import SwiftUI

/// The sidebar: the places first, then the feeds, with OPML subscriptions as folders.
struct FeedListView: View {
    @ObservedObject var store: LibraryStore
    @State private var filter = ""
    @State private var expanded: Set<String> = []

    /// Feeds that are not inside an OPML folder, pinned ones first, then by name.
    private var loose: [IPX.Feed] {
        store.feeds
            .filter { $0.group == nil && !isFolder($0) }
            .filter(matches)
            .sorted { ($0.pinned ? 0 : 1, $0.name.lowercased()) < ($1.pinned ? 0 : 1, $1.name.lowercased()) }
    }

    /// An OPML subscription: other feeds name it as their group.
    private func isFolder(_ feed: IPX.Feed) -> Bool {
        store.feeds.contains { $0.group == feed.id }
    }

    private var folders: [IPX.Feed] {
        store.feeds.filter(isFolder).sorted { $0.name.lowercased() < $1.name.lowercased() }
    }

    private func children(_ folder: IPX.Feed) -> [IPX.Feed] {
        store.feeds.filter { $0.group == folder.id }.filter(matches)
            .sorted { $0.name.lowercased() < $1.name.lowercased() }
    }

    private func matches(_ feed: IPX.Feed) -> Bool {
        filter.isEmpty || feed.name.localizedCaseInsensitiveContains(filter)
    }

    var body: some View {
        List(selection: selection) {
            placesSection
            feedsSection
        }
        .listStyle(.sidebar)
        .scrollContentBackground(.hidden)
        .searchable(text: $filter, placement: .sidebar, prompt: "Filter feeds")
        .navigationTitle("iPodderX")
    }

    private var selection: Binding<LibraryStore.Place?> {
        Binding(get: { store.place }, set: { store.place = $0 ?? .all })
    }

    // Split out because the whole list in one expression is more than the type checker will
    // work through: it gave up rather than compiling it.
    @ViewBuilder private var placesSection: some View {
        Section {
            let unread = store.feeds.reduce(0) { $0 + $1.unread }
            place(.all, "All Subscriptions", "square.3.layers.3d", count: unread)
            place(.listening, "Currently Listening", "headphones", count: nil)
        }
    }

    @ViewBuilder private var feedsSection: some View {
        Section {
            ForEach(loose) { feed in row(feed) }
            ForEach(folders) { folder in folderRow(folder) }
        }
    }

    private func folderRow(_ folder: IPX.Feed) -> some View {
        DisclosureGroup(isExpanded: expansion(folder.id)) {
            ForEach(children(folder)) { row($0) }
        } label: {
            Label(folder.name, systemImage: "folder").foregroundStyle(Glass.text)
        }
    }

    private func expansion(_ id: String) -> Binding<Bool> {
        Binding(get: { expanded.contains(id) },
                set: { open in
                    if open { expanded.insert(id) } else { expanded.remove(id) }
                })
    }

    private func place(_ p: LibraryStore.Place, _ title: String, _ symbol: String, count: Int?) -> some View {
        Label(title, systemImage: symbol)
            .badge(count.map { $0 > 0 ? "\($0)" : "" } ?? "")
            .tag(p)
    }

    private func row(_ feed: IPX.Feed) -> some View {
        HStack(spacing: 10) {
            FeedArt(feed: feed, size: 30)
            VStack(alignment: .leading, spacing: 1) {
                HStack(spacing: 4) {
                    if feed.pinned {
                        Image(systemName: "pin.fill").font(.system(size: 8)).foregroundStyle(Glass.accent)
                    }
                    Text(feed.name).lineLimit(1).foregroundStyle(Glass.text)
                }
                Text("\(feed.entries) items · \(feed.downloaded) downloaded")
                    .font(.caption2).foregroundStyle(Glass.faint).lineLimit(1)
            }
            Spacer(minLength: 4)
            if feed.lastError != nil {
                // Something is wrong with the feed itself, which the counts cannot show.
                Image(systemName: "exclamationmark.triangle.fill")
                    .font(.caption2).foregroundStyle(Glass.bad)
            }
            if feed.unread > 0 {
                Text("\(feed.unread)")
                    .font(.caption2.monospacedDigit())
                    .padding(.horizontal, 6).padding(.vertical, 2)
                    .background(Glass.accent.opacity(0.22), in: Capsule())
                    .foregroundStyle(Glass.accent)
            }
        }
        .tag(LibraryStore.Place.feed(feed.id))
    }
}

/// A feed's picture, or its initials. Two letters read as a thing on purpose; an empty grey
/// square reads as something that failed to load.
struct FeedArt: View {
    let feed: IPX.Feed?
    var size: CGFloat = 30
    @State private var image: UIImage?
    @Environment(\.api) private var api

    var body: some View {
        Group {
            if let image {
                Image(uiImage: image).resizable().aspectRatio(contentMode: .fill)
            } else {
                ZStack {
                    Rectangle().fill(Glass.accent.opacity(0.18))
                    Text(initials)
                        .font(.system(size: size * 0.38, weight: .semibold))
                        .foregroundStyle(Glass.accent)
                }
            }
        }
        .frame(width: size, height: size)
        .clipShape(RoundedRectangle(cornerRadius: size * 0.22, style: .continuous))
        .task(id: feed?.image) {
            guard let path = feed?.image, !path.isEmpty else { return }
            image = await api.image(path)
        }
    }

    private var initials: String {
        let words = (feed?.name ?? "").split(separator: " ").prefix(2)
        let letters = words.compactMap(\.first).map(String.init).joined()
        return letters.isEmpty ? "?" : letters.uppercased()
    }
}

private struct APIKey: EnvironmentKey {
    static let defaultValue = API()
}

extension EnvironmentValues {
    var api: API {
        get { self[APIKey.self] }
        set { self[APIKey.self] = newValue }
    }
}