// Copyright 2015-2016 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import UIKit

///
/// DispatchTimer
///
/// Much like an NSTimer from Cocoa, but implemented using dispatch queues instead.
///
class DispatchTimer: NSObject {
    
    /// Type for the handler block executed when a dispatch timer fires.
    ///
    /// :param: timer The timer which triggered this block
    typealias TimerHandler = (DispatchTimer) -> Void
    
    private let timerBlock: TimerHandler
    private let queue: DispatchQueue
    private let delay: TimeInterval
    
    private var wrappedBlock: (() -> Void)?
    private let source: DispatchSourceTimer
    
    init(delay: TimeInterval, queue: DispatchQueue, block: @escaping TimerHandler) {
        timerBlock = block
        self.queue = queue
        self.delay = delay
        self.source = DispatchSource.makeTimerSource(queue: queue)
        
        super.init()
        
        let wrapper = { () -> Void in
            if !self.source.isCancelled {
                self.source.cancel()
                self.timerBlock(self)
            }
        }
        
        self.wrappedBlock = wrapper
    }
    
    class func scheduledDispatchTimer(delay: TimeInterval, queue: DispatchQueue, block: @escaping TimerHandler) -> DispatchTimer {
        let dt = DispatchTimer(delay: delay, queue: queue, block: block)
        dt.schedule()
        
        return dt
    }
    
    func schedule() {
        self.reschedule()
        self.source.setEventHandler(handler: self.wrappedBlock)
        self.source.resume()
    }
    
    func reschedule() {
        self.source.schedule(deadline: .now() + self.delay)
    }
    
    func suspend() {
        self.source.suspend()
    }
    
    func resume() {
        self.source.resume()
    }
    
    func cancel() {
        self.source.cancel()
    }
    
}