Copyright (c) 2008, 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.
/**
 * Copyright (c) 2008, 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.
/**
 * 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;

    
Params:
in – 
           InputStream to be read/**
     * @param in
     *            InputStream to be read
     */
    public UnicodeReader(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.
Returns:
the name of the character encoding being used by this stream./**
     * Get stream encoding or NULL if stream is uninitialized. Call init() or
     * read() method to initialize it.
     * @return the name of the character encoding being used by this stream.
     */
    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.
Throws:
IOException – if InputStream cannot be created/**
     * Read-ahead four bytes and check for BOM marks. Extra bytes are unread
     * back to the stream, only BOM bytes are skipped.
     * @throws  IOException if InputStream cannot be created
     */
    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);
    }

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

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