import Foundation

/// What the received audio actually sounded like, as far as the counters
/// can say — the distinction a person reporting "it growled" cannot make
/// for us.
///
/// Two failures wear the same description. Loss is the decoder inventing
/// audio that never arrived, and sounds like dropouts and robotic
/// stuttering. Drift is the jitter buffer stretching or compressing the
/// signal because the sender's clock and this device's clock disagree,
/// and stretching a voice is what a growl *is*. Bytes arriving tells you
/// neither.
public struct AudioHealth: Equatable, Sendable {
  /// Samples the decoder invented, against samples it received.
  public let concealed: UInt64
  public let total: UInt64
  /// Samples the jitter buffer added or dropped to track the sender's
  /// clock. Either one running is drift; which one says which way.
  public let inserted: UInt64
  public let removed: UInt64
  public let jitterBufferMs: UInt64

  public init(concealed: UInt64, total: UInt64, inserted: UInt64, removed: UInt64, jitterBufferMs: UInt64) {
    self.concealed = concealed
    self.total = total
    self.inserted = inserted
    self.removed = removed
    self.jitterBufferMs = jitterBufferMs
  }

  public init(_ stats: [String: UInt64]) {
    self.init(
      concealed: stats["concealedSamples"] ?? 0,
      total: stats["totalSamplesReceived"] ?? 0,
      inserted: stats["insertedSamplesForDeceleration"] ?? 0,
      removed: stats["removedSamplesForAcceleration"] ?? 0,
      jitterBufferMs: stats["jitterBufferDelayMs"] ?? 0)
  }

  /// The fraction of received audio the decoder had to invent, 0 to 1.
  /// Zero when nothing has been received, because no audio is not clean
  /// audio and a reader should not be told otherwise by a division.
  public var concealmentRate: Double {
    total == 0 ? 0 : Double(concealed) / Double(total)
  }

  /// The fraction of received audio the jitter buffer stretched or
  /// squeezed. Both directions count: what matters is that the signal was
  /// rescaled, not which way it went.
  public var driftRate: Double {
    total == 0 ? 0 : Double(inserted + removed) / Double(total)
  }

  /// Nothing received yet. Distinct from healthy, and said differently.
  public var silent: Bool { total == 0 }

  /// One plain sentence, for the person who has opened this panel because
  /// something sounds wrong. Thresholds are deliberately blunt: this is a
  /// pointer towards which half of the problem to look at, not a
  /// measurement anyone should tune against.
  ///
  /// Drift is named first when both are up. Loss is common, usually
  /// transient and widely understood; sustained drift is rarer, is what
  /// makes a voice sound wrong rather than broken, and is the one nobody
  /// thinks to look for.
  public var summary: String {
    if silent { return "No audio received yet." }
    let loss = Int((concealmentRate * 100).rounded())
    let drift = Int((driftRate * 100).rounded())
    if driftRate >= 0.02 {
      return "Audio is being resampled to track the sender's clock (\(drift)%). "
        + "That is what makes a voice sound slowed or growling."
    }
    if concealmentRate >= 0.05 {
      return "\(loss)% of audio did not arrive and was filled in. That sounds like dropouts."
    }
    return "Audio is arriving cleanly (\(loss)% filled in, \(drift)% resampled)."
  }
}

/// The one line the device panel shows about audio, and only when
/// something is actually wrong; the full readout is a tap away behind
/// "Audio details". Nil keeps the panel clean. Worst first: a voice that
/// sounds wrong, then one that breaks up, then processing that is not
/// doing what was asked.
public enum AudioWarning {
  public static func line(
    health: AudioHealth?, processing: ProcessingReport?, reduceNoise: Bool
  ) -> String? {
    if let health, !health.silent {
      if health.driftRate >= 0.02 {
        return "Incoming audio is being stretched to keep time, so voices may sound slowed or growling."
      }
      if health.concealmentRate >= 0.05 {
        return "\(Int((health.concealmentRate * 100).rounded()))% of incoming audio is going missing."
      }
    }
    guard let processing, processing.started else { return nil }
    if processing.refused != nil { return "WebRTC refused the audio processing Calls asked for." }
    if processing.echoCancellation == "off" {
      return "Echo cancellation is off, so others may hear themselves."
    }
    if reduceNoise, case .unsupportedRate(let rate) = processing.suppression {
      return "Noise reduction is bypassed: the microphone runs at \(rate / 1000) kHz."
    }
    return nil
  }
}