import SwiftUI

/// Favourites tab — starred stations, ranked cheapest-first for the selected
/// fuel, with the cheapest favourite called out at the top.
struct FavouritesView: View {
    let favourites: [FuelStation]
    let selectedFuel: FuelType
    let location: Coordinate?
    let distanceUnit: DistanceUnit
    let favouriteIDs: Set<String>
    var onToggleFavourite: (FuelStation) -> Void = { _ in }

    /// Favourites that sell the selected fuel, cheapest first (distance tiebreak).
    private var ranked: [FuelStation] {
        let available = favourites.filter { $0.prices[selectedFuel] != nil }
        return available.sorted { lhs, rhs in
            let lPrice = lhs.prices[selectedFuel]!
            let rPrice = rhs.prices[selectedFuel]!
            if lPrice != rPrice { return lPrice < rPrice }
            guard let location else { return false }
            return lhs.distanceKM(to: location.lat, lng2: location.lng) <
                   rhs.distanceKM(to: location.lat, lng2: location.lng)
        }
    }

    private var cheapest: FuelStation? { ranked.first }
    private var cheapestPrice: Double? { cheapest?.prices[selectedFuel] }

    var body: some View {
        NavigationStack {
            List {
                if favourites.isEmpty {
                    Section {
                        VStack(spacing: 10) {
                            Image(systemName: "star")
                                .font(.system(size: 40))
                                .foregroundStyle(.secondary)
                            Text("No favourites yet")
                                .font(.headline)
                            Text("Tap the star on any station in the Stations tab to pin it here, ranked by which is cheapest.")
                                .font(.caption)
                                .foregroundStyle(.secondary)
                                .multilineTextAlignment(.center)
                        }
                        .frame(maxWidth: .infinity)
                        .padding(.vertical, 24)
                    }
                } else {
                    Section {
                        if let cheapest, let price = cheapestPrice {
                            HStack(spacing: 10) {
                                Image(systemName: "crown.fill")
                                    .foregroundStyle(.yellow)
                                Text("Cheapest favourite: \(cheapest.name) — \(String(format: "%.1fp", price))")
                                    .font(.footnote)
                            }
                        }
                    }

                    Section("Favourites — cheapest first") {
                        ForEach(Array(ranked.enumerated()), id: \.element.id) { index, station in
                            StationRow(
                                station: station,
                                fuel: selectedFuel,
                                location: location,
                                distanceUnit: distanceUnit,
                                baselinePrice: cheapestPrice,
                                isTopResult: index == 0,
                                isFavourite: favouriteIDs.contains(station.id),
                                onToggleFavourite: { onToggleFavourite(station) }
                            )
                        }
                    }

                    if let cheapest = cheapest {
                        Section {
                            Text("\(cheapest.name) is your cheapest favourite for \(selectedFuel.displayName). 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.")
                                .font(.caption)
                                .foregroundStyle(.secondary)
                        }
                    }
                }
            }
            .navigationTitle("Favourites")
        }
    }
}