import Queue
import threading
import time

tasks_queue = Queue.Queue()
tasks_queue_items = []
tasks_lock = threading.Lock()

class Task():

    ST_PENDING = 0
    ST_INPROGRESS = 1
    ST_COMPLETE = 3
    ST_ERROR = 2

    def __init__(self, fn, args=[], kwargs={}, desc=''):
        self.id = id(self)
        self.fn = fn
        self.args = args
        self.kwargs = kwargs
        self.desc = desc
        self.status = self.ST_PENDING
        self.scheduled_at = 0
        self.error = None

    def run(self):
        self.status = self.ST_INPROGRESS
        try:
            res = self.fn(*self.args, **self.kwargs)
            self.status = self.ST_COMPLETE
        except BaseException as e:
            res = False
            self.status = self.ST_ERROR
            self.error = e
        return res


def schedule(task):
    with tasks_lock:
        task.scheduled_at = time.time()
        tasks_queue_items[0:0] = [task]
        tasks_queue.put(task)


def tasks_worker():
    while True:
        try:
            task = tasks_queue.get(timeout=5)
            if not task:
                break
            task.run()
            tasks_queue.task_done()
        except Queue.Empty:
            pass
        finally:
            with tasks_lock:
                tasks_queue_items.sort(key=lambda x: -x.scheduled_at)
        time.sleep(0.5)


worker = threading.Thread(target=tasks_worker)

def start():
    worker.start()

def stop():
    tasks_queue.put(False)
    worker.join()