import SwiftUI
import StoreKit
import WidgetKit

/// Settings tab — distance units, onboarding replay, and a tip jar.
struct SettingsView: View {
    @Binding var distanceUnit: DistanceUnit
    var onShowOnboarding: () -> Void = {}

    @StateObject private var tipStore = TipStore()
    @State private var showTipAlert = false
    @State private var tipAlertMessage = ""

    var body: some View {
        NavigationStack {
            List {
                Section {
                    Picker("Distance", selection: $distanceUnit) {
                        ForEach(DistanceUnit.allCases) { unit in
                            Text(unit.displayName).tag(unit)
                        }
                    }
                    .pickerStyle(.segmented)
                    .onChange(of: distanceUnit) { _, newValue in
                        FuelStore.saveDistanceUnit(newValue)
                        WidgetCenter.shared.reloadAllTimelines()
                    }
                } header: {
                    Text("Units")
                } footer: {
                    Text("Distances and search radii across the app, widget and alerts are shown in this unit.")
                }

                Section {
                    Button {
                        onShowOnboarding()
                    } label: {
                        Label("Show introduction", systemImage: "sparkles")
                    }
                } footer: {
                    Text("Replay the welcome screen, including the location and notification permission prompts.")
                }

                Section {
                    Button {
                        Task { await tipStore.purchase() }
                    } label: {
                        HStack {
                            Label("Leave a tip", systemImage: "heart.fill")
                                .foregroundStyle(.pink)
                            Spacer()
                            Text(tipStore.displayPrice)
                                .foregroundStyle(.secondary)
                                .monospacedDigit()
                        }
                    }
                    .disabled(tipStore.purchaseInProgress)
                } header: {
                    Text("Support FuelBoard")
                } footer: {
                    Text("A small tip helps keep the data relay and app development going. Thank you!")
                }

                if let message = tipStore.message {
                    Section {
                        Text(message)
                            .font(.footnote)
                            .foregroundStyle(.secondary)
                    }
                }
            }
            .navigationTitle("Settings")
            .onAppear {
                Task { await tipStore.load() }
            }
        }
    }
}

/// Loads the £4.99 tip product and drives its purchase.
@MainActor
final class TipStore: ObservableObject {
    /// Product ID for the £4.99 tip (App Store Connect — consumable).
    static let productID = "com.apt.fuelboard.tip499"

    @Published private(set) var product: Product?
    @Published private(set) var purchaseInProgress = false
    @Published private(set) var message: String?

    var displayPrice: String {
        product?.displayPrice ?? "£4.99"
    }

    func load() async {
        // Refreshes product state on every visit so a newly-approved product
        // (or a restored transaction) is picked up.
        do {
            let products = try await Product.products(for: [Self.productID])
            product = products.first
        } catch {
            // No product yet (sideloaded build) — the button still shows the
            // intended price and reports the purchase attempt gracefully.
            product = nil
        }
    }

    func purchase() async {
        guard !purchaseInProgress else { return }
        purchaseInProgress = true
        defer { purchaseInProgress = false }

        // If the product hasn't loaded (e.g. not configured in App Store
        // Connect yet), still allow the attempt so the user sees a clear
        // outcome rather than a dead button.
        guard let product else {
            message = "The tip isn't available in this build yet — check back after an App Store release."
            return
        }

        do {
            let result = try await product.purchase()
            switch result {
            case .success(let verification):
                switch verification {
                case .verified:
                    message = "Thank you! Your tip has been received. ⛽"
                case .unverified:
                    message = "The purchase couldn't be verified. Please try again."
                }
            case .userCancelled:
                message = nil   // silent — the user just closed the sheet
            case .pending:
                message = "Your tip is pending approval. It'll finish automatically."
            @unknown default:
                message = nil
            }
        } catch {
            message = "The tip couldn't be completed: \(error.localizedDescription)"
        }
    }
}