import SwiftUI

/// Reusable download state indicator for cloud tracks.
/// Shows four states: not downloaded, downloading (progress), downloaded, error.
/// 20pt frame, designed to sit between Spacer() and duration in track rows.
struct DownloadIndicator: View {
    let track: Track
    @Environment(\.accessibilityReduceMotion) private var reduceMotion

    @State private var downloadManager = DownloadManager.shared
    @State private var showBounce = false

    var body: some View {
        Button {
            handleTap()
        } label: {
            ZStack {
                switch track.downloadState {
                case .none:
                    Image(systemName: "arrow.down.circle")
                        .foregroundStyle(.tertiary)

                case .downloading:
                    let progress = downloadManager.progress(for: track)
                    CircularProgressView(progress: progress)
                        .foregroundStyle(Color.accentColor)

                case .downloaded:
                    Image(systemName: "arrow.down.circle.fill")
                        .foregroundStyle(.green)
                        .scaleEffect(showBounce ? 1.15 : 1.0)

                case .error:
                    Image(systemName: "exclamationmark.circle.fill")
                        .foregroundStyle(.red)
                }
            }
            .font(.system(size: 14))
            .frame(width: 20, height: 20)
            .contentShape(Rectangle())
        }
        .buttonStyle(.plain)
        .help(helpText)
        .onChange(of: track.downloadState) { oldValue, newValue in
            if oldValue == .downloading && newValue == .downloaded {
                triggerBounce()
            }
        }
    }

    private var helpText: String {
        switch track.downloadState {
        case .none: "Download for offline playback"
        case .downloading: "Cancel download"
        case .downloaded: "Downloaded — available offline"
        case .error: "Download failed — tap to retry"
        }
    }

    private func handleTap() {
        switch track.downloadState {
        case .none:
            downloadManager.download(track: track, apiClient: ChadMusicAPIClient.shared)
        case .downloading:
            downloadManager.cancel(track: track)
        case .downloaded:
            break // No action on tap when downloaded — use context menu for remove
        case .error:
            downloadManager.download(track: track, apiClient: ChadMusicAPIClient.shared)
        }
    }

    private func triggerBounce() {
        if reduceMotion {
            return
        }
        withAnimation(.easeInOut(duration: 0.2)) {
            showBounce = true
        }
        DispatchQueue.main.asyncAfter(deadline: .now() + 0.2) {
            withAnimation(.easeInOut(duration: 0.2)) {
                showBounce = false
            }
        }
    }
}

/// Circular progress ring for download indicator.
private struct CircularProgressView: View {
    let progress: Double

    var body: some View {
        ZStack {
            Circle()
                .stroke(lineWidth: 2)
                .opacity(0.2)
            Circle()
                .trim(from: 0, to: CGFloat(max(0.05, progress)))
                .stroke(style: StrokeStyle(lineWidth: 2, lineCap: .round))
                .rotationEffect(.degrees(-90))
        }
        .padding(2)
    }
}