Localized Asset Packs with Managed Background Assets

import BackgroundAssets
import SwiftUI

// MARK: - Asset Pack Manager

@MainActor
class LocalizedAssetPackManager: ObservableObject {
    @Published var packStatus: String = "Checking..."
    @Published var downloadProgress: Double = 0.0

    // The identifier matches the one declared in your asset pack manifest JSON
    // Manifest example (AssetPacks/de.json):
    // {
    //   "id": "com.example.thecoast.audio-de",
    //   "language": "de",
    //   "url": "https://example.com/packs/audio-de.baa",
    //   "version": 1
    // }
    private let germanAudioPackID = "com.example.thecoast.audio-de"

    func checkAndDownloadIfNeeded() async {
        let manager = BADownloadManager.shared

        do {
            // Fetch all currently scheduled or finished downloads
            let downloads = try manager.fetchCurrentDownloads()
            let alreadyQueued = downloads.contains {
                $0.identifier == germanAudioPackID
            }

            if alreadyQueued {
                packStatus = "Download already in progress or complete."
                return
            }

            // Schedule the localized asset pack download
            let download = BAURLDownload(
                identifier: germanAudioPackID,
                request: URLRequest(url: URL(string: "https://example.com/packs/audio-de.baa")!),
                fileSize: 52_428_800, // 50 MB
                applicationGroupIdentifier: "group.com.example.thecoast"
            )

            try manager.startForegroundDownload(download)
            packStatus = "Downloading German audio pack..."

            // Monitor progress
            await monitorProgress(for: download)

        } catch {
            packStatus = "Error: \(error.localizedDescription)"
        }
    }

    private func monitorProgress(for download: BAURLDownload) async {
        // In production, implement BADownloadManagerDelegate
        // to receive -downloadDidBegin:, -download:didWriteBytes:, -downloadDidFinish:
        // Here we simulate a progress observation pattern
        for try? await update in simulatedProgressUpdates() {
            downloadProgress = update
            if update >= 1.0 {
                packStatus = "German audio pack ready!"
                break
            }
        }
    }

    private func simulatedProgressUpdates() -> AsyncStream<Double> {
        AsyncStream { continuation in
            Task {
                for i in 1...10 {
                    try? await Task.sleep(for: .milliseconds(300))
                    continuation.yield(Double(i) / 10.0)
                }
                continuation.finish()
            }
        }
    }
}

// MARK: - SwiftUI View

struct LocalizedPackView: View {
    @StateObject private var manager = LocalizedAssetPackManager()

    var body: some View {
        VStack(spacing: 20) {
            Text("Localized Asset Packs")
                .font(.title2.bold())

            Text(manager.packStatus)
                .foregroundStyle(.secondary)

            if manager.downloadProgress > 0 && manager.downloadProgress < 1.0 {
                ProgressView(value: manager.downloadProgress)
                    .padding(.horizontal)
            }

            Button("Download German Audio Pack") {
                Task { await manager.checkAndDownloadIfNeeded() }
            }
            .buttonStyle(.borderedProminent)
        }
        .padding()
    }
}

#Preview {
    LocalizedPackView()
}