/*
 * #%L
 * HAPI FHIR JPA Model
 * %%
 * Copyright (C) 2014 - 2023 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.jpa.model.util;

import java.io.InputStream;
import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;

import ca.uhn.fhir.i18n.Msg;
import ca.uhn.fhir.rest.param.QuantityParam;
import ca.uhn.fhir.rest.server.exceptions.InvalidRequestException;
import org.fhir.ucum.Decimal;
import org.fhir.ucum.Pair;
import org.fhir.ucum.UcumEssenceService;
import org.fhir.ucum.UcumException;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import ca.uhn.fhir.util.ClasspathUtil;

import javax.annotation.Nullable;

/**
 * It's a wrapper of UcumEssenceService
 *
 */
public class UcumServiceUtil {

        private static final Logger ourLog = LoggerFactory.getLogger(UcumServiceUtil.class);

        public static final String CELSIUS_CODE = "Cel";
        public static final String FAHRENHEIT_CODE = "[degF]";
        public static final float CELSIUS_KELVIN_DIFF = 273.15f;

        public static final String UCUM_CODESYSTEM_URL = "http://unitsofmeasure.org";
        private static final String UCUM_SOURCE = "/ucum-essence.xml";

        private static UcumEssenceService myUcumEssenceService = null;

        private UcumServiceUtil() {
        }

        // lazy load UCUM_SOURCE only once
        private static void init() {

                if (myUcumEssenceService != null)
                        return;

                synchronized (UcumServiceUtil.class) {
                        InputStream input = ClasspathUtil.loadResourceAsStream(UCUM_SOURCE);
                        try {
                                myUcumEssenceService = new UcumEssenceService(input);

                        } catch (UcumException e) {
                                ourLog.warn("Failed to load ucum code from {}: {}", UCUM_SOURCE, e);
                        } finally {
                                ClasspathUtil.close(input);
                        }
                }
        }

        /**
         * Get the canonical form of a code, it's define at
         * <link>http://unitsofmeasure.org</link>
         * 
         * e.g. 12cm -> 0.12m where m is the canonical form of the length.
         * 
         * @param theSystem must be http://unitsofmeasure.org
         * @param theValue  the value in the original form e.g. 0.12
         * @param theCode   the code in the original form e.g. 'cm'
         * @return the CanonicalForm if no error, otherwise return null
         */
        public static Pair getCanonicalForm(String theSystem, BigDecimal theValue, String theCode) {

                // -- only for http://unitsofmeasure.org
                if (!UCUM_CODESYSTEM_URL.equals(theSystem) || theValue == null || theCode == null)
                        return null;

                if ( isCelsiusOrFahrenheit(theCode) ) {
                        try {
                                return getCanonicalFormForCelsiusOrFahrenheit(theValue, theCode);
                        } catch (UcumException theE) {
                                ourLog.error("Exception when trying to obtain canonical form for value {} and code {}: {}", theValue, theCode, theE.getMessage());
                                return null;
                        }
                }

                init();
                Pair theCanonicalPair;

                try {
                        Decimal theDecimal = new Decimal(theValue.toPlainString(), theValue.precision());
                        theCanonicalPair = myUcumEssenceService.getCanonicalForm(new Pair(theDecimal, theCode));
                        // For some reason code [degF], degree Fahrenheit, can't be converted. it returns value null.
                        if (theCanonicalPair.getValue() == null)
                                return null;
                } catch (UcumException e) {
                        return null;
                }

                return theCanonicalPair;
        }


        private static Pair getCanonicalFormForCelsiusOrFahrenheit(BigDecimal theValue, String theCode) throws UcumException {
                return theCode.equals(CELSIUS_CODE)
                        ? canonicalizeCelsius(theValue)
                        : canonicalizeFahrenheit(theValue);
        }

        /**
         * Returns the received Fahrenheit value converted to Kelvin units and code
         * Formula is K = (x°F ? 32) × 5/9 + 273.15
         */
        private static Pair canonicalizeFahrenheit(BigDecimal theValue) throws UcumException {
                BigDecimal converted = theValue
                        .subtract( BigDecimal.valueOf(32) )
                        .multiply( BigDecimal.valueOf(5f / 9f) )
                        .add( BigDecimal.valueOf(CELSIUS_KELVIN_DIFF) );
                // disallow precision larger than input, as it matters when defining ranges
                BigDecimal adjusted = converted.setScale(theValue.precision(), RoundingMode.HALF_UP);

                Decimal newValue = new Decimal(adjusted.toPlainString());
                return new Pair(newValue, "K");
        }

        /**
         * Returns the received Celsius value converted to Kelvin units and code
         */
        private static Pair canonicalizeCelsius(BigDecimal theValue) throws UcumException {
                Decimal valueDec = new Decimal(theValue.toPlainString(), theValue.precision());
                Decimal converted = valueDec
                        .add(new Decimal(Float.toString(CELSIUS_KELVIN_DIFF)));

                return new Pair(converted, "K");
        }


        private static boolean isCelsiusOrFahrenheit(String theCode) {
                return theCode.equals(CELSIUS_CODE) || theCode.equals(FAHRENHEIT_CODE);
        }


        @Nullable
    public static QuantityParam toCanonicalQuantityOrNull(QuantityParam theQuantityParam) {
        Pair canonicalForm = getCanonicalForm(theQuantityParam.getSystem(), theQuantityParam.getValue(), theQuantityParam.getUnits());
        if (canonicalForm != null) {
            BigDecimal valueValue = new BigDecimal(canonicalForm.getValue().asDecimal());
            String unitsValue = canonicalForm.getCode();
            return new QuantityParam()
                .setSystem(theQuantityParam.getSystem())
                .setValue(valueValue)
                .setUnits(unitsValue)
                .setPrefix(theQuantityParam.getPrefix());
        } else {
            return null;
        }
    }

        public static double convert(double theDistanceKm, String theSourceUnits, String theTargetUnits) {
                init();
                try {
                        Decimal distance = new Decimal(Double.toString(theDistanceKm));
                        Decimal output = myUcumEssenceService.convert(distance, theSourceUnits, theTargetUnits);
                        String decimal = output.asDecimal();
                        return Double.parseDouble(decimal);
                } catch (UcumException e) {
                        throw new InvalidRequestException(Msg.code(2309) + e.getMessage());
                }
        }
}