import SwiftUI
import WidgetKit

/// What a widget shows at one moment: the group and its lessons ahead.
struct LessonsEntry: TimelineEntry {
    var date: Date
    var group: String?
    var day: CivilDate?
    var slots: [Slot]
    var message: String?
}

/**
 * Reads the timetable the app saved in the shared container, so widgets work offline.
 * A new entry at every lesson's start and end keeps "Идёт" and "Далее" right without the app.
 */
struct LessonsProvider: TimelineProvider {
    func placeholder(in context: Context) -> LessonsEntry {
        LessonsEntry(date: Date(), group: "23-БА", day: CivilDate.today(), slots: [], message: nil)
    }

    func getSnapshot(in context: Context, completion: @escaping (LessonsEntry) -> Void) {
        completion(entry(at: Date()))
    }

    func getTimeline(in context: Context, completion: @escaping (Timeline<LessonsEntry>) -> Void) {
        let now = Date()
        var moments = [now]
        if let t = Storage.loadTimetable() {
            let settings = Storage.loadSettings()
            let today = CivilDate.today(now)
            for d in [today, today.adding(days: 1)] {
                for slot in t.slots(on: d, subgroup: settings.subgroup, hidden: settings.hidden) {
                    moments.append(d.at(slot.start))
                    moments.append(d.at(slot.end))
                }
            }
        }
        // The next midnight in Minsk turns "Завтра" into "Сегодня".
        moments.append(CivilDate.today(now).adding(days: 1).at(ClockTime(minutes: 0)))
        let entries = Set(moments.filter { $0 >= now }).sorted().prefix(40).map { entry(at: $0) }
        completion(Timeline(entries: entries, policy: .after(now.addingTimeInterval(6 * 3600))))
    }

    private func entry(at date: Date) -> LessonsEntry {
        let settings = Storage.loadSettings()
        guard let t = Storage.loadTimetable(), settings.current != nil else {
            return LessonsEntry(date: date, group: nil, day: nil, slots: [], message: "Откройте приложение и выберите группу")
        }
        guard let next = upcoming(t, settings: settings, now: date) else {
            return LessonsEntry(date: date, group: t.group, day: nil, slots: [], message: "Занятий на неделе нет")
        }
        return LessonsEntry(date: date, group: t.group, day: next.date, slots: next.slots, message: nil)
    }
}

private func dayLabel(_ day: CivilDate, at date: Date) -> String {
    let today = CivilDate.today(date)
    if day == today { return "Сегодня, \(day.longLabel)" }
    if day == today.adding(days: 1) { return "Завтра, \(day.weekdayName.lowercased())" }
    return "\(day.weekdayName), \(day.longLabel)"
}

private func status(_ slot: Slot, day: CivilDate, at date: Date) -> String? {
    guard day == CivilDate.today(date) else { return nil }
    let clock = ClockTime.now(date)
    if clock >= slot.start && clock < slot.end { return "Идёт · ещё \(minutesLabel(slot.end.minutes - clock.minutes))" }
    return nil
}

private func place(_ lesson: Lesson) -> String? {
    if lesson.distance { return "дист." }
    return withPlace(lesson.rooms.isEmpty ? nil : "ауд. " + lesson.rooms.joined(separator: ", "), lesson.place)
}

/// "Сегодня": the day's lessons ahead, with the current one marked.
struct TodayWidgetView: View {
    @Environment(\.widgetFamily) private var family
    var entry: LessonsEntry

    var body: some View {
        VStack(alignment: .leading, spacing: 6) {
            HStack {
                Text(entry.day.map { dayLabel($0, at: entry.date) } ?? "Расписание").font(.caption.weight(.semibold)).foregroundStyle(.tint)
                Spacer()
                if let group = entry.group { Text(group).font(.caption).foregroundStyle(.secondary) }
            }
            if let message = entry.message {
                Spacer()
                Text(message).font(.subheadline).foregroundStyle(.secondary)
                Spacer()
            } else {
                let limit = family == .systemLarge ? 7 : family == .systemMedium ? 3 : 2
                ForEach(entry.slots.prefix(limit)) { slot in
                    let lesson = slot.lessons[0]
                    HStack(alignment: .top, spacing: 8) {
                        Capsule().fill(.tint).frame(width: 3)
                        VStack(alignment: .leading, spacing: 1) {
                            Text(slot.lessons.map(\.subject).joined(separator: " / "))
                                .font(.subheadline.weight(.semibold))
                                .lineLimit(family == .systemSmall ? 2 : 1)
                            Text(([status(slot, day: entry.day!, at: entry.date) ?? slot.timeLabel] + [place(lesson)].compactMap { $0 }).joined(separator: " · "))
                                .font(.caption.monospacedDigit())
                                .foregroundStyle(.secondary)
                                .lineLimit(1)
                        }
                    }
                }
                if entry.slots.count > limit {
                    Text("Ещё \(pairs(entry.slots.count - limit))").font(.caption).foregroundStyle(.secondary)
                }
                Spacer(minLength: 0)
            }
        }
        .containerBackground(.fill.tertiary, for: .widget)
        .widgetURL(URL(string: "psuschedule://day/\(entry.day?.iso ?? "")"))
    }
}

/// "Следующая пара": one lesson, large, also on the Lock Screen.
struct NextLessonView: View {
    @Environment(\.widgetFamily) private var family
    var entry: LessonsEntry

    var body: some View {
        let slot = entry.slots.first
        let lesson = slot?.lessons.first
        Group {
            switch family {
            case .accessoryInline:
                if let slot, let lesson { Text("\(slot.start) \(lesson.subject)") } else { Text("Пар нет") }
            case .accessoryRectangular:
                VStack(alignment: .leading, spacing: 1) {
                    if let slot, let lesson, let day = entry.day {
                        Text(status(slot, day: day, at: entry.date) ?? (day == CivilDate.today(entry.date) ? slot.timeLabel : day.shortWeekday + " " + slot.timeLabel))
                            .font(.caption.weight(.semibold))
                        Text(lesson.subject).font(.headline).lineLimit(1)
                        if let p = place(lesson) { Text(p).font(.caption) }
                    } else {
                        Text(entry.message ?? "Пар нет").font(.caption)
                    }
                }
                .frame(maxWidth: .infinity, alignment: .leading)
            default:
                VStack(alignment: .leading, spacing: 4) {
                    if let slot, let lesson, let day = entry.day {
                        Text(status(slot, day: day, at: entry.date) ?? (day == CivilDate.today(entry.date) ? "Далее · " + slot.start.description : dayLabel(day, at: entry.date)))
                            .font(.caption.weight(.semibold))
                            .foregroundStyle(.tint)
                        Text(lesson.subject).font(.headline).lineLimit(3)
                        Spacer(minLength: 0)
                        Text(slot.timeLabel).font(.subheadline.monospacedDigit())
                        if let p = place(lesson) { Text(p).font(.caption).foregroundStyle(.secondary) }
                    } else {
                        Text(entry.message ?? "Пар нет").font(.subheadline).foregroundStyle(.secondary)
                    }
                }
                .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
            }
        }
        .containerBackground(.fill.tertiary, for: .widget)
    }
}

struct TodayWidget: Widget {
    var body: some WidgetConfiguration {
        StaticConfiguration(kind: "today", provider: LessonsProvider()) { TodayWidgetView(entry: $0) }
            .configurationDisplayName("Сегодня")
            .description("Пары на сегодня или ближайший учебный день.")
            .supportedFamilies([.systemSmall, .systemMedium, .systemLarge])
    }
}

struct NextLessonWidget: Widget {
    var body: some WidgetConfiguration {
        StaticConfiguration(kind: "next", provider: LessonsProvider()) { NextLessonView(entry: $0) }
            .configurationDisplayName("Следующая пара")
            .description("Текущая или следующая пара с аудиторией.")
            .supportedFamilies([.systemSmall, .accessoryRectangular, .accessoryInline])
    }
}

@main
struct ScheduleWidgets: WidgetBundle {
    var body: some Widget {
        TodayWidget()
        NextLessonWidget()
    }
}