import SwiftUI

/// The root of the boards navigation stack: board list → lanes → cards → card detail
/// (`BoardRoute`'s destinations).
///
/// Renders all three of `BoardIndexStore.Phase` — the property the placeholder this replaces
/// existed to prove, and the split this screen keeps.
struct BoardsTabView: View {
    @Environment(BoardIndexStore.self) private var index

    @State private var isPresentingNewBoard = false

    var body: some View {
        NavigationStack {
            content
                .navigationTitle("Boards")
                .toolbar {
                    if case .ready = index.phase {
                        Button("New Board", systemImage: "plus") {
                            isPresentingNewBoard = true
                        }
                    }
                }
                .navigationDestination(for: BoardRoute.self) { route in
                    switch route {
                    case let .lanes(boardRoot):
                        BoardScreen(boardRoot: boardRoot)
                    case let .cards(boardRoot, laneID):
                        LaneScreen(boardRoot: boardRoot, laneID: laneID)
                    case let .card(boardRoot, laneID, cardID):
                        CardDetailScreen(boardRoot: boardRoot, laneID: laneID, cardID: cardID)
                    }
                }
        }
        .task { index.start() }
        .titlePromptAlert("New Board", isPresented: $isPresentingNewBoard, placeholder: "Board Title") { title in
            Task { await index.createBoard(titled: title) }
        }
    }

    @ViewBuilder
    private var content: some View {
        switch index.phase {
        case .idle, .loading:
            ProgressView("Looking for boards")

        case let .unavailable(reason):
            // The hard-iCloud-requirement wall. `reason` distinguishes "sign in" from "the container
            // did not resolve", which are different asks of the user.
            ContentUnavailableView {
                Label("iCloud Required", systemImage: "icloud.slash")
            } description: {
                Text(reason == .noAccount
                     ? "Sign into iCloud in Settings to use Lanework."
                     : "Lanework can't reach its iCloud Drive folder right now.")
            } actions: {
                Button("Try Again") { index.start() }
            }

        case .ready where index.boards.isEmpty:
            ContentUnavailableView(
                "No Boards Yet",
                systemImage: "rectangle.stack",
                description: Text("Boards in your iCloud Drive will appear here.")
            )

        case .ready:
            List(index.boards) { board in
                NavigationLink(value: BoardRoute.lanes(boardRoot: board.rootURL)) {
                    BoardSummaryRow(board: board)
                }
            }
            .refreshable { index.refresh() }
        }
    }
}

/// One board row: title, lane/card counts, modified date, and — while the package is not fully
/// current — a download-state subtitle in place of the counts a shallow scan cannot yet answer.
private struct BoardSummaryRow: View {
    let board: BoardSummary

    var body: some View {
        VStack(alignment: .leading, spacing: 2) {
            Text(board.title)
            Text(subtitle)
                .font(.caption)
                .foregroundStyle(.secondary)
        }
    }

    private var subtitle: String {
        switch board.download {
        case .notDownloaded:
            "Waiting to download"
        case let .downloading(fraction):
            fraction.map { "Downloading \(Int($0 * 100))%" } ?? "Downloading"
        case .current, .unknown:
            countsAndModified
        }
    }

    private var countsAndModified: String {
        let counts: String
        if let lanes = board.laneCount, let cards = board.cardCount {
            counts = "\(lanes) lane\(lanes == 1 ? "" : "s") · \(cards) card\(cards == 1 ? "" : "s")"
        } else {
            counts = "—"
        }
        guard let modified = board.modified else { return counts }
        return "\(counts) · \(modified.formatted(.relative(presentation: .named)))"
    }
}