import Foundation
import CalendarrCore

enum WatchComplicationSupport {
    /// The first event that has not ended yet — including one running now,
    /// which is what "what is next" means when you are already in a meeting.
    /// Matches `WatchPushPolicy.nextEventIdentity`, deliberately.
    static func nextEvent(in snapshot: CalendarrSnapshot?, at now: Date) -> SnapshotEvent? {
        snapshot?.events.filter { $0.end > now }.min { $0.start < $1.start }
    }

    static func upcoming(in snapshot: CalendarrSnapshot?, at now: Date, limit: Int) -> [SnapshotEvent] {
        guard let snapshot else { return [] }
        return Array(snapshot.events.filter { $0.end > now }.sorted { $0.start < $1.start }.prefix(limit))
    }

    static func todayCount(in snapshot: CalendarrSnapshot?, at now: Date,
                           calendar: Calendar = Calendar(identifier: .gregorian)) -> Int {
        guard let snapshot else { return 0 }
        let dayStart = calendar.startOfDay(for: now)
        guard let dayEnd = calendar.date(byAdding: .day, value: 1, to: dayStart) else { return 0 }
        return snapshot.events.filter { $0.start < dayEnd && $0.end > dayStart }.count
    }

    /// What a countdown counts to: the start if it has not begun, otherwise the
    /// end. Counting up from a start time that has passed reads as broken.
    static func countdownTarget(_ event: SnapshotEvent, at now: Date) -> Date {
        event.start > now ? event.start : event.end
    }

    /// How full a draining ring should be, over a two-hour lead window.
    static func gaugeFraction(to target: Date, at now: Date) -> Double {
        let window: TimeInterval = 2 * 3600
        return min(1, max(0, target.timeIntervalSince(now) / window))
    }

    static func time(_ date: Date, language: String) -> String {
        let formatter = DateFormatter()
        formatter.locale = WatchL10n.locale(language)
        formatter.dateFormat = "HH:mm"
        return formatter.string(from: date)
    }

    static func monthAbbreviation(_ date: Date, language: String) -> String {
        let formatter = DateFormatter()
        formatter.locale = WatchL10n.locale(language)
        formatter.dateFormat = "LLL"
        return formatter.string(from: date).uppercased()
    }

    /// The curved bezel label for a corner complication: time plus title, or a
    /// plain "no events".
    static func cornerLabel(_ event: SnapshotEvent?, at now: Date, language: String) -> String {
        guard let event else { return WatchL10n.t("watch.no_events", language) }
        if event.isAllDay { return event.title }
        return "\(time(event.start, language: language)) \(event.title)"
    }
}