import SwiftUI
import WidgetKit

/// 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 baselinePrice: Double?
    let topStationID: String?
    let location: Coordinate?
    let favouriteIDs: Set<String>
    var onToggleFavourite: (FuelStation) -> Void = { _ in }
    var onRefresh: () async -> Void = {}

    /// Pagination: one page = 10 rows, reset whenever the underlying list
    /// changes (new fetch, fuel/sort/radius switch). RAG/TOP/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

    var body: some View {
        NavigationStack {
            List {
                Section {
                    if let location {
                        if sortMode == .closest {
                            Text("Closest \(selectedFuel.displayName) stations — nearest first, best value within \(stationLimit) miles.")
                                .font(.footnote)
                                .foregroundStyle(.secondary)
                        } else {
                            Text("Cheapest \(selectedFuel.displayName) within \(stationLimit) miles — tap a station for directions.")
                                .font(.footnote)
                                .foregroundStyle(.secondary)
                        }
                    } else {
                        Text("\(sortMode == .closest ? "Closest" : "Cheapest") \(selectedFuel.displayName) — tap a station for directions.")
                            .font(.footnote)
                            .foregroundStyle(.secondary)
                    }
                }

                Section("Fuel type") {
                    Picker("Fuel type", selection: $selectedFuel) {
                        ForEach(FuelType.allCases) { fuel in
                            Text(fuel.shortName).tag(fuel)
                        }
                    }
                    .pickerStyle(.segmented)
                    .onChange(of: selectedFuel) { _, newValue in
                        FuelStore.saveSelectedFuel(newValue)
                        WidgetCenter.shared.reloadAllTimelines()
                    }
                }

                Section("Distance") {
                    Picker("Distance", selection: $stationLimit) {
                        ForEach(FuelStore.stationRadiusOptions, id: \.self) { miles in
                            Text("\(miles) miles").tag(miles)
                        }
                    }
                    .pickerStyle(.segmented)
                    // In Closest mode the whole country is the pool — the
                    // radius is meaningless ("nearest" 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)
                    if sortMode == .closest {
                        Text("Distance only applies to Cheapest")
                            .font(.caption2)
                            .foregroundStyle(.secondary)
                    } else {
                        Text("\(totalCount) stations within \(stationLimit) miles")
                            .font(.caption2)
                            .foregroundStyle(.secondary)
                    }
                }

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

                    if isLoading {
                        HStack(spacing: 10) {
                            ProgressView()
                            Text("Fetching prices…")
                        }
                    } else if stations.isEmpty {
                        Text("No \(selectedFuel.displayName) stations found.")
                            .foregroundStyle(.secondary)
                    } else {
                        ForEach(Array(stations.prefix(visibleCount)), id: \.id) { station in
                            StationRow(
                                station: station,
                                fuel: selectedFuel,
                                location: location,
                                baselinePrice: baselinePrice,
                                isTopResult: station.id == topStationID,
                                isFavourite: favouriteIDs.contains(station.id),
                                onToggleFavourite: { onToggleFavourite(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)
                        }
                    }
                }

                Section("Key") {
                    HStack(spacing: 8) {
                        Circle().fill(.green).frame(width: 12, height: 12)
                        Text("Best value — within 1.5p of the cheapest")
                            .font(.caption)
                    }
                    HStack(spacing: 8) {
                        Circle().fill(.orange).frame(width: 12, height: 12)
                        Text("Okay — within 4p of the cheapest")
                            .font(.caption)
                    }
                    HStack(spacing: 8) {
                        Circle().fill(.red).frame(width: 12, height: 12)
                        Text("Pricey — more than 4p over the cheapest")
                            .font(.caption)
                    }
                    HStack(spacing: 8) {
                        Text("TOP")
                            .font(.caption2.bold())
                            .padding(.horizontal, 5)
                            .padding(.vertical, 1)
                            .background(Capsule().fill(.blue.opacity(0.15)))
                            .foregroundStyle(.blue)
                        Text("Top result for the current sort")
                            .font(.caption)
                    }
                    HStack(spacing: 8) {
                        Image(systemName: "star.fill")
                            .font(.caption2)
                            .foregroundStyle(.yellow)
                        Text("Star a station to add it to Favourites")
                            .font(.caption)
                    }
                }
            }
            .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.
            .navigationTitle("FuelBoard")
            .navigationBarTitleDisplayMode(.large)
        }
    }
}

// MARK: - Fuel-type iconography (app target only — FuelStore.swift is Foundation-only)

extension FuelType {
    /// Short segment label ("Unleaded (E10)" / "Premium (E5)" / "Diesel") for
    /// the picker and description.
    var shortName: String {
        switch self {
        case .e10: return "Unleaded (E10)"
        case .e5: return "Premium (E5)"
        case .diesel: return "Diesel"
        }
    }

    /// Pump-handle colour convention (UK): green = unleaded, blue = premium,
    /// dark grey = diesel. Used for the fuel-type tab icons and the title icon.
    var tintColor: Color {
        switch self {
        case .e10: return .green
        case .e5: return .blue
        case .diesel: return Color(red: 0.35, green: 0.38, blue: 0.42)
        }
    }
}