import SwiftUI

// MARK: - Model

struct AppSettings: Equatable {
    var systemName: String
    var timezone: String
    var jwtExpiryHours: Int
    var twoFactorEnabled: Bool
    var serverURL: String

    static let `default` = AppSettings(
        systemName: "AAMOS",
        timezone: "Europe/Stockholm",
        jwtExpiryHours: 24,
        twoFactorEnabled: false,
        serverURL: "https://api.aamos.io"
    )
}

// MARK: - ViewModel

@MainActor
@Observable
final class SettingsViewModel {
    var settings: AppSettings
    var savedSettings: AppSettings
    var isSaving = false
    var showLogoutConfirmation = false
    var saveError: String?

    var hasChanges: Bool { settings != savedSettings }

    init(initial: AppSettings = .default) {
        self.settings = initial
        self.savedSettings = initial
    }

    func save() async {
        isSaving = true
        defer { isSaving = false }
        do {
            try await Task.sleep(for: .milliseconds(400))
            savedSettings = settings
        } catch {
            saveError = error.localizedDescription
        }
    }

    func discardChanges() {
        settings = savedSettings
    }

    func logout() {
        // Clear credentials and navigate to auth screen
    }
}

// MARK: - View

struct SettingsView: View {
    @State private var vm = SettingsViewModel()

    private let timezones: [String] = {
        var zones = TimeZone.knownTimeZoneIdentifiers.sorted()
        if let idx = zones.firstIndex(of: "Europe/Stockholm") {
            zones.move(fromOffsets: IndexSet(integer: idx), toOffset: 0)
        }
        return zones
    }()

    private var appVersion: String {
        Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String ?? "—"
    }

    private var buildNumber: String {
        Bundle.main.infoDictionary?["CFBundleVersion"] as? String ?? "—"
    }

    var body: some View {
        NavigationStack {
            Form {
                generalSection
                securitySection
                aboutSection
                logoutSection
            }
            .navigationTitle("Inställningar")
            .navigationBarTitleDisplayMode(.large)
            .toolbar { toolbarContent }
            .disabled(vm.isSaving)
            .overlay {
                if vm.isSaving {
                    savingOverlay
                }
            }
            .confirmationDialog(
                "Logga ut",
                isPresented: $vm.showLogoutConfirmation,
                titleVisibility: .visible
            ) {
                Button("Logga ut", role: .destructive) { vm.logout() }
                Button("Avbryt", role: .cancel) {}
            } message: {
                Text("Du loggas ut från AAMOS Admin. Osparade ändringar försvinner.")
            }
            .alert("Kunde inte spara", isPresented: Binding(
                get: { vm.saveError != nil },
                set: { if !$0 { vm.saveError = nil } }
            )) {
                Button("OK", role: .cancel) {}
            } message: {
                Text(vm.saveError ?? "")
            }
        }
    }

    // MARK: General

    private var generalSection: some View {
        Section {
            LabeledContent {
                TextField("Systemnamn", text: $vm.settings.systemName)
                    .multilineTextAlignment(.trailing)
                    .foregroundStyle(Color(.systemBlue))
            } label: {
                Label("Systemnamn", systemImage: "server.rack")
            }

            Picker(selection: $vm.settings.timezone) {
                ForEach(timezones, id: \.self) { tz in
                    Text(tz.replacingOccurrences(of: "_", with: " "))
                        .tag(tz)
                }
            } label: {
                Label("Tidszon", systemImage: "globe")
            }
            .pickerStyle(.navigationLink)
        } header: {
            sectionHeader("Allmänt", icon: "gearshape")
        }
    }

    // MARK: Security

    private var securitySection: some View {
        Section {
            LabeledContent {
                Stepper(
                    "\(vm.settings.jwtExpiryHours) tim",
                    value: $vm.settings.jwtExpiryHours,
                    in: 1...168,
                    step: 1
                )
                .fixedSize()
            } label: {
                Label("JWT-utgång", systemImage: "key.fill")
            }

            Toggle(isOn: $vm.settings.twoFactorEnabled) {
                Label("Tvåfaktorsautentisering", systemImage: "lock.shield.fill")
            }
            .tint(Color(.systemGreen))
        } header: {
            sectionHeader("Säkerhet", icon: "lock.fill")
        } footer: {
            Text("JWT-tokens ogiltigförklaras automatiskt efter vald tid. Tvåfaktorsinloggning kräver TOTP-app.")
                .font(.caption)
                .foregroundStyle(.secondary)
        }
    }

    // MARK: About

    private var aboutSection: some View {
        Section {
            LabeledContent {
                TextField("https://api.aamos.io", text: $vm.settings.serverURL)
                    .multilineTextAlignment(.trailing)
                    .foregroundStyle(Color(.systemBlue))
                    .keyboardType(.URL)
                    .autocorrectionDisabled()
                    .textInputAutocapitalization(.never)
            } label: {
                Label("Server-URL", systemImage: "network")
            }

            LabeledContent {
                Text(appVersion)
                    .foregroundStyle(.secondary)
                    .monospacedDigit()
            } label: {
                Label("Version", systemImage: "info.circle")
            }

            LabeledContent {
                Text(buildNumber)
                    .foregroundStyle(.secondary)
                    .monospacedDigit()
            } label: {
                Label("Build", systemImage: "hammer")
            }
        } header: {
            sectionHeader("Om appen", icon: "info.circle")
        }
    }

    // MARK: Logout

    private var logoutSection: some View {
        Section {
            Button(role: .destructive) {
                vm.showLogoutConfirmation = true
            } label: {
                HStack {
                    Spacer()
                    Label("Logga ut", systemImage: "rectangle.portrait.and.arrow.right")
                        .fontWeight(.semibold)
                    Spacer()
                }
            }
        }
    }

    // MARK: Toolbar

    @ToolbarContentBuilder
    private var toolbarContent: some ToolbarContent {
        ToolbarItem(placement: .topBarTrailing) {
            Button {
                Task { await vm.save() }
            } label: {
                if vm.isSaving {
                    ProgressView()
                        .controlSize(.small)
                } else {
                    Text("Spara")
                        .fontWeight(.semibold)
                        .foregroundStyle(vm.hasChanges ? Color(.systemBlue) : .secondary)
                }
            }
            .disabled(!vm.hasChanges || vm.isSaving)
        }

        ToolbarItem(placement: .topBarLeading) {
            if vm.hasChanges {
                Button("Ångra") { vm.discardChanges() }
                    .foregroundStyle(Color(.systemOrange))
            }
        }
    }

    // MARK: Helpers

    private func sectionHeader(_ title: String, icon: String) -> some View {
        Label(title, systemImage: icon)
            .font(.footnote)
            .fontWeight(.semibold)
            .textCase(nil)
            .foregroundStyle(.secondary)
    }

    private var savingOverlay: some View {
        ZStack {
            Color(.systemBackground)
                .opacity(0.6)
                .ignoresSafeArea()
            VStack(spacing: 8) {
                ProgressView()
                    .controlSize(.large)
                Text("Sparar…")
                    .font(.subheadline)
                    .foregroundStyle(.secondary)
            }
            .padding(24)
            .background(
                RoundedRectangle(cornerRadius: 12, style: .continuous)
                    .fill(Color(.secondarySystemBackground))
                    .shadow(color: .black.opacity(0.12), radius: 16, y: 4)
            )
        }
    }
}

// MARK: - Preview

#Preview {
    SettingsView()
}