/*
  * 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 CrossfeedContext {
     const AVClass *class;
 
     double range;
     double strength;
     double level_in;
     double level_out;
 
     double a0, a1, a2;
     double b0, b1, b2;
 
     double i1, i2;
     double o1, o2;
 } CrossfeedContext;
 
 static int query_formats(AVFilterContext *ctx)
 {
     AVFilterFormats *formats = NULL;
     AVFilterChannelLayouts *layout = NULL;
     int ret;
 
     if ((ret = ff_add_format                 (&formats, AV_SAMPLE_FMT_DBL  )) < 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 ||
         (ret = ff_set_common_samplerates     (ctx     , ff_all_samplerates())) < 0)
         return ret;
 
     return 0;
 }
 
 static int config_input(AVFilterLink *inlink)
 {
     AVFilterContext *ctx = inlink->dst;
     CrossfeedContext *s = ctx->priv;
     double A = exp(s->strength * -30 / 40 * log(10.));
     double w0 = 2 * M_PI * (1. - s->range) * 2100 / inlink->sample_rate;
     double alpha;
 
     alpha = sin(w0) / 2 * sqrt(2 * (1 / 0.5 - 1) + 2);
 
     s->a0 =          (A + 1) + (A - 1) * cos(w0) + 2 * sqrt(A) * alpha;
     s->a1 =    -2 * ((A - 1) + (A + 1) * cos(w0));
     s->a2 =          (A + 1) + (A - 1) * cos(w0) - 2 * sqrt(A) * alpha;
     s->b0 =     A * ((A + 1) - (A - 1) * cos(w0) + 2 * sqrt(A) * alpha);
     s->b1 = 2 * A * ((A - 1) - (A + 1) * cos(w0));
     s->b2 =     A * ((A + 1) - (A - 1) * cos(w0) - 2 * sqrt(A) * alpha);
 
     s->a1 /= s->a0;
     s->a2 /= s->a0;
     s->b0 /= s->a0;
     s->b1 /= s->a0;
     s->b2 /= s->a0;
 
     return 0;
 }
 
 static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 {
     AVFilterContext *ctx = inlink->dst;
     AVFilterLink *outlink = ctx->outputs[0];
     CrossfeedContext *s = ctx->priv;
     const double *src = (const double *)in->data[0];
     const double level_in = s->level_in;
     const double level_out = s->level_out;
     const double b0 = s->b0;
     const double b1 = s->b1;
     const double b2 = s->b2;
     const double a1 = s->a1;
     const double a2 = s->a2;
     AVFrame *out;
     double *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 = (double *)out->data[0];
 
     for (n = 0; n < out->nb_samples; n++, src += 2, dst += 2) {
         double mid = (src[0] + src[1]) * level_in * .5;
         double side = (src[0] - src[1]) * level_in * .5;
         double oside = side * b0 + s->i1 * b1 + s->i2 * b2 - s->o1 * a1 - s->o2 * a2;
 
         s->i2 = s->i1;
         s->i1 = side;
         s->o2 = s->o1;
         s->o1 = oside;
 
         dst[0] = (mid + oside) * level_out;
         dst[1] = (mid - oside) * level_out;
     }
 
     if (out != in)
         av_frame_free(&in);
     return ff_filter_frame(outlink, out);
 }
 
 #define OFFSET(x) offsetof(CrossfeedContext, x)
 #define FLAGS AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
 
 static const AVOption crossfeed_options[] = {
     { "strength",  "set crossfeed strength",  OFFSET(strength),  AV_OPT_TYPE_DOUBLE, {.dbl=.2}, 0, 1, FLAGS },
     { "range",     "set soundstage wideness", OFFSET(range),     AV_OPT_TYPE_DOUBLE, {.dbl=.5}, 0, 1, FLAGS },
     { "level_in",  "set level in",            OFFSET(level_in),  AV_OPT_TYPE_DOUBLE, {.dbl=.9}, 0, 1, FLAGS },
     { "level_out", "set level out",           OFFSET(level_out), AV_OPT_TYPE_DOUBLE, {.dbl=1.}, 0, 1, FLAGS },
     { NULL }
 };
 
 AVFILTER_DEFINE_CLASS(crossfeed);
 
 static const AVFilterPad inputs[] = {
     {
         .name         = "default",
         .type         = AVMEDIA_TYPE_AUDIO,
         .filter_frame = filter_frame,
         .config_props = config_input,
     },
     { NULL }
 };
 
 static const AVFilterPad outputs[] = {
     {
         .name = "default",
         .type = AVMEDIA_TYPE_AUDIO,
     },
     { NULL }
 };
 
 AVFilter ff_af_crossfeed = {
     .name           = "crossfeed",
     .description    = NULL_IF_CONFIG_SMALL("Apply headphone crossfeed filter."),
     .query_formats  = query_formats,
     .priv_size      = sizeof(CrossfeedContext),
     .priv_class     = &crossfeed_class,
     .inputs         = inputs,
     .outputs        = outputs,
 };