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: [Double] = []
    @State private var isAnalyzing = false
    @State private var showFilePicker = false
    @State private var fileURL: URL? = nil

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

                if isAnalyzing {
                    ProgressView("Analyzing…")
                } else {
                    GroupBox("Key") {
                        Text(keyLabel)
                            .font(.title)
                            .bold()
                    }
                    GroupBox("Tempo") {
                        Text(bpm.map { String(format: "%.1f BPM", $0) } ?? "—")
                            .font(.title)
                            .bold()
                    }
                    GroupBox("Beats (\(beatTimes.count))") {
                        ScrollView {
                            LazyVStack(alignment: .leading) {
                                ForEach(beatTimes.indices, id: \.self) { i in
                                    Text(String(format: "Beat %d: %.3fs", i + 1, beatTimes[i]))
                                        .font(.caption.monospaced())
                                }
                            }
                        }
                        .frame(maxHeight: 200)
                    }
                }
            }
            .padding()
            .navigationTitle("Music Understanding")
        }
        .fileImporter(isPresented: $showFilePicker, allowedContentTypes: [.audio]) { result in
            if case .success(let url) = result {
                fileURL = url
                Task { await analyze(url: url) }
            }
        }
    }

    @MainActor
    func analyze(url: URL) async {
        isAnalyzing = true
        defer { isAnalyzing = false }

        // Ensure access to the security-scoped resource
        guard url.startAccessingSecurityScopedResource() else { return }
        defer { url.stopAccessingSecurityScopedResource() }

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

        do {
            let session = MusicUnderstandingSession(asset: asset)
            // Only request rhythm and key to avoid unnecessary computation
            let sessionResult = try await session.analyze(for: [.rhythm, .key])

            // Extract BPM
            bpm = sessionResult.rhythm?.beatsPerMinute

            // Extract beat timestamps (CMTime → seconds)
            beatTimes = (sessionResult.rhythm?.beats ?? []).map { $0.seconds }

            // Extract key signature (first range if available)
            if let firstKey = sessionResult.key?.ranges.first?.value {
                let tonicName = firstKey.tonic.description
                let modeName = firstKey.mode == .major ? "Major" : "Minor"
                keyLabel = "\(tonicName) \(modeName)"
            } else {
                keyLabel = "Unknown"
            }
        } catch {
            keyLabel = "Error: \(error.localizedDescription)"
        }
    }
}

#Preview {
    BeatKeyAnalyzerView()
}