/*
 * Copyright 2002-2016 the original author or authors.
 *
 * 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 org.springframework.util.xml;

import java.util.NoSuchElementException;
import javax.xml.stream.XMLEventReader;
import javax.xml.stream.XMLStreamConstants;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.events.Characters;
import javax.xml.stream.events.XMLEvent;

import org.springframework.lang.Nullable;
import org.springframework.util.ClassUtils;

/**
 * Abstract base class for {@code XMLEventReader}s.
 *
 * @author Arjen Poutsma
 * @since 5.0
 */
abstract class AbstractXMLEventReader implements XMLEventReader {

	private boolean closed;


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

	@Override
	public void remove() {
		throw new UnsupportedOperationException(
				"remove not supported on " + ClassUtils.getShortName(getClass()));
	}

	@Override
	public String getElementText() throws XMLStreamException {
		checkIfClosed();
		if (!peek().isStartElement()) {
			throw new XMLStreamException("Not at START_ELEMENT");
		}

		StringBuilder builder = new StringBuilder();
		while (true) {
			XMLEvent event = nextEvent();
			if (event.isEndElement()) {
				break;
			}
			else if (!event.isCharacters()) {
				throw new XMLStreamException(
						"Unexpected event [" + event + "] in getElementText()");
			}
			Characters characters = event.asCharacters();
			if (!characters.isIgnorableWhiteSpace()) {
				builder.append(event.asCharacters().getData());
			}
		}
		return builder.toString();
	}

	@Override
	@Nullable
	public XMLEvent nextTag() throws XMLStreamException {
		checkIfClosed();
		while (true) {
			XMLEvent event = nextEvent();
			switch (event.getEventType()) {
				case XMLStreamConstants.START_ELEMENT:
				case XMLStreamConstants.END_ELEMENT:
					return event;
				case XMLStreamConstants.END_DOCUMENT:
					return null;
				case XMLStreamConstants.SPACE:
				case XMLStreamConstants.COMMENT:
				case XMLStreamConstants.PROCESSING_INSTRUCTION:
					continue;
				case XMLStreamConstants.CDATA:
				case XMLStreamConstants.CHARACTERS:
					if (!event.asCharacters().isWhiteSpace()) {
						throw new XMLStreamException(
								"Non-ignorable whitespace CDATA or CHARACTERS event in nextTag()");
					}
					break;
				default:
					throw new XMLStreamException("Received event [" + event +
							"], instead of START_ELEMENT or END_ELEMENT.");
			}
		}
	}

	/**
	 * Throws an {@code IllegalArgumentException} when called.
	 * @throws IllegalArgumentException when called.
	 */
	@Override
	public Object getProperty(String name) throws IllegalArgumentException {
		throw new IllegalArgumentException("Property not supported: [" + name + "]");
	}

	@Override
	public void close() {
		this.closed = true;
	}

	/**
	 * Returns {@code true} if closed; {@code false} otherwise.
	 * @see #close()
	 */
	protected boolean isClosed() {
		return this.closed;
	}

	/**
	 * Checks if the reader is closed, and throws a {@code XMLStreamException} if so.
	 * @throws XMLStreamException if the reader is closed
	 * @see #close()
	 * @see #isClosed()
	 */
	protected void checkIfClosed() throws XMLStreamException {
		if (isClosed()) {
			throw new XMLStreamException("XMLEventReader has been closed");
		}
	}

}
