import SwiftUI

/// Favourites tab — starred stations, split by fuel type. Each fuel type
/// with at least one favourite appears as its own tab. The list shows the
/// USER'S manual order (drag to reorder — Edit button in the toolbar): the
/// FIRST station in each fuel's list is the one used as "the favourite" in
/// single widgets. Favourites are fuel-scoped entries — starring a station
/// only pins it for the fuel you were viewing, so an Unleaded favourite
/// never shows as Diesel.
struct FavouritesView: View {
    let favourites: [FavouriteEntry]
    /// The app's currently selected fuel — used only as the initial tab.
    let selectedFuel: FuelType
    let location: Coordinate?
    let distanceUnit: DistanceUnit
    let priceDisplayStyle: PriceDisplayStyle
    let stationTapAction: StationTapAction
    /// Fuel Savings config. When it is configured this tab shows the SAME
    /// fill-up control and per-row estimate as the Stations list: one session
    /// amount is shared, so adjusting it in either list updates both, and it
    /// still never touches the Settings default.
    let fuelSavingsSettings: FuelSavingsSettings
    @Binding var fuelSavingsAmount: FuelSavingsFillAmount
    /// Estimated saving for a favourite, against the closest station by
    /// journey distance — the same baseline and definition the Stations list uses.
    var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
    var journeyDiagnosticsForStation: (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil }
    var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
    /// Persists a reordered favourites array (after drag-and-drop).
    var onReorder: ([FavouriteEntry]) -> Void = { _ in }
    /// Propagated from ContentView — Trends' history failure with no data
    /// raises the global connection banner; recovery clears it.
    var onHistoryUnavailable: (() -> Void)? = nil
    var onHistoryRecovered: (() -> Void)? = nil

    /// Fuel types that currently have at least one favourite — these are the
    /// only tabs shown (a fuel with no favourites gets no tab).
    private var availableFuels: [FuelType] {
        FuelType.allCases.filter { fuel in
            favourites.contains { $0.fuel == fuel }
        }
    }

    /// The active tab. Falls back if the chosen fuel ever loses all its
    /// favourites (e.g. the last one is un-starred while viewing it).
    @State private var fuel: FuelType = .e10

    /// Trends sheet (price history chart) presentation state.
    @State private var showTrends = false

    /// Station picked for the More-info sheet (tap action = showDetails).
    @State private var detailStation: FuelStation?

    private var activeFuel: FuelType {
        availableFuels.contains(fuel) ? fuel : (availableFuels.first ?? .e10)
    }

    /// Stations favourited for the active fuel, in the USER'S stored order —
    /// NOT price-sorted. The first row is the favourite used by single
    /// widgets (see footer note).
    private var ordered: [FuelStation] {
        favourites.filter { $0.fuel == activeFuel }.map(\.station)
    }

    /// Cheapest favourited station for the active fuel — the RAG baseline and
    /// the "cheapest favourite" callout, independent of the manual order.
    private var cheapest: FuelStation? {
        ordered.min { ($0.prices[activeFuel] ?? .infinity) < ($1.prices[activeFuel] ?? .infinity) }
    }
    private var cheapestPrice: Double? { cheapest?.prices[activeFuel] }

    /// IDs favourited for the active fuel — the star state on each row.
    private var activeFuelFavouriteIDs: Set<String> {
        Set(favourites.filter { $0.fuel == activeFuel }.map(\.station.id))
    }

    init(favourites: [FavouriteEntry],
         selectedFuel: FuelType,
         location: Coordinate?,
         distanceUnit: DistanceUnit,
         priceDisplayStyle: PriceDisplayStyle,
         stationTapAction: StationTapAction,
         fuelSavingsSettings: FuelSavingsSettings = .defaults,
         fuelSavingsAmount: Binding<FuelSavingsFillAmount>,
         savingsForStation: @escaping (FuelStation) -> FuelSavingsAvailability? = { _ in nil },
         journeyDiagnosticsForStation: @escaping (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil },
         onToggleFavourite: @escaping (FuelStation, FuelType) -> Void = { _, _ in },
         onReorder: @escaping ([FavouriteEntry]) -> Void = { _ in },
         onHistoryUnavailable: (() -> Void)? = nil,
         onHistoryRecovered: (() -> Void)? = nil) {
        self.favourites = favourites
        self.selectedFuel = selectedFuel
        self.location = location
        self.distanceUnit = distanceUnit
        self.priceDisplayStyle = priceDisplayStyle
        self.stationTapAction = stationTapAction
        self.fuelSavingsSettings = fuelSavingsSettings
        _fuelSavingsAmount = fuelSavingsAmount
        self.savingsForStation = savingsForStation
        self.journeyDiagnosticsForStation = journeyDiagnosticsForStation
        self.onToggleFavourite = onToggleFavourite
        self.onReorder = onReorder
        self.onHistoryUnavailable = onHistoryUnavailable
        self.onHistoryRecovered = onHistoryRecovered
        _fuel = State(initialValue: selectedFuel)
    }

    /// Drag-and-drop reorder (List edit mode): the active fuel's entries are
    /// reordered within the global array; the fuel's block keeps its original
    /// position and other fuels keep their relative order (FuelStore helper).
    private func moveFavourite(fromOffsets source: IndexSet, toOffset destination: Int) {
        onReorder(FuelStore.reorderedFavourites(
            favourites, fuel: activeFuel,
            fromOffsets: source, toOffset: destination
        ))
    }

    var body: some View {
        NavigationStack {
            List {
                if favourites.isEmpty {
                    Section {
                        VStack(spacing: 10) {
                            Image(systemName: "star")
                                .font(.system(size: 40))
                                .foregroundStyle(.secondary)
                            Text(String(localized: "No favourites yet", comment: "Favourites empty-state title"))
                                .font(.headline)
                            Text(String(localized: "Tap the star on any station in the Stations tab to pin it here. The first station in each list becomes the favourite used in single widgets — drag to put your pick first.", comment: "Favourites empty-state explanation"))
                                .font(.caption)
                                .foregroundStyle(.secondary)
                                .multilineTextAlignment(.center)
                        }
                        .frame(maxWidth: .infinity)
                        .padding(.vertical, 24)
                    }
                } else {
                    Section(String(localized: "Fuel type", comment: "Fuel type section title")) {
                        FuelTypeSegmentedPicker(
                            selection: $fuel,
                            fuels: availableFuels
                        )
                    }

                    if fuelSavingsSettings.isConfigured {
                        Section {
                            FuelSavingsAdjustmentView(amount: $fuelSavingsAmount)
                        } footer: {
                            Text(String(localized: "Savings below are estimated against the closest station by journey distance — the same baseline as the Stations list.", comment: "Favourites fuel-savings explanation"))
                        }
                    }

                    Section {
                        ForEach(Array(ordered.enumerated()), id: \.element.id) { index, station in
                            StationRow(
                                station: station,
                                fuel: activeFuel,
                                location: location,
                                distanceUnit: distanceUnit,
                                priceDisplayStyle: priceDisplayStyle,
                                baselinePrice: cheapestPrice,
                                isTopResult: station.id == cheapest?.id,
                                isFavourite: activeFuelFavouriteIDs.contains(station.id),
                                tapAction: stationTapAction,
                                fuelSavings: savingsForStation(station),
                                onToggleFavourite: { onToggleFavourite(station, activeFuel) },
                                onShowDetails: { detailStation = $0 }
                            )
                        }
                        .onMove(perform: moveFavourite)
                    } header: {
                        Text(String(format: String(localized: "%@ favourites", comment: "Favourites section title for fuel type"), activeFuel.displayName))
                    } footer: {
                        Text(String(localized: "The first station is the favourite used in single widgets. Tap Edit, then drag to reorder.", comment: "Favourites reorder explanation"))
                    }

                    if let cheapest = cheapest {
                        Section {
                            Text(String(format: String(localized: "%@ is your cheapest %@ favourite. Favourites are monitored automatically — switch to the Alerts tab and enable alerts to get pinged when you approach one that's the cheapest within the radius.", comment: "Cheapest favourite explanation"), cheapest.name, activeFuel.displayName))
                                .font(.caption)
                                .foregroundStyle(.secondary)
                        }
                    }
                }
            }
            .navigationTitle(String(localized: "Favourites", comment: "Favourites tab title"))
            .toolbar {
                if !favourites.isEmpty {
                    ToolbarItemGroup(placement: .topBarTrailing) {
                        Button {
                            showTrends = true
                        } label: {
                            Image(systemName: "chart.xyaxis.line")
                                .accessibilityLabel(String(localized: "Trends", comment: "Trends button accessibility label"))
                        }
                        EditButton()
                    }
                }
            }
            .sheet(isPresented: $showTrends) {
                TrendsView(
                    favourites: favourites,
                    selectedFuel: activeFuel,
                    priceDisplayStyle: priceDisplayStyle,
                    onHistoryUnavailable: onHistoryUnavailable,
                    onHistoryRecovered: onHistoryRecovered
                )
            }
            .sheet(item: $detailStation) { station in
                StationDetailView(
                    station: station,
                    location: location,
                    distanceUnit: distanceUnit,
                    priceStyle: priceDisplayStyle,
                    selectedFuel: activeFuel,
                    fuelSavings: savingsForStation(station),
                    fuelSavingsAmount: fuelSavingsAmount,
                    journeyDiagnostics: journeyDiagnosticsForStation(station),
                    // Every station listed here IS a favourite for the tab's
                    // fuel, so the star starts filled; tapping it unstars.
                    isFavourite: true,
                    onToggleFavourite: { onToggleFavourite(station, activeFuel) }
                )
            }
            .onReceive(NotificationCenter.default.publisher(for: .fuelBoardOpenBestValueSettings)) { _ in
                // "Setup Best Value" from the explanation sheet, opened inside
                // this view's More info sheet. That sheet closes itself; this one
                // is presented from HERE and would otherwise stay over Settings.
                detailStation = nil
            }
            .onAppear {
#if DEBUG
                // QA hook: launch with `-showTrends` to open the sheet
                // without a tap (same pattern as -showKeySheet).
                if ProcessInfo.processInfo.arguments.contains("-showTrends") {
                    showTrends = true
                }
#endif
            }
        }
    }
}