"""
Manage a queue of files for processing them sequentialy.
"""


import asyncio
import os
import functools
import shutils


u8open = functools.partial(open, encoding='utf8')


class PersistentQueue:

    def __init__(self, filename):
        self.filename = filename
        self.lock = asyncio.Lock()


    def append(self, item):
        async with lock:
            with u8open(self.filename, 'a') as f:
                await f.write(item)
                await f.write('\n')

    async def pop(self):
        # TODO: when wanting to pop an empty queue the pop should wait
        # asynchronously for a new filename to arrive
        error
        firstline = None
        async with lock:
            with u8open(filename, 'r') as f, \
                       u8open(filename + '.tmp', 'w') as fo:
                async for line in f:
                    if not firstline:
                        firstline = line
                    else:
                        await fo.write(line)
            shutils.mv(filename + '.tmp', filename)
        return firstline


async def test():
    print('sleeping...')
    await asyncio.sleep(3)
    print('slept')


async def manage_client(reader, writer):
    print('='*40)
    print('manage_client created')
    print('called on connection only ?')
    await asyncio.sleep(1)
    print('after sleep1 in server()')
    while True:
        line = await reader.readline()
        if not line:
            break
        print('line', line)
        writer.write(line)
    writer.close()
    print('end of manage_client')


async def manage_jobs():
    pq = PersistentQueue('queue.txt')
    queue = []
    while True:
        item = await pq.pop()
        async with open('queue.txt') as f:
            line = await next(f)
            if not line:
                # schedule new job
            print('executing next scheduled job')

def read_next_job_arg():
    with open(QUEUE_FILE, 'r') as f:
        line = f.readline()


def main():
    print('getting event loop')
    loop = asyncio.get_event_loop()
    print('got event loop')
    # loop.call_soon(test)
    try:
        os.unlink('server_sock')
        print('creating coro...')
        coro = asyncio.start_unix_server(manage_client, path='server_sock')
        print('coro created')
        loop.run_until_complete(coro)
        print('coro returned')
        # loop.run_until_complete(test())
        loop.run_forever()
    except KeyboardInterrupt:
        pass
    print('loop closed')
    loop.close()


if __name__ == '__main__':
    main()