")) {
          profileUtilities.generateIds(getResult().getElement(), getUrl(), getSourceStructureDefinition().getType(), getSourceStructureDefinition());
          String baseId = id.substring(0, id.length() - lid.length()) + lid.substring(0, lid.indexOf("/")); // this is wrong if there's more than one reslice (todo: one thing at a time)
          template = profileUtilities.getById(getResult().getElement(), baseId);
        }
        outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), template.copy(), true);
        //            outcome = updateURLs(url, diffItem.copy());
        outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
        profileUtilities.updateFromBase(outcome, currentBase, getSourceStructureDefinition().getUrl());
        outcome.setSlicing(null);
        outcome.setMin(0); // we're in a slice, so it's only a mandatory if it's explicitly marked so
        if (!outcome.getPath().startsWith(cursors.resultPathBase))
          throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ADDING_WRONG_PATH));
        ProfileUtilities.markExtensions(outcome, false, sourceStructureDefinition);
        debugCheck(outcome);
        addToResult(outcome);
        profileUtilities.updateFromDefinition(outcome, diffItem, getProfileName(), isTrimDifferential(), getUrl(), getSourceStructureDefinition(), getDerived(), diffPath(diffItem), mapHelper, false);
        
        // do we need to pick up constraints from the type?
        List<String> profiles = new ArrayList<>();
        for (TypeRefComponent tr : outcome.getType()) {
          for (CanonicalType ct : tr.getProfile()) {
            profiles.add(ct.getValueAsString());
          }
        }
        if (profiles.size() == 1) {
          StructureDefinition sdt = profileUtilities.getContext().fetchResource(StructureDefinition.class, profiles.get(0));
          if (sdt != null) {
            ElementDefinition edt = sdt.getSnapshot().getElementFirstRep();
            if (edt.isMandatory() && !outcome.isMandatory()) {
              outcome.setMin(edt.getMin());
            }
            if (!edt.repeats() && outcome.repeats()) {
              outcome.setMax(edt.getMax());
            }
            // todo: should we consider other constraints?
            // throw new Error("Not handled yet: "+sdt.getVersionedUrl()+" / "+outcome.getPath()+":"+outcome.getSliceName());
          }
        } else if (profiles.size() > 1) {
          throw new Error("Not handled: multiple profiles at "+outcome.getPath()+":"+outcome.getSliceName()+": "+CommaSeparatedStringBuilder.join(",", profiles));          
        }
        cursors.diffCursor = getDifferential().getElement().indexOf(diffItem) + 1;        
        if ((!outcome.getType().isEmpty()) && (/*outcome.getType().get(0).getCode().equals("Extension") || */getDifferential().getElement().size() > cursors.diffCursor) && outcome.getPath().contains(".")/* && isDataType(outcome.getType())*/) {  // don't want to do this for the root, since that's base, and we're already processing it
          if (!profileUtilities.baseWalksInto(cursors.base.getElement(), cursors.baseCursor)) {
            if (getDifferential().getElement().size() > cursors.diffCursor && profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), diffMatches.get(0).getPath() + ".")) {
              if (outcome.getType().size() > 1)
                for (ElementDefinition.TypeRefComponent t : outcome.getType()) {
                  if (!t.getCode().equals("Reference"))
                    throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants._HAS_CHILDREN__AND_MULTIPLE_TYPES__IN_PROFILE_, diffMatches.get(0).getPath(), getDifferential().getElement().get(cursors.diffCursor).getPath(), ProfileUtilities.typeCode(outcome.getType()), getProfileName()));
                }
              ElementDefinition.TypeRefComponent t = outcome.getType().get(0);
              if (Utilities.existsInList(t.getCode(), "Base", "Element", "BackboneElement")) {
                int baseStart = cursors.base.getElement().indexOf(currentBase) + 1;
                int baseMax = baseStart + 1;
                while (baseMax < cursors.base.getElement().size() && cursors.base.getElement().get(baseMax).getPath().startsWith(currentBase.getPath() + "."))
                  baseMax++;
                int start = cursors.diffCursor;
                while (getDifferential().getElement().size() > cursors.diffCursor && profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), diffMatches.get(0).getPath() + "."))
                  cursors.diffCursor++;
                ProfilePathProcessorState nc = new ProfilePathProcessorState(cursors.baseSource, cursors.base, baseStart, start - 1,
                    cursors.contextName, cursors.resultPathBase);
                  this.incrementDebugIndent().withBaseLimit(baseMax - 1)
                    .withDiffLimit(cursors.diffCursor - 1)
                    .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, 0))
                    .withContextPathSource(cursors.base.getElement().get(0).getPath())
                    .withContextPathTarget(cursors.base.getElement().get(0).getPath())
                    .withSlicing(new PathSlicingParams())
                    .processPaths(nc, mapHelper, null);
              } else {
                StructureDefinition dt = profileUtilities.getProfileForDataType(outcome.getType().get(0), getWebUrl(), getDerived());
                //                if (t.getCode().equals("Extension") && t.hasProfile() && !t.getProfile().contains(":")) {
                // lloydfix                  dt =
                //                }
                if (dt == null)
                  throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants._HAS_CHILDREN__FOR_TYPE__IN_PROFILE__BUT_CANT_FIND_TYPE, diffMatches.get(0).getPath(), getDifferential().getElement().get(cursors.diffCursor).getPath(), profileUtilities.typeCode(outcome.getType()), getProfileName()));
                cursors.contextName = dt.getUrl();
                int start = cursors.diffCursor;
                while (getDifferential().getElement().size() > cursors.diffCursor && profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), diffMatches.get(0).getPath() + "."))
                  cursors.diffCursor++;
                /* starting again on the data type, but skip the root */
                ProfilePathProcessorState nc = new ProfilePathProcessorState(dt, dt.getSnapshot(), 1 /* starting again on the data type, but skip the root */, start - 1,
                    cursors.contextName, cursors.resultPathBase);
                  this
                    .incrementDebugIndent()
                    .withBaseLimit(dt.getSnapshot().getElement().size() - 1)
                    .withDiffLimit(cursors.diffCursor - 1)
                    .withWebUrl(profileUtilities.getWebUrl(dt, getWebUrl()))
                    .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, 0))
                    .withContextPathSource(diffMatches.get(0).getPath()).withContextPathTarget(outcome.getPath()).withSlicing(new PathSlicingParams())
                    .processPaths(nc, mapHelper, null);
              }
            }
          }
        }
        // ---
        diffpos++;
      }
      if (outcome.hasContentReference() && outcome.hasType()) {
        outcome.getType().clear();
      }
    }
    cursors.baseCursor++;
  }

  private boolean addToResult(ElementDefinition outcome) {    
    return getResult().getElement().add(outcome);
  }

  private void debugCheck(ElementDefinition outcome) {
    if (outcome.getPath().startsWith("List.") && "http://nictiz.nl/fhir/StructureDefinition/Bundle-MedicationOverview".equals(url)) {
      log.debug("wrong!");
    }
  }

  private void processPathWithSlicedBaseWhereDiffsConstrainTypes(String currentBasePath, List<ElementDefinition> diffMatches, List<TypeSlice> typeList, ProfilePathProcessorState cursors, MappingAssistant mapHelper) {
    int start = 0;
    int newBaseLimit = profileUtilities.findEndOfElement(cursors.base, cursors.baseCursor);
    int newDiffCursor = getDifferential().getElement().indexOf(diffMatches.get(0));
    ElementDefinition elementToRemove = null;
    boolean shortCut = (!typeList.isEmpty() && typeList.get(0).type != null) || (diffMatches.get(0).hasSliceName() && !diffMatches.get(0).hasSlicing());
    // we come here whether they are sliced in the diff, or whether the short cut is used.
    if (shortCut) {
      // this is the short cut method, we've just dived in and specified a type slice.
      // in R3 (and unpatched R4, as a workaround right now...
      if (!VersionUtilities.isR4Plus(profileUtilities.getContext().getVersion()) || !profileUtilities.isNewSlicingProcessing()) { // newSlicingProcessing is a work around for editorial loop dependency
        // we insert a cloned element with the right types at the start of the diffMatches
        ElementDefinition ed = new ElementDefinition();
        ed.setPath(profileUtilities.determineTypeSlicePath(diffMatches.get(0).getPath(), currentBasePath));
        for (TypeSlice ts : typeList)
          ed.addType().setCode(ts.type);
        ed.setSlicing(new ElementDefinition.ElementDefinitionSlicingComponent());
        ed.getSlicing().addDiscriminator().setType(ElementDefinition.DiscriminatorType.TYPE).setPath("$this");
        ed.getSlicing().setRules(ElementDefinition.SlicingRules.CLOSED);
        ed.getSlicing().setOrdered(false);
        diffMatches.add(0, ed);
        getDifferential().getElement().add(newDiffCursor, ed);
        elementToRemove = ed;
      } else {
        // as of R4, this changed; if there's no slice, there's no constraint on the slice types, only one the type.
        // so the element we insert specifies no types (= all types) allowed in the base, not just the listed type.
        // see also discussion here: https://chat.fhir.org/#narrow/stream/179177-conformance/topic/Slicing.20a.20non-repeating.20element
        ElementDefinition ed = new ElementDefinition();
        ed.setPath(profileUtilities.determineTypeSlicePath(diffMatches.get(0).getPath(), currentBasePath));
        ed.setSlicing(new ElementDefinition.ElementDefinitionSlicingComponent());
        ed.getSlicing().addDiscriminator().setType(ElementDefinition.DiscriminatorType.TYPE).setPath("$this");
        ed.getSlicing().setRules(ElementDefinition.SlicingRules.CLOSED);
        ed.getSlicing().setOrdered(false);
        diffMatches.add(0, ed);
        getDifferential().getElement().add(newDiffCursor, ed);
        elementToRemove = ed;
      }
    }
    int newDiffLimit = profileUtilities.findEndOfElement(getDifferential(), newDiffCursor);
    // the first element is setting up the slicing

    if (diffMatches.get(0).getSlicing().hasOrdered()) {
      if (diffMatches.get(0).getSlicing().getOrdered()) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__IN__TYPE_SLICING_WITH_SLICINGORDERED__TRUE, currentBasePath, getUrl()));
      }
    }
    if (diffMatches.get(0).getSlicing().hasDiscriminator()) {
      if (diffMatches.get(0).getSlicing().getDiscriminator().size() != 1) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__IN__TYPE_SLICING_WITH_SLICINGDISCRIMINATORCOUNT__1, currentBasePath, getUrl()));
      }
      if (diffMatches.get(0).getSlicing().getDiscriminatorFirstRep().getType() != ElementDefinition.DiscriminatorType.TYPE) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__IN__TYPE_SLICING_WITH_SLICINGDISCRIMINATORTYPE__TYPE, currentBasePath, getUrl()));
      }
      if (!"$this".equals(diffMatches.get(0).getSlicing().getDiscriminatorFirstRep().getPath())) {
        throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__IN__TYPE_SLICING_WITH_SLICINGDISCRIMINATORPATH__THIS, currentBasePath, getUrl()));
      }
    }
    // check the slice names too while we're at it...
    for (TypeSlice ts : typeList) {
      if (ts.type != null) {
        String tn = profileUtilities.rootName(currentBasePath) + Utilities.capitalize(ts.type);
        if (!ts.defn.hasSliceName()) {
          ts.defn.setSliceName(tn);
        } else if (!ts.defn.getSliceName().equals(tn)) {
          throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__SLICE_NAME_MUST_BE__BUT_IS_, (!Utilities.noString(getContextPathSource()) ? getContextPathSource() : currentBasePath), tn, ts.defn.getSliceName()));
        }
        if (!ts.defn.hasType()) {
          ts.defn.addType().setCode(ts.type);
        } else if (ts.defn.getType().size() > 1) {
          throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__SLICE_FOR_TYPE__HAS_MORE_THAN_ONE_TYPE_, (!Utilities.noString(getContextPathSource()) ? getContextPathSource() : currentBasePath), tn, ts.defn.typeSummary()));
        } else if (!ts.defn.getType().get(0).getCode().equals(ts.type)) {
          throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.ERROR_AT_PATH__SLICE_FOR_TYPE__HAS_WRONG_TYPE_, (!Utilities.noString(getContextPathSource()) ? getContextPathSource() : currentBasePath), tn, ts.defn.typeSummary()));
        }
      }
    }

    // ok passed the checks.
    // copy the root diff, and then process any children it has
    ProfilePathProcessorState nc = new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor, newDiffCursor,
        cursors.contextName, cursors.resultPathBase);
    ElementDefinition e =
      this
        .incrementDebugIndent()
        .withBaseLimit(newBaseLimit)
        .withDiffLimit(newDiffLimit)
        .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches,0))
        .withSlicing(new PathSlicingParams(true, null, currentBasePath))
        .processPaths(nc, mapHelper, null);
    if (e == null)
      throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.DID_NOT_FIND_TYPE_ROOT_, diffMatches.get(0).getPath()));
    // now set up slicing on the e (cause it was wiped by what we called.
    e.setSlicing(new ElementDefinition.ElementDefinitionSlicingComponent());
    e.getSlicing().addDiscriminator().setType(ElementDefinition.DiscriminatorType.TYPE).setPath("$this");
    e.getSlicing().setRules(ElementDefinition.SlicingRules.CLOSED); // type slicing is always closed; the differential might call it open, but that just means it's not constraining the slices it doesn't mention
    e.getSlicing().setOrdered(false);
    start++;

    String fixedType = null;
    List<BaseTypeSlice> baseSlices = profileUtilities.findBaseSlices(cursors.base, newBaseLimit);
    // now process the siblings, which should each be type constrained - and may also have their own children. they may match existing slices
    // now we process the base scope repeatedly for each instance of the item in the differential list
    for (int i = start; i < diffMatches.size(); i++) {
      String type = profileUtilities.determineFixedType(diffMatches, fixedType, i);
      // our processing scope for the differential is the item in the list, and all the items before the next one in the list
      if (diffMatches.get(i).getMin() > 0) {
        if (diffMatches.size() > i + 1) {
          throw new FHIRException(profileUtilities.getContext().formatMessage(I18nConstants.INVALID_SLICING__THERE_IS_MORE_THAN_ONE_TYPE_SLICE_AT__BUT_ONE_OF_THEM__HAS_MIN__1_SO_THE_OTHER_SLICES_CANNOT_EXIST, diffMatches.get(i).getPath(), diffMatches.get(i).getSliceName()));
        }
        fixedType = type;
      }
      newDiffCursor = getDifferential().getElement().indexOf(diffMatches.get(i));
      newDiffLimit = profileUtilities.findEndOfElement(getDifferential(), newDiffCursor);
      int sStart = cursors.baseCursor;
      int sEnd = newBaseLimit;
      BaseTypeSlice bs = profileUtilities.chooseMatchingBaseSlice(baseSlices, type);
      if (bs != null) {
        sStart = bs.getStart();
        sEnd = bs.getEnd();
        bs.setHandled(true);
      }
      ProfilePathProcessorState nc2 = new ProfilePathProcessorState(cursors.baseSource, cursors.base, sStart, newDiffCursor, cursors.contextName, cursors.resultPathBase);
        this
          .incrementDebugIndent()
          .withBaseLimit(sEnd)
          .withDiffLimit(newDiffLimit)
          .withProfileName(getProfileName() + profileUtilities.pathTail(diffMatches, i))
          .withSlicing(new PathSlicingParams(true, e, currentBasePath))
          .processPaths(nc2, mapHelper, null);
    }
    if (elementToRemove != null) {
      getDifferential().getElement().remove(elementToRemove);
      newDiffLimit--;
    }
    if (fixedType != null) {
      for (Iterator<ElementDefinition.TypeRefComponent> iter = e.getType().iterator(); iter.hasNext(); ) {
        ElementDefinition.TypeRefComponent tr = iter.next();
        if (!tr.getCode().equals(fixedType)) {
          iter.remove();
        }
      }
    }
    for (BaseTypeSlice bs : baseSlices) {
      if (!bs.isHandled()) {
        // ok we gimme up a fake differential that says nothing, and run that against the slice.
        StructureDefinition.StructureDefinitionDifferentialComponent fakeDiff = new StructureDefinition.StructureDefinitionDifferentialComponent();
        fakeDiff.getElementFirstRep().setPath(bs.getDefn().getPath());
        ProfilePathProcessorState nc3 = new ProfilePathProcessorState(cursors.baseSource, cursors.base, bs.getStart(), 0, cursors.contextName, cursors.resultPathBase);
          this
            .incrementDebugIndent()
            .withDifferential(fakeDiff)
            .withBaseLimit(bs.getEnd())
            .withDiffLimit(0)
            .withProfileName(getProfileName() + profileUtilities.tail(bs.getDefn().getPath())).withSlicing(new PathSlicingParams(true, e, currentBasePath))
            .processPaths(nc3, mapHelper, null);

      }
    }
    // ok, done with that - next in the base list
    cursors.baseCursor = baseSlices.get(baseSlices.size() - 1).getEnd() + 1;
    cursors.diffCursor = newDiffLimit + 1;
    //throw new Error("not done yet - slicing / types @ "+cpath);
  }

  private void processPathWithSlicedBaseAndEmptyDiffMatches(ElementDefinition currentBase, String currentBasePath, List<ElementDefinition> diffMatches, ProfilePathProcessorState cursors, String path, MappingAssistant mapHelper) {
    if (profileUtilities.hasInnerDiffMatches(getDifferential(), path, cursors.diffCursor, getDiffLimit(), cursors.base.getElement(), true)) {
      // so we just copy it in
      ElementDefinition outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), currentBase.copy(), true);
      outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
      profileUtilities.updateFromBase(outcome, currentBase, getSourceStructureDefinition().getUrl());
      profileUtilities.markDerived(outcome);
      if (cursors.resultPathBase == null)
        cursors.resultPathBase = outcome.getPath();
      else if (!outcome.getPath().startsWith(cursors.resultPathBase))
        throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ADDING_WRONG_PATH));
      debugCheck(outcome);
      addToResult(outcome);
      // the profile walks into this, so we need to as well
      // did we implicitly step into a new type?
      if (baseHasChildren(cursors.base, currentBase)) { // not a new type here
        ProfilePathProcessorState nc = new ProfilePathProcessorState(cursors.baseSource, cursors.base, cursors.baseCursor + 1, cursors.diffCursor, cursors.contextName, cursors.resultPathBase);
          this
            .incrementDebugIndent()
            .withSlicing(new PathSlicingParams())
            .processPaths(nc, mapHelper, null);
        cursors.baseCursor = indexOfFirstNonChild(cursors.base, currentBase, cursors.baseCursor, getBaseLimit());
      } else {
        StructureDefinition dt = profileUtilities.getTypeForElement(getDifferential(), cursors.diffCursor, getProfileName(), diffMatches, outcome, getWebUrl(), getDerived());
        cursors.contextName = dt.getUrl();
        int start = cursors.diffCursor;
        if (getDifferential().getElement().get(cursors.diffCursor).getPath().equals(currentBasePath)) {
          cursors.diffCursor++;
        }
        while (getDifferential().getElement().size() > cursors.diffCursor && profileUtilities.pathStartsWith(getDifferential().getElement().get(cursors.diffCursor).getPath(), currentBasePath + ".")) {
          cursors.diffCursor++;
        }
        if (cursors.diffCursor > start) {
          /* starting again on the data type, but skip the root */
          ProfilePathProcessorState nc2 = new ProfilePathProcessorState(dt, dt.getSnapshot(), 1 /* starting again on the data type, but skip the root */, start,
              cursors.contextName, cursors.resultPathBase);
            this
              .incrementDebugIndent()
              .withBaseLimit(dt.getSnapshot().getElement().size() - 1)
              .withDiffLimit(cursors.diffCursor - 1)
              .withWebUrl( profileUtilities.getWebUrl(dt, getWebUrl()))
              .withContextPathSource(currentBasePath)
              .withContextPathTarget(outcome.getPath()).withSlicing(new PathSlicingParams())
              .processPaths(nc2, mapHelper, null);
        }
      }
      cursors.baseCursor++;
    }
    else {
      // the differential doesn't say anything about this item
      // copy across the currentbase, and all of its children and siblings
      while (cursors.baseCursor < cursors.base.getElement().size() && cursors.base.getElement().get(cursors.baseCursor).getPath().startsWith(path)) {
        ElementDefinition outcome = profileUtilities.updateURLs(getUrl(), getWebUrl(), cursors.base.getElement().get(cursors.baseCursor).copy(), true);
        outcome.setPath(profileUtilities.fixedPathDest(getContextPathTarget(), outcome.getPath(), getRedirector(), getContextPathSource()));
        if (!outcome.getPath().startsWith(cursors.resultPathBase))
          throw new DefinitionException(profileUtilities.getContext().formatMessage(I18nConstants.ADDING_WRONG_PATH_IN_PROFILE___VS_, getProfileName(), outcome.getPath(), cursors.resultPathBase));
        debugCheck(outcome);
        profileUtilities.markExtensions(outcome, false, sourceStructureDefinition);
        addToResult(outcome); // so we just copy it in
        outcome.setUserData(UserDataNames.SNAPSHOT_BASE_MODEL, getSourceStructureDefinition().getUrl());
        outcome.setUserData(UserDataNames.SNAPSHOT_BASE_PATH, cursors.resultPathBase);
        cursors.baseCursor++;
      }
    }
  }

  private boolean oneMatchingElementInDifferential(boolean slicingDone, String path, List<ElementDefinition> diffMatches) {
    if (diffMatches.size() != 1) {
      return false;
    }
    if (slicingDone) {
      return true;
    }
    if (profileUtilities.isImplicitSlicing(diffMatches.get(0), path)) {
      return false;
    }
    return !(diffMatches.get(0).hasSlicing()
      || (profileUtilities.isExtension(diffMatches.get(0))
      && diffMatches.get(0).hasSliceName()));
  }


}