#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <math.h>

#include <xas/audio.h>

int xas_audio_format_eq(xas_audio_format a, xas_audio_format b) {
    return a.channels    == b.channels
        && a.sample_size == b.sample_size
        && a.sample_rate == b.sample_rate;
}

void xas_audio_zero(xas_audio_format format,
                      void *dest,
                      size_t index,
                      size_t count) {
    size_t stride = format.channels * format.sample_size;

    memset((uint8_t *)dest + stride * index,
           '\0',
           stride * count);
}

void xas_audio_copy(xas_audio_format format,
                      void *dest,
                      void *src,
                      size_t index_dest,
                      size_t index_src,
                      size_t count) {
    size_t stride = format.channels * format.sample_size;

    memcpy(((uint8_t *)dest) + stride * index_dest,
           ((uint8_t *)src)  + stride * index_src,
           stride * count);
}

static inline void apply_gain_mono(int16_t *samples,
                                   float gain,
                                   size_t index,
                                   size_t count) {
    size_t i;

    for (i=index; i<count; i++) {
        samples[i] *= (int16_t)roundf(gain * samples[i]);
    }
}

static inline void apply_gain_stereo(int16_t *samples,
                                     float gain,
                                     size_t index,
                                     size_t count) {
    size_t i;

    for (i=index; i<count; i++) {
        samples[i*2]   *= (int16_t)roundf(gain * samples[i*2]);
        samples[i*2+1] *= (int16_t)roundf(gain * samples[i*2+1]);
    }
}

void xas_audio_apply_gain(xas_audio_format format,
                            void *dest,
                            float gain,
                            size_t index,
                            size_t count) {
    if (format.channels == XAS_AUDIO_MONO) {
        apply_gain_mono(dest, gain, index, count);
    } else if (format.channels == XAS_AUDIO_STEREO) {
        apply_gain_stereo(dest, gain, index, count);
    }
}

static xas_audio_stream *stream_new(enum xas_audio_stream_type type,
                                      void *callback,
                                      xas_audio_cleanup cleanup,
                                      xas_audio_format format,
                                      size_t buffer_size,
                                      void *ctx) {
    xas_audio_stream *stream;

    size_t total = sizeof(xas_audio_stream)
                 + format.channels * format.sample_size * buffer_size;

    if ((stream = malloc(total)) == NULL) {
        goto error_malloc_stream;
    }

    stream->type               = type;
    stream->format.channels    = format.channels;
    stream->format.sample_size = format.sample_size;
    stream->format.sample_rate = format.sample_rate;
    stream->buffer_size        = buffer_size;
    stream->buffer_count       = 0;
    stream->callback           = callback;
    stream->cleanup            = cleanup;
    stream->ctx                = ctx;

    return stream;

error_malloc_stream:
    return NULL;
}

xas_audio_stream *xas_audio_stream_new_sink(xas_audio_drain drain,
                                                xas_audio_cleanup cleanup,
                                                xas_audio_format format,
                                                size_t buffer_size,
                                                void *ctx) {
    return stream_new(XAS_AUDIO_STREAM_SINK,
                      drain,
                      cleanup,
                      format,
                      buffer_size,
                      ctx);
}

xas_audio_stream *xas_audio_stream_new_source(xas_audio_fill fill,
                                                  xas_audio_cleanup cleanup,
                                                  xas_audio_format format,
                                                  size_t buffer_size,
                                                  void *ctx) {
    return stream_new(XAS_AUDIO_STREAM_SOURCE,
                      fill,
                      cleanup,
                      format,
                      buffer_size,
                      ctx);
}

void xas_audio_stream_destroy(xas_audio_stream *stream) {
    if (stream->cleanup) {
        stream->cleanup(stream->ctx, stream);
    }

    free(stream);
}

void *xas_audio_stream_buffer(xas_audio_stream *stream) {
    return stream + 1;
}

static inline int stream_flush(xas_audio_stream *sink) {
    if (sink->buffer_count == 0) {
        return 0;
    }

    if (sink->drain(sink->ctx,
                    sink + 1,
                    sink->buffer_count,
                    sink) < 0) {
        goto error_sink_drain;
    }

    sink->buffer_count = 0;

    return 0;

error_sink_drain:
    return -1;
}

static inline void *ptr(xas_audio_stream *stream, void *buf, size_t index) {
    return ((uint8_t *)buf)
        + stream->format.channels * stream->format.sample_size * index;
}

ssize_t xas_audio_stream_write(xas_audio_stream *sink,
                                 void *samples,
                                 size_t count) {
    size_t index_i = 0;

    if (sink->buffer_count + count > sink->buffer_size) {
        /*
         * If the number of samples offered, plus the number of items currently
         * in the buffer exceeds the buffer size, fill the buffer to capacity
         * and flush it.
         */
        size_t remaining = sink->buffer_size - sink->buffer_count;

        xas_audio_copy(sink->format,
                         sink+ 1,
                         samples,
                         sink->buffer_count,
                         index_i,
                         remaining);

        if (sink->drain(sink->ctx,
                        sink + 1,
                        sink->buffer_size,
                        sink) < 0) {
            goto error_sink_drain;
        }

        index_i += remaining;

        sink->buffer_count = 0;
    }

    /*
     * While there are still samples to buffer or flush...
     */
    while (index_i < count) {
        size_t remaining = count - index_i;

        if (remaining >= sink->buffer_size) {
            /*
             * If the number of samples remaining is greater than the target
             * buffer size, then drain directly from the source buffer to the
             * output an amount equal to the buffer size.
             */
            if (sink->drain(sink->ctx,
                            ptr(sink, samples, index_i),
                            sink->buffer_size,
                            sink) < 0) {
                goto error_sink_drain;
            }

            index_i += sink->buffer_size;
        } else {
            /*
             * Enough of the input has been drained that it can be copied to
             * the target buffer.
             */
            xas_audio_copy(sink->format,
                             sink + 1,
                             samples,
                             sink->buffer_count,
                             index_i,
                             remaining);

            index_i += remaining;

            sink->buffer_count += remaining;
        }
    }

    return index_i;

error_sink_drain:
    return -1;
}

int xas_audio_stream_flush(xas_audio_stream *sink) {
    if (sink->type == XAS_AUDIO_STREAM_SINK) {
        return stream_flush(sink);
    }

    errno = EINVAL;

    return -1;
}

ssize_t xas_audio_stream_read(xas_audio_stream *source,
                                void **samples,
                                size_t count) {
    *samples = source + 1;

    if (count > source->buffer_size) {
        count = source->buffer_size;
    }

    return source->fill(source->ctx,
                        *samples,
                        count,
                        source);
}