import SwiftUI
import WidgetKit

/// The "Key" legend: price ratings, savings capsules, station labels, the
/// favourite glyph, then the two deeper explanations. One sheet for both list
/// tabs — Stations opens it from the info button in the navigation bar,
/// Favourites from the button beside Edit — so the legend cannot drift between
/// them.
///
/// Dismisses through the environment rather than the presenting view's state, and
/// takes the two nested-sheet flags as bindings, so each tab keeps owning its own
/// QA launch-argument hooks.
struct KeySheetView: View {
    @Binding var showBestValueInfo: Bool
    @Binding var showImportantInformation: Bool

    @Environment(\.dismiss) private var dismiss
    /// Where the user last dragged the sheet. Bound rather than fixed at 0.6 so
    /// dragging it up to read the Station labels section sticks, instead of
    /// snapping back every time the sheet is reopened.
    ///
    /// The QA launch argument sets the INITIAL detent rather than assigning one
    /// after the sheet appears: assigning a new selection while the sheet is still
    /// presenting is ignored, which left the legend stuck at 0.6 and the Station
    /// labels section off screen.
    @State private var detent: PresentationDetent =
        ProcessInfo.processInfo.arguments.contains("-qaKeySheetLarge") ? .large : .fraction(0.6)

    var body: some View {
        NavigationStack {
            List {
                Section {
                    KeySheetDescriptionRow(item: KeySheetContent.priceRatings[0]) {
                        KeyPriceRatingIndicator(item: KeySheetContent.priceRatings[0], color: .green)
                    }
                    KeySheetDescriptionRow(item: KeySheetContent.priceRatings[1]) {
                        KeyPriceRatingIndicator(item: KeySheetContent.priceRatings[1], color: .orange)
                    }
                    KeySheetDescriptionRow(item: KeySheetContent.priceRatings[2]) {
                        KeyPriceRatingIndicator(item: KeySheetContent.priceRatings[2], color: .red)
                    }
                } header: {
                    Text("Price ratings")
                }

                Section {
                    ForEach(KeySheetContent.savings, id: \.label) { item in
                        KeySheetDescriptionRow(item: item) {
                            KeySavingsCapsule(label: item.label)
                        }
                    }
                } header: {
                    Text("Savings")
                }

                Section {
                    ForEach(StationLabelKind.allCases, id: \.self) { kind in
                        KeySheetDescriptionRow(item: item(for: kind)) {
                            StationLabelBadge(kind: kind)
                        }
                    }
                } header: {
                    Text("Station labels")
                }

                Section {
                    KeySheetDescriptionRow(item: KeySheetContent.favourite) {
                        FavouriteStarGlyph(isFavourite: true)
                    }
                } header: {
                    Text("Favourites")
                }

                Section {
                    HowBestValueRow { showBestValueInfo = true }
                }

                Section {
                    ImportantInformationRow { showImportantInformation = true }
                }
            }
            .navigationTitle("Key")
            .navigationBarTitleDisplayMode(.inline)
            .toolbar {
                ToolbarItem(placement: .confirmationAction) {
                    Button("Done") { dismiss() }
                }
            }
            // Nested sheet: the Key sheet stays behind the explanation.
            .sheet(isPresented: $showBestValueInfo) { HowBestValueSheet() }
            // Nested sheet: the Key sheet stays behind the disclaimer.
            .importantInformationSheet(isPresented: $showImportantInformation)
        }
        // QA hook: `-qaKeySheetLarge` opens the legend at full height — see the
        // `detent` state. The 0.6 detent puts the Station labels section below the
        // fold on every device, including the tallest iPhone, so the three label
        // badges cannot otherwise be seen on screen.
        .presentationDetents([.fraction(0.6), .large], selection: $detent)
        .presentationBackground(Color(UIColor.systemGroupedBackground))
    }

    /// The Key row's copy for a label kind. Fails loudly in debug rather than
    /// silently rendering a blank row if a kind is ever added without its entry.
    private func item(for kind: StationLabelKind) -> KeySheetContent.Item {
        if let match = KeySheetContent.stationLabels.first(where: { $0.label == kind.label }) {
            return match
        }
        assertionFailure("No KeySheetContent.stationLabels entry for \(kind)")
        return KeySheetContent.Item(label: kind.label, description: "")
    }
}

/// Stations tab — the main list with fuel picker, distance filter, sort, pagination.
struct StationsView: View {
    let stations: [FuelStation]
    let totalCount: Int
    let isLoading: Bool
    @Binding var selectedFuel: FuelType
    @Binding var sortMode: SortMode
    @Binding var stationLimit: Int
    let distanceUnit: DistanceUnit
    let priceDisplayStyle: PriceDisplayStyle
    let baselinePrice: Double?
    let cheapestStationID: String?
    /// The station the savings are measured against — the closest station with an
    /// eligible price. Passed in from the owner of the scaffold baseline so this
    /// list's Closest badge and the reference station cannot disagree.
    let closestStationID: String?
    let location: Coordinate?
    let favouriteIDs: Set<String>
    let stationTapAction: StationTapAction
    let fuelSavingsSettings: FuelSavingsSettings
    @Binding var fuelSavingsAmount: FuelSavingsFillAmount
    var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
    var journeyDiagnosticsForStation: (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil }
    var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
    var onRefresh: () async -> Void = {}

    /// Pagination: one page = 10 rows, reset whenever the underlying list
    /// changes (new fetch, fuel/sort/radius switch). RAG/badge/deltas still come
    /// from the whole radius pool via `cheapestPrice` — paging never changes
    /// which station is "best".
    @State private var pageSize = 10
    @State private var visibleCount = 10

    /// Price-rating legend (the "Key") lives in a sheet, opened from the
    /// info button in the header — keeps the list focused on stations.
    @State private var showKey = false

    /// The "How Best Value works" sheet. The explanation used to be a section in
    /// the Key sheet; it is its own sheet now, opened from a row at the bottom of
    /// the Key sheet and from the More info sheet.
    @State private var showBestValueInfo = false

    /// The shared "Important information" disclaimer sheet. It lives at the
    /// bottom of the Key sheet here; the same sheet is reused wherever else the
    /// disclaimer is needed.
    @State private var showImportantInformation = false

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

    /// Bottom-of-tab explainer (moved from the top 2026-08-16): mode/radius/
    /// directions context + "N/TOTAL stations updated". The numerator is the
    /// current list pool; the denominator is the full UK station total from
    /// the last chain fetch (8,022 mirror snapshot) — hidden until known.
    private var footerCaption: String {
        let miles = distanceUnit.displayMiles(stationLimit)
        let unit = distanceUnit.label(for: Double(miles))
        let fuel = selectedFuel.displayName
        let mode: String
        switch sortMode {
        case .closest: mode = "Closest"
        case .cheapest: mode = "Cheapest"
        case .worthTheDrive: mode = "Best Value"
        }
        let tapHint = stationTapAction == .openMap
            ? "tap a station for directions."
            : "tap a station for details."
        let ratio: String
        if let total = FuelStore.loadStationCount() {
            ratio = "\(totalCount)/\(total)"
        } else {
            ratio = "\(totalCount)"
        }
        if location != nil {
            if sortMode == .closest {
                return "\(mode) \(fuel) stations — closest first, lowest price within \(miles) \(unit) · \(ratio) stations updated"
            }
            return "\(mode) \(fuel) within \(miles) \(unit) — \(ratio) stations updated · \(tapHint)"
        }
        return "\(mode) \(fuel) — \(ratio) stations updated · \(tapHint)"
    }

    var body: some View {
        NavigationStack {
            List {
                Section("Fuel type") {
                    FuelTypeSegmentedPicker(selection: $selectedFuel) { newValue in
                        FuelStore.saveSelectedFuel(newValue)
                        WidgetCenter.shared.reloadAllTimelines()
                    }
                }

                Section("Distance") {
                    Picker("Distance", selection: $stationLimit) {
                        ForEach(FuelStore.stationRadiusOptions, id: \.self) { miles in
                            let shown = distanceUnit.displayMiles(miles)
                            Text("\(shown) \(distanceUnit.label(for: Double(shown)))").tag(miles)
                        }
                    }
                    .pickerStyle(.segmented)
                    // In Closest mode the whole country is the pool — the
                    // radius is meaningless ("closest" must never return an
                    // empty state), so the picker is disabled but its value is
                    // kept for when the user switches back to Cheapest.
                    .disabled(sortMode == .closest)
                    .opacity(sortMode == .closest ? 0.5 : 1)
                    .onChange(of: stationLimit) { _, newValue in
                        FuelStore.saveStationLimit(newValue)
                    }
                    .padding(.vertical, 2)
                }

                Section("Stations") {
                    Picker("Sort by", selection: $sortMode) {
                        ForEach(availableSortModes) { mode in
                            Text(mode.displayName).tag(mode)
                        }
                    }
                    .pickerStyle(.segmented)
                    .onChange(of: sortMode) { _, newValue in
                        FuelStore.saveSortMode(newValue)
                    }
                    .padding(.vertical, 2)

                    // Only offered while the feature is actually configured — a
                    // stale stored sort mode must not keep the control on screen
                    // for a switched-off feature.
                    if sortMode == .worthTheDrive && fuelSavingsSettings.isConfigured {
                        FuelSavingsAdjustmentView(amount: $fuelSavingsAmount)
                    }

                    if fuelSavingsSettings.isConfigured && !stations.isEmpty {
                        Text(String(localized: "Price colours show pump price competitiveness. Savings compare with your closest station, including journey costs.", comment: "Station listing price and savings explanation"))
                            .font(.footnote)
                            .foregroundStyle(.secondary)
                            .fixedSize(horizontal: false, vertical: true)
                    }

                    if isLoading && stations.isEmpty {
                        HStack(spacing: 10) {
                            ProgressView()
                            Text("Fetching prices…")
                        }
                    } else if stations.isEmpty {
                        let miles = distanceUnit.displayMiles(stationLimit)
                        let unit = distanceUnit.label(for: Double(miles))
                        VStack(alignment: .leading, spacing: 6) {
                            Text(String(format: NSLocalizedString("No %@ stations within %lld %@.", comment: "Empty state when the radius finds nothing nearby"), selectedFuel.displayName, miles, unit))
                                .foregroundStyle(.secondary)
                            Text("FuelBoard covers the whole UK — try Closest to browse every station.")
                                .font(.caption)
                                .foregroundStyle(.secondary)
                            Button("Browse all UK stations") {
                                sortMode = .closest
                            }
                            .font(.caption)
                        }
                        .padding(.vertical, 4)
                    } else {
                        ForEach(Array(stations.prefix(visibleCount)), id: \.id) { station in
                            stationRow(station)
                        }

                        if visibleCount < stations.count {
                            Button {
                                visibleCount += pageSize
                            } label: {
                                HStack {
                                    Spacer()
                                    Text("Show \(min(pageSize, stations.count - visibleCount)) more (\(stations.count - visibleCount) remaining)")
                                    Spacer()
                                }
                            }
                        } else {
                            Text("All \(stations.count) stations shown")
                                .font(.caption2)
                                .foregroundStyle(.secondary)
                                .frame(maxWidth: .infinity)
                        }
                    }
                }

                // Bottom-of-tab explainer (moved from the top 2026-08-16),
                // styled like the Favourites tab's cheapest callout: a caption
                // paragraph in its own section cell.
                Section {
                    Text(footerCaption)
                        .font(.caption)
                        .foregroundStyle(.secondary)
                }

            }
            .refreshable {
                // Manual override for the twice-a-day cache policy.
                await onRefresh()
            }
            .onChange(of: stations) { _, _ in
                // New fetch or filter switch → back to the first page.
                visibleCount = pageSize
            }
            // Native large-title behaviour (Mail-style): the system shows the
            // large title at rest, scrolls it away and fades the compact
            // inline title in. No custom toolbar needed — the native mechanism
            // only renders text, which is exactly what we want here.
            // No numeric field is left on this screen — the Worth the Drive
            // fill-up control is a slider — so no keyboard should appear here.
            // The Done bar and interactive dismissal stay as the escape hatch
            // for any field that returns.
            .keyboardDoneButton()
            .scrollDismissesKeyboard(.interactively)
            .navigationTitle("FuelBoard")
            .navigationBarTitleDisplayMode(.large)
            .onAppear {
#if DEBUG
                // QA hook: launch with `-showKeySheet` to verify the legend
                // sheet without driving a tap (simctl has no tap command).
                if ProcessInfo.processInfo.arguments.contains("-showKeySheet") {
                    showKey = true
                }
                // QA hook: `-showBestValueInfo` opens the Key sheet and then the
                // explanation on top of it, so the copy can be screenshotted
                // without a tap. It has to chain: the explanation's `.sheet` lives
                // inside the Key sheet's content, so it cannot present while the
                // Key sheet is shut.
                if BestValueInfoQA.isRequested {
                    showKey = true
                    Task { @MainActor in
                        try? await Task.sleep(nanoseconds: 1_200_000_000)
                        showBestValueInfo = true
                    }
                }
                // QA hook: `-showImportantInfo` opens the Key sheet and then the
                // shared disclaimer on top of it, so the copy can be
                // screenshotted without a tap. Same chained requirement as
                // `-showBestValueInfo` above.
                if ImportantInformationQA.isRequested {
                    showKey = true
                    Task { @MainActor in
                        try? await Task.sleep(nanoseconds: 1_200_000_000)
                        showImportantInformation = true
                    }
                }
#endif
            }
            .onReceive(NotificationCenter.default.publisher(for: .fuelBoardOpenBestValueSettings)) { _ in
                // "Setup Best Value" from the explanation sheet. That sheet closes
                // itself and ContentView switches to Settings, but both of the
                // sheets this view can have open are presented from HERE and each
                // survived the tab switch, floating over Settings: the Key sheet
                // and the More info sheet. Close whichever is up.
                showKey = false
                detailStation = nil
            }
            .task(id: stations.count) {
#if DEBUG
                // QA hook: `-showDetail` opens the More info sheet for the first
                // listed station, so the sheet can be screenshotted without a
                // tap. Waits for the list to arrive first.
                guard ProcessInfo.processInfo.arguments.contains("-showDetail"),
                      detailStation == nil,
                      let first = stations.first else { return }
                try? await Task.sleep(nanoseconds: 2_000_000_000)
                detailStation = first
#endif
            }
            .toolbar {
                ToolbarItem(placement: .topBarTrailing) {
                    Button {
                        showKey = true
                    } label: {
                        Image(systemName: "info.circle")
                    }
                    .accessibilityLabel("Key")
                }
            }
            .sheet(isPresented: $showKey) {
                keySheet
            }
            .sheet(item: $detailStation) { station in
                detailSheet(for: station)
            }
        }
    }

    private func detailSheet(for station: FuelStation) -> some View {
        StationDetailView(
            station: station,
            location: location,
            distanceUnit: distanceUnit,
            priceStyle: priceDisplayStyle,
            selectedFuel: selectedFuel,
            fuelSavings: savingsForStation(station),
            fuelSavingsAmount: fuelSavingsAmount,
            journeyDiagnostics: journeyDiagnosticsForStation(station),
            // The same flag the row gets from `cheapestStationID`.
            isCheapestInRange: station.id == cheapestStationID,
            // The same flag the row gets from `closestStationID`.
            isClosestInRange: station.id == closestStationID,
            isFavourite: favouriteIDs.contains(station.id),
            onToggleFavourite: { onToggleFavourite(station, selectedFuel) }
        )
    }

    /// The legend sheet, shared with the Favourites tab. Nothing varies by fuel:
    /// every station label has a fixed semantic tone, so the legend reads the same
    /// whichever grade the reader is looking at.
    private var keySheet: some View {
        KeySheetView(
            showBestValueInfo: $showBestValueInfo,
            showImportantInformation: $showImportantInformation
        )
    }

    private func stationRow(_ station: FuelStation) -> some View {
        StationRow(
            station: station,
            fuel: selectedFuel,
            location: location,
            distanceUnit: distanceUnit,
            priceDisplayStyle: priceDisplayStyle,
            baselinePrice: baselinePrice,
            isCheapestResult: station.id == cheapestStationID,
            isClosestResult: station.id == closestStationID,
            isFavourite: favouriteIDs.contains(station.id),
            tapAction: stationTapAction,
            fuelSavings: savingsForStation(station),
            onToggleFavourite: { onToggleFavourite(station, selectedFuel) },
            onShowDetails: { detailStation = $0 }
        )
    }

    private var availableSortModes: [SortMode] {
        var modes: [SortMode] = [.closest, .cheapest]
        if fuelSavingsSettings.isConfigured {
            modes.append(.worthTheDrive)
        }
        return modes
    }

}

/// The station list's real RAG dot, paired with the rating name. The range lives
/// in the aligned description column rather than as a separate trailing value.
private struct KeyPriceRatingIndicator: View {
    let item: KeySheetContent.Item
    let color: Color

    var body: some View {
        HStack(spacing: 5) {
            PriceRatingDot(color: color)
            Text(LocalizedStringKey(item.label))
                .font(.caption.weight(.semibold))
                .fixedSize(horizontal: false, vertical: true)
        }
    }
}

/// Every Key section shares this one two-column row. The scaled first-column
/// width keeps every description on the same leading axis while preserving the
/// inline layout at accessibility sizes; descriptions own the flexible column
/// and grow vertically without truncating.
private struct KeySheetDescriptionRow<Indicator: View>: View {
    private let indicatorColumnWidth: CGFloat = 128

    let item: KeySheetContent.Item
    @ViewBuilder let indicator: Indicator

    var body: some View {
        HStack(alignment: .top, spacing: 12) {
            indicator
                .frame(width: indicatorColumnWidth, alignment: .leading)
            description
        }
        .padding(.vertical, 3)
        .accessibilityElement(children: .ignore)
        .accessibilityLabel("\(item.label). \(item.description)")
    }

    private var description: some View {
        Text(LocalizedStringKey(item.description))
            .font(.subheadline)
            .foregroundStyle(.secondary)
            .fixedSize(horizontal: false, vertical: true)
            .frame(maxWidth: .infinity, alignment: .leading)
    }
}

/// Uses the same listing capsule component as real station rows, with neutral
/// fixture numbers: only the verdict is visible in this compact variant.
private struct KeySavingsCapsule: View {
    let label: String

    /// Keyed on the shared label so the legend cannot demonstrate a word the
    /// listing capsule never draws.
    private var status: FuelSavingsStatus {
        switch label {
        case String(localized: "Saves"): return .worthTheDrive
        case String(localized: "Costs"): return .notWorthTheDrive
        default: return .breakEven
        }
    }

    private var result: FuelSavingsResult {
        let netSaving = status == .worthTheDrive ? 1.0 : (status == .notWorthTheDrive ? -1.0 : 0)
        return FuelSavingsResult(
            fillLitres: 30,
            grossSavingGBP: netSaving,
            extraDrivingCostGBP: 0,
            extraDistanceMiles: 0,
            netSavingGBP: netSaving,
            status: status,
            journeyConfidence: .confirmed
        )
    }

    var body: some View {
        // The legend demonstrates the wording, not a figure: `result` above is a
        // placeholder verdict, and its £1.00 must never reach the screen.
        ListingFuelSavingsCapsule(result: result, showsAmount: false)
    }
}

/// Shared RAG dot used beside live station prices and in the Key.
///
/// 12pt is the app's one diameter: it reads at a glance beside a 22pt price
/// without competing with it, and it is large enough that the three colours are
/// distinguishable for colour-vision-deficient users at arm's length. The widget
/// keeps a smaller dot of its own — its rows are far tighter than a phone row —
/// so this size is deliberately the APP's.
struct PriceRatingDot: View {
    let color: Color
    var diameter: CGFloat = PriceRatingDot.standardDiameter

    /// The app's standard dot diameter, in points.
    static let standardDiameter: CGFloat = 12

    var body: some View {
        Circle()
            .fill(color)
            .frame(width: diameter, height: diameter)
            .accessibilityHidden(true)
    }
}

/// Shared favourite glyph used by station rows and the Key.
struct FavouriteStarGlyph: View {
    let isFavourite: Bool

    var body: some View {
        Image(systemName: isFavourite ? "star.fill" : "star")
            .foregroundStyle(isFavourite ? .yellow : .secondary)
    }
}

/// Shared station-label capsule. `StationRow` uses the same view for its live
/// BEST VALUE/CHEAPEST badge, so the Key cannot drift from the listing style.
///
/// One tone per label kind, from the shared palette: purple for best value, blue
/// for cheapest and top (a top favourite IS the cheapest favourite, so they share
/// a class), neutral for proximity. The symbol is the label's own meaning, sized
/// to sit on the caption's cap height rather than to dominate it.
struct StationLabelBadge: View {
    let kind: StationLabelKind

    private var tone: CapsuleTone {
        switch kind {
        case .bestValue: return .bestValue
        case .cheapest: return .cheapest
        case .closest: return .closest
        }
    }

    var body: some View {
        HStack(spacing: 3) {
            Image(systemName: kind.symbol)
                .font(.caption2.weight(.semibold))
                .accessibilityHidden(true)
            Text(LocalizedStringKey(kind.label))
                .font(.caption.weight(.semibold))
                .fixedSize(horizontal: true, vertical: false)
        }
        .foregroundStyle(tone.foreground)
        .padding(.horizontal, 7)
        .padding(.vertical, 3)
        .background(Capsule().fill(tone.background))
    }
}

/// Every station label in the Key is the SAME `StationLabelBadge` the listing rows
/// and the More info sheet draw.
///
/// The closest station used to be the exception — the legend rendered the real
/// verdict capsule for it, a wider pill with different fill and shape, so it read as
/// a different class of thing from Best value and Cheapest sitting above it. Now
/// that its label is the single word "Closest", it belongs in the same column, in
/// the same capsule, at the same size.
// MARK: - Fuel-type iconography (app target only — FuelStore.swift is Foundation-only)

extension FuelType {
    /// Short segment label ("Unleaded" / "Premium" / "Diesel") for
    /// the picker and description.
    var shortName: String {
        switch self {
        case .e10: return "Unleaded"
        case .e5: return "Premium"
        case .diesel: return "Diesel"
        }
    }
}

/// Fuel-type selector styled like a segmented control, with a coloured pump
/// icon per fuel (green = unleaded, yellow = premium, cyan = diesel). Built
/// custom because the native `.segmented` picker tints every segment the same
/// accent colour — it can't show per-fuel pump colours. Shared by the Stations
/// and Favourites tabs.
struct FuelTypeSegmentedPicker: View {
    @Binding var selection: FuelType
    /// Which fuels to show. Defaults to all; the Favourites tab passes only
    /// the fuels that actually have favourites.
    var fuels: [FuelType] = FuelType.allCases
    var onSelect: (FuelType) -> Void = { _ in }

    @Namespace private var selectionSlider

    var body: some View {
        HStack(spacing: 3) {
            ForEach(fuels) { fuel in
                let isSelected = fuel == selection
                Button {
                    withAnimation(.spring(response: 0.42, dampingFraction: 0.78)) {
                        selection = fuel
                    }
                    onSelect(fuel)
                } label: {
                    HStack(spacing: 5) {
                        Image(systemName: "fuelpump.fill")
                            .font(.caption2)
                            .foregroundStyle(fuel.tintColor)
                            .scaleEffect(isSelected ? 1.08 : 0.94)
                        Text(fuel.shortName)
                            .font(.subheadline.weight(isSelected ? .semibold : .regular))
                            .contentTransition(.opacity)
                    }
                    .foregroundStyle(isSelected ? Color.primary : Color.secondary)
                    .frame(maxWidth: .infinity)
                    .padding(.vertical, 7)
                    .background {
                        if isSelected {
                            Capsule()
                                .fill(Color(UIColor.systemBackground))
                                .overlay {
                                    Capsule()
                                        .stroke(fuel.tintColor.opacity(0.28), lineWidth: 1)
                                }
                                .shadow(color: fuel.tintColor.opacity(0.16), radius: 6, y: 2)
                                .matchedGeometryEffect(id: "fuelSelectionSlider", in: selectionSlider)
                        }
                    }
                    .scaleEffect(isSelected ? 1.02 : 0.98)
                    .contentShape(Capsule())
                }
                .buttonStyle(.plain)
            }
        }
        .padding(3)
        .background(Capsule().fill(Color(.secondarySystemBackground)))
        .animation(.spring(response: 0.42, dampingFraction: 0.78), value: selection)
    }
}

#Preview("Fuel Picker") {
    @Previewable @State var selectedFuel: FuelType = .e10
    FuelTypeSegmentedPicker(selection: $selectedFuel)
        .padding()
        .background(Color(.systemGroupedBackground))
}