/*
 * Copyright (C) 2010 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "third_party/blink/renderer/platform/audio/fft_convolver.h"

#include <algorithm>

#include "third_party/blink/renderer/platform/audio/vector_math.h"
#include "third_party/blink/renderer/platform/instrumentation/tracing/trace_event.h"

namespace blink {

FFTConvolver::FFTConvolver(unsigned fft_size)
    : frame_(fft_size),
      read_write_index_(0),
      input_buffer_(fft_size),  // 2nd half of buffer is always zeroed
      output_buffer_(fft_size),
      last_overlap_buffer_(fft_size / 2) {}

void FFTConvolver::Process(const FFTFrame* fft_kernel,
                           base::span<const float> source,
                           base::span<float> dest) {
  DCHECK_EQ(source.size(), dest.size());

  unsigned half_size = FftSize() / 2;

  base::span<float> input_buffer_span = input_buffer_.as_span();
  base::span<float> output_buffer_span = output_buffer_.as_span();

  while (!source.empty()) {
    size_t frames_to_copy =
        std::min(source.size(), half_size - read_write_index_);

    // Copy samples to input buffer
    DCHECK_LE(read_write_index_ + frames_to_copy, input_buffer_.size());

    input_buffer_span.subspan(read_write_index_, frames_to_copy)
        .copy_from(source.take_first(frames_to_copy));

    // Copy samples from output buffer
    DCHECK_LE(read_write_index_ + frames_to_copy, output_buffer_.size());

    dest.take_first(frames_to_copy)
        .copy_from(
            output_buffer_span.subspan(read_write_index_, frames_to_copy));
    read_write_index_ += frames_to_copy;

    // Check if it's time to perform the next FFT
    if (read_write_index_ == half_size) {
      {
        TRACE_EVENT0(TRACE_DISABLED_BY_DEFAULT("webaudio.audionode"),
                     "FFTConvolver::ExecuteFFT");
        // The input buffer is now filled (get frequency-domain version)
        frame_.DoFFT(input_buffer_span);
        frame_.Multiply(*fft_kernel);
        frame_.DoInverseFFT(output_buffer_span);
      }

      // Overlap-add 1st half from previous time
      vector_math::Vadd(output_buffer_.as_span(),
                        last_overlap_buffer_.as_span(),
                        output_buffer_.as_span(), half_size);

      // Finally, save 2nd half of result
      DCHECK_EQ(output_buffer_.size(), 2 * half_size);
      DCHECK_EQ(last_overlap_buffer_.size(), half_size);

      last_overlap_buffer_.as_span().copy_from(
          output_buffer_span.subspan(half_size, half_size));

      // Reset index back to start for next time
      read_write_index_ = 0;
    }
  }
}

void FFTConvolver::Reset() {
  last_overlap_buffer_.Zero();
  read_write_index_ = 0;
}

}  // namespace blink