/*
 * shrink_block_v1.c - LZSA1 block compressor implementation
 *
 * Copyright (C) 2019 Emmanuel Marty
 *
 * This software is provided 'as-is', without any express or implied
 * warranty.  In no event will the authors be held liable for any damages
 * arising from the use of this software.
 *
 * Permission is granted to anyone to use this software for any purpose,
 * including commercial applications, and to alter it and redistribute it
 * freely, subject to the following restrictions:
 *
 * 1. The origin of this software must not be misrepresented; you must not
 *    claim that you wrote the original software. If you use this software
 *    in a product, an acknowledgment in the product documentation would be
 *    appreciated but is not required.
 * 2. Altered source versions must be plainly marked as such, and must not be
 *    misrepresented as being the original software.
 * 3. This notice may not be removed or altered from any source distribution.
 */

/*
 * Uses the libdivsufsort library Copyright (c) 2003-2008 Yuta Mori
 *
 * Inspired by LZ4 by Yann Collet. https://github.com/lz4/lz4
 * With help, ideas, optimizations and speed measurements by spke <zxintrospec@gmail.com>
 * With ideas from Lizard by Przemyslaw Skibinski and Yann Collet. https://github.com/inikep/lizard
 * Also with ideas from smallz4 by Stephan Brumme. https://create.stephan-brumme.com/smallz4/
 *
 */

#include <stdlib.h>
#include <string.h>
#include "lib.h"
#include "shrink_block_v1.h"
#include "format.h"

/**
 * Get the number of extra bits required to represent a literals length
 *
 * @param nLength literals length
 *
 * @return number of extra bits required
 */
static inline int lzsa_get_literals_varlen_size_v1(const int nLength) {
   if (nLength < LITERALS_RUN_LEN_V1) {
      return 0;
   }
   else {
      if (nLength < 256)
         return 8;
      else {
         if (nLength < 512)
            return 16;
         else
            return 24;
      }
   }
}

/**
 * Write extra literals length bytes to output (compressed) buffer. The caller must first check that there is enough
 * room to write the bytes.
 *
 * @param pOutData pointer to output buffer
 * @param nOutOffset current write index into output buffer
 * @param nLength literals length
 */
static inline int lzsa_write_literals_varlen_v1(unsigned char *pOutData, int nOutOffset, int nLength) {
   if (nLength >= LITERALS_RUN_LEN_V1) {
      if (nLength < 256)
         pOutData[nOutOffset++] = nLength - LITERALS_RUN_LEN_V1;
      else {
         if (nLength < 512) {
            pOutData[nOutOffset++] = 250;
            pOutData[nOutOffset++] = nLength - 256;
         }
         else {
            pOutData[nOutOffset++] = 249;
            pOutData[nOutOffset++] = nLength & 0xff;
            pOutData[nOutOffset++] = (nLength >> 8) & 0xff;
         }
      }
   }

   return nOutOffset;
}

/**
 * Get the number of extra bits required to represent an encoded match length
 *
 * @param nLength encoded match length (actual match length - MIN_MATCH_SIZE_V1)
 *
 * @return number of extra bits required
 */
static inline int lzsa_get_match_varlen_size_v1(const int nLength) {
   if (nLength < MATCH_RUN_LEN_V1) {
      return 0;
   }
   else {
      if ((nLength + MIN_MATCH_SIZE_V1) < 256)
         return 8;
      else {
         if ((nLength + MIN_MATCH_SIZE_V1) < 512)
            return 16;
         else
            return 24;
      }
   }
}

/**
 * Write extra encoded match length bytes to output (compressed) buffer. The caller must first check that there is enough
 * room to write the bytes.
 *
 * @param pOutData pointer to output buffer
 * @param nOutOffset current write index into output buffer
 * @param nLength encoded match length (actual match length - MIN_MATCH_SIZE_V1)
 */
static inline int lzsa_write_match_varlen_v1(unsigned char *pOutData, int nOutOffset, int nLength) {
   if (nLength >= MATCH_RUN_LEN_V1) {
      if ((nLength + MIN_MATCH_SIZE_V1) < 256)
         pOutData[nOutOffset++] = nLength - MATCH_RUN_LEN_V1;
      else {
         if ((nLength + MIN_MATCH_SIZE_V1) < 512) {
            pOutData[nOutOffset++] = 239;
            pOutData[nOutOffset++] = nLength + MIN_MATCH_SIZE_V1 - 256;
         }
         else {
            pOutData[nOutOffset++] = 238;
            pOutData[nOutOffset++] = (nLength + MIN_MATCH_SIZE_V1) & 0xff;
            pOutData[nOutOffset++] = ((nLength + MIN_MATCH_SIZE_V1) >> 8) & 0xff;
         }
      }
   }

   return nOutOffset;
}

/**
 * Get offset encoding cost in bits
 *
 * @param nMatchOffset offset to get cost of
 *
 * @return cost in bits
 */
static inline int lzsa_get_offset_cost_v1(const unsigned int nMatchOffset) {
   return (nMatchOffset <= 256) ? 8 : 16;
}

/**
 * Attempt to pick optimal matches using a forward arrivals parser, so as to produce the smallest possible output that decompresses to the same input
 *
 * @param pCompressor compression context
 * @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
 * @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
 */
static void lzsa_optimize_forward_v1(lzsa_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
   lzsa_arrival *arrival = pCompressor->arrival;
   const int nMinMatchSize = pCompressor->min_match_size;
   const int nFavorRatio = (pCompressor->flags & LZSA_FLAG_FAVOR_RATIO) ? 1 : 0;
   int i, j, n;

   memset(arrival + (nStartOffset << MATCHES_PER_OFFSET_SHIFT), 0, sizeof(lzsa_arrival) * ((nEndOffset - nStartOffset) << MATCHES_PER_OFFSET_SHIFT));

   arrival[nStartOffset << MATCHES_PER_OFFSET_SHIFT].from_slot = -1;

   for (i = nStartOffset; i != (nEndOffset - 1); i++) {
      const lzsa_match *pMatch = pCompressor->match + (i << MATCHES_PER_OFFSET_SHIFT);
      int m;

      for (j = 0; j < NMATCHES_PER_OFFSET && arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].from_slot; j++) {
         int nPrevCost = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].cost;
         int nCodingChoiceCost = nPrevCost + 8 /* literal */;
         int nNumLiterals = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].num_literals + 1;

         if (nNumLiterals == LITERALS_RUN_LEN_V1 || nNumLiterals == 256 || nNumLiterals == 512) {
            nCodingChoiceCost += 8;
         }

         if (!nFavorRatio && nNumLiterals == 1)
            nCodingChoiceCost += MODESWITCH_PENALTY * 3;

         lzsa_arrival *pDestArrival = &arrival[((i + 1) << MATCHES_PER_OFFSET_SHIFT)];
         if (pDestArrival->from_slot == 0 ||
            nCodingChoiceCost <= pDestArrival->cost) {

            memmove(&arrival[((i + 1) << MATCHES_PER_OFFSET_SHIFT) + 1],
               &arrival[((i + 1) << MATCHES_PER_OFFSET_SHIFT)],
               sizeof(lzsa_arrival) * (NMATCHES_PER_OFFSET - 1));

            pDestArrival->cost = nCodingChoiceCost;
            pDestArrival->from_pos = i;
            pDestArrival->from_slot = j + 1;
            pDestArrival->match_offset = 0;
            pDestArrival->match_len = 0;
            pDestArrival->num_literals = nNumLiterals;
            pDestArrival->rep_offset = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].rep_offset;
         }
      }

      for (m = 0; m < NMATCHES_PER_OFFSET && pMatch[m].length >= nMinMatchSize; m++) {
         int nMatchLen = pMatch[m].length;
         int nMatchOffsetCost = lzsa_get_offset_cost_v1(pMatch[m].offset);
         int nStartingMatchLen, k;

         if ((i + nMatchLen) > (nEndOffset - LAST_LITERALS))
            nMatchLen = nEndOffset - LAST_LITERALS - i;

         if (nMatchLen >= LEAVE_ALONE_MATCH_SIZE)
            nStartingMatchLen = nMatchLen;
         else
            nStartingMatchLen = nMinMatchSize;
         for (k = nStartingMatchLen; k <= nMatchLen; k++) {
            int nMatchLenCost = lzsa_get_match_varlen_size_v1(k - MIN_MATCH_SIZE_V1);

            for (j = 0; j < NMATCHES_PER_OFFSET && arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].from_slot; j++) {
               int nPrevCost = arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].cost;
               int nCodingChoiceCost = nPrevCost + 8 /* token */ /* the actual cost of the literals themselves accumulates up the chain */ + nMatchOffsetCost + nMatchLenCost;
               int exists = 0;

               if (!nFavorRatio && !arrival[(i << MATCHES_PER_OFFSET_SHIFT) + j].num_literals)
                  nCodingChoiceCost += MODESWITCH_PENALTY * 3;

               for (n = 0;
                  n < 3 && arrival[((i + k) << MATCHES_PER_OFFSET_SHIFT) + n].from_slot && arrival[((i + k) << MATCHES_PER_OFFSET_SHIFT) + n].cost <= nCodingChoiceCost;
                  n++) {
                  if (lzsa_get_offset_cost_v1(arrival[((i + k) << MATCHES_PER_OFFSET_SHIFT) + n].rep_offset) == lzsa_get_offset_cost_v1(pMatch[m].offset)) {
                     exists = 1;
                     break;
                  }
               }

               for (n = 0; !exists && n < 3 /* we only need the literals + short match cost + long match cost cases */; n++) {
                  lzsa_arrival *pDestArrival = &arrival[((i + k) << MATCHES_PER_OFFSET_SHIFT) + n];

                  if (pDestArrival->from_slot == 0 ||
                     nCodingChoiceCost <= pDestArrival->cost) {
                     memmove(&arrival[((i + k) << MATCHES_PER_OFFSET_SHIFT) + n + 1],
                        &arrival[((i + k) << MATCHES_PER_OFFSET_SHIFT) + n],
                        sizeof(lzsa_arrival) * (NMATCHES_PER_OFFSET - n - 1));

                     pDestArrival->cost = nCodingChoiceCost;
                     pDestArrival->from_pos = i;
                     pDestArrival->from_slot = j + 1;
                     pDestArrival->match_offset = pMatch[m].offset;
                     pDestArrival->match_len = k;
                     pDestArrival->num_literals = 0;
                     pDestArrival->rep_offset = pMatch[m].offset;
                     break;
                  }
               }
            }
         }
      }
   }

   lzsa_arrival *end_arrival = &arrival[(i << MATCHES_PER_OFFSET_SHIFT) + 0];
   pCompressor->match[i << MATCHES_PER_OFFSET_SHIFT].length = 0;
   pCompressor->match[i << MATCHES_PER_OFFSET_SHIFT].offset = 0;

   while (end_arrival->from_slot > 0 && end_arrival->from_pos >= 0) {
      pCompressor->match[end_arrival->from_pos << MATCHES_PER_OFFSET_SHIFT].length = end_arrival->match_len;
      pCompressor->match[end_arrival->from_pos << MATCHES_PER_OFFSET_SHIFT].offset = end_arrival->match_offset;

      end_arrival = &arrival[(end_arrival->from_pos << MATCHES_PER_OFFSET_SHIFT) + (end_arrival->from_slot - 1)];
   }
}

/**
 * Attempt to minimize the number of commands issued in the compressed data block, in order to speed up decompression without
 * impacting the compression ratio
 *
 * @param pCompressor compression context
 * @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
 * @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
 *
 * @return non-zero if the number of tokens was reduced, 0 if it wasn't
 */
static int lzsa_optimize_command_count_v1(lzsa_compressor *pCompressor, const int nStartOffset, const int nEndOffset) {
   int i;
   int nNumLiterals = 0;
   int nDidReduce = 0;

   for (i = nStartOffset; i < nEndOffset; ) {
      lzsa_match *pMatch = pCompressor->match + (i << MATCHES_PER_OFFSET_SHIFT);

      if (pMatch->length >= MIN_MATCH_SIZE_V1) {
         if (pMatch->length <= 9 /* Don't waste time considering large matches, they will always win over literals */ &&
            (i + pMatch->length) < nEndOffset /* Don't consider the last token in the block, we can only reduce a match inbetween other tokens */) {
            int nNextIndex = i + pMatch->length;
            int nNextLiterals = 0;

            while (nNextIndex < nEndOffset && pCompressor->match[nNextIndex << MATCHES_PER_OFFSET_SHIFT].length < MIN_MATCH_SIZE_V1) {
               nNextLiterals++;
               nNextIndex++;
            }

            /* This command is a match, is followed by 'nNextLiterals' literals and then by another match, or the end of the input. Calculate this command's current cost (excluding 'nNumLiterals' bytes) */
            if ((8 /* token */ + lzsa_get_literals_varlen_size_v1(nNumLiterals) + ((pMatch->offset <= 256) ? 8 : 16) /* match offset */ + lzsa_get_match_varlen_size_v1(pMatch->length - MIN_MATCH_SIZE_V1) +
               8 /* token */ + lzsa_get_literals_varlen_size_v1(nNextLiterals)) >=
               (8 /* token */ + (pMatch->length << 3) + lzsa_get_literals_varlen_size_v1(nNumLiterals + pMatch->length + nNextLiterals))) {
               /* Reduce */
               int nMatchLen = pMatch->length;
               int j;

               for (j = 0; j < nMatchLen; j++) {
                  pCompressor->match[(i + j) << MATCHES_PER_OFFSET_SHIFT].length = 0;
               }

               nDidReduce = 1;
               continue;
            }
         }

         if ((i + pMatch->length) < nEndOffset && pMatch->length >= LCP_MAX &&
            pMatch->offset && pMatch->offset <= 32 && pCompressor->match[(i + pMatch->length) << MATCHES_PER_OFFSET_SHIFT].offset == pMatch->offset && (pMatch->length % pMatch->offset) == 0 &&
            (pMatch->length + pCompressor->match[(i + pMatch->length) << MATCHES_PER_OFFSET_SHIFT].length) <= MAX_VARLEN) {
            int nMatchLen = pMatch->length;

            /* Join */

            pMatch->length += pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].length;
            pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].offset = 0;
            pCompressor->match[(i + nMatchLen) << MATCHES_PER_OFFSET_SHIFT].length = -1;
            continue;
         }

         i += pMatch->length;
         nNumLiterals = 0;
      }
      else {
         nNumLiterals++;
         i++;
      }
   }

   return nDidReduce;
}

/**
 * Emit block of compressed data
 *
 * @param pCompressor compression context
 * @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
 * @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
 * @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
 * @param pOutData pointer to output buffer
 * @param nMaxOutDataSize maximum size of output buffer, in bytes
 *
 * @return size of compressed data in output buffer, or -1 if the data is uncompressible
 */
static int lzsa_write_block_v1(lzsa_compressor *pCompressor, const unsigned char *pInWindow, const int nStartOffset, const int nEndOffset, unsigned char *pOutData, const int nMaxOutDataSize) {
   int i;
   int nNumLiterals = 0;
   int nInFirstLiteralOffset = 0;
   int nOutOffset = 0;

   for (i = nStartOffset; i < nEndOffset; ) {
      lzsa_match *pMatch = pCompressor->match + (i << MATCHES_PER_OFFSET_SHIFT);

      if (pMatch->length >= MIN_MATCH_SIZE_V1) {
         int nMatchOffset = pMatch->offset;
         int nMatchLen = pMatch->length;
         int nEncodedMatchLen = nMatchLen - MIN_MATCH_SIZE_V1;
         int nTokenLiteralsLen = (nNumLiterals >= LITERALS_RUN_LEN_V1) ? LITERALS_RUN_LEN_V1 : nNumLiterals;
         int nTokenMatchLen = (nEncodedMatchLen >= MATCH_RUN_LEN_V1) ? MATCH_RUN_LEN_V1 : nEncodedMatchLen;
         int nTokenLongOffset = (nMatchOffset <= 256) ? 0x00 : 0x80;
         int nCommandSize = 8 /* token */ + lzsa_get_literals_varlen_size_v1(nNumLiterals) + (nNumLiterals << 3) + (nTokenLongOffset ? 16 : 8) /* match offset */ + lzsa_get_match_varlen_size_v1(nEncodedMatchLen);

         if ((nOutOffset + (nCommandSize >> 3)) > nMaxOutDataSize)
            return -1;
         if (nMatchOffset < MIN_OFFSET || nMatchOffset > MAX_OFFSET)
            return -1;

         pOutData[nOutOffset++] = nTokenLongOffset | (nTokenLiteralsLen << 4) | nTokenMatchLen;
         nOutOffset = lzsa_write_literals_varlen_v1(pOutData, nOutOffset, nNumLiterals);

         if (nNumLiterals != 0) {
            memcpy(pOutData + nOutOffset, pInWindow + nInFirstLiteralOffset, nNumLiterals);
            nOutOffset += nNumLiterals;
            nNumLiterals = 0;
         }

         pOutData[nOutOffset++] = (-nMatchOffset) & 0xff;
         if (nTokenLongOffset) {
            pOutData[nOutOffset++] = (-nMatchOffset) >> 8;
         }
         nOutOffset = lzsa_write_match_varlen_v1(pOutData, nOutOffset, nEncodedMatchLen);
         i += nMatchLen;

         if (pCompressor->flags & LZSA_FLAG_RAW_BLOCK) {
            int nCurSafeDist = (i - nStartOffset) - nOutOffset;
            if (nCurSafeDist >= 0 && pCompressor->safe_dist < nCurSafeDist)
               pCompressor->safe_dist = nCurSafeDist;
         }

         pCompressor->num_commands++;
      }
      else {
         if (nNumLiterals == 0)
            nInFirstLiteralOffset = i;
         nNumLiterals++;
         i++;
      }
   }

   {
      int nTokenLiteralsLen = (nNumLiterals >= LITERALS_RUN_LEN_V1) ? LITERALS_RUN_LEN_V1 : nNumLiterals;
      int nCommandSize = 8 /* token */ + lzsa_get_literals_varlen_size_v1(nNumLiterals) + (nNumLiterals << 3);

      if ((nOutOffset + (nCommandSize >> 3)) > nMaxOutDataSize)
         return -1;

      if (pCompressor->flags & LZSA_FLAG_RAW_BLOCK)
         pOutData[nOutOffset++] = (nTokenLiteralsLen << 4) | 0x0f;
      else
         pOutData[nOutOffset++] = (nTokenLiteralsLen << 4) | 0x00;
      nOutOffset = lzsa_write_literals_varlen_v1(pOutData, nOutOffset, nNumLiterals);

      if (nNumLiterals != 0) {
         memcpy(pOutData + nOutOffset, pInWindow + nInFirstLiteralOffset, nNumLiterals);
         nOutOffset += nNumLiterals;
         nNumLiterals = 0;
      }

      if (pCompressor->flags & LZSA_FLAG_RAW_BLOCK) {
         int nCurSafeDist = (i - nStartOffset) - nOutOffset;
         if (nCurSafeDist >= 0 && pCompressor->safe_dist < nCurSafeDist)
            pCompressor->safe_dist = nCurSafeDist;
      }

      pCompressor->num_commands++;
   }

   if (pCompressor->flags & LZSA_FLAG_RAW_BLOCK) {
      /* Emit EOD marker for raw block */

      if ((nOutOffset + 4) > nMaxOutDataSize)
         return -1;

      pOutData[nOutOffset++] = 0;
      pOutData[nOutOffset++] = 238;
      pOutData[nOutOffset++] = 0;
      pOutData[nOutOffset++] = 0;
   }

   return nOutOffset;
}

/**
 * Emit raw block of uncompressible data
 *
 * @param pCompressor compression context
 * @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
 * @param nStartOffset current offset in input window (typically the number of previously compressed bytes)
 * @param nEndOffset offset to end finding matches at (typically the size of the total input window in bytes
 * @param pOutData pointer to output buffer
 * @param nMaxOutDataSize maximum size of output buffer, in bytes
 *
 * @return size of compressed data in output buffer, or -1 if the data is uncompressible
 */
static int lzsa_write_raw_uncompressed_block_v1(lzsa_compressor *pCompressor, const unsigned char *pInWindow, const int nStartOffset, const int nEndOffset, unsigned char *pOutData, const int nMaxOutDataSize) {
   int nNumLiterals = nEndOffset - nStartOffset;
   int nTokenLiteralsLen = (nNumLiterals >= LITERALS_RUN_LEN_V1) ? LITERALS_RUN_LEN_V1 : nNumLiterals;
   int nOutOffset = 0;

   int nCommandSize = 8 /* token */ + lzsa_get_literals_varlen_size_v1(nNumLiterals) + (nNumLiterals << 3) + 4;
   if ((nOutOffset + (nCommandSize >> 3)) > nMaxOutDataSize)
      return -1;

   pCompressor->num_commands = 0;
   pOutData[nOutOffset++] = (nTokenLiteralsLen << 4) | 0x0f;
   
   nOutOffset = lzsa_write_literals_varlen_v1(pOutData, nOutOffset, nNumLiterals);

   if (nNumLiterals != 0) {
      memcpy(pOutData + nOutOffset, pInWindow + nStartOffset, nNumLiterals);
      nOutOffset += nNumLiterals;
      nNumLiterals = 0;
   }

   pCompressor->num_commands++;

   /* Emit EOD marker for raw block */

   pOutData[nOutOffset++] = 0;
   pOutData[nOutOffset++] = 238;
   pOutData[nOutOffset++] = 0;
   pOutData[nOutOffset++] = 0;

   return nOutOffset;
}

/**
 * Select the most optimal matches, reduce the token count if possible, and then emit a block of compressed LZSA1 data
 *
 * @param pCompressor compression context
 * @param pInWindow pointer to input data window (previously compressed bytes + bytes to compress)
 * @param nPreviousBlockSize number of previously compressed bytes (or 0 for none)
 * @param nInDataSize number of input bytes to compress
 * @param pOutData pointer to output buffer
 * @param nMaxOutDataSize maximum size of output buffer, in bytes
 *
 * @return size of compressed data in output buffer, or -1 if the data is uncompressible
 */
int lzsa_optimize_and_write_block_v1(lzsa_compressor *pCompressor, const unsigned char *pInWindow, const int nPreviousBlockSize, const int nInDataSize, unsigned char *pOutData, const int nMaxOutDataSize) {
   int nResult;

   lzsa_optimize_forward_v1(pCompressor, nPreviousBlockSize, nPreviousBlockSize + nInDataSize);

   int nDidReduce;
   int nPasses = 0;
   do {
      nDidReduce = lzsa_optimize_command_count_v1(pCompressor, nPreviousBlockSize, nPreviousBlockSize + nInDataSize);
      nPasses++;
   } while (nDidReduce && nPasses < 20);

   nResult = lzsa_write_block_v1(pCompressor, pInWindow, nPreviousBlockSize, nPreviousBlockSize + nInDataSize, pOutData, nMaxOutDataSize);
   if (nResult < 0 && pCompressor->flags & LZSA_FLAG_RAW_BLOCK) {
      nResult = lzsa_write_raw_uncompressed_block_v1(pCompressor, pInWindow, nPreviousBlockSize, nPreviousBlockSize + nInDataSize, pOutData, nMaxOutDataSize);
   }

   return nResult;
}