// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_SIMPLE_FFT_CONVOLVER_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_SIMPLE_FFT_CONVOLVER_H_

#include "third_party/blink/renderer/platform/audio/audio_array.h"
#include "third_party/blink/renderer/platform/audio/fft_frame.h"
#include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"

namespace blink {

// The SimpleFFTConvolver does an FFT convolution. It differs from
// the FFTConvolver in that it restricts the maximum size of
// |convolution_kernel| to |input_block_size|. This restriction allows it to do
// an FFT on every Process call. Therefore, the processing delay of
// the SimpleFFTConvolver is the same as that of the DirectConvolver and thus
// smaller than that of the FFTConvolver.
class SimpleFFTConvolver final {
  USING_FAST_MALLOC(SimpleFFTConvolver);

 public:
  SimpleFFTConvolver(unsigned input_block_size,
                     const AudioFloatArray& convolution_kernel);
  SimpleFFTConvolver(const SimpleFFTConvolver&) = delete;
  SimpleFFTConvolver& operator=(const SimpleFFTConvolver&) = delete;

  void Process(base::span<const float> source, base::span<float> dest);

  void Reset();

  uint32_t ConvolutionKernelSize() const { return convolution_kernel_size_; }

 private:
  unsigned FftSize() const { return frame_.FftSize(); }

  uint32_t convolution_kernel_size_;
  FFTFrame fft_kernel_;
  FFTFrame frame_;

  // Buffer input until we get fftSize / 2 samples then do an FFT
  AudioFloatArray input_buffer_;

  // Stores output which we read a little at a time
  AudioFloatArray output_buffer_;

  // Saves the 2nd half of the FFT buffer, so we can do an overlap-add with the
  // 1st half of the next one
  AudioFloatArray last_overlap_buffer_;
};

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_SIMPLE_FFT_CONVOLVER_H_