import Foundation

extension Date {
    // Cached formatters — DateFormatter init is expensive and these are called
    // in list rows on every render pass.
    private static let shortDateTime: DateFormatter = {
        let f = DateFormatter(); f.dateStyle = .short; f.timeStyle = .short; return f
    }()
    private static let timeOnly: DateFormatter = {
        let f = DateFormatter(); f.dateStyle = .none; f.timeStyle = .short; return f
    }()
    private static let mediumDate: DateFormatter = {
        let f = DateFormatter(); f.dateStyle = .medium; f.timeStyle = .none; return f
    }()
    private static let monthAbbrev: DateFormatter = {
        let f = DateFormatter(); f.dateFormat = "MMM"; return f
    }()
    private static let weekdayAbbrev: DateFormatter = {
        let f = DateFormatter(); f.dateFormat = "EEE"; return f
    }()
    private static let relativeDateTime: DateFormatter = {
        let f = DateFormatter()
        f.dateStyle = .medium; f.timeStyle = .short
        f.doesRelativeDateFormatting = true
        return f
    }()

    func formattedDate() -> String { Self.shortDateTime.string(from: self) }
    /// "Today at 10:44 AM" / "Yesterday at 9:12 AM" / "Jul 3, 2026 at 8:00 AM".
    func formattedRelativeDateTime() -> String { Self.relativeDateTime.string(from: self) }
    func formattedTime() -> String { Self.timeOnly.string(from: self) }
    func formatDate() -> String { Self.mediumDate.string(from: self) }

    func isSameDay(as other: Date) -> Bool {
        Calendar.current.isDate(self, inSameDayAs: other)
    }

    var abbreviatedMonth: String { Self.monthAbbrev.string(from: self) }
    var abbreviatedWeekday: String { Self.weekdayAbbrev.string(from: self) }
    var dayOfMonth: Int { Calendar.current.component(.day, from: self) }

    /// "Today", "Yesterday", or "N days ago" by calendar-day difference.
    func daysAgoLabel(relativeTo now: Date = Date()) -> String {
        let calendar = Calendar.current
        let days = calendar.dateComponents(
            [.day],
            from: calendar.startOfDay(for: self),
            to: calendar.startOfDay(for: now)
        ).day ?? 0
        switch days {
        case ..<1: return "Today"
        case 1: return "Yesterday"
        default: return "\(days) days ago"
        }
    }

    func humanTimeInterval(to other: Date) -> String {
        let interval = other.timeIntervalSince(self)
        let hours = Int(interval) / 3600
        let minutes = (Int(interval) % 3600) / 60
        return hours > 0 ? "\(hours)h \(minutes)m" : "\(minutes)m"
    }
}
