import Foundation

public final class ThreadPoolTaskState {
    public var cancelled = false
}

public final class ThreadPoolTask {
    private let state = ThreadPoolTaskState()
    private let action: ThreadPoolTaskState -> ()
    
    public init(_ action: ThreadPoolTaskState -> ()) {
        self.action = action
    }
    
    internal func execute() {
        if !state.cancelled {
            self.action(self.state)
        }
    }
    
    public func cancel() {
        self.state.cancelled = true
    }
}

public final class ThreadPoolQueue : Equatable {
    private weak var threadPool: ThreadPool?
    private var tasks: [ThreadPoolTask] = []
    
    public init(threadPool: ThreadPool) {
        self.threadPool = threadPool
    }
    
    public func addTask(task: ThreadPoolTask) {
        if let threadPool = self.threadPool {
            threadPool.workOnQueue(self, action: {
                self.tasks.append(task)
            })
        }
    }
    
    private func popFirstTask() -> ThreadPoolTask? {
        if self.tasks.count != 0 {
            let task = self.tasks[0];
            self.tasks.removeAtIndex(0)
            return task
        } else {
            return nil
        }
    }
    
    private func hasTasks() -> Bool {
        return self.tasks.count != 0
    }
}

public func ==(lhs: ThreadPoolQueue, rhs: ThreadPoolQueue) -> Bool {
    return lhs === rhs
}

@objc public final class ThreadPool {
    private var threads: [NSThread] = []
    private var queues: [ThreadPoolQueue] = []
    private var takenQueues: [ThreadPoolQueue] = []
    private var mutex: pthread_mutex_t
    private var condition: pthread_cond_t
    
    private class func threadEntryPoint(threadPool: ThreadPool) {
        var queue: ThreadPoolQueue!
        
        while (true) {
            var task: ThreadPoolTask!
            
            pthread_mutex_lock(&threadPool.mutex);
            
            if queue != nil {
                if let index = find(threadPool.takenQueues, queue) {
                    threadPool.takenQueues.removeAtIndex(index)
                }
                
                if queue.hasTasks() {
                    threadPool.queues.append(queue);
                }
            }
            
            while (true)
            {
                while threadPool.queues.count == 0 {
                    pthread_cond_wait(&threadPool.condition, &threadPool.mutex);
                }
                
                if threadPool.queues.count != 0 {
                    queue = threadPool.queues[0]
                }
                
                if queue != nil {
                    task = queue.popFirstTask()
                    threadPool.takenQueues.append(queue)
                    
                    if let index = find(threadPool.queues, queue) {
                        threadPool.queues.removeAtIndex(index)
                    }
                    
                    break
                }
            }
            pthread_mutex_unlock(&threadPool.mutex);
            
            if task != nil {
                task.execute()
            }
        }
    }
    
    public init(threadCount: Int, threadPriority: Double) {
        assert(threadCount > 0, "threadCount < 0")
        
        self.mutex = pthread_mutex_t()
        self.condition = pthread_cond_t()
        pthread_mutex_init(&self.mutex, nil)
        pthread_cond_init(&self.condition, nil)
        
        for i in 0 ..< threadCount {
            var thread = NSThread(target: ThreadPool.self, selector: Selector("threadEntryPoint"), object: self)
            thread.threadPriority = threadPriority
            self.threads.append(thread)
            thread.start()
        }
    }
    
    deinit {
        pthread_mutex_destroy(&self.mutex)
        pthread_cond_destroy(&self.condition)
    }
    
    public func addTask(task: ThreadPoolTask) {
        let tempQueue = self.nextQueue()
        tempQueue.addTask(task)
    }
    
    private func workOnQueue(queue: ThreadPoolQueue, action: () -> ()) {
        pthread_mutex_lock(&self.mutex)
        action()
        if !contains(self.queues, queue) && !contains(self.takenQueues, queue) {
            self.queues.append(queue)
        }
        pthread_cond_broadcast(&self.condition)
        pthread_mutex_unlock(&self.mutex)
    }
    
    public func nextQueue() -> ThreadPoolQueue {
        return ThreadPoolQueue(threadPool: self)
    }
}