// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "media/base/audio_pull_fifo.h"

#include <algorithm>

#include "base/check_op.h"
#include "base/numerics/checked_math.h"
#include "base/numerics/safe_conversions.h"
#include "base/types/zip.h"
#include "media/base/audio_bus.h"

namespace media {

AudioPullFifo::AudioPullFifo(int channels, int frames, ReadCB read_cb)
    : read_cb_(std::move(read_cb)),
      fifo_(AudioBus::Create(channels, frames)),
      fifo_index_(base::checked_cast<size_t>(frames)) {}

AudioPullFifo::~AudioPullFifo() = default;

void AudioPullFifo::Consume(AudioBus* destination, int frames_to_consume) {
  DCHECK_LE(frames_to_consume, destination->frames());

  int remaining_frames_to_provide = frames_to_consume;

  // Try to fulfill the request using what's available in the FIFO.
  int frames_read = ReadFromFifo(destination, remaining_frames_to_provide, 0);
  int write_pos = frames_read;
  remaining_frames_to_provide -= frames_read;

  // Get the remaining audio frames from the producer using the callback.
  while (remaining_frames_to_provide > 0) {
    DCHECK_EQ(fifo_index_, static_cast<size_t>(fifo_->frames()));
    fifo_index_ = 0u;

    // Fill up the FIFO by acquiring audio data from the producer.
    read_cb_.Run(write_pos, fifo_.get());

    // Try to fulfill the request using what's available in the FIFO.
    frames_read =
        ReadFromFifo(destination, remaining_frames_to_provide, write_pos);
    write_pos += frames_read;
    remaining_frames_to_provide -= frames_read;
  }
}

void AudioPullFifo::Clear() { fifo_index_ = fifo_->frames(); }

int AudioPullFifo::SizeInFrames() const {
  return fifo_->frames();
}

int AudioPullFifo::ReadFromFifo(AudioBus* destination,
                                int frames_to_provide,
                                int write_pos) {
  CHECK_GE(frames_to_provide, 0);
  const size_t frames_in_fifo =
      base::CheckSub(static_cast<size_t>(fifo_->frames()), fifo_index_)
          .ValueOrDie();
  const size_t frames =
      std::min(static_cast<size_t>(frames_to_provide), frames_in_fifo);
  if (!frames) {
    return 0;
  }

  for (auto [fifo, dest] :
       base::zip(fifo_->AllChannels(), destination->AllChannels())) {
    auto fifo_data = fifo.subspan(fifo_index_, frames);

    dest.subspan(base::checked_cast<size_t>(write_pos), frames)
        .copy_from_nonoverlapping(fifo_data);
  }

  fifo_index_ += frames;
  return frames;
}

}  // namespace media