import SwiftUI
import FlixyDesign
import FlixyDownloads
import PlexKit

/// Der Download-Knopf auf einer Detailseite.
///
/// Zeigt vier Zustände in einem Knopf: nicht geladen, lädt gerade, offline
/// verfügbar, gescheitert. Ein getrennter Knopf je Zustand würde die
/// Kopfzeile überfüllen — und der Zustand ist ohnehin immer genau einer.
struct DownloadButton: View {
    let item: PlexItem
    var mediaIndex: Int = 0

    @Environment(FlixySession.self) private var session
    @Environment(DownloadCoordinator.self) private var downloads
    @Environment(\.flixyAccent) private var accent

    @State private var refusal: DownloadRefusal?

    private var existing: DownloadItem? {
        downloads.items.first { $0.ratingKey == item.ratingKey }
    }

    var body: some View {
        Button {
            act()
        } label: {
            Label(label, systemImage: symbol)
                .labelStyle(.iconOnly)
                .font(.flixyCardTitle)
                .padding(FlixySpacing.snug)
        }
        .buttonStyle(.bordered)
        .tint(existing?.state == .completed ? accent : Color.flixyTextSecondary)
        .accessibilityLabel(Text(label))
        .alert(
            Text("downloads.refused.title"),
            isPresented: Binding(get: { refusal != nil }, set: { if !$0 { refusal = nil } })
        ) {
            Button("action.close") { refusal = nil }
        } message: {
            if let refusal { Text(refusal.explanation) }
        }
    }

    private var symbol: String {
        switch existing?.state {
        case .completed: "checkmark.circle.fill"
        case .downloading, .queued, .waiting: "stop.circle"
        case .paused: "play.circle"
        case .failed: "exclamationmark.arrow.trianglehead.2.clockwise.rotate.90"
        case nil: "arrow.down.circle"
        }
    }

    private var label: LocalizedStringKey {
        switch existing?.state {
        case .completed: "downloads.available"
        case .downloading, .queued, .waiting: "downloads.cancel"
        case .paused: "downloads.resume"
        case .failed: "action.retry"
        case nil: "downloads.download"
        }
    }

    private func act() {
        guard let existing else {
            enqueue()
            return
        }

        switch existing.state {
        case .completed:
            // Ein fertiger Download wird hier nicht angetastet. Löschen geht
            // über die Downloads-Ansicht — ein Fehlgriff in der Kopfzeile
            // soll nicht 40 GB verwerfen.
            break
        case .downloading, .queued, .waiting:
            Task { await downloads.cancel(existing) }
        case .paused, .failed:
            Task { await downloads.resume(existing) }
        }
    }

    private func enqueue() {
        let service = DownloadService(server: session.server, coordinator: downloads)
        do {
            _ = try service.download(item, mediaIndex: mediaIndex)
        } catch {
            refusal = error
        }
    }
}

/// Der Knopf für eine ganze Staffel oder Serie.
struct DownloadAllButton: View {
    let container: PlexItem

    @Environment(FlixySession.self) private var session
    @Environment(DownloadCoordinator.self) private var downloads
    @Environment(\.flixyAccent) private var accent

    @State private var isWorking = false
    @State private var summary: String?

    var body: some View {
        Button {
            Task { await downloadAll() }
        } label: {
            if isWorking {
                ProgressView().controlSize(.small)
            } else {
                Label(
                    container.kind == .show ? "downloads.allEpisodes" : "downloads.season",
                    systemImage: "arrow.down.circle"
                )
            }
        }
        .buttonStyle(.bordered)
        .tint(Color.flixyTextSecondary)
        .disabled(isWorking)
        .alert(
            Text("downloads.batch.title"),
            isPresented: Binding(get: { summary != nil }, set: { if !$0 { summary = nil } })
        ) {
            Button("action.close") { summary = nil }
        } message: {
            if let summary { Text(summary) }
        }
    }

    private func downloadAll() async {
        isWorking = true
        defer { isWorking = false }

        let service = DownloadService(server: session.server, coordinator: downloads)
        let result = await service.downloadAll(in: container)

        var lines = [String(localized: "downloads.batch.queued \(result.accepted)")]
        if !result.refused.isEmpty {
            // Der erste Grund reicht: bei einem erreichten Speicherlimit ist
            // er für alle übrigen derselbe.
            lines.append(result.refused[0].1.explanation)
        }
        if result.unavailable > 0 {
            lines.append(String(localized: "downloads.batch.unavailable \(result.unavailable)"))
        }
        summary = lines.joined(separator: "\n")
    }
}

extension DownloadRefusal {
    /// Der Grund im Klartext.
    var explanation: String {
        switch self {
        case .alreadyExists:
            String(localized: "downloads.refused.exists")
        case .storageLimitReached(let limit, let used):
            String(localized: "downloads.refused.limit \(used.formatted(.byteCount(style: .file))) \(limit.formatted(.byteCount(style: .file)))")
        case .insufficientDeviceSpace(let required, let available):
            String(localized: "downloads.refused.space \(required.formatted(.byteCount(style: .file))) \(available.formatted(.byteCount(style: .file)))")
        }
    }
}