/*
  * Copyright (c) 2015 Kyle Swanson <k@ylo.ph>.
  *
  * 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/opt.h"
 #include "avfilter.h"
 #include "internal.h"
 #include "audio.h"
 
 typedef struct TremoloContext {
     const AVClass *class;
     double freq;
     double depth;

     double *table;
     int index;

 } TremoloContext;
 
 #define OFFSET(x) offsetof(TremoloContext, x)
 #define FLAGS AV_OPT_FLAG_AUDIO_PARAM|AV_OPT_FLAG_FILTERING_PARAM
 
 static const AVOption tremolo_options[] = {
     { "f", "set frequency in hertz",    OFFSET(freq),    AV_OPT_TYPE_DOUBLE,   {.dbl = 5.0},   0.1,   20000.0, FLAGS },
     { "d", "set depth as percentage",   OFFSET(depth),   AV_OPT_TYPE_DOUBLE,   {.dbl = 0.5},   0.0,   1.0,     FLAGS },
     { NULL }
 };
 
 AVFILTER_DEFINE_CLASS(tremolo);
 
 static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 {
     AVFilterContext *ctx = inlink->dst;
     AVFilterLink *outlink = ctx->outputs[0];

     TremoloContext *s = ctx->priv;

     const double *src = (const double *)in->data[0];
     const int channels = inlink->channels;
     const int nb_samples = in->nb_samples;
     AVFrame *out;
     double *dst;
     int n, c;
 
     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 < nb_samples; n++) {
         for (c = 0; c < channels; c++)

             dst[c] = src[c] * s->table[s->index];

         dst += channels;
         src += channels;

         s->index++;

         if (s->index >= inlink->sample_rate / s->freq)

             s->index = 0;

     }
 
     if (in != out)
         av_frame_free(&in);
 
     return ff_filter_frame(outlink, out);
 }
 
 static int query_formats(AVFilterContext *ctx)
 {
     AVFilterFormats *formats;
     AVFilterChannelLayouts *layouts;
     static const enum AVSampleFormat sample_fmts[] = {
         AV_SAMPLE_FMT_DBL,
         AV_SAMPLE_FMT_NONE
     };
     int ret;
 
     layouts = ff_all_channel_counts();
     if (!layouts)
         return AVERROR(ENOMEM);
     ret = ff_set_common_channel_layouts(ctx, layouts);
     if (ret < 0)
         return ret;
 
     formats = ff_make_format_list(sample_fmts);
     if (!formats)
         return AVERROR(ENOMEM);
     ret = ff_set_common_formats(ctx, formats);
     if (ret < 0)
         return ret;
 
     formats = ff_all_samplerates();
     if (!formats)
         return AVERROR(ENOMEM);
     return ff_set_common_samplerates(ctx, formats);
 }
 
 static av_cold void uninit(AVFilterContext *ctx)
 {
     TremoloContext *s = ctx->priv;

     av_freep(&s->table);

 }
 
 static int config_input(AVFilterLink *inlink)
 {
     AVFilterContext *ctx = inlink->dst;
     TremoloContext *s = ctx->priv;

     const double offset = 1. - s->depth / 2.;
     int i;

     s->table = av_malloc_array(inlink->sample_rate / s->freq, sizeof(*s->table));

     if (!s->table)

         return AVERROR(ENOMEM);
 

     for (i = 0; i < inlink->sample_rate / s->freq; i++) {

         double env = s->freq * i / inlink->sample_rate;
         env = sin(2 * M_PI * fmod(env + 0.25, 1.0));
         s->table[i] = env * (1 - fabs(offset)) + offset;
     }
 
     s->index = 0;
 

     return 0;
 }
 
 static const AVFilterPad avfilter_af_tremolo_inputs[] = {
     {
         .name         = "default",
         .type         = AVMEDIA_TYPE_AUDIO,
         .config_props = config_input,
         .filter_frame = filter_frame,
     },
     { NULL }
 };
 
 static const AVFilterPad avfilter_af_tremolo_outputs[] = {
     {
         .name = "default",
         .type = AVMEDIA_TYPE_AUDIO,
     },
     { NULL }
 };
 
 AVFilter ff_af_tremolo = {
     .name          = "tremolo",
     .description   = NULL_IF_CONFIG_SMALL("Apply tremolo effect."),
     .priv_size     = sizeof(TremoloContext),
     .priv_class    = &tremolo_class,
     .uninit        = uninit,
     .query_formats = query_formats,
     .inputs        = avfilter_af_tremolo_inputs,
     .outputs       = avfilter_af_tremolo_outputs,
 };