Calendar와 DateComponents

import Foundation

let cal = Calendar.current
print("Calendar identifier: \(cal.identifier)")

import Foundation

let cal = Calendar.current
let comps = cal.dateComponents([.year, .month, .day], from: Date())
print("Year is set: \(comps.year != nil)")

import Foundation

let cal = Calendar.current
let weekday = cal.component(.weekday, from: Date())
print("Weekday number between 1 and 7: \(1...7 ~= weekday)")

import Foundation

var comps = DateComponents()
comps.year = 2024
comps.month = 12
comps.day = 25
let cal = Calendar.current
if let date = cal.date(from: comps) {
    print("Built a date: \(date.timeIntervalSince1970 > 0)")
}

import Foundation

let cal = Calendar.current
let now = Date()
if let nextWeek = cal.date(byAdding: .day, value: 7, to: now) {
    print(nextWeek > now)
}

import Foundation

let cal = Calendar.current
var offset = DateComponents()
offset.month = 1
offset.day = 3
if let future = cal.date(byAdding: offset, to: Date()) {
    print(future > Date())
}

import Foundation

let cal = Calendar.current
let now = Date()
let later = now.addingTimeInterval(3 * 86400)
let diff = cal.dateComponents([.day], from: now, to: later)
print("Days apart: \(diff.day ?? -1)")

import Foundation

let cal = Calendar.current
let midnight = cal.startOfDay(for: Date())
print(midnight <= Date())

import Foundation

let cal = Calendar.current
let now = Date()
let soon = now.addingTimeInterval(60)
print(cal.isDate(now, inSameDayAs: soon))

import Foundation

let cal = Calendar.current
// Correct: add 1 month, not 30 * 86400 seconds.
if let d = cal.date(byAdding: .month, value: 1, to: Date()) {
    print("Added a month correctly: \(d > Date())")
}