Generated Subtitles & Subtitle Style Preview

import SwiftUI
import AVFoundation
import AVKit

struct SubtitleStylePreviewView: View {
    private let player: AVPlayer
    private let playerLayer: AVPlayerLayer

    // Each style in the system has a profile ID
    @State private var styleProfiles: [(id: String, name: String)] = []
    @State private var selectedProfileID: String? = nil

    init() {
        let url = URL(string: "https://devstreaming-cdn.apple.com/videos/wwdc/2023/101/4/3CB5A0B4-B344-4173-98E6-C5A6C0B0A14D/cmaf/hvc/2160p_16800/hvc_2160p_16800.m3u8")!
        self.player = AVPlayer(url: url)
        self.playerLayer = AVPlayerLayer(player: player)
    }

    var body: some View {
        VStack(spacing: 0) {
            PlayerLayerView(playerLayer: playerLayer)
                .frame(maxWidth: .infinity)
                .aspectRatio(16/9, contentMode: .fit)

            ScrollView(.horizontal, showsIndicators: false) {
                HStack(spacing: 12) {
                    ForEach(styleProfiles, id: \.id) { profile in
                        Button(profile.name) {
                            previewStyle(profileID: profile.id)
                        }
                        .padding(.horizontal, 14)
                        .padding(.vertical, 8)
                        .background(
                            selectedProfileID == profile.id
                                ? Color.accentColor
                                : Color.secondary.opacity(0.2)
                        )
                        .foregroundStyle(
                            selectedProfileID == profile.id ? .white : .primary
                        )
                        .clipShape(Capsule())
                    }
                }
                .padding()
            }

            HStack {
                Button("Cancel") {
                    // Removes preview, restores active subtitles
                    playerLayer.stopSubtitleStylePreview()
                    selectedProfileID = nil
                }
                Spacer()
                Button("Apply Style") {
                    if let id = selectedProfileID {
                        // Persist the chosen style system-wide
                        AVCaptionStyleProfile.setCurrentProfileID(id)
                    }
                    playerLayer.stopSubtitleStylePreview()
                }
                .disabled(selectedProfileID == nil)
                .buttonStyle(.borderedProminent)
            }
            .padding()
        }
        .onAppear {
            loadStyleProfiles()
            player.play()
        }
    }

    private func loadStyleProfiles() {
        // Fetch all system caption style profile IDs and their display names
        let profiles = AVCaptionStyleProfile.profileIDs.compactMap { id -> (id: String, name: String)? in
            guard let name = AVCaptionStyleProfile.localizedName(forProfileID: id) else { return nil }
            return (id: id, name: name)
        }
        styleProfiles = profiles
    }

    private func previewStyle(profileID: String) {
        selectedProfileID = profileID
        // Show live styled preview on the player layer.
        // nil text → system shows localized placeholder string.
        // position offsets the preview text downward to avoid our HStack controls.
        playerLayer.showSubtitleStylePreview(
            forProfileID: profileID,
            text: nil,
            position: CGPoint(x: 0, y: -60)
        )
    }
}

// MARK: - UIViewRepresentable wrapper for AVPlayerLayer
struct PlayerLayerView: UIViewRepresentable {
    let playerLayer: AVPlayerLayer

    func makeUIView(context: Context) -> UIView {
        let view = UIView()
        view.backgroundColor = .black
        playerLayer.videoGravity = .resizeAspect
        view.layer.addSublayer(playerLayer)
        return view
    }

    func updateUIView(_ uiView: UIView, context: Context) {
        playerLayer.frame = uiView.bounds
    }
}