// @ts-nocheck

/*
 * Copyright (c) 2019 Genome Research Ltd.
 * Author(s): James Bonfield
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *    1. Redistributions of source code must retain the above copyright notice,
 *       this list of conditions and the following disclaimer.
 *
 *    2. Redistributions in binary form must reproduce the above
 *       copyright notice, this list of conditions and the following
 *       disclaimer in the documentation and/or other materials provided
 *       with the distribution.
 *
 *    3. Neither the names Genome Research Ltd and Wellcome Trust Sanger
 *       Institute nor the names of its contributors may be used to endorse
 *       or promote products derived from this software without specific
 *       prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY GENOME RESEARCH LTD AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL GENOME RESEARCH
 * LTD OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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 */

// An arithmetic coder, based on Eugene Shelwien's reimplementation of
// Michael Schindler range coder.
//
// Order-0 byte stream of ~/scratch/data/q40b
// C:              3.1s decode  (approx same vs 32-bit and 64-bit)
// Arith_sh.js     6.7s decode  (32-bit with carries)
// Arith.js      317.0s decode  (64-bit no carries); int64 crippling it.

// ----------------------------------------------------------------------
// Arithmetic (range) coder
export default class RangeCoder {
  constructor(src) {
    this.low = 0
    this.range = 0xffffffff
    this.code = 0
    this.FFnum = 0
    this.carry = 0
    this.cache = 0
  }

  RangeStartDecode(src) {
    for (let i = 0; i < 5; i++) {
      this.code = (this.code << 8) + src.ReadByte()
    }
    this.code &= 0xffffffff
    this.code >>>= 0 // force to be +ve int
  }

  RangeGetFrequency(tot_freq) {
    this.range = Math.floor(this.range / tot_freq)
    // return this.code / this.range;
    return Math.floor(this.code / this.range)

    // Conceptual scenario; return freq only and don't modify range yet
    // return Math.floor(this.code / (Math.floor(this.range / tot_freq)));
  }

  RangeDecode(src, sym_low, sym_freq, tot_freq) {
    // Conceptually we divide range here, but in practice we cached it earlier
    // this.range = Math.floor(this.range / tot_freq);

    this.code -= sym_low * this.range
    this.range *= sym_freq

    while (this.range < 1 << 24) {
      this.range *= 256
      this.code = this.code * 256 + src.ReadByte()
    }
  }

  RangeShiftLow(dst) {
    // We know range is < (1<<24) as we got here.  We already have a
    // cached copy of 8 bits from low.  Is this correct, or does it need
    // fixing?  Possible scenarios.
    // 1. Low < 0xff000000 thus low+range < 0xffffffff and cache
    //    cannot possibly change.  Output cache and as many ffs as needed.
    // 2. We already detected an overflow in RangeEncode, setting carry.
    //    In this case output cached byte + 1 and any 00s needed.
    // 3. Neither case - range is low but we haven't yet detected if we're
    //    XXffffff or XY000000 scenario.  Increase counter for ff/00s.

    if ((this.low < 0xff000000) | this.carry) {
      // cached byte if no overflow, byte+1 otherwise
      dst.WriteByte(this.cache + this.carry)

      // Flush any tracked FFs (no carry) or 00s (carry).
      while (this.FFnum) {
        dst.WriteByte(this.carry - 1)
        this.FFnum--
      }

      // Take a copy of top byte ready for next flush
      this.cache = this.low >>> 24
      this.carry = 0
    } else {
      this.FFnum++ // keep track of number of trailing ff/00 bytes to write
    }
    this.low <<= 8
    this.low >>>= 0 // force to be +ve int
  }

  RangeEncode(dst, sym_low, sym_freq, tot_freq) {
    const old_low = this.low
    this.range = Math.floor(this.range / tot_freq)
    this.low += sym_low * this.range
    this.low >>>= 0 // Truncate to +ve int so we can spot overflow
    this.range *= sym_freq

    // "low + sym*range < old_low" means we overflow; set carry.
    // NB: can this.low < old_low occur twice before range < (1<<24)?
    // We claim not, but prove it!
    if (this.low < old_low) {
      if (this.carry != 0) {
        console.log('ERROR: Multiple carry')
      }
      this.carry = 1
    }

    // Renormalise if range gets too small
    while (this.range < 1 << 24) {
      this.range *= 256
      this.RangeShiftLow(dst)
    }
  }

  RangeFinishEncode(dst) {
    for (let i = 0; i < 5; i++) {
      this.RangeShiftLow(dst)
    }
  }
}