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 a plain-language explainer
/// 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 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?

    /// 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 "\(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 "\(shown) \(distanceUnit.label(for: Double(shown)))"
    }

    /// Situational guidance for the currently-selected alert radius, shown
    /// under the picker so users know what each choice is best for. Labels
    /// mirror the picker row text (unit-aware) and explain the trade-off:
    /// smaller radii ping more often but later; larger radii ping rarely in
    /// town but earlier from afar.
    private var alertRadiusGuidance: String {
        switch alertChoice.wrappedValue {
        case .followSearch:
            return "Set-and-forget: alerts behave exactly like the Stations-tab search distance (capped at 8 miles for reliable geofencing)."
        case .fixed(let value):
            let optionLabel = "\(value) \(distanceUnit.label(for: Double(value)))"
            let body: String
            switch value {
            case 1:
                body = "Town driving. Fires most often — you're rarely inside the circle for long, so pings are meaningful. Best for stop-start local trips."
            case 2:
                body = "City or suburb commute. Slightly earlier heads-up than the smallest option; still fires regularly around town."
            case 3:
                body = "Mixed driving. Middle ground: heads-up a few minutes out, still works in most towns."
            case 5:
                body = "A-roads and motorway exits. Wide early warning for longer trips — but in town it rarely fires, because you're usually already inside the circle."
            default:
                body = "Long-distance journeys. Maximum reach: a ping when a cheap station is coming up from far out. In town this essentially never fires."
            }
            return "\(optionLabel) — \(body)"
        }
    }

    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("Cheapest favourite", isOn: $favouriteDropEnabled)
                    Picker("Fuel", selection: $favouriteDropFuel) {
                        ForEach(FuelType.allCases) { fuel in
                            Text(fuel.displayName).tag(fuel)
                        }
                    }
                } header: {
                    Text("Price-drop alerts")
                } footer: {
                    Text("Watches your cheapest saved favourite for the fuel you pick here. FuelBoard alerts when a different favourite becomes the cheapest, or when your current cheapest favourite drops by at least 1.0p. This is separate from the nearby-geofence alert, so you can monitor favourites without extra location noise.")
                }

                Section {
                    Toggle("Enabled", isOn: $enabled)
                    Picker("Fuel", selection: $fuel) {
                        ForEach(FuelType.allCases) { fuel in
                            Text(fuel.displayName).tag(fuel)
                        }
                    }
                    Picker("Radius", selection: alertChoice) {
                        Text("Follow search (\(searchInUnitLabel))").tag(AlertRadiusChoice.followSearch)
                        ForEach(FuelStore.alertRadiusOptions, id: \.self) { value in
                            Text("\(value) \(distanceUnit.label(for: Double(value)))").tag(AlertRadiusChoice.fixed(value))
                        }
                    }
                    Text(alertRadiusGuidance)
                        .font(.caption)
                        .foregroundStyle(.secondary)
                    if enabled && monitoredCount == 0 {
                        Text("No stations monitored yet — open the Stations tab to load prices first.")
                            .font(.caption)
                            .foregroundStyle(.secondary)
                    }
                } header: {
                    Text("Cheapest station")
                } footer: {
                    Text("When you approach a station that is the cheapest within the radius, FuelBoard sends a notification — even with the app closed. Nearby stations selling \(fuel.displayName.lowercased()) are watched — favourites get priority — and each station alerts at most once per hour. Follow search mirrors the Stations-tab distance, capped at 8 miles for reliable geofencing. Smaller radii ping more often but later; larger radii ping rarely in town but earlier from afar.")
                }

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

                Section {
                    Toggle("Live Activity", isOn: $liveActivityEnabled)
                    Picker("Fuel", selection: $liveActivityFuel) {
                        ForEach(FuelType.allCases) { fuel in
                            Text(fuel.displayName).tag(fuel)
                        }
                    }
                    Picker("Distance", selection: laChoice) {
                        Text("Follow search (\(searchInUnitLabel))").tag(LADistanceChoice.followSearch)
                        ForEach(FuelStore.stationRadiusOptions, id: \.self) { miles in
                            Text(distanceLabel(forMiles: miles)).tag(LADistanceChoice.fixed(miles))
                        }
                    }
                } header: {
                    Text("Live Activity")
                } footer: {
                    Text("Shows the cheapest station for the fuel and distance you pick here on the Lock Screen and Dynamic Island — independent of the Stations tab (choose Follow search to mirror its distance instead). Updates as you drive; tap to open directions. Live Activities can be disabled in System Settings → Live Activities.")
                }
            }
            .navigationTitle("Alerts")
        }
    }
}