package freemind.common;

/**
 * 
 * fc, 2010-12-23 Taken from http://koti.mbnet.fi/akini/java/unicodereader/UnicodeReader.java.txt
 * asuming public domain.
 * 
 version: 1.1 / 2007-01-25
 - changed BOM recognition ordering (longer boms first)

 Original pseudocode   : Thomas Weidenfeller
 Implementation tweaked: Aki Nieminen

 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;

/**
 * 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 {
	PushbackInputStream internalIn;
	InputStreamReader internalIn2 = null;
	String defaultEnc;

	private static final int BOM_SIZE = 4;

	/**
	 * 
	 * @param in
	 *            inputstream to be read
	 * @param defaultEnc
	 *            default encoding if stream does not have BOM marker. Give NULL
	 *            to use system-level default.
	 */
	public UnicodeReader(InputStream in, String defaultEnc) {
		internalIn = new PushbackInputStream(in, BOM_SIZE);
		this.defaultEnc = defaultEnc;
	}

	public String getDefaultEncoding() {
		return defaultEnc;
	}

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

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

		if ((bom[0] == (byte) 0x00) && (bom[1] == (byte) 0x00)
				&& (bom[2] == (byte) 0xFE) && (bom[3] == (byte) 0xFF)) {
			encoding = "UTF-32BE";
			unread = n - 4;
		} else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)
				&& (bom[2] == (byte) 0x00) && (bom[3] == (byte) 0x00)) {
			encoding = "UTF-32LE";
			unread = n - 4;
		} else if ((bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB)
				&& (bom[2] == (byte) 0xBF)) {
			encoding = "UTF-8";
			unread = n - 3;
		} else if ((bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF)) {
			encoding = "UTF-16BE";
			unread = n - 2;
		} else if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)) {
			encoding = "UTF-16LE";
			unread = n - 2;
		} else {
			// Unicode BOM mark not found, unread all bytes
			encoding = defaultEnc;
			unread = n;
		}
		// System.out.println("read=" + n + ", unread=" + unread);

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

		// Use given encoding
		if (encoding == null) {
			internalIn2 = new InputStreamReader(internalIn);
		} else {
			internalIn2 = new InputStreamReader(internalIn, encoding);
		}
	}

	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);
	}

}