/*
  * MJPEG encoder
  * Copyright (c) 2016 William Ma, Ted Ying, Jerry Jiang
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 #include <string.h>
 #include <stdint.h>
 #include <stdlib.h>

 #include "libavutil/avassert.h"

 #include "libavutil/common.h"
 #include "libavutil/error.h"
 #include "libavutil/qsort.h"
 #include "mjpegenc_huffman.h"
 
 /**
  * Comparison function for two PTables by prob
  *
  * @param a First PTable to compare
  * @param b Second PTable to compare
  * @return < 0 for less than, 0 for equals, > 0 for greater than
  */
 static int compare_by_prob(const void *a, const void *b)
 {
     PTable a_val = *(PTable *) a;
     PTable b_val = *(PTable *) b;
     return a_val.prob - b_val.prob;
 }
 
 /**
  * Comparison function for two HuffTables by length
  *
  * @param a First HuffTable to compare
  * @param b Second HuffTable to compare
  * @return < 0 for less than, 0 for equals, > 0 for greater than
  */
 static int compare_by_length(const void *a, const void *b)
 {
     HuffTable a_val = *(HuffTable *) a;
     HuffTable b_val = *(HuffTable *) b;
     return a_val.length - b_val.length;
 }
 
 /**
  * Computes the length of the Huffman encoding for each distinct input value.
  * Uses package merge algorithm as follows:
  * 1. start with an empty list, lets call it list(0), set i = 0
  * 2. add 1 entry to list(i) for each symbol we have and give each a score equal to the probability of the respective symbol
  * 3. merge the 2 symbols of least score and put them in list(i+1), and remove them from list(i). The new score will be the sum of the 2 scores
  * 4. if there is more than 1 symbol left in the current list(i), then goto 3
  * 5. i++
  * 6. if i < 16 goto 2
  * 7. select the n-1 elements in the last list with the lowest score (n = the number of symbols)
  * 8. the length of the huffman code for symbol s will be equal to the number of times the symbol occurs in the select elements
  * Go to guru.multimedia.cx/small-tasks-for-ffmpeg/ for more details
  *
  * All probabilities should be positive integers. The output is sorted by code,
  * not by length.
  *
  * @param prob_table input array of a PTable for each distinct input value
  * @param distincts  output array of a HuffTable that will be populated by this function
  * @param size       size of the prob_table array
  * @param max_length max length of an encoding
  */
 void ff_mjpegenc_huffman_compute_bits(PTable *prob_table, HuffTable *distincts, int size, int max_length)
 {
     PackageMergerList list_a, list_b, *to = &list_a, *from = &list_b, *temp;
 
     int times, i, j, k;
 
     int nbits[257] = {0};
 
     int min;
 

     av_assert0(max_length > 0);
 

     to->nitems = 0;
     from->nitems = 0;
     to->item_idx[0] = 0;
     from->item_idx[0] = 0;
     AV_QSORT(prob_table, size, PTable, compare_by_prob);
 
     for (times = 0; times <= max_length; times++) {
         to->nitems = 0;
         to->item_idx[0] = 0;
 
         j = 0;
         k = 0;
 
         if (times < max_length) {
             i = 0;
         }
         while (i < size || j + 1 < from->nitems) {
             to->nitems++;
             to->item_idx[to->nitems] = to->item_idx[to->nitems - 1];
             if (i < size &&
                 (j + 1 >= from->nitems ||
                  prob_table[i].prob <
                      from->probability[j] + from->probability[j + 1])) {
                 to->items[to->item_idx[to->nitems]++] = prob_table[i].value;
                 to->probability[to->nitems - 1] = prob_table[i].prob;
                 i++;
             } else {
                 for (k = from->item_idx[j]; k < from->item_idx[j + 2]; k++) {
                     to->items[to->item_idx[to->nitems]++] = from->items[k];
                 }
                 to->probability[to->nitems - 1] =
                     from->probability[j] + from->probability[j + 1];
                 j += 2;
             }
         }
         temp = to;
         to = from;
         from = temp;
     }
 
     min = (size - 1 < from->nitems) ? size - 1 : from->nitems;
     for (i = 0; i < from->item_idx[min]; i++) {
         nbits[from->items[i]]++;
     }
     // we don't want to return the 256 bit count (it was just in here to prevent
     // all 1s encoding)
     j = 0;
     for (i = 0; i < 256; i++) {
         if (nbits[i] > 0) {
             distincts[j].code = i;
             distincts[j].length = nbits[i];
             j++;
         }
     }
 }
 
 void ff_mjpeg_encode_huffman_init(MJpegEncHuffmanContext *s)
 {
     memset(s->val_count, 0, sizeof(s->val_count));
 }
 
 /**
  * Produces a Huffman encoding with a given input
  *
  * @param s         input to encode
  * @param bits      output array where the ith character represents how many input values have i length encoding
  * @param val       output array of input values sorted by their encoded length
  * @param max_nval  maximum number of distinct input values
  */

 void ff_mjpeg_encode_huffman_close(MJpegEncHuffmanContext *s, uint8_t bits[17],
                                    uint8_t val[], int max_nval)

 {
     int i, j;
     int nval = 0;
     PTable val_counts[257];
     HuffTable distincts[256];
 
     for (i = 0; i < 256; i++) {
         if (s->val_count[i]) nval++;
     }

     av_assert0 (nval <= max_nval);

 
     j = 0;
     for (i = 0; i < 256; i++) {
         if (s->val_count[i]) {
             val_counts[j].value = i;
             val_counts[j].prob = s->val_count[i];
             j++;
         }
     }
     val_counts[j].value = 256;
     val_counts[j].prob = 0;
     ff_mjpegenc_huffman_compute_bits(val_counts, distincts, nval + 1, 16);
     AV_QSORT(distincts, nval, HuffTable, compare_by_length);
 
     memset(bits, 0, sizeof(bits[0]) * 17);
     for (i = 0; i < nval; i++) {
         val[i] = distincts[i].code;
         bits[distincts[i].length]++;
     }
 }