/*
 * This file is part of ***  M y C o R e  ***
 * See http://www.mycore.de/ for details.
 *
 * MyCoRe is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * MyCoRe is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with MyCoRe.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.mycore.frontend.xeditor;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.StreamSupport;

import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.TransformerFactoryConfigurationError;
import javax.xml.transform.dom.DOMResult;

import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.xalan.extensions.ExpressionContext;
import org.apache.xpath.NodeSet;
import org.apache.xpath.XPathContext;
import org.apache.xpath.objects.XNodeSet;
import org.apache.xpath.objects.XNodeSetForDOM;
import org.jdom2.Element;
import org.jdom2.filter.ElementFilter;
import org.jdom2.transform.JDOMSource;
import org.jdom2.util.IteratorIterable;
import org.mycore.common.MCRUsageException;
import org.mycore.common.xml.MCRURIResolver;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * Handles xed:include, xed:preload and xed:modify|xed:extend to include XEditor components by URI and ID.
 *
 * @author Frank L\U00FCtzenkirchen
 */
public class MCRIncludeHandler {

    private static final String ATTR_AFTER = "after";

    private static final String ATTR_BEFORE = "before";

    private static final String ATTR_ID = "id";

    private static final String ATTR_REF = "ref";

    private static final Logger LOGGER = LogManager.getLogger(MCRIncludeHandler.class);

    /** Caches preloaded components at application level: resolved only once, used many times (static) */
    private static final Map<String, Element> CACHE_AT_APPLICATION_LEVEL = new ConcurrentHashMap<>();

    /** Caches preloaded components at transformation level, resolved on every reload of editor form page */
    private Map<String, Element> cacheAtTransformationLevel = new HashMap<>();

    /**
     * Preloads editor components from one or more URIs.
     *
     * @param uris a list of URIs to preload, separated by whitespace
     * @param sStatic if true, use static cache on application level,
     *               otherwise reload at each XEditor form transformation
     */
    public void preloadFromURIs(String uris, String sStatic)
        throws TransformerFactoryConfigurationError {
        for (String uri : uris.split(",")) {
            preloadFromURI(uri, sStatic);
        }
    }

    private void preloadFromURI(String uri, String sStatic)
        throws TransformerFactoryConfigurationError {
        if (uri.trim().isEmpty()) {
            return;
        }

        LOGGER.debug("preloading " + uri);

        Element xml;
        try {
            xml = resolve(uri.trim(), sStatic);
        } catch (Exception ex) {
            LOGGER.warn("Exception preloading " + uri, ex);
            return;
        }

        Map<String, Element> cache = chooseCacheLevel(uri, sStatic);
        handlePreloadedComponents(xml, cache);
    }

    /**
     * Cache all descendant components that have an @id, handle xed:modify|xed:extend afterwards
     */
    private void handlePreloadedComponents(Element xml, Map<String, Element> cache) {
        for (Element component : xml.getChildren()) {
            cacheComponent(cache, component);
            handlePreloadedComponents(component, cache);
            handleModify(cache, component);
        }
    }

    private void cacheComponent(Map<String, Element> cache, Element element) {
        String id = element.getAttributeValue(ATTR_ID);
        if ((id != null) && !id.isEmpty()) {
            LOGGER.debug("preloaded component " + id);
            cache.put(id, element);
        }
    }

    private void handleModify(Map<String, Element> cache, Element element) {
        if ("modify".equals(element.getName())) {
            String refID = element.getAttributeValue(ATTR_REF);
            if (refID == null) {
                throw new MCRUsageException("<xed:modify /> must have a @ref attribute!");
            }

            Element container = cache.get(refID);
            if (container == null) {
                LOGGER.warn("Ignoring xed:modify of " + refID + ", no component with that @id found");
                return;
            }

            container = container.clone();

            String newID = element.getAttributeValue(ATTR_ID);
            if (newID != null) {
                container.setAttribute(ATTR_ID, newID); // extend rather that modify
                LOGGER.debug("extending " + refID + " to " + newID);
            } else {
                LOGGER.debug("modifying " + refID);
            }

            for (Element command : element.getChildren()) {
                String commandType = command.getName();
                if (Objects.equals(commandType, "remove")) {
                    handleRemove(container, command);
                } else if (Objects.equals(commandType, "include")) {
                    handleInclude(container, command);
                }
            }
            cacheComponent(cache, container);
        }
    }

    private void handleRemove(Element container, Element removeRule) {
        String id = removeRule.getAttributeValue(ATTR_REF);
        LOGGER.debug("removing " + id);
        findDescendant(container, id).ifPresent(Element::detach);
    }

    private Optional<Element> findDescendant(Element container, String id) {
        IteratorIterable<Element> descendants = container.getDescendants(new ElementFilter());
        return StreamSupport.stream(descendants.spliterator(), false)
            .filter(e -> hasOrIncludesID(e, id)).findFirst();
    }

    private boolean hasOrIncludesID(Element e, String id) {
        if (id.equals(e.getAttributeValue(ATTR_ID))) {
            return true;
        } else {
            return "include".equals(e.getName()) && id.equals(e.getAttributeValue(ATTR_REF));
        }
    }

    private void handleInclude(Element container, Element includeRule) {
        boolean modified = handleBeforeAfter(container, includeRule, ATTR_BEFORE, 0, 0);
        if (!modified) {
            includeRule.setAttribute(ATTR_AFTER, includeRule.getAttributeValue(ATTR_AFTER, "*"));
            handleBeforeAfter(container, includeRule, ATTR_AFTER, 1, container.getChildren().size());
        }
    }

    private boolean handleBeforeAfter(Element container, Element includeRule, String attributeName, int offset,
        int defaultPos) {
        String refID = includeRule.getAttributeValue(attributeName);
        if (refID != null) {
            includeRule.removeAttribute(attributeName);

            Element parent = container;
            int pos = defaultPos;

            Optional<Element> neighbor = findDescendant(container, refID);
            if (neighbor.isPresent()) {
                Element n = neighbor.get();
                parent = n.getParentElement();
                List<Element> children = parent.getChildren();
                pos = children.indexOf(n) + offset;
            }

            LOGGER.debug("including  " + Arrays.toString(includeRule.getAttributes().toArray()) + " at pos " + pos);
            parent.getChildren().add(pos, includeRule.clone());
        }
        return refID != null;
    }

    public XNodeSet resolve(ExpressionContext context, String ref) throws TransformerException {
        LOGGER.debug("including component " + ref);
        Map<String, Element> cache = chooseCacheLevel(ref, Boolean.FALSE.toString());
        Element resolved = cache.get(ref);
        return (resolved == null ? null : asNodeSet(context, jdom2dom(resolved)));
    }

    public XNodeSet resolve(ExpressionContext context, String uri, String sStatic)
        throws TransformerException {
        LOGGER.debug("including xml " + uri);

        Element xml = resolve(uri, sStatic);
        Node node = jdom2dom(xml);

        try {
            return asNodeSet(context, node);
        } catch (Exception ex) {
            LOGGER.error(ex);
            throw ex;
        }
    }

    private Element resolve(String uri, String sStatic)
        throws TransformerFactoryConfigurationError {
        Map<String, Element> cache = chooseCacheLevel(uri, sStatic);

        if (cache.containsKey(uri)) {
            LOGGER.debug("uri was cached: " + uri);
            return cache.get(uri);
        } else {
            Element xml = MCRURIResolver.instance().resolve(uri);
            cache.put(uri, xml);
            return xml;
        }
    }

    private Map<String, Element> chooseCacheLevel(String key, String sStatic) {
        if (Objects.equals(sStatic, "true") || CACHE_AT_APPLICATION_LEVEL.containsKey(key)) {
            return CACHE_AT_APPLICATION_LEVEL;
        } else {
            return cacheAtTransformationLevel;
        }
    }

    private Node jdom2dom(Element element) throws TransformerException {
        DOMResult result = new DOMResult();
        JDOMSource source = new JDOMSource(element);
        TransformerFactory.newInstance().newTransformer().transform(source, result);
        return result.getNode();
    }

    private XNodeSet asNodeSet(ExpressionContext context, Node node) throws TransformerException {
        NodeSet nodeSet = new NodeSet();
        nodeSet.addNode(node);
        XPathContext xpc = context.getXPathContext();
        return new XNodeSetForDOM((NodeList) nodeSet, xpc);
    }
}
