import WidgetKit
import SwiftUI
import AppIntents

// MARK: - Configuration Intent
//
// Each widget instance stores its own event. The user sets a name, the day the
// countdown starts ("Counting from" — defaults to the day they add the widget,
// which acts as the creation anchor) and the event date. Because these values are
// persisted per-instance by WidgetKit, the widget is fully self-contained and does
// not depend on App Group data sharing.

struct EventConfigIntent: WidgetConfigurationIntent {
    static var title: LocalizedStringResource = "Event Countdown"
    static var description = IntentDescription("Count down to any upcoming event with a dot grid.")

    // Pick one of your existing events (tasks with a due date). When set, it
    // overrides the manual name/date fields below.
    @Parameter(title: "Track event")
    var event: EventEntity?

    @Parameter(title: "Or event name", default: "My Event")
    var eventName: String

    @Parameter(title: "Event date", default: Date.now)
    var targetDate: Date

    @Parameter(title: "Counting from", default: Date.now)
    var startDate: Date
}

// MARK: - Event picker (reads your tasks from the App Group)

struct EventEntity: AppEntity {
    let id: String          // task UUID string
    let title: String
    let dueDate: Date?

    static var typeDisplayRepresentation: TypeDisplayRepresentation = "Event"
    static var defaultQuery = EventQuery()

    var displayRepresentation: DisplayRepresentation {
        if let d = dueDate {
            let f = DateFormatter(); f.dateStyle = .medium
            return DisplayRepresentation(title: "\(title)", subtitle: "\(f.string(from: d))")
        }
        return DisplayRepresentation(title: "\(title)")
    }
}

struct EventQuery: EntityQuery {
    func entities(for identifiers: [String]) async throws -> [EventEntity] {
        allEvents().filter { identifiers.contains($0.id) }
    }

    func suggestedEntities() async throws -> [EventEntity] {
        allEvents()
    }

    private func allEvents() -> [EventEntity] {
        loadWidgetTasks()
            .filter { !$0.isComplete && $0.dueDate != nil }
            .sorted { ($0.dueDate ?? .distantFuture) < ($1.dueDate ?? .distantFuture) }
            .map { EventEntity(id: $0.id.uuidString, title: $0.title, dueDate: $0.dueDate) }
    }
}

// MARK: - Entry

// Tapping the countdown label cycles this unit (shared by all event widgets).
let countdownUnitKey = "kisani.widget.countdownUnit"   // 0 = days, 1 = weeks, 2 = time

struct CycleCountdownUnitIntent: AppIntent {
    static var title: LocalizedStringResource = "Change Countdown Unit"

    func perform() async throws -> some IntentResult {
        let cur = UserDefaults.kisani.integer(forKey: countdownUnitKey)
        UserDefaults.kisani.set((cur + 1) % 3, forKey: countdownUnitKey)
        return .result()
    }
}

struct EventEntry: TimelineEntry {
    let date: Date
    let eventName: String
    let start: Date
    let target: Date
    var unitMode: Int = 0   // 0 days, 1 weeks, 2 time

    /// Fraction of the countdown window that has elapsed (0…1).
    var progress: Double {
        let span = target.timeIntervalSince(start)
        guard span > 0 else { return target <= date ? 1 : 0 }
        return min(1, max(0, date.timeIntervalSince(start) / span))
    }

    /// Whole days from start to target (the number of dots in the grid).
    var totalDays: Int {
        let cal = Calendar.current
        let d = cal.dateComponents([.day],
                                   from: cal.startOfDay(for: start),
                                   to: cal.startOfDay(for: target)).day ?? 0
        return max(1, d)
    }

    /// Days remaining until the event (never negative).
    var daysLeft: Int {
        let cal = Calendar.current
        let d = cal.dateComponents([.day],
                                   from: cal.startOfDay(for: date),
                                   to: cal.startOfDay(for: target)).day ?? 0
        return max(0, d)
    }

    /// Countdown from the current date. Tapping the label cycles the unit:
    /// days → weeks → time remaining.
    var timeLeftLabel: String {
        if target <= date { return "Today" }
        let cal = Calendar.current
        switch unitMode {
        case 1: // weeks
            let days = cal.dateComponents([.day], from: cal.startOfDay(for: date),
                                          to: cal.startOfDay(for: target)).day ?? 0
            if days < 7 { return "< 1 week left" }
            let weeks = days / 7
            return "\(weeks) week\(weeks == 1 ? "" : "s") left"
        case 2: // time remaining (detailed)
            let c = cal.dateComponents([.day, .hour], from: date, to: target)
            let days = c.day ?? 0, hours = c.hour ?? 0
            if days == 0 { return hours <= 0 ? "Due now" : "\(hours) hr left" }
            return hours > 0 ? "\(days)d, \(hours) hr left" : "\(days) day\(days == 1 ? "" : "s") left"
        default: // days
            let days = cal.dateComponents([.day], from: cal.startOfDay(for: date),
                                          to: cal.startOfDay(for: target)).day ?? 0
            return "\(days) day\(days == 1 ? "" : "s") left"
        }
    }
}

// MARK: - Provider

struct EventProvider: AppIntentTimelineProvider {
    func placeholder(in context: Context) -> EventEntry {
        EventEntry(date: .now,
                   eventName: "Mum's Birthday",
                   start: Date().addingTimeInterval(-86400 * 320),
                   target: Date().addingTimeInterval(86400 * 60))
    }

    func snapshot(for configuration: EventConfigIntent, in context: Context) async -> EventEntry {
        entry(for: configuration)
    }

    func timeline(for configuration: EventConfigIntent, in context: Context) async -> Timeline<EventEntry> {
        let entry = entry(for: configuration)
        // Recompute at the next midnight so the grid advances one dot per day.
        let nextMidnight = Calendar.current.startOfDay(for: Date().addingTimeInterval(86400))
        return Timeline(entries: [entry], policy: .after(nextMidnight))
    }

    private func entry(for config: EventConfigIntent) -> EventEntry {
        let name: String
        let target: Date
        if let ev = config.event, let due = ev.dueDate {
            // A picked event supplies its own name + date.
            name = ev.title
            target = due
        } else {
            name = config.eventName.isEmpty ? "My Event" : config.eventName
            target = config.targetDate
        }
        // Never let the start sit after the target.
        let start = min(config.startDate, target)
        let mode = UserDefaults.kisani.integer(forKey: countdownUnitKey)
        return EventEntry(date: .now, eventName: name, start: start, target: target, unitMode: mode)
    }
}

// MARK: - Widget

struct EventCountdownWidget: Widget {
    let kind = "KisaniEventCountdown"

    var body: some WidgetConfiguration {
        AppIntentConfiguration(kind: kind, intent: EventConfigIntent.self, provider: EventProvider()) { entry in
            EventCountdownView(entry: entry)
        }
        .configurationDisplayName("Event Countdown")
        .description("Track the days until any upcoming event with a dot grid.")
        .supportedFamilies([.systemMedium, .systemSmall])
    }
}