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/*
 * Copyright 2011, 2012 Odysseus Software GmbH
 *
 * 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.
 */
package de.odysseus.staxon.event;

import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamReader;
import javax.xml.stream.events.XMLEvent;
import javax.xml.stream.util.XMLEventAllocator;

/**
 * Simple implementation of {@link XMLEventReader}.
 */
public class SimpleXMLEventReader implements XMLEventReader {
	private final XMLEventAllocator allocator;
	private final XMLStreamReader delegate;

	private int currentEventType = -1;
	private XMLEvent peekedEvent = null;

	public SimpleXMLEventReader(XMLStreamReader delegate) {
		this(delegate, new SimpleXMLEventAllocator());
	}

	public SimpleXMLEventReader(XMLStreamReader delegate, XMLEventAllocator allocator) {
		this.delegate = delegate;
		this.allocator = allocator;
	}

	protected XMLEvent allocate() throws XMLStreamException {
		return allocator.allocate(delegate);
	}

	@Override
	public void close() throws XMLStreamException {
		delegate.close();
	}

	@Override
	public String getElementText() throws XMLStreamException {
		if (currentEventType != XMLStreamConstants.START_ELEMENT) {
			throw new XMLStreamException("Expected start element event");
		}

		if (peekedEvent == null) {
			String result = delegate.getElementText();
			currentEventType = delegate.getEventType();
			if (currentEventType != XMLStreamConstants.END_ELEMENT) {
				throw new XMLStreamException("Expected end element event");
			}
			return result;
		}

		currentEventType = peekedEvent.getEventType();
		assert currentEventType == delegate.getEventType();
		peekedEvent = null;

		String leadText = null;
		switch (currentEventType) {
		case XMLStreamConstants.CDATA:
		case XMLStreamConstants.CHARACTERS:
		case XMLStreamConstants.ENTITY_REFERENCE:
			leadText = delegate.getText();
			break;
		case XMLStreamConstants.COMMENT:
		case XMLStreamConstants.PROCESSING_INSTRUCTION:
		case XMLStreamConstants.SPACE:
			break;
		case XMLStreamConstants.END_ELEMENT:
			return "";
		default:
			throw new XMLStreamException("Unexpected event type " + currentEventType, delegate.getLocation());
		}

		StringBuilder builder = null;
		while (true) {
			currentEventType = delegate.next();
			switch (currentEventType) {
			case XMLStreamConstants.CDATA:
			case XMLStreamConstants.CHARACTERS:
			case XMLStreamConstants.ENTITY_REFERENCE:
				if (leadText == null) { // first event?
					leadText = delegate.getText();
				} else {
					if (builder == null) { // second event?
						builder = new StringBuilder(leadText);
					}
					builder.append(delegate.getText());
				}
				break;
			case XMLStreamConstants.COMMENT:
			case XMLStreamConstants.PROCESSING_INSTRUCTION:
			case XMLStreamConstants.SPACE:
				break;
			case XMLStreamConstants.END_ELEMENT:
				return builder == null ? (leadText == null ? "" : leadText) : builder.toString();
			default:
				throw new XMLStreamException("Unexpected event type " + currentEventType, delegate.getLocation());
			}
		}
	}

	@Override
	public Object getProperty(String name) {
		return delegate.getProperty(name);
	}
	

	@Override
	public boolean hasNext() {
		try {
			return peek() != null;
		} catch (XMLStreamException e) {
			throw new RuntimeException("Cannot determine next state", e);
		}
	}

	@Override
	public XMLEvent nextEvent() throws XMLStreamException {
		XMLEvent currentEvent = peek();
		if (currentEvent == null) {
			throw new XMLStreamException("no more events");
		}
		currentEventType = currentEvent.getEventType();
		peekedEvent = null;
		return currentEvent;
	}

	@Override
	public Object next() {
		try {
			return nextEvent();
		} catch (XMLStreamException e) {
			throw new RuntimeException(e);
		}
	}

	@Override
	public XMLEvent nextTag() throws XMLStreamException {
		if (peekedEvent == null) {
			currentEventType = delegate.nextTag();
			if (currentEventType != XMLStreamConstants.START_ELEMENT && currentEventType != XMLStreamConstants.END_ELEMENT) {
				throw new XMLStreamException("Expected start element event or end element event");
				
			}
			return allocate();
		}

		currentEventType = peekedEvent.getEventType();
		assert currentEventType == delegate.getEventType();
		XMLEvent event = peekedEvent;
		peekedEvent = null;

		switch (event.getEventType()) {
		case XMLStreamConstants.START_DOCUMENT:
			break;
		case XMLStreamConstants.COMMENT:
		case XMLStreamConstants.PROCESSING_INSTRUCTION:
		case XMLStreamConstants.SPACE:
			break;
		case XMLStreamConstants.CDATA:
		case XMLStreamConstants.CHARACTERS:
			if (!event.asCharacters().isWhiteSpace()) {
				throw new XMLStreamException("Encountered non-whitespace text");
			}
			break;
		case XMLStreamConstants.START_ELEMENT:
		case XMLStreamConstants.END_ELEMENT:
			return event;
		default:
			throw new XMLStreamException("Encountered unexpected event: " + event.getEventType());
		}
		
		while (true) {
			currentEventType = delegate.next();
			switch (currentEventType) {
			case XMLStreamConstants.COMMENT:
			case XMLStreamConstants.PROCESSING_INSTRUCTION:
			case XMLStreamConstants.SPACE:
				continue;
			case XMLStreamConstants.CDATA:
			case XMLStreamConstants.CHARACTERS:
				if (!delegate.isWhiteSpace()) {
					throw new XMLStreamException("Encountered non-whitespace text");
				}
				continue;
			case XMLStreamConstants.START_ELEMENT:
			case XMLStreamConstants.END_ELEMENT:
				return allocate();
			default:
				throw new XMLStreamException("Encountered unexpected event: " + delegate.getEventType());
			}
		}
	}

	@Override
	public XMLEvent peek() throws XMLStreamException {
		if (peekedEvent == null) {
			if (currentEventType < 0) { // first event
				peekedEvent = allocate();
			} else if (delegate.hasNext()) {
				delegate.next();
				peekedEvent = allocate();
			}
		}
		return peekedEvent;
	}

	@Override
	public void remove() {
		throw new UnsupportedOperationException("Cannot remove events");
	}
}