/*
 *******************************************************************************
 * Copyright (C) 1996-2004, International Business Machines Corporation and    *
 * others. All Rights Reserved.                                                *
 *******************************************************************************
 */

package com.ibm.icu.text;

/**
* A decompression engine implementing the Standard Compression Scheme
* for Unicode (SCSU) as outlined in <A
* HREF="http://www.unicode.org/unicode/reports/tr6">Unicode Technical
* Report #6</A>.
*
* <P><STRONG>USAGE</STRONG></P>
*
* <P>The static methods on <TT>UnicodeDecompressor</TT> may be used in a
* straightforward manner to decompress simple strings:</P>
*
* <PRE>
*  byte [] compressed = ... ; // get compressed bytes from somewhere
*  String result = UnicodeDecompressor.decompress(compressed);
* </PRE>
*
* <P>The static methods have a fairly large memory footprint.
* For finer-grained control over memory usage, 
* <TT>UnicodeDecompressor</TT> offers more powerful APIs allowing
* iterative decompression:</P>
*
* <PRE>
*  // Decompress an array "bytes" of length "len" using a buffer of 512 chars
*  // to the Writer "out"
*
*  UnicodeDecompressor myDecompressor         = new UnicodeDecompressor();
*  final static int    BUFSIZE                = 512;
*  char []             charBuffer             = new char [ BUFSIZE ];
*  int                 charsWritten           = 0;
*  int []              bytesRead              = new int [1];
*  int                 totalBytesDecompressed = 0;
*  int                 totalCharsWritten      = 0;
*
*  do {
*    // do the decompression
*    charsWritten = myDecompressor.decompress(bytes, totalBytesDecompressed, 
*                                             len, bytesRead,
*                                             charBuffer, 0, BUFSIZE);
*
*    // do something with the current set of chars
*    out.write(charBuffer, 0, charsWritten);
*
*    // update the no. of bytes decompressed
*    totalBytesDecompressed += bytesRead[0];
*
*    // update the no. of chars written
*    totalCharsWritten += charsWritten;
*
*  } while(totalBytesDecompressed < len);
*
*  myDecompressor.reset(); // reuse decompressor
* </PRE>
*
* <P>Decompression is performed according to the standard set forth in 
* <A HREF="http://www.unicode.org/unicode/reports/tr6">Unicode Technical 
* Report #6</A></P>
*
* @see UnicodeCompressor
*
* @author Stephen F. Booth
* @stable ICU 2.4
*/
public final class UnicodeDecompressor implements SCSU
{
    //==========================
    // Instance variables
    //==========================
    
    /** Alias to current dynamic window */
    private int       fCurrentWindow   = 0;

    /** Dynamic compression window offsets */
    private int []    fOffsets         = new int [ NUMWINDOWS ];

    /** Current compression mode */
    private int       fMode            = SINGLEBYTEMODE;

    /** Size of our internal buffer */
    private final static int BUFSIZE   = 3;

    /** Internal buffer for saving state */
    private byte []   fBuffer          = new byte [BUFSIZE];

    /** Number of characters in our internal buffer */
    private int       fBufferLength    = 0;
    

    /**
     * Create a UnicodeDecompressor.
     * Sets all windows to their default values.
     * @see #reset
     * @stable ICU 2.4
     */
    public UnicodeDecompressor()
    {
	reset();              // initialize to defaults
    }

    /**
     * Decompress a byte array into a String.
     * @param buffer The byte array to decompress.
     * @return A String containing the decompressed characters.
     * @see #decompress(byte [], int, int)
     * @stable ICU 2.4
     */
    public static String decompress(byte [] buffer)
    {
	char [] buf = decompress(buffer, 0, buffer.length);
	return new String(buf);
    }

    /**
     * Decompress a byte array into a Unicode character array.
     * @param buffer The byte array to decompress.
     * @param start The start of the byte run to decompress.
     * @param limit The limit of the byte run to decompress.
     * @return A character array containing the decompressed bytes.
     * @see #decompress(byte [])
     * @stable ICU 2.4
     */
    public static char [] decompress(byte [] buffer,
				     int start,
				     int limit)
    {
	UnicodeDecompressor comp = new UnicodeDecompressor();

	// use a buffer we know will never overflow
	// in the worst case, each byte will decompress
	// to a surrogate pair (buffer must be at least 2 chars)
	int len = Math.max(2, 2 * (limit - start));
	char [] temp = new char [len];

	int charCount = comp.decompress(buffer, start, limit, null, 
					temp, 0, len);

	char [] result = new char [charCount];
	System.arraycopy(temp, 0, result, 0, charCount);
	return result;
    }
    
    /**
     * Decompress a byte array into a Unicode character array.
     *
     * This function will either completely fill the output buffer, 
     * or consume the entire input.  
     *
     * @param byteBuffer The byte buffer to decompress.
     * @param byteBufferStart The start of the byte run to decompress.
     * @param byteBufferLimit The limit of the byte run to decompress.
     * @param bytesRead A one-element array.  If not null, on return
     * the number of bytes read from byteBuffer.
     * @param charBuffer A buffer to receive the decompressed data. 
     * This buffer must be at minimum two characters in size.
     * @param charBufferStart The starting offset to which to write 
     * decompressed data.
     * @param charBufferLimit The limiting offset for writing 
     * decompressed data.
     * @return The number of Unicode characters written to charBuffer.
     * @stable ICU 2.4
     */
    public int decompress(byte []    byteBuffer,
			  int        byteBufferStart,
			  int        byteBufferLimit,
			  int []     bytesRead,
			  char []    charBuffer,
			  int        charBufferStart,
			  int        charBufferLimit)
    {
	// the current position in the source byte buffer
	int bytePos      = byteBufferStart;
	
	// the current position in the target char buffer
	int ucPos        = charBufferStart;
        
        // the current byte from the source buffer
	int aByte        = 0x00;


	// charBuffer must be at least 2 chars in size
	if(charBuffer.length < 2 || (charBufferLimit - charBufferStart) < 2)
	    throw new IllegalArgumentException("charBuffer.length < 2");
	
	// if our internal buffer isn't empty, flush its contents
	// to the output buffer before doing any more decompression
	if(fBufferLength > 0) {

	    int newBytes = 0;

	    // fill the buffer completely, to guarantee one full character
	    if(fBufferLength != BUFSIZE) {
		newBytes = fBuffer.length - fBufferLength;

		// verify there are newBytes bytes in byteBuffer
		if(byteBufferLimit - byteBufferStart < newBytes)
		    newBytes = byteBufferLimit - byteBufferStart;

		System.arraycopy(byteBuffer, byteBufferStart, 
				 fBuffer, fBufferLength, newBytes);
	    }

	    // reset buffer length to 0 before recursive call
	    fBufferLength = 0;

	    // call self recursively to decompress the buffer
	    int count = decompress(fBuffer, 0, fBuffer.length, null,
				   charBuffer, charBufferStart, 
				   charBufferLimit);

	    // update the positions into the arrays
	    ucPos += count;
	    bytePos += newBytes;
	}

        // the main decompression loop
    mainLoop:
	while(bytePos < byteBufferLimit && ucPos < charBufferLimit) {
	    switch(fMode) {  
	    case SINGLEBYTEMODE:
		// single-byte mode decompression loop
	    singleByteModeLoop:
	    while(bytePos < byteBufferLimit && ucPos < charBufferLimit) {
		aByte = byteBuffer[bytePos++] & 0xFF;
		switch(aByte) {
		    // All bytes from 0x80 through 0xFF are remapped
		    // to chars or surrogate pairs according to the
		    // currently active window
		case 0x80: case 0x81: case 0x82: case 0x83: case 0x84: 
		case 0x85: case 0x86: case 0x87: case 0x88: case 0x89:
		case 0x8A: case 0x8B: case 0x8C: case 0x8D: case 0x8E:
		case 0x8F: case 0x90: case 0x91: case 0x92: case 0x93:
		case 0x94: case 0x95: case 0x96: case 0x97: case 0x98:
		case 0x99: case 0x9A: case 0x9B: case 0x9C: case 0x9D:
		case 0x9E: case 0x9F: case 0xA0: case 0xA1: case 0xA2:
		case 0xA3: case 0xA4: case 0xA5: case 0xA6: case 0xA7:
		case 0xA8: case 0xA9: case 0xAA: case 0xAB: case 0xAC:
		case 0xAD: case 0xAE: case 0xAF: case 0xB0: case 0xB1:
		case 0xB2: case 0xB3: case 0xB4: case 0xB5: case 0xB6:
		case 0xB7: case 0xB8: case 0xB9: case 0xBA: case 0xBB:
		case 0xBC: case 0xBD: case 0xBE: case 0xBF: case 0xC0:
		case 0xC1: case 0xC2: case 0xC3: case 0xC4: case 0xC5:
		case 0xC6: case 0xC7: case 0xC8: case 0xC9: case 0xCA:
		case 0xCB: case 0xCC: case 0xCD: case 0xCE: case 0xCF:
		case 0xD0: case 0xD1: case 0xD2: case 0xD3: case 0xD4:
		case 0xD5: case 0xD6: case 0xD7: case 0xD8: case 0xD9:
		case 0xDA: case 0xDB: case 0xDC: case 0xDD: case 0xDE:
		case 0xDF: case 0xE0: case 0xE1: case 0xE2: case 0xE3:
		case 0xE4: case 0xE5: case 0xE6: case 0xE7: case 0xE8:
		case 0xE9: case 0xEA: case 0xEB: case 0xEC: case 0xED:
		case 0xEE: case 0xEF: case 0xF0: case 0xF1: case 0xF2:
		case 0xF3: case 0xF4: case 0xF5: case 0xF6: case 0xF7:
		case 0xF8: case 0xF9: case 0xFA: case 0xFB: case 0xFC:
		case 0xFD: case 0xFE: case 0xFF: 
		    // For offsets <= 0xFFFF, convert to a single char
		    // by adding the window's offset and subtracting
		    // the generic compression offset
		    if(fOffsets[ fCurrentWindow ] <= 0xFFFF) {
			charBuffer[ucPos++] = (char) 
			    (aByte + fOffsets[ fCurrentWindow ] 
			     - COMPRESSIONOFFSET);
		    }
		    // For offsets > 0x10000, convert to a surrogate pair by 
		    // normBase = window's offset - 0x10000
		    // high surr. = 0xD800 + (normBase >> 10)
		    // low  surr. = 0xDC00 + (normBase & 0x3FF) + (byte & 0x7F)
		    else {
			// make sure there is enough room to write
			// both characters 
			// if not, save state and break out
			if((ucPos + 1) >= charBufferLimit) {
			    --bytePos;
			    System.arraycopy(byteBuffer, bytePos,
					     fBuffer, 0, 
					     byteBufferLimit - bytePos);
			    fBufferLength = byteBufferLimit - bytePos;
			    bytePos += fBufferLength;
			    break mainLoop; 
			}
			
			int normalizedBase = fOffsets[ fCurrentWindow ] 
			    - 0x10000;
			charBuffer[ucPos++] = (char) 
			    (0xD800 + (normalizedBase >> 10));
			charBuffer[ucPos++] = (char) 
			    (0xDC00 + (normalizedBase & 0x3FF)+(aByte & 0x7F));
		    }
		    break;

		    // bytes from 0x20 through 0x7F are treated as ASCII and
		    // are remapped to chars by padding the high byte
		    // (this is the same as quoting from static window 0)
		    // NUL (0x00), HT (0x09), CR (0x0A), LF (0x0D) 
		    // are treated as ASCII as well
		case 0x00: case 0x09: case 0x0A: case 0x0D:
		case 0x20: case 0x21: case 0x22: case 0x23: case 0x24:
		case 0x25: case 0x26: case 0x27: case 0x28: case 0x29:
		case 0x2A: case 0x2B: case 0x2C: case 0x2D: case 0x2E:
		case 0x2F: case 0x30: case 0x31: case 0x32: case 0x33:
		case 0x34: case 0x35: case 0x36: case 0x37: case 0x38:
		case 0x39: case 0x3A: case 0x3B: case 0x3C: case 0x3D:
		case 0x3E: case 0x3F: case 0x40: case 0x41: case 0x42:
		case 0x43: case 0x44: case 0x45: case 0x46: case 0x47:
		case 0x48: case 0x49: case 0x4A: case 0x4B: case 0x4C:
		case 0x4D: case 0x4E: case 0x4F: case 0x50: case 0x51:
		case 0x52: case 0x53: case 0x54: case 0x55: case 0x56:
		case 0x57: case 0x58: case 0x59: case 0x5A: case 0x5B:
		case 0x5C: case 0x5D: case 0x5E: case 0x5F: case 0x60:
		case 0x61: case 0x62: case 0x63: case 0x64: case 0x65:
		case 0x66: case 0x67: case 0x68: case 0x69: case 0x6A:
		case 0x6B: case 0x6C: case 0x6D: case 0x6E: case 0x6F:
		case 0x70: case 0x71: case 0x72: case 0x73: case 0x74:
		case 0x75: case 0x76: case 0x77: case 0x78: case 0x79:
		case 0x7A: case 0x7B: case 0x7C: case 0x7D: case 0x7E:
		case 0x7F: 
		    charBuffer[ucPos++] = (char) aByte;
		    break;

		    // quote unicode
		case SQUOTEU:
		    // verify we have two bytes following tag
		    // if not, save state and break out
		    if( (bytePos + 1) >= byteBufferLimit ) {
			--bytePos;
			System.arraycopy(byteBuffer, bytePos,
					 fBuffer, 0, 
					 byteBufferLimit - bytePos);
			fBufferLength = byteBufferLimit - bytePos;
			bytePos += fBufferLength;
			break mainLoop; 
		    }
                
		    aByte = byteBuffer[bytePos++];
		    charBuffer[ucPos++] = (char)
			(aByte << 8 | (byteBuffer[bytePos++] & 0xFF));
		    break;

		    // switch to Unicode mode
		case SCHANGEU:
		    fMode = UNICODEMODE;
		    break singleByteModeLoop;
		    //break;

		    // handle all quote tags
		case SQUOTE0: case SQUOTE1: case SQUOTE2: case SQUOTE3:
		case SQUOTE4: case SQUOTE5: case SQUOTE6: case SQUOTE7:
		    // verify there is a byte following the tag
		    // if not, save state and break out
		    if(bytePos >= byteBufferLimit) {
			--bytePos;
			System.arraycopy(byteBuffer, bytePos,
					 fBuffer, 0, 
					 byteBufferLimit - bytePos);
			fBufferLength = byteBufferLimit - bytePos;
			bytePos += fBufferLength;
			break mainLoop; 
		    }
                
		    // if the byte is in the range 0x00 - 0x7F, use
		    // static window n otherwise, use dynamic window n
		    int dByte = byteBuffer[bytePos++] & 0xFF;
		    charBuffer[ucPos++] = (char) 
			(dByte+ (dByte >= 0x00 && dByte < 0x80 
				 ? sOffsets[aByte - SQUOTE0] 
				 : (fOffsets[aByte - SQUOTE0] 
				    - COMPRESSIONOFFSET))); 
		    break;

		    // handle all change tags
		case SCHANGE0: case SCHANGE1: case SCHANGE2: case SCHANGE3:
		case SCHANGE4: case SCHANGE5: case SCHANGE6: case SCHANGE7:
		    fCurrentWindow = aByte - SCHANGE0;
		    break;

		    // handle all define tags
		case SDEFINE0: case SDEFINE1: case SDEFINE2: case SDEFINE3:
		case SDEFINE4: case SDEFINE5: case SDEFINE6: case SDEFINE7:
		    // verify there is a byte following the tag
		    // if not, save state and break out
		    if(bytePos >= byteBufferLimit) {
			--bytePos;
			System.arraycopy(byteBuffer, bytePos,
					 fBuffer, 0, 
					 byteBufferLimit - bytePos);
			fBufferLength = byteBufferLimit - bytePos;
			bytePos += fBufferLength;
			break mainLoop; 
		    }

		    fCurrentWindow = aByte - SDEFINE0;
		    fOffsets[fCurrentWindow] = 
			sOffsetTable[byteBuffer[bytePos++] & 0xFF];
		    break;

		    // handle define extended tag
		case SDEFINEX:
		    // verify we have two bytes following tag
		    // if not, save state and break out
		    if((bytePos + 1) >= byteBufferLimit ) {
			--bytePos;
			System.arraycopy(byteBuffer, bytePos,
					 fBuffer, 0, 
					 byteBufferLimit - bytePos);
			fBufferLength = byteBufferLimit - bytePos;
			bytePos += fBufferLength;
			break mainLoop; 
		    }
                
		    aByte = byteBuffer[bytePos++] & 0xFF;
		    fCurrentWindow = (aByte & 0xE0) >> 5;
		    fOffsets[fCurrentWindow] = 0x10000 + 
			(0x80 * (((aByte & 0x1F) << 8) 
				 | (byteBuffer[bytePos++] & 0xFF)));
		    break;
                            
            // reserved, shouldn't happen
		case SRESERVED:
		    break;

		} // end switch
	    } // end while
	    break;

	    case UNICODEMODE:
		// unicode mode decompression loop
	    unicodeModeLoop:
	    while(bytePos < byteBufferLimit && ucPos < charBufferLimit) {
		aByte = byteBuffer[bytePos++] & 0xFF;
		switch(aByte) {
		    // handle all define tags
		case UDEFINE0: case UDEFINE1: case UDEFINE2: case UDEFINE3:
		case UDEFINE4: case UDEFINE5: case UDEFINE6: case UDEFINE7:
		    // verify there is a byte following tag
		    // if not, save state and break out
		    if(bytePos >= byteBufferLimit ) {
			--bytePos;
			System.arraycopy(byteBuffer, bytePos,
					 fBuffer, 0, 
					 byteBufferLimit - bytePos);
			fBufferLength = byteBufferLimit - bytePos;
			bytePos += fBufferLength;
			break mainLoop; 
		    }
                
		    fCurrentWindow = aByte - UDEFINE0;
		    fOffsets[fCurrentWindow] = 
			sOffsetTable[byteBuffer[bytePos++] & 0xFF];
		    fMode = SINGLEBYTEMODE;
		    break unicodeModeLoop;
		    //break;

		    // handle define extended tag
		case UDEFINEX:
		    // verify we have two bytes following tag
		    // if not, save state and break out
		    if((bytePos + 1) >= byteBufferLimit ) {
			--bytePos;
			System.arraycopy(byteBuffer, bytePos,
					 fBuffer, 0, 
					 byteBufferLimit - bytePos);
			fBufferLength = byteBufferLimit - bytePos;
			bytePos += fBufferLength;
			break mainLoop; 
		    }
		    
		    aByte = byteBuffer[bytePos++] & 0xFF;
		    fCurrentWindow = (aByte & 0xE0) >> 5;
		    fOffsets[fCurrentWindow] = 0x10000 + 
			(0x80 * (((aByte & 0x1F) << 8) 
				 | (byteBuffer[bytePos++] & 0xFF)));
		    fMode = SINGLEBYTEMODE;
		    break unicodeModeLoop;
		    //break;

		    // handle all change tags
		case UCHANGE0: case UCHANGE1: case UCHANGE2: case UCHANGE3:
		case UCHANGE4: case UCHANGE5: case UCHANGE6: case UCHANGE7:
		    fCurrentWindow = aByte - UCHANGE0;
		    fMode = SINGLEBYTEMODE;
		    break unicodeModeLoop;
		    //break;

		    // quote unicode
		case UQUOTEU:
		    // verify we have two bytes following tag
		    // if not, save state and break out
		    if(bytePos >= byteBufferLimit  - 1) {
			--bytePos;
			System.arraycopy(byteBuffer, bytePos,
					 fBuffer, 0, 
					 byteBufferLimit - bytePos);
			fBufferLength = byteBufferLimit - bytePos;
			bytePos += fBufferLength;
			break mainLoop; 
		    }
                
		    aByte = byteBuffer[bytePos++];
		    charBuffer[ucPos++] = (char) 
			(aByte << 8 | (byteBuffer[bytePos++] & 0xFF));
		    break;

		default:
		    // verify there is a byte following tag
		    // if not, save state and break out
		    if(bytePos >= byteBufferLimit ) {
			--bytePos;
			System.arraycopy(byteBuffer, bytePos,
					 fBuffer, 0, 
					 byteBufferLimit - bytePos);
			fBufferLength = byteBufferLimit - bytePos;
			bytePos += fBufferLength;
			break mainLoop; 
		    }

		    charBuffer[ucPos++] = (char) 
			(aByte << 8 | (byteBuffer[bytePos++] & 0xFF));
		    break;

		} // end switch
	    } // end while
	    break;
	    
	    } // end switch( fMode )
	} // end while

        // fill in output parameter
	if(bytesRead != null)
	    bytesRead [0] = (bytePos - byteBufferStart);

        // return # of chars written
	return (ucPos - charBufferStart);
    }

    /** 
     * Reset the decompressor to its initial state. 
     * @stable ICU 2.4
     */
    public void reset()
    {
        // reset dynamic windows
        fOffsets[0] = 0x0080;    // Latin-1
        fOffsets[1] = 0x00C0;    // Latin-1 Supplement + Latin Extended-A
        fOffsets[2] = 0x0400;    // Cyrillic
        fOffsets[3] = 0x0600;    // Arabic
        fOffsets[4] = 0x0900;    // Devanagari
        fOffsets[5] = 0x3040;    // Hiragana
        fOffsets[6] = 0x30A0;    // Katakana
        fOffsets[7] = 0xFF00;    // Fullwidth ASCII


        fCurrentWindow  = 0;                // Make current window Latin-1
        fMode           = SINGLEBYTEMODE;   // Always start in single-byte mode
	fBufferLength   = 0;                // Empty buffer
    }
};