import SwiftUI
import FlixyDesign
import MediaKit

/// Die Detailseite einer Serie oder Staffel.
///
/// Beide nutzen dieselbe Ansicht, weil sie sich nur im Inhalt der Liste
/// unterscheiden: eine Serie führt zu Staffeln, eine Staffel zu Folgen.
struct SeriesDetailView: View {
    let item: MediaItem

    @Environment(FlixySession.self) private var session
    @Environment(\.horizontalSizeClass) private var sizeClass
    @State private var children: LoadState<[MediaItem]> = .loading

    var body: some View {
        ScrollView {
            VStack(alignment: .leading, spacing: FlixySpacing.section) {
                header

                ParentLinks(item: item)

                if let summary = item.summary, !summary.isEmpty {
                    Text(summary)
                        .font(.flixyBody)
                        .foregroundStyle(Color.flixyTextSecondary)
                        .padding(.horizontal, FlixySpacing.screenMargin)
                }

                if !item.genres.isEmpty { TagStrip(tags: item.genres) }

                // **Nur bei der Serie, nicht bei der Staffel.** Die Ebene
                // heisst Serie; sie zweimal anzubieten hiesse, zwei Orte für
                // dieselbe Einstellung zu haben, von denen einer nie gelesen
                // wird.
                if item.kind == .show {
                    AudioLanguagePicker(
                        scope: .series(item.id),
                        title: "languages.forThisSeries"
                    )
                    .padding(.horizontal, FlixySpacing.screenMargin)
                }

                childList

                if !item.cast.isEmpty { CastRow(cast: item.cast) }
            }
            .padding(.bottom, FlixySpacing.section)
        }
        .scrollIndicators(.never)
        .flixyRevealsTopChrome()
        .task(id: item.id) { await loadChildren() }
    }

    private var header: some View {
        HeroBanner(
            title: item.rowTitle,
            metadata: metadataLine,
            summary: nil,
            // Über `HeroArtwork`, nicht von Hand: hier standen 900×1200 —
            // hochkant — für ein Bild, das im 16:9-Rahmen landet. Zu sehen war
            // davon ein Streifen aus der Mitte. Derselbe Fehler war im
            // Aufmacher schon einmal behoben worden, nur hier nicht.
            artworkURL: session.backend.flatMap {
                HeroArtwork.backdropURL(for: item, backend: $0, compact: sizeClass == .compact)
            },
            logoURL: session.backend?.rawImageURL(path: item.clearLogoPath)
        ) {
            DownloadAllButton(container: item)
        }
    }

    @ViewBuilder
    private var childList: some View {
        switch children {
        case .loading:
            ProgressView().frame(maxWidth: .infinity).padding(.vertical, FlixySpacing.section)

        case .failed(let message):
            Text(message)
                .font(.flixyCaption)
                .foregroundStyle(Color.flixyTextMuted)
                .padding(.horizontal, FlixySpacing.screenMargin)

        case .loaded(let entries):
            VStack(alignment: .leading, spacing: FlixySpacing.regular) {
                Text(item.kind == .show ? "detail.seasons" : "detail.episodes")
                    .font(.flixyRowHeader)
                    .foregroundStyle(Color.flixyTextPrimary)
                    .padding(.horizontal, FlixySpacing.screenMargin)

                LazyVStack(spacing: 0) {
                    ForEach(entries) { entry in
                        NavigationLink(value: MediaRoute(ratingKey: entry.id, title: entry.title)) {
                            ChildRow(item: entry)
                        }
                        .buttonStyle(.plain)

                        Divider().overlay(Color.flixySeparator)
                    }
                }
            }
        }
    }

    private var metadataLine: String? {
        var pieces: [String] = []
        // Bei einer Staffel steht oben der Serienname — welche Staffel es
        // ist, muss deshalb hierher.
        if item.kind == .season, let number = item.index {
            pieces.append(String(localized: "season.short \(number)"))
        }
        if let year = item.year { pieces.append(String(year)) }
        if let episodeCount = item.episodeCount {
            pieces.append(String(localized: "detail.episodeCount \(episodeCount)"))
        }
        if let viewed = item.playedEpisodeCount, let total = item.episodeCount, viewed < total {
            pieces.append(String(localized: "detail.unwatchedCount \(total - viewed)"))
        }
        if let rating = item.contentRating { pieces.append(rating) }
        return pieces.isEmpty ? nil : pieces.joined(separator: " · ")
    }

    private func loadChildren() async {
        guard let server = session.backend else { return }
        children = await LoadState.load {
            try await server.children(of: item.id)
        }
    }
}

/// Eine Staffel- oder Folgenzeile.
private struct ChildRow: View {
    let item: MediaItem
    @Environment(FlixySession.self) private var session

    var body: some View {
        HStack(spacing: FlixySpacing.regular) {
            FlixyArtwork(
                url: session.backend?.artworkURL(
                    path: item.thumb,
                    width: item.kind == .season ? 120 : 240,
                    height: item.kind == .season ? 180 : 135
                ),
                aspectRatio: item.kind == .season ? PosterCard.aspectRatio : LandscapeCard.aspectRatio,
                fallbackSymbol: "play.rectangle"
            )
            .frame(width: item.kind == .season ? 48 : 96)
            .clipShape(.rect(cornerRadius: 4))
            .overlay(alignment: .bottom) {
                if let progress = item.watchProgress {
                    WatchProgressBar(fraction: progress)
                }
            }
            .clipShape(.rect(cornerRadius: 4))

            VStack(alignment: .leading, spacing: 2) {
                Text(rowTitle)
                    .font(.flixyCardTitle)
                    .foregroundStyle(Color.flixyTextPrimary)
                    .lineLimit(2)

                if let subtitle {
                    Text(subtitle)
                        .font(.flixyCaption)
                        .foregroundStyle(Color.flixyTextMuted)
                        .lineLimit(1)
                }
            }

            Spacer()

            if item.isWatched {
                Image(systemName: "checkmark.circle.fill")
                    .foregroundStyle(Color.flixyTextMuted)
                    .accessibilityLabel(Text("item.watched"))
            }
        }
        .padding(.horizontal, FlixySpacing.screenMargin)
        .padding(.vertical, FlixySpacing.snug)
        .contentShape(.rect)
        .accessibilityElement(children: .combine)
    }

    private var rowTitle: String {
        if item.kind == .episode, let episode = item.index {
            return "\(episode). \(item.title)"
        }
        return item.title
    }

    private var subtitle: String? {
        switch item.kind {
        case .season:
            item.episodeCount.map { String(localized: "detail.episodeCount \($0)") }
        case .episode:
            item.duration.map { Duration.milliseconds($0).runtimeLabel }
        default:
            nil
        }
    }
}