/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */
package org.apache.sis.xml;

import java.util.Map;
import java.util.Set;
import java.util.List;
import java.util.HashMap;
import java.util.HashSet;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.Collections;
import javax.xml.namespace.QName;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLEventReader;
import javax.xml.stream.events.XMLEvent;
import javax.xml.stream.events.Attribute;
import javax.xml.stream.events.Namespace;
import javax.xml.stream.events.EndElement;
import javax.xml.stream.events.StartElement;
import org.apache.sis.util.collection.BackingStoreException;

import static javax.xml.stream.XMLStreamConstants.*;


/**
 * A XML reader replacing the namespaces found in XML documents by the namespaces expected by SIS at unmarshalling time.
 * This class forwards every method calls to the wrapped {@link XMLEventReader}, but with some {@code namespaceURI}
 * modified before being transferred. This class uses a dictionary for identifying the XML namespaces expected by JAXB
 * implementation. This is needed when a single namespace in a legacy schema has been splitted into many namespaces
 * in the newer schema. This happen for example in the upgrade from ISO 19139:2007 to ISO 19115-3.
 * In such cases, we need to check which attribute is being mapped in order to determine the new namespace.
 *
 * @author  Cullen Rombach (Image Matters)
 * @author  Martin Desruisseaux (Geomatys)
 * @version 1.0
 * @since   1.0
 * @module
 */
final class TransformingReader extends Transformer implements XMLEventReader {
    /**
     * Location of the file listing types and their properties contained in various namespaces.
     * This is used for mapping legacy ISO 19139:2007 namespace to newer ISO 19115-3:2016 ones,
     * where the same legacy {@code "http://www.isotc211.org/2005/gmd"} URI can be replaced by
     * different URIs under {@code "http://standards.iso.org/iso/19115/-3/…"} depending on the
     * class name. Syntax is documented in the <a href="readme.html">readme.html</a> page.
     */
    static final String FILENAME = "RenameOnImport.lst";

    /**
     * Namespaces of classes containing elements to move in different namespaces.
     * This set will contain at least the following namespaces:
     *
     * <ul>
     *   <li>{@value org.apache.sis.internal.xml.LegacyNamespaces#GMI}</li>
     *   <li>{@value org.apache.sis.internal.xml.LegacyNamespaces#GMI_ALIAS}</li>
     *   <li>{@value org.apache.sis.internal.xml.LegacyNamespaces#GMD}</li>
     *   <li>{@value org.apache.sis.internal.xml.LegacyNamespaces#SRV}</li>
     *   <li>{@value org.apache.sis.internal.xml.LegacyNamespaces#GCO}</li>
     *   <li>{@value org.apache.sis.internal.xml.LegacyNamespaces#GMX}</li>
     *   <li>{@value org.apache.sis.internal.xml.LegacyNamespaces#GML}</li>
     * </ul>
     *
     * More namespaces may appear depending on the optional module on the classpath.
     * For example {@code sis-french-profile} adds {@code "http://www.cnig.gouv.fr/2005/fra"}.
     */
    private static final Set<String> LEGACY_NAMESPACES = new HashSet<>(12);

    /**
     * The mapping from (<var>type</var>, <var>attribute</var>) pairs to new namespaces.
     * This mapping will be applied only to namespaces enumerated in {@link #LEGACY_NAMESPACES}.
     *
     * <ul>
     *   <li>Keys are XML names of types, ignoring {@code "_TYPE"} suffix (e.g. {@code "CI_Citation"})</li>
     *   <li>Values are maps where:<ul>
     *     <li>Keys are XML names of properties (e.g. {@code "title"}).</li>
     *     <li>Values are either:<ul>
     *       <li>Namespace URI if {@link #isNamespace(String)} returns {@code true} for that value.</li>
     *       <li>New name of the element otherwise. In such case, the map must be queried again with
     *           that new name for obtaining the namespace.</li>
     *     </ul></li>
     *   </ul></li>
     * </ul>
     *
     * This map is initialized only once and should not be modified after that point.
     */
    private static final Map<String, Map<String,String>> NAMESPACES = load(false, FILENAME, LEGACY_NAMESPACES, 260);
    // TODO: use Set.copyOf(…) with JDK10.

    /**
     * Returns the namespace for the given ISO type, or {@code null} if unknown.
     * This is the namespace used in JAXB annotations.
     *
     * @param  type  a class name defined by ISO 19115 or related standards (e.g. {@code "CI_Citation"}).
     * @return a namespace for the given type, or {@code null} if unknown.
     */
    static String namespace(final String type) {
        final Map<String,String> attributes = NAMESPACES.get(type);
        return (attributes != null) ? attributes.get(type) : null;
    }

    /**
     * The reader from which to read events.
     */
    private final XMLEventReader in;

    /**
     * The prefixes for namespace URIs. Keys are URIs used in JAXB annotations and values are prefixes
     * computed by {@link Namespaces#getPreferredPrefix(String, String)} or any other means. We store
     * the prefix both for performance reasons and for improving the guarantees that the URI → prefix
     * mapping is stable.
     *
     * @see #prefixReplacement(String, String)
     */
    private final Map<String,String> prefixes;

    /**
     * The next event to return after a call to {@link #peek()}. This is used for avoiding to recompute
     * the same object many times when {@link #peek()} is invoked before a call to {@link #nextEvent()}.
     * This is also required for avoiding to duplicate additions and removals of elements in the
     * {@code outerElements} list.
     */
    private XMLEvent nextEvent;

    /**
     * Creates a new reader for the given version of the standards.
     */
    TransformingReader(final XMLEventReader in, final TransformVersion version) {
        super(version);
        this.in = in;
        prefixes = new HashMap<>();
    }

    /**
     * Returns {@code true} if the given {@code wrapper} is a wrapper for the given {@code event}.
     * This method is used for assertions only.
     */
    private static boolean isWrapper(final XMLEvent event, final XMLEvent wrapper) {
        return (event == wrapper) || (wrapper instanceof TransformedEvent && ((TransformedEvent) wrapper).event == event);
    }

    /**
     * Checks if there are more events.
     */
    @Override
    public boolean hasNext() {
        return (nextEvent != null) || in.hasNext();
    }

    /**
     * Checks the next {@code XMLEvent} without removing it from the stream.
     */
    @Override
    public XMLEvent peek() throws XMLStreamException {
        if (nextEvent == null) {
            final XMLEvent event = in.peek();
            if (event != null) {
                nextEvent = convert(event);
            }
        }
        return nextEvent;
    }

    /**
     * Returns the next element. Use {@link #nextEvent()} instead.
     */
    @Override
    public Object next() {
        try {
            return nextEvent();
        } catch (XMLStreamException e) {
            throw new BackingStoreException(e);
        }
    }

    /**
     * Forwards the call and keep trace of the XML elements opened up to this point.
     */
    @Override
    public XMLEvent nextEvent() throws XMLStreamException {
        final XMLEvent event = in.nextEvent();
        final XMLEvent next  = nextEvent;
        if (next != null) {
            nextEvent = null;
            assert isWrapper(event, next) : event;
            return next;
        }
        return convert(event);
    }

    /**
     * Forwards the call and keep trace of the XML elements opened up to this point.
     */
    @Override
    public XMLEvent nextTag() throws XMLStreamException {
        final XMLEvent event = in.nextTag();
        final XMLEvent next  = nextEvent;
        if (next != null) {
            nextEvent = null;
            switch (event.getEventType()) {
                case START_ELEMENT:
                case END_ELEMENT: {
                    assert isWrapper(event, next) : event;
                    return event;
                }
            }
        }
        return convert(event);
    }

    /**
     * Keeps trace of XML elements opened up to this point and imports the given event.
     * This method replaces the namespaces used in XML document by the namespace used by JAXB annotations.
     * It is caller's responsibility to ensure that this method is invoked exactly once for each element,
     * or at least for each {@code START_ELEMENT} and {@code END_ELEMENT}.
     *
     * @param  event  the event read from the underlying event reader.
     * @return the converted event (may be the same instance).
     */
    private XMLEvent convert(XMLEvent event) throws XMLStreamException {
        switch (event.getEventType()) {
            case ATTRIBUTE: {
                event = convert((Attribute) event);
                break;
            }
            case NAMESPACE: {
                event = importNS((Namespace) event, null, null);
                break;
            }
            case START_ELEMENT: {
                final StartElement e = event.asStartElement();
                final QName originalName = e.getName();
                open(originalName);                             // Must be invoked before 'convert(QName)'.
                final QName name  = convert(originalName);      // Name in the transformed XML document.
                boolean changed   = name != originalName;       // Whether the name or an attribute changed.
                Namespace localNS = null;                       // Additional namespace required by "xsi:type".
                for (final Iterator<Attribute> it = e.getAttributes(); it.hasNext();) {
                    final Attribute a = it.next();
                    final Attribute ae = convert(a);
                    renamedAttributes.add(ae);
                    if (a != ae) {
                        changed = true;
                        if (localNS == null && ae instanceof TransformedEvent.Type) {
                            localNS = ((TransformedEvent.Type) ae).namespace;
                        }
                    }
                }
                /*
                 * The list of namespaces is determined by the "xmlns:foo" attributes, which are handled in a
                 * special way. This list is typically non-empty only in the root element, but it is legal to
                 * have namespace declaration in non-root elements as well.
                 *
                 * Special case: if this element contains a "xsi:type" attribute and if we changed its value
                 * (for example from "gmd:PT_FreeText_PropertyType" to "lan:PT_FreeText_PropertyType"), then
                 * we may need to add an extra namespace declaration (e.g. for the "lan" prefix).
                 */
                List<Namespace> namespaces = importNS(e.getNamespaces(),
                        originalName.getNamespaceURI(), name.getNamespaceURI(), changed);
                if (namespaces != null) {
                    if (localNS != null) {
                        if (namespaces.isEmpty()) {
                            namespaces = Collections.singletonList(localNS);
                        } else {
                            namespaces.add(localNS);
                        }
                    }
                    event = new TransformedEvent.Start(e, name, namespaces, attributes(), version);
                } else {
                    renamedAttributes.clear();          // Note: above call to attributes() also cleared that list.
                }
                break;
            }
            case END_ELEMENT: {
                final EndElement e = event.asEndElement();
                final QName originalName = e.getName();
                final QName name = convert(originalName);
                final List<Namespace> namespaces = importNS(e.getNamespaces(),
                        originalName.getNamespaceURI(), name.getNamespaceURI(), name != originalName);
                if (namespaces != null) {
                    event = new TransformedEvent.End(e, name, namespaces);
                }
                close(originalName);                    // Must be invoked only after 'convert(QName)'
                break;
            }
        }
        return event;
    }

    /**
     * Returns the map loaded by {@link #load(boolean, String, Set, int)} if the given namespace is a known legacy namespace.
     * This method returns a non-empty map only for legacy namespaces for which the {@value #FILENAME} file has been designed.
     * This is necessary for avoiding confusion with classes of the same name defined in other standards.
     * For example the {@code Record} class name is used by other standards like Catalog Service for the Web (OGC CSW),
     * and we don't want to replace the namespace of CSW classes.
     *
     * @param  namespace  the namespace URI for which to get the substitution map.
     * @return the substitution map for the given namespace, or an empty map if none.
     */
    @Override
    @SuppressWarnings("ReturnOfCollectionOrArrayField")
    final Map<String, Map<String,String>> renamingMap(final String namespace) {
        if (!namespace.isEmpty()) {
            if (LEGACY_NAMESPACES.contains(removeTrailingSlash(namespace))) {
                return NAMESPACES;
            }
        }
        return Collections.emptyMap();
    }

    /**
     * Returns the new namespace for elements (types and properties) in the given namespace.
     * This method is used only for default relocations, i.e. the fallback to apply when no
     * explicit rule has been found.
     */
    @Override
    final String relocate(final String namespace) {
        return version.importNS(namespace);
    }

    /**
     * Returns the prefix to use for a name in a new namespace. The prefix should have been specified (indirectly)
     * by a previous call to {@code importNS(Namespace, …)}, for example as a result of a {@code NAMESPACE} event.
     * If not, we compute it now using the same algorithm than in {@code importNS}.
     *
     * @param  previous   the prefix associated to old namespace.
     * @param  namespace  the new namespace URI.
     * @return prefix to use for the new namespace.
     */
    @Override
    final String prefixReplacement(final String previous, final String namespace) {
        return prefixes.computeIfAbsent(namespace, (ns) -> Namespaces.getPreferredPrefix(ns, previous));
    }

    /**
     * Converts a namespace read from the XML document to the namespace used by JAXB annotations.
     * This methods can convert the namespace for which there is a bijective mapping, for example
     * {@code "http://www.isotc211.org/2005/gco"} to {@code "http://standards.iso.org/iso/19115/-3/gco/1.0"}.
     * However some namespaces like {@code "http://www.isotc211.org/2005/gmd"} may be left unchanged,
     * because that namespace from legacy ISO 19139:2007 can be mapped to many different namespaces
     * in newer ISO 19115-3:2016 standard. However in some cases the context allows us to determines
     * which newer namespace is used. In such case, that mapping is specified by the
     * ({@code oldURI}, {@code newURI}) pair.
     *
     * @param  namespace  the namespace to import.
     * @param  oldURI     an old URI which has been renamed as {@code newURI}, or {@code null} if none.
     * @param  newURI     the new URI for {@code oldURI}, or {@code null} if {@code newURI} is null.
     */
    private Namespace importNS(final Namespace namespace, final String oldURI, final String newURI) {
        notify(namespace);
        String uri = namespace.getNamespaceURI();
        if (uri != null && !uri.isEmpty()) {
            uri = removeTrailingSlash(uri);
            final String imported = uri.equals(oldURI) ? newURI : relocate(uri);
            if (imported != uri) {
                final String prefix = prefixReplacement(namespace.getPrefix(), imported);
                return new TransformedEvent.NS(namespace, prefix, imported);
            }
        }
        return namespace;
    }

    /**
     * Imports the namespaces read from the XML document.
     *
     * @param  namespaces  the namespaces to transform.
     * @param  oldURI      an old URI which has been renamed as {@code newURI}, or {@code null} if none.
     * @param  newURI      the new URI for {@code oldURI}, or {@code null} if {@code newURI} is null.
     * @param  changed     whether to unconditionally pretend that there is a change.
     * @return the updated namespaces, or {@code null} if there is no changes.
     */
    private List<Namespace> importNS(final Iterator<Namespace> namespaces,
            final String oldURI, final String newURI, boolean changed)
    {
        if (!namespaces.hasNext()) {
            return changed ? Collections.emptyList() : null;
        }
        final List<Namespace> modified = new ArrayList<>();
        do {
            Namespace namespace = namespaces.next();
            changed |= (namespace != (namespace = importNS(namespace, oldURI, newURI)));
            modified.add(namespace);
        } while (namespaces.hasNext());
        return changed ? modified : null;
    }

    /**
     * Reads the content of a text-only element. Forwards from the underlying reader as-is.
     *
     * @todo Untested. In particular, it is not clear how to update {@code outerElements}.
     *       By chance, JAXB does not seem to invoke this method.
     */
    @Override
    public String getElementText() throws XMLStreamException {
        return in.getElementText();
    }

    /**
     * Get the value of a feature/property from the underlying implementation.
     */
    @Override
    public Object getProperty​(final String name) {
        return in.getProperty(name);
    }

    /**
     * Frees any resources associated with this reader.
     * This method does not close the underlying input source.
     */
    @Override
    public void close() throws XMLStreamException {
        super.close();
        in.close();
    }
}
