/*
  * Copyright (c) 2011 Smartjog S.A.S, Clément Bœsch <clement.boesch@smartjog.com>
  *
  * 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
  */
 
 /**
  * @file
  * Potential thumbnail lookup filter to reduce the risk of an inappropriate
  * selection (such as a black frame) we could get with an absolute seek.
  *
  * Simplified version of algorithm by Vadim Zaliva <lord@crocodile.org>.
  * @url http://notbrainsurgery.livejournal.com/29773.html
  */
 
 #include "avfilter.h"
 
 #define HIST_SIZE (3*256)
 
 struct thumb_frame {
     AVFilterBufferRef *buf;     ///< cached frame
     int histogram[HIST_SIZE];   ///< RGB color distribution histogram of the frame
 };
 
 typedef struct {
     int n;                      ///< current frame
     int n_frames;               ///< number of frames for analysis
     struct thumb_frame *frames; ///< the n_frames frames
 } ThumbContext;
 
 static av_cold int init(AVFilterContext *ctx, const char *args, void *opaque)
 {
     ThumbContext *thumb = ctx->priv;
 
     if (!args) {
         thumb->n_frames = 100;
     } else {
         int n = sscanf(args, "%d", &thumb->n_frames);
         if (n != 1 || thumb->n_frames < 2) {
             thumb->n_frames = 0;
             av_log(ctx, AV_LOG_ERROR,
                    "Invalid number of frames specified (minimum is 2).\n");

             return AVERROR(EINVAL);

         }
     }
     thumb->frames = av_calloc(thumb->n_frames, sizeof(*thumb->frames));
     if (!thumb->frames) {
         av_log(ctx, AV_LOG_ERROR,
                "Allocation failure, try to lower the number of frames\n");
         return AVERROR(ENOMEM);
     }
     av_log(ctx, AV_LOG_INFO, "batch size: %d frames\n", thumb->n_frames);
     return 0;
 }
 
 static void draw_slice(AVFilterLink *inlink, int y, int h, int slice_dir)
 {
     int i, j;
     AVFilterContext *ctx = inlink->dst;
     ThumbContext *thumb = ctx->priv;
     int *hist = thumb->frames[thumb->n].histogram;
     AVFilterBufferRef *picref = inlink->cur_buf;
     const uint8_t *p = picref->data[0] + y * picref->linesize[0];
 
     // update current frame RGB histogram
     for (j = 0; j < h; j++) {
         for (i = 0; i < inlink->w; i++) {
             hist[0*256 + p[i*3    ]]++;
             hist[1*256 + p[i*3 + 1]]++;
             hist[2*256 + p[i*3 + 2]]++;
         }
         p += picref->linesize[0];
     }
 }
 
 /**
  * @brief        Compute Sum-square deviation to estimate "closeness".
  * @param hist   color distribution histogram
  * @param median average color distribution histogram
  * @return       sum of squared errors
  */
 static double frame_sum_square_err(const int *hist, const double *median)
 {
     int i;
     double err, sum_sq_err = 0;
 
     for (i = 0; i < HIST_SIZE; i++) {
         err = median[i] - (double)hist[i];
         sum_sq_err += err*err;
     }
     return sum_sq_err;
 }
 
 static void end_frame(AVFilterLink *inlink)
 {
     int i, j, best_frame_idx = 0;
     double avg_hist[HIST_SIZE] = {0}, sq_err, min_sq_err = -1;
     AVFilterLink *outlink = inlink->dst->outputs[0];
     ThumbContext *thumb   = inlink->dst->priv;
     AVFilterContext *ctx  = inlink->dst;
     AVFilterBufferRef *picref;
 
     // keep a reference of each frame
     thumb->frames[thumb->n].buf = inlink->cur_buf;
 
     // no selection until the buffer of N frames is filled up
     if (thumb->n < thumb->n_frames - 1) {
         thumb->n++;
         return;
     }
 
     // average histogram of the N frames
     for (j = 0; j < FF_ARRAY_ELEMS(avg_hist); j++) {
         for (i = 0; i < thumb->n_frames; i++)
             avg_hist[j] += (double)thumb->frames[i].histogram[j];
         avg_hist[j] /= thumb->n_frames;
     }
 
     // find the frame closer to the average using the sum of squared errors
     for (i = 0; i < thumb->n_frames; i++) {
         sq_err = frame_sum_square_err(thumb->frames[i].histogram, avg_hist);
         if (i == 0 || sq_err < min_sq_err)
             best_frame_idx = i, min_sq_err = sq_err;
     }
 
     // free and reset everything (except the best frame buffer)
     for (i = 0; i < thumb->n_frames; i++) {
         memset(thumb->frames[i].histogram, 0, sizeof(thumb->frames[i].histogram));
         if (i == best_frame_idx)
             continue;
         avfilter_unref_buffer(thumb->frames[i].buf);
         thumb->frames[i].buf = NULL;
     }
     thumb->n = 0;
 
     // raise the chosen one
     picref = thumb->frames[best_frame_idx].buf;
     av_log(ctx, AV_LOG_INFO, "frame id #%d (pts_time=%f) selected\n",
            best_frame_idx, picref->pts * av_q2d(inlink->time_base));
     avfilter_start_frame(outlink, picref);
     thumb->frames[best_frame_idx].buf = NULL;
     avfilter_draw_slice(outlink, 0, inlink->h, 1);
     avfilter_end_frame(outlink);
 }
 
 static av_cold void uninit(AVFilterContext *ctx)
 {
     int i;
     ThumbContext *thumb = ctx->priv;
     for (i = 0; i < thumb->n_frames && thumb->frames[i].buf; i++) {
         avfilter_unref_buffer(thumb->frames[i].buf);
         thumb->frames[i].buf = NULL;
     }
     av_freep(&thumb->frames);
 }
 
 static void null_start_frame(AVFilterLink *link, AVFilterBufferRef *picref) { }
 
 static int request_frame(AVFilterLink *link)
 {
     ThumbContext *thumb = link->src->priv;
 
     /* loop until a frame thumbnail is available (when a frame is queued,
      * thumb->n is reset to zero) */
     while (thumb->n) {
         int ret = avfilter_request_frame(link->src->inputs[0]);
         if (ret < 0)
             return ret;
     }
     return 0;
 }
 
 static int poll_frame(AVFilterLink *link)
 {
     ThumbContext *thumb  = link->src->priv;
     AVFilterLink *inlink = link->src->inputs[0];
     int ret, available_frames = avfilter_poll_frame(inlink);
 
     /* If the input link is not able to provide any frame, we can't do anything
      * at the moment and thus have zero thumbnail available. */
     if (!available_frames)
         return 0;
 
     /* Since at least one frame is available and the next frame will allow us
      * to compute a thumbnail, we can return 1 frame. */
     if (thumb->n == thumb->n_frames - 1)
         return 1;
 
     /* we have some frame(s) available in the input link, but not yet enough to
      * output a thumbnail, so we request more */
     ret = avfilter_request_frame(inlink);
     return ret < 0 ? ret : 0;
 }
 
 static int query_formats(AVFilterContext *ctx)
 {
     static const enum PixelFormat pix_fmts[] = {
         PIX_FMT_RGB24, PIX_FMT_BGR24,
         PIX_FMT_NONE
     };
     avfilter_set_common_pixel_formats(ctx, avfilter_make_format_list(pix_fmts));
     return 0;
 }
 
 AVFilter avfilter_vf_thumbnail = {
     .name          = "thumbnail",
     .description   = NULL_IF_CONFIG_SMALL("Select the most representative frame in a given sequence of consecutive frames."),
     .priv_size     = sizeof(ThumbContext),
     .init          = init,
     .uninit        = uninit,
     .query_formats = query_formats,
     .inputs        = (const AVFilterPad[]) {
         {   .name             = "default",
             .type             = AVMEDIA_TYPE_VIDEO,
             .get_video_buffer = avfilter_null_get_video_buffer,
             .start_frame      = null_start_frame,
             .draw_slice       = draw_slice,
             .end_frame        = end_frame,
         },{ .name = NULL }
     },
     .outputs       = (const AVFilterPad[]) {
         {   .name             = "default",
             .type             = AVMEDIA_TYPE_VIDEO,
             .request_frame    = request_frame,
             .poll_frame       = poll_frame,
             .rej_perms        = AV_PERM_REUSE2,
         },{ .name = NULL }
     },
 };