import SwiftUI

/// Three sections and search: the calendar lives inside the plans, the subjects inside the overview.
enum AppTab: Hashable {
    case home, schedule, plans, search
}

/// Where the screens send the student: another tab, a day of the schedule, the groups or settings.
@MainActor
@Observable
final class Router {
    var tab: AppTab = .home
    var groups = false
    var settings = false
    /** A day or week the schedule should show next (from the overview, calendar, widgets). */
    var focus: CivilDate?
    /** The schedule as a week grid instead of days; iPad starts with the grid. */
    var weekView: Bool?
    /** The plans as a month calendar instead of a list. */
    var plansCalendar = false
    /** What the search tab looks for: its field lives in the tab bar. */
    var searchQuery = ""

    func openDay(_ date: CivilDate) {
        focus = date
        weekView = false
        tab = .schedule
    }

    func openWeek(_ date: CivilDate) {
        focus = date
        weekView = true
        tab = .schedule
    }
}

struct RootView: View {
    @Environment(AppModel.self) private var model
    // Decided once: picking the group mid-onboarding must not cut the remaining steps short.
    @State private var onboarding = Storage.loadSettings().current == nil
    @State private var router = Router()

    var body: some View {
        ZStack {
            if onboarding {
                OnboardingView { withAnimation(.smooth(duration: 0.5)) { onboarding = false } }
                    .transition(.opacity.combined(with: .scale(scale: 1.04)))
            } else {
                MainTabs()
                    .transition(.opacity)
            }
        }
        .environment(router)
        .onOpenURL { url in
            // A widget tapped: psuschedule://day/2026-10-19 opens that day.
            if url.host() == "day", let date = CivilDate(url.lastPathComponent) { router.openDay(date) }
            else if url.host() == "day" { router.openDay(model.today) }
        }
        .environment(\.palette, Palette(slots: model.timetable?.subjectSlots ?? [:], enabled: model.settings.display.colors))
        .environment(\.display, model.settings.display)
    }
}

/// The sections in the Liquid Glass tab bar; on iPad they become a sidebar.
struct MainTabs: View {
    @Environment(AppModel.self) private var model
    @Environment(Router.self) private var router

    var body: some View {
        @Bindable var router = router
        TabView(selection: $router.tab) {
            Tab("Обзор", systemImage: "house", value: AppTab.home) { HomeView() }
            Tab("Расписание", systemImage: "calendar.day.timeline.left", value: AppTab.schedule) { ScheduleView() }
            Tab("Планы", systemImage: "checklist", value: AppTab.plans) { PlansTab() }
            Tab("Поиск", systemImage: "magnifyingglass", value: AppTab.search, role: .search) {
                SearchView().searchable(text: $router.searchQuery, prompt: "Фамилия или номер аудитории")
            }
        }
        // Search stands apart from the three sections as its own glass button; tapping it turns
        // the button into the field above the keyboard, as in Apple's own apps. The field belongs
        // to the search tab only, so the other sections keep their bars clean.
        .tabViewSearchActivation(.searchTabSelection)
        .tabViewStyle(.sidebarAdaptable)
        .tabBarMinimizeBehavior(.onScrollDown)
        .sheet(isPresented: $router.groups) {
            NavigationStack { GroupsView(onboarding: false) { router.groups = false } }
        }
        .sheet(isPresented: $router.settings) { SettingsView() }
    }
}

/// The open group as a glass capsule in the toolbar: one tap from switching.
struct GroupButton: View {
    @Environment(AppModel.self) private var model
    @Environment(Router.self) private var router
    var body: some View {
        let group = model.timetable?.group ?? model.settings.current?.group
        Button { router.groups = true } label: {
            Label(group ?? "Группа", systemImage: "person.2.fill").labelStyle(.titleAndIcon)
        }
        .accessibilityLabel(group.map { "Группа \($0), сменить" } ?? "Выбрать группу")
    }
}

/// The plans tab: the list of plans or the month calendar, switched from the toolbar.
struct PlansTab: View {
    @Environment(Router.self) private var router
    var body: some View {
        ZStack {
            if router.plansCalendar { CalendarView().transition(.opacity) } else { PlansView().transition(.opacity) }
        }
        .animation(.smooth(duration: 0.3), value: router.plansCalendar)
    }
}

/// Switches the plans between the list and the calendar, as the schedule switches day and week.
struct PlansModeButton: View {
    @Environment(Router.self) private var router
    var body: some View {
        Button(router.plansCalendar ? "Показать список" : "Показать календарь", systemImage: router.plansCalendar ? "list.bullet" : "calendar") {
            router.plansCalendar.toggle()
        }
        .contentTransition(.symbolEffect(.replace))
    }
}

struct SettingsButton: View {
    @Environment(Router.self) private var router
    var body: some View {
        Button("Настройки", systemImage: "gearshape") { router.settings = true }
    }
}