/*-
 * #%L
 * HAPI FHIR Storage api
 * %%
 * Copyright (C) 2014 - 2025 Smile CDR, Inc.
 * %%
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * #L%
 */
package ca.uhn.fhir.replacereferences;

import ca.uhn.fhir.i18n.Msg;
import ca.uhn.fhir.interceptor.model.RequestPartitionId;
import ca.uhn.fhir.jpa.api.dao.DaoRegistry;
import ca.uhn.fhir.jpa.api.dao.IFhirResourceDao;
import ca.uhn.fhir.jpa.dao.tx.HapiTransactionService;
import ca.uhn.fhir.model.primitive.IdDt;
import ca.uhn.fhir.rest.api.server.RequestDetails;
import ca.uhn.fhir.rest.server.exceptions.ResourceVersionConflictException;
import org.hl7.fhir.instance.model.api.IBaseResource;
import org.hl7.fhir.instance.model.api.IIdType;
import org.hl7.fhir.r4.model.Reference;

import java.util.List;

/**
 * This is a class to restore resources to their previous versions based on the provided versioned resource references.
 * It is used in the context of undoing changes made by the $hapi.fhir.replace-references operation.
 */
public class PreviousResourceVersionRestorer {

        private final HapiTransactionService myHapiTransactionService;
        private final DaoRegistry myDaoRegistry;

        public PreviousResourceVersionRestorer(
                        DaoRegistry theDaoRegistry, HapiTransactionService theHapiTransactionService) {
                myDaoRegistry = theDaoRegistry;
                myHapiTransactionService = theHapiTransactionService;
        }

        /**
         * Given a list of versioned resource references, this method restores each resource to its previous version
         * if the resource's current version is the same as specified in the given reference
         * (i.e. the resource was not updated since the reference was created).
         *
         * This method is transactional and will attempt to restore all resources in a single transaction.
         *
         * Note that this method updates a resource using its previous version's content,
         * so it will actually cause a new version to be created (i.e. it does not rewrite the history).
         *
         * @throws IllegalArgumentException if a given reference is versionless
         * @throws IllegalArgumentException a given reference has version 1, so it cannot have a previous version to restore to.
         * @throws ResourceVersionConflictException if the current version of the resource does not match the version specified in the reference.
         */
        public void restoreToPreviousVersionsInTrx(
                        List<Reference> theReferences, RequestDetails theRequestDetails, RequestPartitionId thePartitionId) {
                myHapiTransactionService
                                .withRequest(theRequestDetails)
                                .withRequestPartitionId(thePartitionId)
                                .execute(() -> restoreToPreviousVersions(theReferences, theRequestDetails));
        }

        private void restoreToPreviousVersions(List<Reference> theReferences, RequestDetails theRequestDetails) {
                for (Reference reference : theReferences) {
                        String referenceStr = reference.getReference();
                        IIdType referenceId = new IdDt(referenceStr);

                        if (!referenceId.hasVersionIdPart()) {
                                throw new IllegalArgumentException(
                                                Msg.code(2730) + "Reference does not have a version: " + referenceStr);
                        }
                        Long referenceVersion = referenceId.getVersionIdPartAsLong();

                        // Restore previous version (version - 1)
                        long previousVersion = referenceVersion - 1;
                        if (previousVersion < 1) {
                                throw new IllegalArgumentException(Msg.code(2731)
                                                + "Resource cannot be restored to a previous as the provided version is 1: " + referenceStr);
                        }

                        // Read the current resource
                        IFhirResourceDao<IBaseResource> dao = myDaoRegistry.getResourceDao(referenceId.getResourceType());
                        IBaseResource currentResource = dao.read(referenceId.toUnqualifiedVersionless(), theRequestDetails);

                        // Check current version
                        Long currentVersion = currentResource.getIdElement().getVersionIdPartAsLong();
                        if (!currentVersion.equals(referenceVersion)) {
                                String msg = String.format(
                                                "The resource cannot be restored because the current version of resource %s (%s) does not match the expected version (%s)",
                                                referenceStr, currentVersion, referenceVersion);
                                throw new ResourceVersionConflictException(Msg.code(2732) + msg);
                        }

                        IIdType previousId = referenceId.withVersion(Long.toString(previousVersion));
                        IBaseResource previousResource = dao.read(previousId, theRequestDetails);
                        previousResource.setId(previousResource.getIdElement().toUnqualifiedVersionless());

                        // Update the resource to the previous version's content
                        dao.update(previousResource, theRequestDetails);
                }
        }
}