Debouncer.swift

//
//    Repeat
//    A modern alternative to NSTimer made in GCD with debouncer and throttle
//    -----------------------------------------------------------------------
//    Created by:    Daniele Margutti
//                hello@danielemargutti.com
//                http://www.danielemargutti.com
//
//    Twitter:    @danielemargutti
//
//
//    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

/// The Debouncer will delay a function call, and every time it's getting called it will
/// delay the preceding call until the delay time is over.
open class Debouncer {
    
    /// Typealias for callback type
    public typealias Callback = (() -> Void)
    
    /// Delay interval
    public let delay: Repeater.Interval
    
    /// Callback to activate
    public var callback: Callback?
    
    /// Internal timer to fire callback event.
    private var timer: Repeater?
    
    private let queue: DispatchQueue?
    
    /// Initialize a new debouncer with given delay and callback.
    /// Debouncer class to delay functions that only get delay each other until the timer fires.
    ///
    /// - Parameters:
    ///   - delay: delay interval
    ///   - queue: queue to schedule the backing Repeater on
    ///   - callback: callback to activate
    public init(_ delay: Repeater.Interval, queue: DispatchQueue? = nil, callback: Callback? = nil) {
        self.delay = delay
        self.callback = callback
        self.queue = queue
    }
    
    /// Call debouncer to start the callback after the delayed time.
    /// Multiple calls will ignore the older calls and overwrite the firing time.
    public func call() {
        if self.timer == nil {
            self.timer = Repeater.once(after: self.delay, queue: queue, { _ in
                guard let callback = self.callback else {
                    debugPrint("Debouncer fired but callback not set.")
                    return
                }
                callback()
            })
        } else {
            self.timer?.reset(self.delay, restart: true)
        }
    }
}