Music Understanding Framework

import SwiftUI
import MusicUnderstanding
import AVFoundation

struct BeatKeyAnalyzerView: View {
    @State private var bpm: Double? = nil
    @State private var keyLabel: String = "—"
    @State private var beatTimes: [String] = []
    @State private var isAnalyzing = false
    @State private var showFilePicker = false
    @State private var selectedURL: URL? = nil

    var body: some View {
        NavigationStack {
            VStack(spacing: 20) {
                Button("Select Audio File") {
                    showFilePicker = true
                }
                .buttonStyle(.borderedProminent)

                if isAnalyzing {
                    ProgressView("Analyzing…")
                } else {
                    VStack(alignment: .leading, spacing: 12) {
                        Label("Key: \(keyLabel)", systemImage: "music.note")
                            .font(.title2.bold())
                        Label("BPM: \(bpm.map { String(format: "%.1f", $0) } ?? "—")", systemImage: "metronome")
                            .font(.title2.bold())
                        Divider()
                        Text("First 10 Beat Timestamps")
                            .font(.headline)
                        ForEach(beatTimes, id: \.self) { t in
                            Text(t)
                                .font(.caption)
                                .foregroundStyle(.secondary)
                        }
                    }
                    .padding()
                    .frame(maxWidth: .infinity, alignment: .leading)
                    .background(.regularMaterial, in: RoundedRectangle(cornerRadius: 16))
                    .padding(.horizontal)
                }
                Spacer()
            }
            .navigationTitle("Music Understanding")
            .fileImporter(
                isPresented: $showFilePicker,
                allowedContentTypes: [.audio]
            ) { result in
                if case .success(let url) = result {
                    selectedURL = url
                    Task { await analyzeAudio(url: url) }
                }
            }
        }
    }

    func analyzeAudio(url: URL) async {
        isAnalyzing = true
        defer { isAnalyzing = false }

        let asset = AVURLAsset(
            url: url,
            options: [AVURLAssetPreferPreciseDurationAndTimingKey: true]
        )

        do {
            let session = try MusicUnderstandingSession(asset: asset)
            let results = try await session.analyze(for: [.rhythm, .key])

            // Key
            if let keyResult = results.key,
               let firstRange = keyResult.ranges.first {
                let sig = firstRange.value
                keyLabel = "\(sig.tonic) \(sig.mode == .major ? "Major" : "Minor")"
            }

            // Rhythm
            if let rhythmResult = results.rhythm {
                bpm = rhythmResult.beatsPerMinute
                beatTimes = rhythmResult.beats.prefix(10).map { beat in
                    let seconds = beat.seconds
                    return String(format: "%.3f s", seconds)
                }
            }
        } catch {
            keyLabel = "Error: \(error.localizedDescription)"
        }
    }
}

#Preview {
    BeatKeyAnalyzerView()
}