NSDate+timeAgo.swift

//
//  NSDate+timeAgo.swift
//
//
//  Created by Nicholas Tian on 19/08/2015.
//  Copyright (c) 2015 nickTD. All rights reserved.
//

import Foundation

// Note: Inspired by NSDate-TimeAgo
// https://github.com/kevinlawler/NSDate-TimeAgo/blob/master/NSDate%2BExtension.swift

// TODO:
//  1. Create a Xcode project
//  2. Test with Quick and Nimble
//  3. Carthage compatible
//  4. i18n maybe?

private struct Seconds {
    static let Minute = 60 as Double
    static let Hour = 60 * Seconds.Minute
    static let Day = 24 * Seconds.Hour
    static let Week = 7 * Seconds.Day
    static let Month = 31 * Seconds.Day
    static let Year = 365 * Seconds.Day

    static func toSeconds(seconds: Double) -> Int {
        return flooredAsInt(seconds)
    }

    static func toMinutes(seconds: Double) -> Int {
        return flooredAsInt(seconds/Seconds.Minute)
    }

    static func toHours(seconds: Double) -> Int {
        return flooredAsInt(seconds/Seconds.Hour)
    }

    static func toDays(seconds: Double) -> Int {
        return flooredAsInt(seconds/Seconds.Day)
    }

    static func toWeeks(seconds: Double) -> Int {
        return flooredAsInt(seconds/Seconds.Week)
    }

    static func toMonths(seconds: Double) -> Int {
        return flooredAsInt(seconds/Seconds.Month)
    }

    static func toYears(seconds: Double) -> Int {
        return flooredAsInt(seconds/Seconds.Year)
    }

    private static func flooredAsInt(value: Double) -> Int {
        return Int(floor(value))
    }
}

extension NSDate {
    var timeAgo: String {
        let now = NSDate()
        let deltaSeconds = fabs(timeIntervalSinceNow) as Double

        switch deltaSeconds {
        case 0..<Seconds.Minute: // within a minute, seconds
            let seconds = Seconds.toSeconds(deltaSeconds)
            return "\(seconds)secs"
        case Seconds.Minute..<Seconds.Hour: // within an hour, minutes
            let minutes = Seconds.toMinutes(deltaSeconds)
            return "\(minutes)mins"
        case Seconds.Hour..<Seconds.Day: // within a day, hours
            let hours = Seconds.toHours(deltaSeconds)
            return "\(hours)hours"
        case Seconds.Day..<Seconds.Week: // within a week, days
            let days = Seconds.toDays(deltaSeconds)
            return "\(days)days"
        case Seconds.Week..<Seconds.Month: // within a month, weeks
            let weeks = Seconds.toWeeks(deltaSeconds)
            return "\(weeks)weeks"
        case Seconds.Month..<Seconds.Year: // within a year, months
            let months = Seconds.toMonths(deltaSeconds)
            return "\(months)months"
        case Seconds.Year...Double.infinity: // years
            let years = Seconds.toYears(deltaSeconds)
            return "\(years)years"
        default:
            return "oops"
        }
    }
}