import SwiftUI

/// Download button for playlist headers — visible only when playlist has cloud tracks.
/// Shows downloaded/total count (e.g., "↓ 2/4").
struct PlaylistDownloadButton: View {
    let playlist: Playlist

    @State private var downloadManager = DownloadManager.shared

    private var cloudTracks: [Track] {
        playlist.sortedEntries.compactMap(\.track).filter(\.isCloud)
    }

    private var downloadedCount: Int {
        cloudTracks.filter { $0.downloadState == .downloaded }.count
    }

    private var downloadingCount: Int {
        cloudTracks.filter { $0.downloadState == .downloading }.count
    }

    var body: some View {
        let cloud = cloudTracks
        if !cloud.isEmpty {
            Button {
                handleTap(cloud)
            } label: {
                Label(buttonLabel(cloud), systemImage: "arrow.down.circle")
            }
            .help(helpText(cloud))
        }
    }

    private func buttonLabel(_ cloud: [Track]) -> String {
        let total = cloud.count
        if downloadedCount == total {
            return "↓ \(total)/\(total)"
        }
        return "↓ \(downloadedCount)/\(total)"
    }

    private func helpText(_ cloud: [Track]) -> String {
        let total = cloud.count
        if downloadedCount == total {
            return "All cloud tracks downloaded"
        }
        if downloadingCount > 0 {
            return "Downloading... tap to cancel"
        }
        return "Download \(total - downloadedCount) cloud tracks for offline playback"
    }

    private func handleTap(_ cloud: [Track]) {
        if downloadingCount > 0 {
            downloadManager.cancelBatch(tracks: cloud)
        } else if downloadedCount < cloud.count {
            downloadManager.downloadBatch(tracks: cloud, apiClient: ChadMusicAPIClient.shared)
        }
    }
}