5 minute interval clock

clock.swift

// Copyright (c) 2016 Justin Driscoll <justin@driscolldev.com>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

import Foundation


/// Wraps a function to be executed on every clock 'tick'
public class Ticker {

    let id: Int
    let label: String
    let f: (tick: Int) -> Void

    init(id: Int, label: String, f: (tick: Int) -> Void) {
        self.id = id
        self.label = label
        self.f = f
    }

    func stop() {
        Clock.sharedInstance.removeTicker(self)
    }
}

/// Singleton object that vends Tickers
public class Clock: NSObject {

    // MARK: Public API

    public static func ticker(label label: String?, _ f:(tick: Int) -> Void) -> Ticker {
        return self.sharedInstance.addTicker((label == nil ? self.UNLABELED : label!), f: f)
    }

    public static func stop(label label: String) {
        self.sharedInstance.removeLabel(label)
    }

    public static func stop(ticker ticker: Ticker) {
        self.sharedInstance.removeTicker(ticker)
    }

    public static func pause() {
        self.sharedInstance.pauseTimer()
    }

    public static func resume() {
        self.sharedInstance.startTimer()
    }

    // MARK: Internal

    private static let UNLABELED = "UNLABLED"

    private static let sharedInstance = Clock()

    private override init() { }

    /// The default group label applied to Tickers

    private var ticks = 0

    private var nextId = 0

    private var tickers: [String: [Int: Ticker]] = [:]

    private var timer: NSTimer?

    private func addTicker(label: String, f: (ticks: Int) -> Void) -> Ticker {
        nextId += 1

        let ticker = Ticker(id: nextId, label: label, f: f)

        if tickers[label] == nil {
            tickers[label] = [nextId: ticker]
        }
        else {
            tickers[label]![nextId] = ticker
        }

        startTimer()

        return ticker
    }

    private func removeTicker(ticker: Ticker) {
        tickers[ticker.label]?.removeValueForKey(ticker.id)
        if let label = tickers[ticker.label] where label.isEmpty {
            removeLabel(ticker.label)
        }
    }

    private func removeLabel(label: String) {
        tickers.removeValueForKey(label)
        if tickers.isEmpty {
            pauseTimer()
        }
    }

    private func pauseTimer() {
        if let t = timer {
            t.invalidate()
            timer = nil
        }

        assert(timer == nil, "Ticker timer should be nil after being paused.")
    }

    private func startTimer() {
        if tickers.isEmpty { return }

        if timer == nil {
            let roundedTimestamp = NSDate().roundedBackTo5MinuteInterval()
            let nextFireDate = roundedTimestamp.dateByAddingTimeInterval(1 * 60)
            let t = NSTimer(fireDate: nextFireDate, interval: 1 * 60, target: self, selector: #selector(tick), userInfo: nil, repeats: true)
            NSRunLoop.currentRunLoop().addTimer(t, forMode: NSRunLoopCommonModes)
            timer = t
        }
        
        assert(timer != nil, "Ticker timer should not be nil after being started.")
    }

    func tick() {
        tickers.values.flatMap { $0 }.forEach { $1.f(tick: self.ticks) }
        self.ticks += 1
    }
    
    deinit {
        timer?.invalidate()
    }
    
}

private extension NSDate {

    func roundedBackTo5MinuteInterval() -> NSDate {
        let calendar = NSCalendar.currentCalendar()
        var components = calendar.components([.Year, .Month, .Day, .Hour, .Minute, .Second], fromDate: self)
        components.minute -= components.minute % 5
        components.second = 0
        return calendar.dateFromComponents(components)!
    }
}