/**
 * Copyright (c) 2008-2013, http://www.snakeyaml.org
 *
 * 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.yaml.snakeyaml.reader;

/**
 version: 1.1 / 2007-01-25
 - changed BOM recognition ordering (longer boms first)

 Original pseudocode   : Thomas Weidenfeller
 Implementation tweaked: Aki Nieminen
 Implementation changed: Andrey Somov 
 * UTF-32 removed because it is not supported by YAML
 * no default encoding

 http://www.unicode.org/unicode/faq/utf_bom.html
 BOMs:
 00 00 FE FF    = UTF-32, big-endian
 FF FE 00 00    = UTF-32, little-endian
 EF BB BF       = UTF-8,
 FE FF          = UTF-16, big-endian
 FF FE          = UTF-16, little-endian

 Win2k Notepad:
 Unicode format = UTF-16LE
 ***/

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackInputStream;
import java.io.Reader;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CodingErrorAction;

/**
 * Generic unicode textreader, which will use BOM mark to identify the encoding to be used. If BOM is not found then use a given default or
 * system encoding.
 */
public class UnicodeReader extends Reader {
	private static final Charset UTF8 = Charset.forName("UTF-8");
	private static final Charset UTF16BE = Charset.forName("UTF-16BE");
	private static final Charset UTF16LE = Charset.forName("UTF-16LE");

	PushbackInputStream internalIn;
	InputStreamReader internalIn2 = null;

	private static final int BOM_SIZE = 3;

	/**
	 * @param in
	 *            InputStream to be read
	 */
	public UnicodeReader(final InputStream in) {
		internalIn = new PushbackInputStream(in, BOM_SIZE);
	}

	/**
	 * Get stream encoding or NULL if stream is uninitialized. Call init() or read() method to initialize it.
	 */
	public String getEncoding() {
		return internalIn2.getEncoding();
	}

	/**
	 * Read-ahead four bytes and check for BOM marks. Extra bytes are unread back to the stream, only BOM bytes are skipped.
	 */
	protected void init() throws IOException {
		if (internalIn2 != null)
			return;

		Charset encoding;
		byte bom[] = new byte[BOM_SIZE];
		int n, unread;
		n = internalIn.read(bom, 0, bom.length);

		if ((bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB) && (bom[2] == (byte) 0xBF)) {
			encoding = UTF8;
			unread = n - 3;
		} else if ((bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF)) {
			encoding = UTF16BE;
			unread = n - 2;
		} else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)) {
			encoding = UTF16LE;
			unread = n - 2;
		} else {
			// Unicode BOM mark not found, unread all bytes
			encoding = UTF8;
			unread = n;
		}

		if (unread > 0)
			internalIn.unread(bom, (n - unread), unread);

		// Use given encoding
		CharsetDecoder decoder = encoding.newDecoder().onUnmappableCharacter(CodingErrorAction.REPORT);
		internalIn2 = new InputStreamReader(internalIn, decoder);
	}

	@Override
	public void close() throws IOException {
		init();
		internalIn2.close();
	}

	@Override
	public int read(final char[] cbuf, final int off, final int len) throws IOException {
		init();
		return internalIn2.read(cbuf, off, len);
	}
}