/* Copyright (C) 2011, 2012, 2013 by Bundesanstalt für Gewässerkunde
 * Software engineering by Intevation GmbH
 *
 * This file is Free Software under the GNU AGPL (>=v3)
 * and comes with ABSOLUTELY NO WARRANTY! Check out the
 * documentation coming with Dive4Elements River for details.
 */

package org.dive4elements.river.artifacts.services;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.Date;
import java.util.List;

import javax.xml.xpath.XPathConstants;

import org.dive4elements.artifacts.CallMeta;
import org.dive4elements.artifacts.GlobalContext;
import org.dive4elements.artifacts.common.ArtifactNamespaceContext;
import org.dive4elements.artifacts.common.utils.XMLUtils;
import org.dive4elements.artifacts.common.utils.XMLUtils.ElementCreator;
import org.dive4elements.river.artifacts.resources.Resources;
import org.dive4elements.river.artifacts.services.AbstractMainValuesService.MainValuesServiceException;
import org.dive4elements.river.model.Gauge;
import org.dive4elements.river.model.River;
import org.dive4elements.river.model.sinfo.DailyDischargeValue;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.NodeList;

/**
 * This service returns the list of gauges with daily discharge time periods and error messages
 */
public class DynamicMainValuesTimeRangeDeterminationService extends D4EService {

    private static final long serialVersionUID = 1L;

    private static final String ROOT_NODE = "dynamic-mainvalues-input";

    private static final Long DATE_DELTA_ERROR_MSG = (long) (60 * 60 * 24 * 1000);

    public static final class ServiceException extends Exception {

        private static final long serialVersionUID = 1L;

        public ServiceException(final String message) {
            super(message);
        }
    }

    private static class GaugeInfoResult {
        protected final String globalErrorMsg;
        protected final List<GaugeInfo> gaugeInfos;

        protected GaugeInfoResult(final List<GaugeInfo> gaugeInfos, final String globalErrorMsg) {
            this.gaugeInfos = gaugeInfos;
            this.globalErrorMsg = globalErrorMsg;
        }

        private static class GaugeInfo {
            protected final String errorMsg;
            protected final Gauge gauge;
            protected final Date startdate;
            protected final Date enddate;

            public GaugeInfo(final String errorMsg, final Gauge gauge, final Date startdate, final Date enddate) {
                this.errorMsg = errorMsg;
                this.gauge = gauge;
                this.startdate = startdate;
                this.enddate = enddate;
            }
        }
    }

    /**
     * Queries the available daily discharge time periods of a list of gauges from the database and checks the overlapping
     *
     * @throws ServiceException
     */
    private GaugeInfoResult getCommonTimeRangeForGauges(final List<Gauge> gauges, final Date startTime, final Date endTime, final CallMeta meta)
            throws ServiceException {

        // Query the gauge's daily Q values
        String globalErrorMsg = "";
        final List<GaugeInfoResult.GaugeInfo> gaugeResults = new ArrayList<>();
        Date min = startTime;
        Date max = endTime;

        for (final Gauge gauge : gauges) {

            final Date[] gaugeDates = DailyDischargeValue.getTimePeriod(gauge, startTime, endTime);
            if (gaugeDates[0] == null) {
                final String msg = Resources.getMsg(meta, "bundu.wst_no_data_at_all", "bundu.wst_no_data_at_all", gauge.getName());
                final GaugeInfoResult.GaugeInfo gi = new GaugeInfoResult.GaugeInfo(msg, gauge, null, null);
                gaugeResults.add(gi);
                if (globalErrorMsg.isEmpty())
                    globalErrorMsg = msg;
                continue;
            }

            if (gaugeDates[0].getTime() > startTime.getTime())
                min = gaugeDates[0];

            if (gaugeDates[1].getTime() < endTime.getTime())
                max = gaugeDates[1];

            String errormsg = null;
            if ((gaugeDates[1].getTime() < endTime.getTime()) || (gaugeDates[0].getTime() > startTime.getTime()))
                errormsg = makeDoesNotCoverErrorMsg(gaugeDates[0], gaugeDates[1], meta);

            gaugeResults.add(new GaugeInfoResult.GaugeInfo(errormsg, gauge, min, max));
        }

        // common Range and correct errorMsg
        final List<GaugeInfoResult.GaugeInfo> gaugeResultsSecondTurn = new ArrayList<>();
        for (final GaugeInfoResult.GaugeInfo gi : gaugeResults) {
            gaugeResultsSecondTurn.add(new GaugeInfoResult.GaugeInfo(gi.errorMsg, gi.gauge, gi.startdate != null ? min : null,
                    gi.enddate != null ? max : null));
        }
        if (globalErrorMsg.isEmpty() && (min.getTime() > max.getTime()))
            globalErrorMsg = getMsg(meta, "bundu.wst.gauge_timeranges_disjoint");
        final GaugeInfoResult result = new GaugeInfoResult(gaugeResultsSecondTurn, globalErrorMsg);

        return result;
    }

    private String makeDoesNotCoverErrorMsg(final Date start, final Date end, final CallMeta meta) {
        final Calendar cal = Calendar.getInstance();
        cal.setTime(start);
        final String startyear = String.valueOf(cal.get(Calendar.YEAR));
        cal.setTime(end);
        final String endyear = String.valueOf(cal.get(Calendar.YEAR));
        return Resources.getMsg(meta, "bundu.wst.range_does_not_cover", new Object[] { startyear, endyear });
    }

    @Override
    public Document doProcess(final Document data, final GlobalContext context, final CallMeta callMeta) {
        try {
            final River river = AbstractMainValuesService.getRequestedRiver(data, "/art:" + ROOT_NODE + "/art:river/text()");
            final List<Gauge> gauges = getRequestedGauges(data, river, callMeta);
            final Date start = getRequestedStartYear(data, "/art:" + ROOT_NODE + "/art:startYear/text()");
            final Date end = getRequestedEndYear(data, "/art:" + ROOT_NODE + "/art:endYear/text()");

            final GaugeInfoResult result = getCommonTimeRangeForGauges(gauges, start, end, callMeta);

            return buildDocument(result, context, callMeta);
        }
        catch (final ServiceException | MainValuesServiceException e) {
            e.printStackTrace();
            return AbstractMainValuesService.error(e.getMessage());
        }
    }

    public static final Date getRequestedEndYear(final Document data, final String XPATH_END_YEAR) throws MainValuesServiceException {

        final String endStr = XMLUtils.xpathString(data, XPATH_END_YEAR, ArtifactNamespaceContext.INSTANCE);

        if (endStr == null)
            throw new MainValuesServiceException("no end year"); // should not happen

        try {
            final int year = Integer.parseInt(endStr);

            // FIXME: timezone? probably must match timezone of database
            final Calendar cal = Calendar.getInstance();
            cal.clear();
            cal.set(year, 11, 31);
            return cal.getTime();
        }
        catch (final NumberFormatException e) {
            e.printStackTrace();
            throw new MainValuesServiceException("invalid end year"); // should not happen
        }
    }

    public static final Date getRequestedStartYear(final Document data, final String XPATH_START_YEAR) throws MainValuesServiceException {

        final String startStr = XMLUtils.xpathString(data, XPATH_START_YEAR, ArtifactNamespaceContext.INSTANCE);

        if (startStr == null)
            throw new MainValuesServiceException("no start year");// should not happen

        try {
            final int year = Integer.parseInt(startStr);

            // FIXME: timezone? probably must match timezone of database
            final Calendar cal = Calendar.getInstance();
            cal.clear();
            cal.set(year, 0, 1);
            return cal.getTime();
        }
        catch (final NumberFormatException e) {
            e.printStackTrace();
            throw new MainValuesServiceException("invalid start year"); // should not happen
        }
    }

    private Document buildDocument(final GaugeInfoResult result, final GlobalContext context, final CallMeta meta) {

        final Document doc = XMLUtils.newDocument();

        final ElementCreator cr = new ElementCreator(doc, ArtifactNamespaceContext.NAMESPACE_URI, ArtifactNamespaceContext.NAMESPACE_PREFIX);

        final Element rootEl = cr.create(ROOT_NODE);

        doc.appendChild(rootEl);

        final Element globalErrElement = cr.create("global-error-msg");
        globalErrElement.setTextContent(result.globalErrorMsg);
        rootEl.appendChild(globalErrElement);

        final List<GaugeInfoResult.GaugeInfo> values = result.gaugeInfos;

        for (final GaugeInfoResult.GaugeInfo gauge : values) {
            final Element gaugeElement = cr.create("gauge");
            cr.addAttr(gaugeElement, "name", gauge.gauge.getName());
            if (gauge.startdate != null)
                cr.addAttr(gaugeElement, "date-from", String.valueOf(gauge.startdate.getTime()));

            if (gauge.enddate != null)
                cr.addAttr(gaugeElement, "date-to", String.valueOf(gauge.enddate.getTime()));

            if (gauge.errorMsg != null)
                cr.addAttr(gaugeElement, "error-message", gauge.errorMsg);

            rootEl.appendChild(gaugeElement);
        }

        return doc;

    }

    final Element buildElement(final ElementCreator cr, final String type, final Date date) {
        final Element el = cr.create(type);
        cr.addAttr(el, "value", String.valueOf(date.getTime()));
        return el;
    }

    private static final List<Gauge> getRequestedGauges(final Document data, final River river, final CallMeta meta) throws ServiceException {

        final NodeList gaugeNodes = data.getElementsByTagNameNS(ArtifactNamespaceContext.NAMESPACE_URI, "gauge");

        final List<Gauge> gauges = new ArrayList<>();

        for (int i = 0; i < gaugeNodes.getLength(); i++) {
            final Element gaugeElt = (Element) gaugeNodes.item(i);

            final String gaugeName = (String) XMLUtils.xpath(gaugeElt, "text()", XPathConstants.STRING);
            final Gauge gauge = Gauge.getGaugeByNameAndRiver(gaugeName, river);
            if (gauge != null)
                gauges.add(gauge);
            else {
                throw new ServiceException("bundu_wst_error_reading_gauges");
            }
        }

        return gauges;
    }

    private static String getMsg(final CallMeta meta, final String key) {
        return Resources.getMsg(meta, key);
    }
}