import CallsKit
import Foundation

/// The harness's microphone: a voiced, syllable-shaped tone over steady
/// noise, so the far side receives audio with speech-like structure and
/// the capture processing has something to work on. Real speech it is
/// not; the fixture test in CallsKitTests is where suppression is judged.
final class SyntheticVoice: AudioInputSource, @unchecked Sendable {
  private var t = 0.0
  private var seed: UInt32 = 0x1234_5678

  func render(_ samples: UnsafeMutablePointer<Float>, count: Int, sampleRate: Double) {
    for i in 0..<count {
      // Four syllables a second, a 140 Hz voice with two harmonics.
      let envelope = max(0, sin(2 * .pi * 2 * t))
      let voice =
        envelope
        * (sin(2 * .pi * 140 * t) + 0.5 * sin(2 * .pi * 280 * t) + 0.25 * sin(2 * .pi * 420 * t))
      seed = seed &* 1_664_525 &+ 1_013_904_223
      let noise = Double(Int32(bitPattern: seed)) / Double(Int32.max)
      samples[i] = Float(0.2 * voice + 0.02 * noise)
      t += 1 / sampleRate
    }
  }
}