import SwiftUI

/// Download button for album headers — shows aggregate download state across all tracks.
/// States: "Download All" / "3 of 12" / "Downloaded" / "5 remaining"
struct AlbumDownloadButton: View {
    let tracks: [Track]
    let apiClient: ChadMusicAPIClient

    @State private var downloadManager = DownloadManager.shared

    private var cloudTracks: [Track] {
        tracks.filter { $0.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 {
        if !cloudTracks.isEmpty {
            Button {
                handleTap()
            } label: {
                Label(buttonLabel, systemImage: buttonIcon)
                    .font(.caption)
            }
            .buttonStyle(.plain)
            .foregroundStyle(.secondary)
            .fixedSize()
        }
    }

    private var buttonLabel: String {
        let total = cloudTracks.count
        if downloadedCount == total {
            return "Downloaded"
        }
        if downloadingCount > 0 {
            return "\(downloadedCount + downloadingCount) of \(total)"
        }
        if downloadedCount > 0 {
            return "\(total - downloadedCount) remaining"
        }
        return "Download All"
    }

    private var buttonIcon: String {
        if downloadedCount == cloudTracks.count {
            return "checkmark.circle.fill"
        }
        if downloadingCount > 0 {
            return "arrow.down.circle"
        }
        return "arrow.down.circle"
    }

    private func handleTap() {
        let total = cloudTracks.count
        if downloadedCount == total {
            return // All downloaded
        }
        if downloadingCount > 0 {
            // Cancel all active
            downloadManager.cancelBatch(tracks: cloudTracks)
        } else {
            // Download remaining
            downloadManager.downloadBatch(tracks: cloudTracks, apiClient: apiClient)
        }
    }
}