//
//  BackgroundAudioKeeper.swift
//  Keging
//
//  운동 중 무음 오디오 루프 재생 — 앱을 나가도 타이머·진동·Live Activity 갱신이 유지되게 한다.
//  (UIBackgroundModes=audio, .mixWithOthers라 음악 재생을 방해하지 않음)
//

import AVFoundation

@MainActor
final class BackgroundAudioKeeper {
    static let shared = BackgroundAudioKeeper()

    private var player: AVAudioPlayer?

    private init() {}

    func start() {
        guard player == nil else { return }
        let session = AVAudioSession.sharedInstance()
        try? session.setCategory(.playback, mode: .default, options: [.mixWithOthers])
        try? session.setActive(true)
        player = try? AVAudioPlayer(data: Self.silenceWAV)
        player?.numberOfLoops = -1
        player?.volume = 0
        player?.play()
    }

    func stop() {
        player?.stop()
        player = nil
        try? AVAudioSession.sharedInstance().setActive(false, options: [.notifyOthersOnDeactivation])
    }

    /// 1초짜리 무음 WAV (8kHz 16bit mono) — 파일 없이 메모리에서 생성
    private static let silenceWAV: Data = {
        let sampleRate = 8000
        let dataSize = sampleRate * 2
        var d = Data()
        func append(_ s: String) { d.append(s.data(using: .ascii)!) }
        func appendU32(_ v: UInt32) { withUnsafeBytes(of: v.littleEndian) { d.append(contentsOf: $0) } }
        func appendU16(_ v: UInt16) { withUnsafeBytes(of: v.littleEndian) { d.append(contentsOf: $0) } }
        append("RIFF"); appendU32(UInt32(36 + dataSize)); append("WAVE")
        append("fmt "); appendU32(16); appendU16(1); appendU16(1)
        appendU32(UInt32(sampleRate)); appendU32(UInt32(sampleRate * 2)); appendU16(2); appendU16(16)
        append("data"); appendU32(UInt32(dataSize))
        d.append(Data(count: dataSize))
        return d
    }()
}