// Copyright 2023 Google Inc. All Rights Reserved.

//

// Use of this source code is governed by a BSD-style license

// that can be found in the COPYING file in the root of the source

// tree. An additional intellectual property rights grant can be found

// in the file PATENTS. All contributing project authors may

// be found in the AUTHORS file in the root of the source tree.

// -----------------------------------------------------------------------------

//

// Utilities for palette analysis.

//

// Author: Vincent Rabaud (vrabaud@google.com)

#include "src/utils/palette.h"

#include <assert.h>

#include <stdlib.h>

#include "src/dsp/lossless_common.h"

#include "src/utils/color_cache_utils.h"

#include "src/utils/utils.h"

#include "src/webp/encode.h"

#include "src/webp/format_constants.h"

// -----------------------------------------------------------------------------

// Palette reordering for smaller sum of deltas (and for smaller storage).

static int PaletteCompareColorsForQsort(const void* p1, const void* p2) {

  const uint32_t a = WebPMemToUint32((uint8_t*)p1);

  const uint32_t b = WebPMemToUint32((uint8_t*)p2);

  assert(a != b);

  return (a < b) ? -1 : 1;

}

static WEBP_INLINE uint32_t PaletteComponentDistance(uint32_t v) {

  return (v <= 128) ? v : (256 - v);

}

// Computes a value that is related to the entropy created by the

// palette entry diff.

//

// Note that the last & 0xff is a no-operation in the next statement, but

// removed by most compilers and is here only for regularity of the code.

static WEBP_INLINE uint32_t PaletteColorDistance(uint32_t col1, uint32_t col2) {

  const uint32_t diff = VP8LSubPixels(col1, col2);

  const int kMoreWeightForRGBThanForAlpha = 9;

  uint32_t score;

  score = PaletteComponentDistance((diff >> 0) & 0xff);

  score += PaletteComponentDistance((diff >> 8) & 0xff);

  score += PaletteComponentDistance((diff >> 16) & 0xff);

  score *= kMoreWeightForRGBThanForAlpha;

  score += PaletteComponentDistance((diff >> 24) & 0xff);

  return score;

}

static WEBP_INLINE void SwapColor(uint32_t* const col1, uint32_t* const col2) {

  const uint32_t tmp = *col1;

  *col1 = *col2;

  *col2 = tmp;

}

int SearchColorNoIdx(const uint32_t sorted[], uint32_t color, int num_colors) {

  int low = 0, hi = num_colors;

  if (sorted[low] == color) return low;  // loop invariant: sorted[low] != color

  while (1) {

    const int mid = (low + hi) >> 1;

    if (sorted[mid] == color) {

      return mid;

    } else if (sorted[mid] < color) {

      low = mid;

    } else {

      hi = mid;

    }

  }

  assert(0);

  return 0;

}

void PrepareMapToPalette(const uint32_t palette[], uint32_t num_colors,

                         uint32_t sorted[], uint32_t idx_map[]) {

  uint32_t i;

  memcpy(sorted, palette, num_colors * sizeof(*sorted));

  qsort(sorted, num_colors, sizeof(*sorted), PaletteCompareColorsForQsort);

  for (i = 0; i < num_colors; ++i) {

    idx_map[SearchColorNoIdx(sorted, palette[i], num_colors)] = i;

  }

}

//------------------------------------------------------------------------------

#define COLOR_HASH_SIZE (MAX_PALETTE_SIZE * 4)

#define COLOR_HASH_RIGHT_SHIFT 22  // 32 - log2(COLOR_HASH_SIZE).

int GetColorPalette(const WebPPicture* const pic, uint32_t* const palette) {

  int i;

  int x, y;

  int num_colors = 0;

  uint8_t in_use[COLOR_HASH_SIZE] = {0};

  uint32_t colors[COLOR_HASH_SIZE] = {0};

  const uint32_t* argb = pic->argb;

  const int width = pic->width;

  const int height = pic->height;

  uint32_t last_pix = ~argb[0];  // so we're sure that last_pix != argb[0]

  assert(pic != NULL);

  assert(pic->use_argb);

  for (y = 0; y < height; ++y) {

    for (x = 0; x < width; ++x) {

      int key;

      if (argb[x] == last_pix) {

        continue;

      }

      last_pix = argb[x];

      key = VP8LHashPix(last_pix, COLOR_HASH_RIGHT_SHIFT);

      while (1) {

        if (!in_use[key]) {

          colors[key] = last_pix;

          in_use[key] = 1;

          ++num_colors;

          if (num_colors > MAX_PALETTE_SIZE) {

            return MAX_PALETTE_SIZE + 1;  // Exact count not needed.

          }

          break;

        } else if (colors[key] == last_pix) {

          break;  // The color is already there.

        } else {

          // Some other color sits here, so do linear conflict resolution.

          ++key;

          key &= (COLOR_HASH_SIZE - 1);  // Key mask.

        }

      }

    }

    argb += pic->argb_stride;

  }

  if (palette != NULL) {  // Fill the colors into palette.

    num_colors = 0;

    for (i = 0; i < COLOR_HASH_SIZE; ++i) {

      if (in_use[i]) {

        palette[num_colors] = colors[i];

        ++num_colors;

      }

    }

    qsort(palette, num_colors, sizeof(*palette), PaletteCompareColorsForQsort);

  }

  return num_colors;

}

#undef COLOR_HASH_SIZE

#undef COLOR_HASH_RIGHT_SHIFT

// -----------------------------------------------------------------------------

// The palette has been sorted by alpha. This function checks if the other

// components of the palette have a monotonic development with regards to

// position in the palette. If all have monotonic development, there is

// no benefit to re-organize them greedily. A monotonic development

// would be spotted in green-only situations (like lossy alpha) or gray-scale

// images.

static int PaletteHasNonMonotonousDeltas(const uint32_t* const palette,

                                         int num_colors) {

  uint32_t predict = 0x000000;

  int i;

  uint8_t sign_found = 0x00;

  for (i = 0; i < num_colors; ++i) {

    const uint32_t diff = VP8LSubPixels(palette[i], predict);

    const uint8_t rd = (diff >> 16) & 0xff;

    const uint8_t gd = (diff >> 8) & 0xff;

    const uint8_t bd = (diff >> 0) & 0xff;

    if (rd != 0x00) {

      sign_found |= (rd < 0x80) ? 1 : 2;

    }

    if (gd != 0x00) {

      sign_found |= (gd < 0x80) ? 8 : 16;

    }

    if (bd != 0x00) {

      sign_found |= (bd < 0x80) ? 64 : 128;

    }

    predict = palette[i];

  }

  return (sign_found & (sign_found << 1)) != 0;  // two consequent signs.

}

static void PaletteSortMinimizeDeltas(const uint32_t* const palette_sorted,

                                      int num_colors, uint32_t* const palette) {

  uint32_t predict = 0x00000000;

  int i, k;

  memcpy(palette, palette_sorted, num_colors * sizeof(*palette));

  if (!PaletteHasNonMonotonousDeltas(palette_sorted, num_colors)) return;

  // Find greedily always the closest color of the predicted color to minimize

  // deltas in the palette. This reduces storage needs since the

  // palette is stored with delta encoding.

  if (num_colors > 17) {

    if (palette[0] == 0) {

      --num_colors;

      SwapColor(&palette[num_colors], &palette[0]);

    }

  }

  for (i = 0; i < num_colors; ++i) {

    int best_ix = i;

    uint32_t best_score = ~0U;

    for (k = i; k < num_colors; ++k) {

      const uint32_t cur_score = PaletteColorDistance(palette[k], predict);

      if (best_score > cur_score) {

        best_score = cur_score;

        best_ix = k;

      }

    }

    SwapColor(&palette[best_ix], &palette[i]);

    predict = palette[i];

  }

}

// -----------------------------------------------------------------------------

// Modified Zeng method from "A Survey on Palette Reordering

// Methods for Improving the Compression of Color-Indexed Images" by Armando J.

// Pinho and Antonio J. R. Neves.

// Finds the biggest cooccurrence in the matrix.

static void CoOccurrenceFindMax(const uint32_t* const cooccurrence,

                                uint32_t num_colors, uint8_t* const c1,

                                uint8_t* const c2) {

  // Find the index that is most frequently located adjacent to other

  // (different) indexes.

  uint32_t best_sum = 0u;

  uint32_t i, j, best_cooccurrence;

  *c1 = 0u;

  for (i = 0; i < num_colors; ++i) {

    uint32_t sum = 0;

    for (j = 0; j < num_colors; ++j) sum += cooccurrence[i * num_colors + j];

    if (sum > best_sum) {

      best_sum = sum;

      *c1 = i;

    }

  }

  // Find the index that is most frequently found adjacent to *c1.

  *c2 = 0u;

  best_cooccurrence = 0u;

  for (i = 0; i < num_colors; ++i) {

    if (cooccurrence[*c1 * num_colors + i] > best_cooccurrence) {

      best_cooccurrence = cooccurrence[*c1 * num_colors + i];

      *c2 = i;

    }

  }

  assert(*c1 != *c2);

}

// Builds the cooccurrence matrix

static int CoOccurrenceBuild(const WebPPicture* const pic,

                             const uint32_t* const palette, uint32_t num_colors,

                             uint32_t* cooccurrence) {

  uint32_t *lines, *line_top, *line_current, *line_tmp;

  int x, y;

  const uint32_t* src = pic->argb;

  uint32_t prev_pix = ~src[0];

  uint32_t prev_idx = 0u;

  uint32_t idx_map[MAX_PALETTE_SIZE] = {0};

  uint32_t palette_sorted[MAX_PALETTE_SIZE];

  lines = (uint32_t*)WebPSafeMalloc(2 * pic->width, sizeof(*lines));

  if (lines == NULL) {

    return 0;

  }

  line_top = &lines[0];

  line_current = &lines[pic->width];

  PrepareMapToPalette(palette, num_colors, palette_sorted, idx_map);

  for (y = 0; y < pic->height; ++y) {

    for (x = 0; x < pic->width; ++x) {

      const uint32_t pix = src[x];

      if (pix != prev_pix) {

        prev_idx = idx_map[SearchColorNoIdx(palette_sorted, pix, num_colors)];

        prev_pix = pix;

      }

      line_current[x] = prev_idx;

      // 4-connectivity is what works best as mentioned in "On the relation

      // between Memon's and the modified Zeng's palette reordering methods".

      if (x > 0 && prev_idx != line_current[x - 1]) {

        const uint32_t left_idx = line_current[x - 1];

        ++cooccurrence[prev_idx * num_colors + left_idx];

        ++cooccurrence[left_idx * num_colors + prev_idx];

      }

      if (y > 0 && prev_idx != line_top[x]) {

        const uint32_t top_idx = line_top[x];

        ++cooccurrence[prev_idx * num_colors + top_idx];

        ++cooccurrence[top_idx * num_colors + prev_idx];

      }

    }

    line_tmp = line_top;

    line_top = line_current;

    line_current = line_tmp;

    src += pic->argb_stride;

  }

  WebPSafeFree(lines);

  return 1;

}

struct Sum {

  uint8_t index;

  uint32_t sum;

};

static int PaletteSortModifiedZeng(const WebPPicture* const pic,

                                   const uint32_t* const palette_in,

                                   uint32_t num_colors,

                                   uint32_t* const palette) {

  uint32_t i, j, ind;

  uint8_t remapping[MAX_PALETTE_SIZE];

  uint32_t* cooccurrence;

  struct Sum sums[MAX_PALETTE_SIZE];

  uint32_t first, last;

  uint32_t num_sums;

  // TODO(vrabaud) check whether one color images should use palette or not.

  if (num_colors <= 1) return 1;

  // Build the co-occurrence matrix.

  cooccurrence =

      (uint32_t*)WebPSafeCalloc(num_colors * num_colors, sizeof(*cooccurrence));

  if (cooccurrence == NULL) {

    return 0;

  }

  if (!CoOccurrenceBuild(pic, palette_in, num_colors, cooccurrence)) {

    WebPSafeFree(cooccurrence);

    return 0;

  }

  // Initialize the mapping list with the two best indices.

  CoOccurrenceFindMax(cooccurrence, num_colors, &remapping[0], &remapping[1]);

  // We need to append and prepend to the list of remapping. To this end, we

  // actually define the next start/end of the list as indices in a vector (with

  // a wrap around when the end is reached).

  first = 0;

  last = 1;

  num_sums = num_colors - 2;  // -2 because we know the first two values

  if (num_sums > 0) {

    // Initialize the sums with the first two remappings and find the best one

    struct Sum* best_sum = &sums[0];

    best_sum->index = 0u;

    best_sum->sum = 0u;

    for (i = 0, j = 0; i < num_colors; ++i) {

      if (i == remapping[0] || i == remapping[1]) continue;

      sums[j].index = i;

      sums[j].sum = cooccurrence[i * num_colors + remapping[0]] +

                    cooccurrence[i * num_colors + remapping[1]];

      if (sums[j].sum > best_sum->sum) best_sum = &sums[j];

      ++j;

    }

    while (num_sums > 0) {

      const uint8_t best_index = best_sum->index;

      // Compute delta to know if we need to prepend or append the best index.

      int32_t delta = 0;

      const int32_t n = num_colors - num_sums;

      for (ind = first, j = 0; (ind + j) % num_colors != last + 1; ++j) {

        const uint16_t l_j = remapping[(ind + j) % num_colors];

        delta += (n - 1 - 2 * (int32_t)j) *

                 (int32_t)cooccurrence[best_index * num_colors + l_j];

      }

      if (delta > 0) {

        first = (first == 0) ? num_colors - 1 : first - 1;

        remapping[first] = best_index;

      } else {

        ++last;

        remapping[last] = best_index;

      }

      // Remove best_sum from sums.

      *best_sum = sums[num_sums - 1];

      --num_sums;

      // Update all the sums and find the best one.

      best_sum = &sums[0];

      for (i = 0; i < num_sums; ++i) {

        sums[i].sum += cooccurrence[best_index * num_colors + sums[i].index];

        if (sums[i].sum > best_sum->sum) best_sum = &sums[i];

      }

    }

  }

  assert((last + 1) % num_colors == first);

  WebPSafeFree(cooccurrence);

  // Re-map the palette.

  for (i = 0; i < num_colors; ++i) {

    palette[i] = palette_in[remapping[(first + i) % num_colors]];

  }

  return 1;

}

// -----------------------------------------------------------------------------

int PaletteSort(PaletteSorting method, const struct WebPPicture* const pic,

                const uint32_t* const palette_sorted, uint32_t num_colors,

                uint32_t* const palette) {

  switch (method) {

    case kSortedDefault:

      if (palette_sorted[0] == 0 && num_colors > 17) {

        memcpy(palette, palette_sorted + 1,

               (num_colors - 1) * sizeof(*palette_sorted));

        palette[num_colors - 1] = 0;

      } else {

        memcpy(palette, palette_sorted, num_colors * sizeof(*palette));

      }

      return 1;

    case kMinimizeDelta:

      PaletteSortMinimizeDeltas(palette_sorted, num_colors, palette);

      return 1;

    case kModifiedZeng:

      return PaletteSortModifiedZeng(pic, palette_sorted, num_colors, palette);

    case kUnusedPalette:

    case kPaletteSortingNum:

      break;

  }

  assert(0);

  return 0;

}