Convenience initializers and helpers for Foundation Dates

DateHelpers.swift

import Foundation

extension Calendar {
    static let gregorian = Calendar(identifier: .gregorian)
}

extension TimeZone {
    static let utc = TimeZone(secondsFromGMT: 0)
}

extension Date {
    /// Enumeration of the days of the week in the Gregorian calendar.
    enum DayOfWeek: Int {
        case sunday = 1, monday, tuesday, wednesday, thursday, friday, saturday
    }

    /// Creates a date in the Gregorian calendar and UTC timezone.
    init?(year: Int, month: Int, day: Int, hour: Int = 0, minute: Int = 0, second: Int = 0) {
        let components = DateComponents(
            calendar: .gregorian, timeZone: .utc,
            year: year, month: month, day: day, hour: hour, minute: minute, second: second
        )
        guard components.isValidDate, let date = components.date else { return nil }
        self = date
    }

    /// Convenience shorthand initializer for a date in the Gregorian calendar and UTC timezone.
    init?(_ year: Int, _ month: Int, _ day: Int) {
        self.init(year: year, month: month, day: day)
    }

    /// The date's day of the week in the Gregorian calendar and UTC timezone.
    var dayOfWeek: DayOfWeek? {
        DayOfWeek(rawValue: Calendar.gregorian.component(.weekday, from: self))
    }

    /// Returns a new date by adding a component in the Gregorian calendar and UTC timezone.
    func adding(_ value: Int, _ component: Calendar.Component = .day) -> Date? {
        Calendar.gregorian.date(byAdding: component, value: value, to: self)
    }
}