import SwiftUI

/// Alerts tab — enables the cheapest-station proximity alerts and shows what's
/// being monitored. 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).
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
    let distanceUnit: DistanceUnit
    let monitoredCount: Int
    let lastAlert: String?

    /// The radius slider works in the user's chosen unit; the stored value
    /// stays km so ProximityMonitor and persistence never change.
    private var radiusInUnit: Double { distanceUnit.fromKM(radius) }

    var body: some View {
        NavigationStack {
            List {
                Section {
                    Toggle("Cheapest-station alerts", isOn: $enabled)
                } footer: {
                    Text("When you approach a station that is the cheapest within the radius, FuelBoard sends a notification — even with the app closed.")
                }

                if enabled {
                    Section {
                        Picker("Fuel", selection: $fuel) {
                            ForEach(FuelType.allCases) { fuel in
                                Text(fuel.shortName).tag(fuel)
                            }
                        }
                        .pickerStyle(.segmented)
                    } header: {
                        Text("Fuel to monitor")
                    } footer: {
                        Text("Alerts watch for the cheapest \(fuel.displayName.lowercased()) station within the radius.")
                    }

                    Section("Trigger radius") {
                        VStack(alignment: .leading, spacing: 8) {
                            HStack {
                                Text("Radius")
                                Spacer()
                                Text(String(format: "%.1f %@", radiusInUnit, distanceUnit.shortName))
                                    .foregroundStyle(.secondary)
                                    .monospacedDigit()
                            }
                            // 1–10 in the user's unit; convert back to km on change.
                            Slider(value: Binding(
                                get: { radiusInUnit },
                                set: { radius = distanceUnit.toKM($0) }
                            ), in: 1...10, step: distanceUnit == .kilometers ? 1 : 0.5)
                        }
                    }

                    Section("Monitoring") {
                        if monitoredCount == 0 {
                            Text("No stations monitored yet — open the Stations tab to load prices first.")
                                .font(.caption)
                                .foregroundStyle(.secondary)
                        } else {
                            LabeledContent("Geofenced stations", value: "\(monitoredCount)")
                            Text("Your favourites for \(fuel.displayName.lowercased()) get priority, then the closest stations selling that fuel fill the rest (18 max, iOS region limit).")
                                .font(.caption)
                                .foregroundStyle(.secondary)
                            Text("Alerts are checked against the cheapest station within the trigger radius for the fuel chosen above. Each station alerts at most once per hour.")
                                .font(.caption)
                                .foregroundStyle(.secondary)
                        }
                    }

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