Calendrical Calculations

NextDay.swift

import Foundation

extension Calendar {
    func startOfNextDay(for date: Date) -> Date? {
        let start = startOfDay(for: date)
        return self.date(byAdding: .day, value: 1, to: start)
    }


    func endOfDay(for date: Date) -> Date? {
        let start = startOfDay(for: date)
        let components = DateComponents(day: 1, nanosecond: -1000000)
        return self.date(byAdding: components, to: start)
    }
}


func randomDate() -> Date {
    let fiveYearsInSeconds = 5 * 365 * 24 * 3600
    let timeInterval = Double(arc4random_uniform(UInt32(fiveYearsInSeconds))) * (arc4random_uniform(2) == 0 ? 1 : -1)
    return Date(timeInterval: timeInterval, since: Date())
}


func timeBlock(_ block: () -> Void) -> TimeInterval {
    let start = Date()
    block()
    return Date().timeIntervalSince(start)
}



let calendar = Calendar(identifier: .gregorian)

var startOfDayTime: TimeInterval = 0
var startOfNextDayTime: TimeInterval = 0
var endOfDayTime: TimeInterval = 0

let iterationCount = 10000
for _ in 0 ..< iterationCount {
    let date = randomDate()

    startOfDayTime += timeBlock {
        _ = calendar.startOfDay(for: date)
    }

    startOfNextDayTime += timeBlock {
        _ = calendar.startOfNextDay(for: date)
    }

    endOfDayTime += timeBlock {
        _ = calendar.endOfDay(for: date)
    }
}

print("Iteration count = \(iterationCount)")
print("Time interval for startOfDay(for:) = \(startOfDayTime)")
print("Time interval for startOfNextDay(for:) = \(startOfNextDayTime)")
print("Time interval for endOfDay(for:) = \(endOfDayTime)")

Output:

Iteration count = 10000
Time interval for startOfDay(for:) = 2.34334194660187
Time interval for startOfNextDay(for:) = 6.10344672203064
Time interval for endOfDay(for:) = 8.15246593952179