// Copyright (c) 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

/**
 * A AudioWorklet-based BitCrusher demo from the spec example.
 *
 * @class BitCrusherProcessor
 * @extends AudioWorkletProcessor
 * @see https://webaudio.github.io/web-audio-api/#the-bitcrusher-node
 */
class BitCrusherProcessor extends AudioWorkletProcessor {
  static get parameterDescriptors() {
    return [
      {name: 'bitDepth', defaultValue: 12, minValue: 1, maxValue: 16}, {
        name: 'frequencyReduction',
        defaultValue: 0.5,
        minValue: 0,
        maxValue: 1,
      },
    ];
  }

  constructor() {
    super();
    this.phase_ = 0;
    this.lastSampleValue_ = 0;
  }

  process(inputs, outputs, parameters) {
    const input = inputs[0];
    const output = outputs[0];

    // AudioParam array can be either length of 1 or 128. Generally, the code
    // should prepare for both cases. In this particular example, |bitDepth|
    // AudioParam is constant but |frequencyReduction| is being automated.
    const bitDepth = parameters.bitDepth;
    const frequencyReduction = parameters.frequencyReduction;
    const isBitDepthConstant = bitDepth.length === 1;

    for (let channel = 0; channel < input.length; ++channel) {
      const inputChannel = input[channel];
      const outputChannel = output[channel];
      let step = Math.pow(0.5, bitDepth[0]);
      for (let i = 0; i < inputChannel.length; ++i) {
        // We only take care |bitDepth| because |frequencuReduction| will always
        // have 128 values.
        if (!isBitDepthConstant) {
          step = Math.pow(0.5, bitDepth[i]);
        }
        this.phase_ += frequencyReduction[i];
        if (this.phase_ >= 1.0) {
          this.phase_ -= 1.0;
          this.lastSampleValue_ =
              step * Math.floor(inputChannel[i] / step + 0.5);
        }
        outputChannel[i] = this.lastSampleValue_;
      }
    }

    return true;
  }
}

registerProcessor('bit-crusher-processor', BitCrusherProcessor);