/**
 * Copyright (c) 2026 Dominic Masters
 *
 * This software is released under the MIT License.
 * https://opensource.org/licenses/MIT
 */

#include "audiostreamlinux.h"
#include "audio/audiostream.h"
#include "assert/assert.h"
#include "util/memory.h"

// How many frames of lead time to keep queued ahead of playback. Matches
// SDL_AudioSpec.samples below - the device's own internal buffer size - so
// this is "never let the queue run drier than one SDL-internal buffer."
#define AUDIO_LINUX_LEAD_FRAMES 4096

errorret_t audioStreamLinuxInit(audiostream_t *stream) {
  assertNotNull(stream, "Stream cannot be NULL.");

  SDL_AudioSpec desired;
  memoryZero(&desired, sizeof(SDL_AudioSpec));
  desired.freq = (int) stream->pcm.sampleRate;
  desired.format = AUDIO_S16SYS;
  desired.channels = stream->pcm.channels;
  desired.samples = AUDIO_LINUX_LEAD_FRAMES;

  stream->platform.device = SDL_OpenAudioDevice(NULL, 0, &desired, NULL, 0);
  if(stream->platform.device == 0) {
    errorThrow("Failed to open SDL2 audio device: %s", SDL_GetError());
  }

  errorOk();
}

errorret_t audioStreamLinuxDispose(audiostream_t *stream) {
  assertNotNull(stream, "Stream cannot be NULL.");

  SDL_CloseAudioDevice(stream->platform.device);

  errorOk();
}

errorret_t audioStreamLinuxBuffer(audiostream_t *stream) {
  assertNotNull(stream, "Stream cannot be NULL.");

  uint8_t *mixed = memoryAllocate(stream->dataSize);
  memoryZero(mixed, stream->dataSize);
  SDL_MixAudioFormat(
    mixed, stream->data, AUDIO_S16SYS, (Uint32) stream->dataSize,
    (stream->volume * SDL_MIX_MAXVOLUME) / 0xFF
  );

  int queued = SDL_QueueAudio(
    stream->platform.device, mixed, (Uint32) stream->dataSize
  );
  memoryFree(mixed);

  if(queued != 0) {
    errorThrow("Failed to queue SDL2 audio data: %s", SDL_GetError());
  }

  SDL_PauseAudioDevice(stream->platform.device, 0);

  errorOk();
}

bool_t audioStreamLinuxIsFinished(audiostream_t *stream) {
  assertNotNull(stream, "Stream cannot be NULL.");

  // Reports "finished" (ready to be re-buffered) with AUDIO_LINUX_LEAD_FRAMES
  // of margin still queued, rather than waiting for the queue to actually
  // run dry. SDL_QueueAudio only ever appends to a FIFO, so queuing the next
  // loop this early never causes overlap - it just avoids ever going silent
  // while our once-per-frame Update() notices and catches up. Waiting for
  // truly empty (as this used to) guarantees a gap by definition: silence
  // has already started by the time "empty" can be observed.
  const Uint32 leadBytes = (Uint32) (
    AUDIO_LINUX_LEAD_FRAMES * stream->pcm.channels * sizeof(int16_t)
  );

  return SDL_GetQueuedAudioSize(stream->platform.device) <= leadBytes;
}