import Foundation

final class CalendarBoundaryService {
    private let preferences: AppPreferences

    init(preferences: AppPreferences) {
        self.preferences = preferences
    }

    private var calendar: Calendar {
        var cal = Calendar.current
        cal.firstWeekday = preferences.weekStartDay
        return cal
    }

    func customDayStart(for date: Date) -> Date {
        // TODO: apply dayStartHour / dayStartMinute boundary shift in milestone 2
        var comps = calendar.dateComponents([.year, .month, .day], from: date)
        comps.hour   = preferences.dayStartHour
        comps.minute = preferences.dayStartMinute
        comps.second = 0
        return calendar.date(from: comps) ?? date
    }

    func dayRange(for date: Date) -> DateInterval {
        let start = customDayStart(for: date)
        let end   = calendar.date(byAdding: .day, value: 1, to: start) ?? start
        return DateInterval(start: start, end: end)
    }

    func weekRange(for date: Date) -> DateInterval {
        // TODO: align to custom day-start boundary in milestone 2
        guard let interval = calendar.dateInterval(of: .weekOfYear, for: date) else {
            return DateInterval(start: date, duration: 7 * 86_400)
        }
        return interval
    }

    func monthRange(for date: Date) -> DateInterval {
        // TODO: align to custom day-start boundary in milestone 2
        guard let interval = calendar.dateInterval(of: .month, for: date) else {
            return DateInterval(start: date, duration: 30 * 86_400)
        }
        return interval
    }
}