/*
 * Copyright 2002-2017 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
 *
 *      https://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.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import javax.xml.XMLConstants;
import javax.xml.namespace.QName;
import javax.xml.stream.XMLStreamException;

import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;
import org.xml.sax.ext.LexicalHandler;

import org.springframework.lang.Nullable;

/**
 * Abstract base class for SAX {@code ContentHandler} and {@code LexicalHandler}
 * implementations that use StAX as a basis. All methods delegate to internal template
 * methods, capable of throwing a {@code XMLStreamException}. Additionally, an namespace
 * context stack is used to keep track of declared namespaces.
 *
 * @author Arjen Poutsma
 * @since 4.0.3
 */
abstract class AbstractStaxHandler implements ContentHandler, LexicalHandler {

	private final List<Map<String, String>> namespaceMappings = new ArrayList<>();

	private boolean inCData;


	@Override
	public final void startDocument() throws SAXException {
		removeAllNamespaceMappings();
		newNamespaceMapping();
		try {
			startDocumentInternal();
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle startDocument: " + ex.getMessage(), ex);
		}
	}

	@Override
	public final void endDocument() throws SAXException {
		removeAllNamespaceMappings();
		try {
			endDocumentInternal();
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle endDocument: " + ex.getMessage(), ex);
		}
	}

	@Override
	public final void startPrefixMapping(String prefix, String uri) {
		currentNamespaceMapping().put(prefix, uri);
	}

	@Override
	public final void endPrefixMapping(String prefix) {
	}

	@Override
	public final void startElement(String uri, String localName, String qName, Attributes atts) throws SAXException {
		try {
			startElementInternal(toQName(uri, qName), atts, currentNamespaceMapping());
			newNamespaceMapping();
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle startElement: " + ex.getMessage(), ex);
		}
	}

	@Override
	public final void endElement(String uri, String localName, String qName) throws SAXException {
		try {
			endElementInternal(toQName(uri, qName), currentNamespaceMapping());
			removeNamespaceMapping();
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle endElement: " + ex.getMessage(), ex);
		}
	}

	@Override
	public final void characters(char[] ch, int start, int length) throws SAXException {
		try {
			String data = new String(ch, start, length);
			if (!this.inCData) {
				charactersInternal(data);
			}
			else {
				cDataInternal(data);
			}
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle characters: " + ex.getMessage(), ex);
		}
	}

	@Override
	public final void ignorableWhitespace(char[] ch, int start, int length) throws SAXException {
		try {
			ignorableWhitespaceInternal(new String(ch, start, length));
		}
		catch (XMLStreamException ex) {
			throw new SAXException(
					"Could not handle ignorableWhitespace:" + ex.getMessage(), ex);
		}
	}

	@Override
	public final void processingInstruction(String target, String data) throws SAXException {
		try {
			processingInstructionInternal(target, data);
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle processingInstruction: " + ex.getMessage(), ex);
		}
	}

	@Override
	public final void skippedEntity(String name) throws SAXException {
		try {
			skippedEntityInternal(name);
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle skippedEntity: " + ex.getMessage(), ex);
		}
	}

	@Override
	public final void startDTD(String name, @Nullable String publicId, String systemId) throws SAXException {
		try {
			StringBuilder builder = new StringBuilder("<!DOCTYPE ");
			builder.append(name);
			if (publicId != null) {
				builder.append(" PUBLIC \"");
				builder.append(publicId);
				builder.append("\" \"");
			}
			else {
				builder.append(" SYSTEM \"");
			}
			builder.append(systemId);
			builder.append("\">");

			dtdInternal(builder.toString());
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle startDTD: " + ex.getMessage(), ex);
		}
	}

	@Override
	public final void endDTD() throws SAXException {
	}

	@Override
	public final void startCDATA() throws SAXException {
		this.inCData = true;
	}

	@Override
	public final void endCDATA() throws SAXException {
		this.inCData = false;
	}

	@Override
	public final void comment(char[] ch, int start, int length) throws SAXException {
		try {
			commentInternal(new String(ch, start, length));
		}
		catch (XMLStreamException ex) {
			throw new SAXException("Could not handle comment: " + ex.getMessage(), ex);
		}
	}

	@Override
	public void startEntity(String name) throws SAXException {
	}

	@Override
	public void endEntity(String name) throws SAXException {
	}

	/**
	 * Convert a namespace URI and DOM or SAX qualified name to a {@code QName}. The
	 * qualified name can have the form {@code prefix:localname} or {@code localName}.
	 * @param namespaceUri the namespace URI
	 * @param qualifiedName the qualified name
	 * @return a QName
	 */
	protected QName toQName(String namespaceUri, String qualifiedName) {
		int idx = qualifiedName.indexOf(':');
		if (idx == -1) {
			return new QName(namespaceUri, qualifiedName);
		}
		else {
			String prefix = qualifiedName.substring(0, idx);
			String localPart = qualifiedName.substring(idx + 1);
			return new QName(namespaceUri, localPart, prefix);
		}
	}

	protected boolean isNamespaceDeclaration(QName qName) {
		String prefix = qName.getPrefix();
		String localPart = qName.getLocalPart();
		return (XMLConstants.XMLNS_ATTRIBUTE.equals(localPart) && prefix.isEmpty()) ||
				(XMLConstants.XMLNS_ATTRIBUTE.equals(prefix) && !localPart.isEmpty());
	}


	private Map<String, String> currentNamespaceMapping() {
		return this.namespaceMappings.get(this.namespaceMappings.size() - 1);
	}

	private void newNamespaceMapping() {
		this.namespaceMappings.add(new HashMap<>());
	}

	private void removeNamespaceMapping() {
		this.namespaceMappings.remove(this.namespaceMappings.size() - 1);
	}

	private void removeAllNamespaceMappings() {
		this.namespaceMappings.clear();
	}


	protected abstract void startDocumentInternal() throws XMLStreamException;

	protected abstract void endDocumentInternal() throws XMLStreamException;

	protected abstract void startElementInternal(QName name, Attributes attributes,
			Map<String, String> namespaceMapping) throws XMLStreamException;

	protected abstract void endElementInternal(QName name, Map<String, String> namespaceMapping)
			throws XMLStreamException;

	protected abstract void charactersInternal(String data) throws XMLStreamException;

	protected abstract void cDataInternal(String data) throws XMLStreamException;

	protected abstract void ignorableWhitespaceInternal(String data) throws XMLStreamException;

	protected abstract void processingInstructionInternal(String target, String data)
			throws XMLStreamException;

	protected abstract void skippedEntityInternal(String name) throws XMLStreamException;

	protected abstract void dtdInternal(String dtd) throws XMLStreamException;

	protected abstract void commentInternal(String comment) throws XMLStreamException;

}
