Date-progress.swift

import Foundation

extension Date{
    // Calculates the progress made from the start of the given range to the current date
    // Returns a percentage value between 0 and 100
    func getProgress(range: ClosedRange<Date>) -> Double {
        if (self >= range.upperBound ) {
           return 100
        } else if (self <= range.lowerBound) {
           return 0
        } 
        
        let totalTime = range.upperBound.timeIntervalSince(start)
        let elapsed = self.timeIntervalSince(start)
        // Calculate the progress made so far as a percentage of the total time
        return  (elapsed / totalTime) * 100
           
    }
}

let start = Date() - 100000
let now = Date()
let end = Date() + 2500000
print("Start: \(start)\nEnd: \(end)\nNow: \(now)")

let progress = now.getProgress(range: start...end)

print("progress: \(progress)%")