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/*
 * $Id: BaseXMLEventWriter.java,v 1.9 2005/03/09 22:34:34 cniles Exp $
 * 
 * Copyright (c) 2004, Christian Niles, Unit12
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 *		*   Redistributions of source code must retain the above copyright
 *          notice, this list of conditions and the following disclaimer.
 * 
 *	    *	Redistributions in binary form must reproduce the above copyright
 *          notice, this list of conditions and the following disclaimer in the
 *          documentation and/or other materials provided with the distribution.
 * 
 *      *   Neither the name of Christian Niles, Unit12, nor the names of its
 *          contributors may be used to endorse or promote products derived from
 *          this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 */
package javanet.staxutils;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

import javax.xml.namespace.NamespaceContext;
import javax.xml.namespace.QName;
import javax.xml.stream.XMLEventFactory;
import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLEventWriter;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.events.*;

/**
 * Base class for {@link XMLEventWriter} implementations. This implemenation
 * buffers Attribute and Namespace events as specified in the specification,
 * maintains a stack of NamespaceContext instances based on the events it
 * receives, and repairs any missing namespaces. Subclasses should implement the
 * {@link #sendEvent(XMLEvent)} method to receive the processed events and
 * perform additional processing.
 * 
 * @author Christian Niles
 * @version $Revision: 1.9 $
 */
public abstract class BaseXMLEventWriter implements XMLEventWriter {

    /**
     * XMLEventFactory used to construct XMLEvent instances.
     */
    protected XMLEventFactory factory;

    /** list of {@link SimpleNamespaceContext}s. */
    protected List nsStack = new ArrayList();

    /** 
     * Reference to the last StartElement sent. This will be null if no
     * StartElement has been sent, or after a non Attribute/Namespace
     * event is received.
     */
    protected StartElement lastStart;

    /**
     * LinkedHashMap of attribute events sent surrounding the last
     * StartElement. By using LinkedHashMap, the attributes will stay in the
     * order they were defined.
     */
    protected Map attrBuff = new LinkedHashMap();

    /**
     * LinkedHashMap of namespace events sent surrounding the last
     * StartElement. By using LinkedHashMap, the namespaces will stay in the
     * order they were defined.
     */
    protected Map nsBuff = new LinkedHashMap();

    /**
     * Whether this writer has been closed or not.
     */
    protected boolean closed;

    protected BaseXMLEventWriter() {

        this(null, null);

    }

    protected BaseXMLEventWriter(XMLEventFactory eventFactory,
            NamespaceContext nsCtx) {

        if (nsCtx != null) {

            nsStack.add(new SimpleNamespaceContext(nsCtx));

        } else {

            nsStack.add(new SimpleNamespaceContext());

        }

        if (eventFactory != null) {

            factory = eventFactory;

        } else {

            factory = XMLEventFactory.newInstance();

        }

    }

    public synchronized void flush() throws XMLStreamException {

        if (!closed) {

            sendCachedEvents();

        }

    }

    /**
     * Sends any events that have been cached in anticipation of further events.
     * 
     * @throws XMLStreamException If an error occurs sending the events.
     */
    private void sendCachedEvents() throws XMLStreamException {

        if (lastStart != null) {

            // A StartElement, and possibly attributes and namespaces, have been
            // cached. We need to combine them all into a single StartElement
            // event to send to sendEvent(XMLEvent)

            // First, construct the new NamespaceContext for the tag
            SimpleNamespaceContext nsCtx = this.pushNamespaceStack();

            // List used to store any defaulted/rewritten namespaces
            List namespaces = new ArrayList();

            // merge namespaces
            mergeNamespaces(lastStart.getNamespaces(), namespaces);
            mergeNamespaces(nsBuff.values().iterator(), namespaces);
            nsBuff.clear();

            // merge attributes
            List attributes = new ArrayList();
            mergeAttributes(lastStart.getAttributes(), namespaces, attributes);
            mergeAttributes(attrBuff.values().iterator(), namespaces,
                    attributes);
            attrBuff.clear();

            // determine the name of the new start tag
            QName tagName = lastStart.getName();
            QName newName = processQName(tagName, namespaces);

            // construct new element
            StartElement newStart = factory.createStartElement(
                    newName.getPrefix(), newName.getNamespaceURI(),
                    newName.getLocalPart(), attributes.iterator(),
                    namespaces.iterator(), nsCtx);

            lastStart = null;
            sendEvent(newStart);

        } else {

            // no start element was cached, but we may have cached some
            // namespaces and attributes that need to be written.

            for (Iterator i = nsBuff.values().iterator(); i.hasNext();) {

                XMLEvent evt = (XMLEvent) i.next();
                sendEvent(evt);

            }
            nsBuff.clear();

            for (Iterator i = attrBuff.values().iterator(); i.hasNext();) {

                XMLEvent evt = (XMLEvent) i.next();
                sendEvent(evt);

            }
            attrBuff.clear();

        }

    }

    /**
     * Merges a set of {@link Attribute} events, possibly adding additional
     * {@link Namespace} events if the attribute's prefix isn't bound in the
     * provided context.
     * 
     * @param iter An {@link Iterator} of {@link Attribute} events.
     * @param namespaces A {@link List} to which any new {@link Namespace}
     * 		events should be added.
     * @param attributes A {@link List} to which all {@link Attributes} events
     * 		should be merged.
     */
    private void mergeAttributes(Iterator iter, List namespaces, List attributes) {

        while (iter.hasNext()) {

            Attribute attr = (Attribute) iter.next();

            // check if the attribute QName has the proper mapping
            QName attrName = attr.getName();
            QName newName = processQName(attrName, namespaces);
            if (!attrName.equals(newName)) {

                // need to generate a new attribute with the new qualified name
                Attribute newAttr = factory.createAttribute(newName,
                        attr.getValue());
                attributes.add(newAttr);

            } else {

                // the attribute is fine
                attributes.add(attr);

            }

        }

    }

    /**
     * Merges a set of {@link Namespaces} events into the provided {@link List}.
     * 
     * @param iter An {@link Iterator} of {@link Namespace}s to merge.
     * @param namespaces A {@link List} containing all added {@link Namespace}
     * 		events.
     * @throws XMLStreamException If a conflicting namespace binding is
     * 		encountered.
     */
    private void mergeNamespaces(Iterator iter, List namespaces)
            throws XMLStreamException {

        // for each namespace, add it to the context, and place it in the list
        while (iter.hasNext()) {

            Namespace ns = (Namespace) iter.next();
            String prefix = ns.getPrefix();
            String nsURI = ns.getNamespaceURI();
            SimpleNamespaceContext nsCtx = this.peekNamespaceStack();

            if (!nsCtx.isPrefixDeclared(prefix)) {

                // mapping doesn't exist, so add it to the context/list
                if (prefix == null || prefix.length() == 0) {

                    nsCtx.setDefaultNamespace(nsURI);

                } else {

                    nsCtx.setPrefix(prefix, nsURI);

                }

                namespaces.add(ns);

            } else if (!nsCtx.getNamespaceURI(prefix).equals(nsURI)) {

                throw new XMLStreamException("Prefix already declared: " + ns,
                        ns.getLocation());

            } else {

                // duplicate namespace declaration

            }

        }

    }

    /**
     * Processes a {@link QName}, possibly rewriting it to match the current
     * namespace context.
     * 
     * @param name The {@link QName} to process.
     * @param namespaces A {@link List} of {@link Namespace} events to which any
     * 		new namespace bindings should be added.
     * @return The new name, or the name parameter if no changes
     * 		were necessary.
     */
    private QName processQName(QName name, List namespaces) {

        // get current context
        SimpleNamespaceContext nsCtx = this.peekNamespaceStack();

        // get name parts
        String nsURI = name.getNamespaceURI();
        String prefix = name.getPrefix();
        if (prefix != null && prefix.length() > 0) {

            // prefix provided; see if it is okay in current context, otherwise we'll
            // have to rewrite it
            String resolvedNS = nsCtx.getNamespaceURI(prefix);
            if (resolvedNS != null) {

                if (!resolvedNS.equals(nsURI)) {

                    // prefix is already bound to a different namespace; we have to
                    // find or generate and alternative prefix
                    String newPrefix = nsCtx.getPrefix(nsURI);
                    if (newPrefix == null) {

                        // no existing prefix; need to generate a new prefix
                        newPrefix = generatePrefix(nsURI, nsCtx, namespaces);

                    }

                    // return the newly prefixed name
                    return new QName(nsURI, name.getLocalPart(), newPrefix);

                } else {

                    // prefix bound to proper namespace; name is already ok

                }

            } else if (nsURI != null && nsURI.length() > 0) {

                // prefix isn't bound yet; bind it and the name is good to go
                nsCtx.setPrefix(prefix, nsURI);
                namespaces.add(factory.createNamespace(prefix, nsURI));

            }

            return name;

        } else if (nsURI != null && nsURI.length() > 0) {

            // name is namespaced, but has no prefix associated with it. Look for an
            // existing prefix, or generate one.
            String newPrefix = nsCtx.getPrefix(nsURI);
            if (newPrefix == null) {

                // no existing prefix; need to generate a new prefix
                newPrefix = generatePrefix(nsURI, nsCtx, namespaces);

            }

            // return the newly prefixed name
            return new QName(nsURI, name.getLocalPart(), newPrefix);

        } else {

            // name belongs to no namespace and has no prefix.
            return name;

        }

    }

    /**
     * Generates a new namespace prefix for the specified namespace URI that
     * doesn't collide with any existing prefix.
     * 
     * @param nsURI The URI for which to generate a prefix.
     * @param nsCtx The namespace context in which to set the prefix.
     * @param namespaces A {@link List} of {@link Namespace} events to which the
     * 		new prefix will be added.
     * @return The new prefix.
     */
    private String generatePrefix(String nsURI, SimpleNamespaceContext nsCtx,
            List namespaces) {

        String newPrefix;
        int nsCount = 0;
        do {

            newPrefix = "ns" + nsCount;
            nsCount++;

        } while (nsCtx.getNamespaceURI(newPrefix) != null);

        nsCtx.setPrefix(newPrefix, nsURI);
        namespaces.add(factory.createNamespace(newPrefix, nsURI));
        return newPrefix;

    }

    public synchronized void close() throws XMLStreamException {

        if (closed) {

            return;

        }

        try {

            flush();

        } finally {

            closed = true;

        }

    }

    public synchronized void add(XMLEvent event) throws XMLStreamException {

        if (closed) {

            throw new XMLStreamException("Writer has been closed");

        }

        // If the event is an Attribute or Namespace, cache it; otherwise, we
        // should send any previously cached items
        switch (event.getEventType()) {

            case XMLEvent.NAMESPACE :
                cacheNamespace((Namespace) event);
                return;

            case XMLEvent.ATTRIBUTE :
                cacheAttribute((Attribute) event);
                return;

            default :
                // send any cached events
                sendCachedEvents();

        }

        if (event.isStartElement()) {

            // cache the start element in case any following Attribute or
            // Namespace events occur
            lastStart = event.asStartElement();
            return;

        } else if (event.isEndElement()) {

            if (nsStack.isEmpty()) {

                throw new XMLStreamException("Mismatched end element event: "
                        + event);

            }

            SimpleNamespaceContext nsCtx = this.peekNamespaceStack();
            EndElement endTag = event.asEndElement();
            QName endElemName = endTag.getName();

            String prefix = endElemName.getPrefix();
            String nsURI = endElemName.getNamespaceURI();
            if (nsURI != null && nsURI.length() > 0) {

                // check that the prefix used in the name is bound to the same
                // namespace
                String boundURI = nsCtx.getNamespaceURI(prefix);
                if (!nsURI.equals(boundURI)) {

                    // not equal! now we must see what prefix it's actually
                    // bound to
                    String newPrefix = nsCtx.getPrefix(nsURI);
                    if (newPrefix != null) {

                        QName newName = new QName(nsURI,
                                endElemName.getLocalPart(), newPrefix);
                        event = factory.createEndElement(newName,
                                endTag.getNamespaces());

                    } else {

                        // no prefix is bound! report an error
                        throw new XMLStreamException("EndElement namespace ("
                                + nsURI + ") isn't bound [" + endTag + "]");

                    }

                }

            } else {

                // default namespace
                String defaultURI = nsCtx.getNamespaceURI("");
                if (defaultURI != null && defaultURI.length() > 0) {

                    throw new XMLStreamException("Unable to write " + event
                            + " because default namespace is occluded by "
                            + defaultURI);

                }

                // else, namespace matches and can be written directly

            }

            // pop the stack
            popNamespaceStack();

        }

        sendEvent(event);

    }

    public void add(XMLEventReader reader) throws XMLStreamException {

        while (reader.hasNext()) {

            add(reader.nextEvent());

        }

    }

    public synchronized String getPrefix(String nsURI)
            throws XMLStreamException {

        return getNamespaceContext().getPrefix(nsURI);

    }

    public synchronized void setPrefix(String prefix, String nsURI)
            throws XMLStreamException {

        peekNamespaceStack().setPrefix(prefix, nsURI);

    }

    public synchronized void setDefaultNamespace(String nsURI)
            throws XMLStreamException {

        peekNamespaceStack().setDefaultNamespace(nsURI);

    }

    public synchronized void setNamespaceContext(NamespaceContext root)
            throws XMLStreamException {

        SimpleNamespaceContext parent = (SimpleNamespaceContext) nsStack.get(0);
        parent.setParent(root);

    }

    public synchronized NamespaceContext getNamespaceContext() {

        return peekNamespaceStack();

    }

    /**
     * Removes the active {@link SimpleNamespaceContext} from the top of the
     * stack.
     * 
     * @return The {@link SimpleNamespaceContext} removed from the namespace 
     * 		stack.
     */
    protected SimpleNamespaceContext popNamespaceStack() {

        return (SimpleNamespaceContext) nsStack.remove(nsStack.size() - 1);

    }

    /**
     * Returns the active {@link SimpleNamespaceContext} from the top of the
     * stack.
     * 
     * @return The active {@link SimpleNamespaceContext} from the top of the
     * stack.
     */
    protected SimpleNamespaceContext peekNamespaceStack() {

        return (SimpleNamespaceContext) nsStack.get(nsStack.size() - 1);

    }

    /**
     * Creates a new {@link SimpleNamespaceContext} and adds it to the top of
     * the stack.
     * 
     * @return The new {@link SimpleNamespaceContext}.
     */
    protected SimpleNamespaceContext pushNamespaceStack() {

        SimpleNamespaceContext nsCtx;

        SimpleNamespaceContext parent = peekNamespaceStack();
        if (parent != null) {

            nsCtx = new SimpleNamespaceContext(parent);

        } else {

            nsCtx = new SimpleNamespaceContext();

        }

        nsStack.add(nsCtx);
        return nsCtx;

    }

    /**
     * Adds the specified {@link Attribute} to the attribute cache.
     * 
     * @param attr The attribute to cache.
     */
    protected void cacheAttribute(Attribute attr) {

        attrBuff.put(attr.getName(), attr);

    }

    /**
     * Adds the provided {@link Namespace} event to the namespace cache. The
     * current namespace context will not be affected.
     * 
     * @param ns The namespace to add to the cache.
     */
    protected void cacheNamespace(Namespace ns) {

        nsBuff.put(ns.getPrefix(), ns);

    }

    /**
     * Called by the methods of this class to write the event to the stream.
     * 
     * @param event The event to write.
     * @throws XMLStreamException If an error occurs processing the event.
     */
    protected abstract void sendEvent(XMLEvent event) throws XMLStreamException;

}




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