/*
  LZWEncoder.js

  Authors
  Kevin Weiner (original Java version - kweiner@fmsware.com)
  Thibault Imbert (AS3 version - bytearray.org)
  Johan Nordberg (JS version - code@johan-nordberg.com)

  Acknowledgements
  GIFCOMPR.C - GIF Image compression routines
  Lempel-Ziv compression based on 'compress'. GIF modifications by
  David Rowley (mgardi@watdcsu.waterloo.edu)
  GIF Image compression - modified 'compress'
  Based on: compress.c - File compression ala IEEE Computer, June 1984.
  By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
  Jim McKie (decvax!mcvax!jim)
  Steve Davies (decvax!vax135!petsd!peora!srd)
  Ken Turkowski (decvax!decwrl!turtlevax!ken)
  James A. Woods (decvax!ihnp4!ames!jaw)
  Joe Orost (decvax!vax135!petsd!joe)
*/
var EOF = -1;
var BITS = 12;
var HSIZE = 5003; // 80% occupancy
var masks = [0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F,
    0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF,
    0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF];
function LZWEncoder(width, height, pixels, colorDepth) {
    var initCodeSize = Math.max(2, colorDepth);
    var accum = new Uint8Array(256);
    var htab = new Int32Array(HSIZE);
    var codetab = new Int32Array(HSIZE);
    var cur_accum, cur_bits = 0;
    var a_count;
    var free_ent = 0; // first unused entry
    var maxcode;
    // block compression parameters -- after all codes are used up,
    // and compression rate changes, start over.
    var clear_flg = false;
    // Algorithm: use open addressing double hashing (no chaining) on the
    // prefix code / next character combination. We do a variant of Knuth's
    // algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
    // secondary probe. Here, the modular division first probe is gives way
    // to a faster exclusive-or manipulation. Also do block compression with
    // an adaptive reset, whereby the code table is cleared when the compression
    // ratio decreases, but after the table fills. The variable-length output
    // codes are re-sized at this point, and a special CLEAR code is generated
    // for the decompressor. Late addition: construct the table according to
    // file size for noticeable speed improvement on small files. Please direct
    // questions about this implementation to ames!jaw.
    var g_init_bits, ClearCode, EOFCode;
    var remaining, curPixel, n_bits;
    // Add a character to the end of the current packet, and if it is 254
    // characters, flush the packet to disk.
    function char_out(c, outs) {
        accum[a_count++] = c;
        if (a_count >= 254)
            flush_char(outs);
    }
    // Clear out the hash table
    // table clear for block compress
    function cl_block(outs) {
        cl_hash(HSIZE);
        free_ent = ClearCode + 2;
        clear_flg = true;
        output(ClearCode, outs);
    }
    // Reset code table
    function cl_hash(hsize) {
        for (var i = 0; i < hsize; ++i)
            htab[i] = -1;
    }
    function compress(init_bits, outs) {
        var fcode, c, i, ent, disp, hsize_reg, hshift;
        // Set up the globals: g_init_bits - initial number of bits
        g_init_bits = init_bits;
        // Set up the necessary values
        clear_flg = false;
        n_bits = g_init_bits;
        maxcode = MAXCODE(n_bits);
        ClearCode = 1 << (init_bits - 1);
        EOFCode = ClearCode + 1;
        free_ent = ClearCode + 2;
        a_count = 0; // clear packet
        ent = nextPixel();
        hshift = 0;
        for (fcode = HSIZE; fcode < 65536; fcode *= 2)
            ++hshift;
        hshift = 8 - hshift; // set hash code range bound
        hsize_reg = HSIZE;
        cl_hash(hsize_reg); // clear hash table
        output(ClearCode, outs);
        outer_loop: while ((c = nextPixel()) != EOF) {
            fcode = (c << BITS) + ent;
            i = (c << hshift) ^ ent; // xor hashing
            if (htab[i] === fcode) {
                ent = codetab[i];
                continue;
            }
            else if (htab[i] >= 0) { // non-empty slot
                disp = hsize_reg - i; // secondary hash (after G. Knott)
                if (i === 0)
                    disp = 1;
                do {
                    if ((i -= disp) < 0)
                        i += hsize_reg;
                    if (htab[i] === fcode) {
                        ent = codetab[i];
                        continue outer_loop;
                    }
                } while (htab[i] >= 0);
            }
            output(ent, outs);
            ent = c;
            if (free_ent < 1 << BITS) {
                codetab[i] = free_ent++; // code -> hashtable
                htab[i] = fcode;
            }
            else {
                cl_block(outs);
            }
        }
        // Put out the final code.
        output(ent, outs);
        output(EOFCode, outs);
    }
    function encode(outs) {
        outs.writeByte(initCodeSize); // write "initial code size" byte
        remaining = width * height; // reset navigation variables
        curPixel = 0;
        compress(initCodeSize + 1, outs); // compress and write the pixel data
        outs.writeByte(0); // write block terminator
    }
    // Flush the packet to disk, and reset the accumulator
    function flush_char(outs) {
        if (a_count > 0) {
            outs.writeByte(a_count);
            outs.writeBytes(accum, 0, a_count);
            a_count = 0;
        }
    }
    function MAXCODE(n_bits) {
        return (1 << n_bits) - 1;
    }
    // Return the next pixel from the image
    function nextPixel() {
        if (remaining === 0)
            return EOF;
        --remaining;
        var pix = pixels[curPixel++];
        return pix & 0xff;
    }
    function output(code, outs) {
        cur_accum &= masks[cur_bits];
        if (cur_bits > 0)
            cur_accum |= (code << cur_bits);
        else
            cur_accum = code;
        cur_bits += n_bits;
        while (cur_bits >= 8) {
            char_out((cur_accum & 0xff), outs);
            cur_accum >>= 8;
            cur_bits -= 8;
        }
        // If the next entry is going to be too big for the code size,
        // then increase it, if possible.
        if (free_ent > maxcode || clear_flg) {
            if (clear_flg) {
                maxcode = MAXCODE(n_bits = g_init_bits);
                clear_flg = false;
            }
            else {
                ++n_bits;
                if (n_bits == BITS)
                    maxcode = 1 << BITS;
                else
                    maxcode = MAXCODE(n_bits);
            }
        }
        if (code == EOFCode) {
            // At EOF, write the rest of the buffer.
            while (cur_bits > 0) {
                char_out((cur_accum & 0xff), outs);
                cur_accum >>= 8;
                cur_bits -= 8;
            }
            flush_char(outs);
        }
    }
    this.encode = encode;
}
// module.exports = LZWEncoder;
export default LZWEncoder;