import SwiftUI

/// Alerts tab — enables the cheapest-station proximity alerts. The fuel being
/// monitored is chosen HERE, independently of the Stations-tab selection:
/// users can browse any fuel without re-targeting their alerts (and vice
/// versa). The Live Activity section also lives here — it mirrors this page's
/// shape (toggle + fuel + distance) so the two "notify me while driving"
/// surfaces sit together. Geofence plumbing (count, 18-limit) lives in
/// Settings → Debug; the user-facing page keeps short descriptions that follow
/// the selected alert type and radius, plus a 0-stations hint.
struct AlertsView: View {
    @Binding var enabled: Bool
    @Binding var radius: Double   // stored in km (monitor + storage)
    @Binding var fuel: FuelType   // the fuel alerts monitor for
    @Binding var alertMode: AlertMode
    /// Read-only here: the threshold is edited in Settings → Fuel Savings, where
    /// the fill size and MPG that decide the saving live. Read back so the
    /// alert's own rule is visible without leaving the tab.
    let bestValueThresholdGBP: Double
    let bestValueConfigured: Bool
    @Binding var favouriteDropEnabled: Bool
    @Binding var favouriteDropFuel: FuelType
    /// Whether alerts mirror the Stations-tab search distance (capped at 8 mi).
    @Binding var followsSearch: Bool
    /// Whether the "cheapest nearby" Live Activity is shown on the Lock Screen
    /// / Dynamic Island. Tracks its OWN fuel + radius (below) — independent of
    /// the Stations tab.
    @Binding var liveActivityEnabled: Bool
    /// Fuel the Live Activity tracks (independent of the Stations tab).
    @Binding var liveActivityFuel: FuelType
    /// Search radius (miles, 5/10/15) the Live Activity uses.
    @Binding var liveActivityRadiusMiles: Int
    /// Whether the Live Activity mirrors the Stations-tab search distance.
    @Binding var liveActivityFollowsSearch: Bool
    /// Current Stations-tab search distance (miles) — the value "Follow search"
    /// mirrors.
    let stationLimit: Int
    let distanceUnit: DistanceUnit
    let monitoredCount: Int
    let lastAlert: String?
    let onCheckFavouriteDropNow: () -> Void

    /// The Stations-tab search distance shown in the user's unit, e.g.
    /// "5 miles" or "8 km" — for the "Follow search" rows.
    private var searchInUnitLabel: String {
        let shown = distanceUnit.displayMiles(stationLimit)   // stationLimit is always miles
        return String(format: String(localized: "%lld %@", comment: "Distance label"), shown, distanceUnit.label(for: Double(shown)))
    }

    /// A miles value (5/10/15) shown truthfully in the user's unit, e.g.
    /// "5 miles" (miles unit) or "8 km" (km unit) — picker labels must match
    /// what the option really means.
    private func distanceLabel(forMiles miles: Int) -> String {
        let shown = distanceUnit.displayMiles(miles)
        return String(format: String(localized: "%lld %@", comment: "Distance label"), shown, distanceUnit.label(for: Double(shown)))
    }

    /// The distance the geofence actually caps "Follow search" at, in miles
    /// (FuelStore stores the cap in km so the monitor and storage are unit-free).
    private var followSearchCapMiles: Int {
        Int((FuelStore.alertFollowCapKM / FuelSavingsCalculator.kilometresPerMile).rounded())
    }

    /// What the selected alert type actually does. Swapped with the picker so
    /// the copy can never describe the wrong mode.
    private var alertModeDescription: String {
        switch alertMode {
        case .cheapest:
            return String(localized: "Get notified when you're near one of the cheapest stations for your chosen fuel.", comment: "Cheapest station proximity alert description")
        case .bestValue:
            return String(localized: "Get notified when you're near a station that could save you money after travel costs.", comment: "Best Value proximity alert description")
        }
    }

    /// The radius the selected option really monitors, stated in the user's
    /// unit — e.g. "Get alerts when you're within 2 miles of a matching
    /// station." "Follow search" mirrors the Stations-tab distance, which the
    /// geofence caps; said plainly, and only when the search distance really
    /// exceeds the cap, so the sentence never contradicts the picker row.
    private var alertRadiusDescription: String {
        switch alertChoice.wrappedValue {
        case .followSearch:
            let capped = stationLimit > followSearchCapMiles
            let label = distanceLabel(forMiles: capped ? followSearchCapMiles : stationLimit)
            if capped {
                return String(format: String(localized: "Get alerts when you're within %@ of a matching station (your search distance is capped for reliable alerts).", comment: "Proximity alert radius description, follow search capped"), label)
            }
            return String(format: String(localized: "Get alerts when you're within %@ of a matching station.", comment: "Proximity alert radius description"), label)
        case .fixed(let value):
            let label = String(format: String(localized: "%lld %@", comment: "Distance label"), value, distanceUnit.label(for: Double(value)))
            return String(format: String(localized: "Get alerts when you're within %@ of a matching station.", comment: "Proximity alert radius description"), label)
        }
    }

    private enum AlertRadiusChoice: Hashable {
        case followSearch
        case fixed(Int)
    }

    /// The radius picker works in the user's chosen unit; the stored value
    /// stays km so ProximityMonitor and persistence never change. Options are
    /// snapped to the nearest picker value so any stored radius still selects.
    /// "Follow search" mirrors the Stations-tab distance (capped at 8 miles).
    private var alertChoice: Binding<AlertRadiusChoice> {
        Binding(
            get: {
                if followsSearch { return .followSearch }
                let inUnit = distanceUnit.fromKM(radius)
                let snapped = FuelStore.alertRadiusOptions
                    .min(by: { abs(Double($0) - inUnit) < abs(Double($1) - inUnit) }) ?? 3
                return .fixed(snapped)
            },
            set: { choice in
                switch choice {
                case .followSearch:
                    followsSearch = true
                case .fixed(let value):
                    followsSearch = false
                    radius = distanceUnit.toKM(Double(value))
                }
            }
        )
    }

    private enum LADistanceChoice: Hashable {
        case followSearch
        case fixed(Int)
    }

    private var laChoice: Binding<LADistanceChoice> {
        Binding(
            get: {
                if liveActivityFollowsSearch { return .followSearch }
                return .fixed(liveActivityRadiusMiles)
            },
            set: { choice in
                switch choice {
                case .followSearch:
                    liveActivityFollowsSearch = true
                case .fixed(let miles):
                    liveActivityFollowsSearch = false
                    liveActivityRadiusMiles = miles
                }
            }
        )
    }

    var body: some View {
        NavigationStack {
            List {
                Section {
                    Toggle(String(localized: "Cheapest favourite", comment: "Favourite price-drop alert toggle"), isOn: $favouriteDropEnabled)
                    Picker(String(localized: "Fuel", comment: "Fuel picker title"), selection: $favouriteDropFuel) {
                        ForEach(FuelType.allCases) { fuel in
                            Text(fuel.displayName).tag(fuel)
                        }
                    }
                    Button(String(localized: "Check now", comment: "Manual favourite price-drop check button"), action: onCheckFavouriteDropNow)
                        .disabled(!favouriteDropEnabled)
                    Text(String(localized: "Get notified when a different favourite becomes the cheapest, or your cheapest favourite drops in price.", comment: "Favourite price alerts section description"))
                        .font(.footnote)
                        .foregroundStyle(.secondary)
                } header: {
                    Text(String(localized: "Favourite price alerts", comment: "Favourite price alerts section title"))
                }

                Section {
                    Toggle(String(localized: "Cheapest station", comment: "Proximity alert toggle"), isOn: $enabled)
                    Picker(String(localized: "Alert type", comment: "Proximity alert type picker title"), selection: $alertMode) {
                        ForEach(AlertMode.allCases.filter { mode in mode != .bestValue || bestValueConfigured }) { mode in
                            Text(mode.displayName).tag(mode)
                        }
                    }
                    if !bestValueConfigured {
                        Text(String(localized: "Set up Best Value first so Best Value alerts can account for your fill size, MPG and travel cost.", comment: "Best Value alert unavailable hint"))
                            .font(.footnote)
                            .foregroundStyle(.secondary)
                    }
                    Text(alertModeDescription)
                        .font(.footnote)
                        .foregroundStyle(.secondary)
                    if alertMode == .bestValue {
                        // The threshold is edited in Settings → Fuel Savings: it
                        // labels station rows BEST VALUE as well as gating this
                        // alert, so it lives with the fill size and MPG that
                        // produce the saving. Read back here, not offered twice.
                        Text(String(format: String(localized: "Minimum saving %@ — change in Settings, Fuel Savings.", comment: "Best Value alert threshold read-back"), FuelSavingsFormat.money(bestValueThresholdGBP)))
                            .font(.footnote)
                            .foregroundStyle(.secondary)
                    }
                    Picker(String(localized: "Fuel", comment: "Fuel picker title"), selection: $fuel) {
                        ForEach(FuelType.allCases) { fuel in
                            Text(fuel.displayName).tag(fuel)
                        }
                    }
                    Picker(String(localized: "Radius", comment: "Alert radius picker title"), selection: alertChoice) {
                        Text(String(format: String(localized: "Follow search (%@)", comment: "Follow current station search distance option"), searchInUnitLabel)).tag(AlertRadiusChoice.followSearch)
                        ForEach(FuelStore.alertRadiusOptions, id: \.self) { value in
                            Text(String(format: String(localized: "%lld %@", comment: "Distance label"), value, distanceUnit.label(for: Double(value)))).tag(AlertRadiusChoice.fixed(value))
                        }
                    }
                    Text(alertRadiusDescription)
                        .font(.footnote)
                        .foregroundStyle(.secondary)
                    if enabled && monitoredCount == 0 {
                        Text(String(localized: "No stations monitored yet — open the Stations tab to load prices first.", comment: "No monitored stations hint"))
                            .font(.footnote)
                            .foregroundStyle(.secondary)
                    }
                    Text(String(localized: "Background alerts depend on when your iPhone allows them; each station alerts at most once an hour.", comment: "Proximity alerts background limitation note"))
                        .font(.footnote)
                        .foregroundStyle(.secondary)
                } header: {
                    Text(String(localized: "Proximity alerts", comment: "Proximity alerts section title"))
                }

                if enabled, let lastAlert {
                    Section(String(localized: "Last alert", comment: "Last alert section title")) {
                        Label(lastAlert, systemImage: "bell.badge.fill")
                            .font(.footnote)
                    }
                }

                Section {
                    Toggle(String(localized: "Cheapest station", comment: "Live Activity toggle"), isOn: $liveActivityEnabled)
                    Picker(String(localized: "Fuel", comment: "Fuel picker title"), selection: $liveActivityFuel) {
                        ForEach(FuelType.allCases) { fuel in
                            Text(fuel.displayName).tag(fuel)
                        }
                    }
                    Picker(String(localized: "Distance", comment: "Distance picker title"), selection: laChoice) {
                        Text(String(format: String(localized: "Follow search (%@)", comment: "Follow current station search distance option"), searchInUnitLabel)).tag(LADistanceChoice.followSearch)
                        ForEach(FuelStore.stationRadiusOptions, id: \.self) { miles in
                            Text(distanceLabel(forMiles: miles)).tag(LADistanceChoice.fixed(miles))
                        }
                    }
                    if liveActivityFollowsSearch {
                        Text(String(localized: "Uses the same distance as your station search.", comment: "Live Activity distance description, follow search"))
                            .font(.footnote)
                            .foregroundStyle(.secondary)
                    }
                    Text(String(localized: "See the cheapest nearby station on your Lock Screen and Dynamic Island, with updates as you travel.", comment: "Live Activity section description"))
                        .font(.footnote)
                        .foregroundStyle(.secondary)
                } header: {
                    Text(String(localized: "Live Activity", comment: "Live Activity section title"))
                }
            }
            .navigationTitle(String(localized: "Alerts", comment: "Alerts tab title"))
        }
    }
}