/*
  * Copyright (c) 2015 The FFmpeg Project
  *
  * 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 "libavutil/channel_layout.h"
 #include "libavutil/opt.h"
 #include "avfilter.h"
 #include "audio.h"
 #include "formats.h"
 
 typedef struct ExtraStereoContext {
     const AVClass *class;
     float mult;
     int clip;
 } ExtraStereoContext;
 
 #define OFFSET(x) offsetof(ExtraStereoContext, x)
 #define A AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
 
 static const AVOption extrastereo_options[] = {
     { "m", "set the difference coefficient", OFFSET(mult), AV_OPT_TYPE_FLOAT, {.dbl=2.5}, -10, 10, A },

     { "c", "enable clipping",                OFFSET(clip), AV_OPT_TYPE_BOOL,  {.i64=1},     0,  1, A },

     { NULL }
 };
 
 AVFILTER_DEFINE_CLASS(extrastereo);
 
 static int query_formats(AVFilterContext *ctx)
 {
     AVFilterFormats *formats = NULL;
     AVFilterChannelLayouts *layout = NULL;

     int ret;

     if ((ret = ff_add_format                 (&formats, AV_SAMPLE_FMT_FLT  )) < 0 ||
         (ret = ff_set_common_formats         (ctx     , formats            )) < 0 ||
         (ret = ff_add_channel_layout         (&layout , AV_CH_LAYOUT_STEREO)) < 0 ||
         (ret = ff_set_common_channel_layouts (ctx     , layout             )) < 0)
         return ret;

 
     formats = ff_all_samplerates();
     return ff_set_common_samplerates(ctx, formats);
 }
 
 static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 {
     AVFilterContext *ctx = inlink->dst;
     AVFilterLink *outlink = ctx->outputs[0];
     ExtraStereoContext *s = ctx->priv;
     const float *src = (const float *)in->data[0];
     const float mult = s->mult;

     AVFrame *out;

     float *dst;
     int n;
 
     if (av_frame_is_writable(in)) {
         out = in;
     } else {

         out = ff_get_audio_buffer(inlink, in->nb_samples);

         if (!out) {
             av_frame_free(&in);
             return AVERROR(ENOMEM);
         }
         av_frame_copy_props(out, in);
     }
     dst = (float *)out->data[0];
 
     for (n = 0; n < in->nb_samples; n++) {
         float average, left, right;
 
         left    = src[n * 2    ];
         right   = src[n * 2 + 1];
         average = (left + right) / 2.;
         left    = average + mult * (left  - average);
         right   = average + mult * (right - average);
 
         if (s->clip) {
             dst[n * 2    ] = av_clipf(left,  -1, 1);
             dst[n * 2 + 1] = av_clipf(right, -1, 1);
         }
     }
 
     if (out != in)
         av_frame_free(&in);
     return ff_filter_frame(outlink, out);
 }
 
 static const AVFilterPad inputs[] = {
     {
         .name         = "default",
         .type         = AVMEDIA_TYPE_AUDIO,
         .filter_frame = filter_frame,
     },
     { NULL }
 };
 
 static const AVFilterPad outputs[] = {
     {
         .name = "default",
         .type = AVMEDIA_TYPE_AUDIO,
     },
     { NULL }
 };
 
 AVFilter ff_af_extrastereo = {
     .name           = "extrastereo",
     .description    = NULL_IF_CONFIG_SMALL("Increase difference between stereo audio channels."),
     .query_formats  = query_formats,
     .priv_size      = sizeof(ExtraStereoContext),
     .priv_class     = &extrastereo_class,
     .inputs         = inputs,
     .outputs        = outputs,
 };