class SVFProcessor extends AudioWorkletProcessor {
  static get parameterDescriptors() {
    return [
      {
        name: 'frequency',
        defaultValue: 1000,
        minValue: 20,
        maxValue: 20000,
        automationRate: 'k-rate'
      },
      {
        name: 'resonance',
        defaultValue: 0.707,
        minValue: 0.05,
        maxValue: 10,
        automationRate: 'k-rate'
      }
    ]
  }

  constructor() {
    super()

    this.mode = 'lowpass'
    this.ic1eq = 0
    this.ic2eq = 0

    this.port.onmessage = (event) => {
      const { type, value } = event.data
      if (type === 'mode') {
        this.mode = value
      }
    }
  }

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

    if (input.length === 0 || output.length === 0) {
      return true
    }

    const inputChannel = input[0]
    const outputChannel = output[0]
    const frequency = parameters.frequency
    const resonance = parameters.resonance

    const sampleRate = globalThis.sampleRate || 44100
    const isFreqArray = frequency.length > 1
    const isResArray = resonance.length > 1

    for (let i = 0; i < inputChannel.length; i++) {
      const freq = isFreqArray ? frequency[i] : frequency[0]
      const res = isResArray ? resonance[i] : resonance[0]

      const g = Math.tan(Math.PI * Math.min(freq, sampleRate * 0.49) / sampleRate)
      const k = 1 / Math.max(0.05, res)

      const inputSample = inputChannel[i]

      const a1 = 1 / (1 + g * (g + k))
      const a2 = g * a1
      const a3 = g * a2

      const v3 = inputSample - this.ic2eq
      const v1 = a1 * this.ic1eq + a2 * v3
      const v2 = this.ic2eq + a2 * this.ic1eq + a3 * v3

      this.ic1eq = 2 * v1 - this.ic1eq
      this.ic2eq = 2 * v2 - this.ic2eq

      const lp = v2
      const bp = v1
      const hp = inputSample - k * v1 - v2
      const notch = inputSample - k * v1

      let outSample
      switch (this.mode) {
        case 'lowpass':
          outSample = lp
          break
        case 'highpass':
          outSample = hp
          break
        case 'bandpass':
          outSample = bp
          break
        case 'notch':
          outSample = notch
          break
        default:
          outSample = lp
      }

      outputChannel[i] = outSample
    }

    return true
  }
}

registerProcessor('svf-processor', SVFProcessor)