"""File-system Transport module for kombu.

Transport using the file-system as the message store. Messages written to the
queue are stored in `data_folder_in` directory and
messages read from the queue are read from `data_folder_out` directory. Both
directories must be created manually. Simple example:

* Producer:

.. code-block:: python

    import kombu

    conn = kombu.Connection(
        'filesystem://', transport_options={
            'data_folder_in': 'data_in', 'data_folder_out': 'data_out'
        }
    )
    conn.connect()

    test_queue = kombu.Queue('test', routing_key='test')

    with conn as conn:
        with conn.default_channel as channel:
            producer = kombu.Producer(channel)
            producer.publish(
                        {'hello': 'world'},
                        retry=True,
                        exchange=test_queue.exchange,
                        routing_key=test_queue.routing_key,
                        declare=[test_queue],
                        serializer='pickle'
            )

* Consumer:

.. code-block:: python

    import kombu

    conn = kombu.Connection(
        'filesystem://', transport_options={
            'data_folder_in': 'data_out', 'data_folder_out': 'data_in'
        }
    )
    conn.connect()

    def callback(body, message):
        print(body, message)
        message.ack()

    test_queue = kombu.Queue('test', routing_key='test')

    with conn as conn:
        with conn.default_channel as channel:
            consumer = kombu.Consumer(
                conn, [test_queue], accept=['pickle']
            )
            consumer.register_callback(callback)
            with consumer:
                conn.drain_events(timeout=1)

Features
========
* Type: Virtual
* Supports Direct: Yes
* Supports Topic: Yes
* Supports Fanout: No
* Supports Priority: No
* Supports TTL: No

Connection String
=================
Connection string is in the following format:

.. code-block::

    filesystem://

Transport Options
=================
* ``data_folder_in`` - directory where are messages stored when written
  to queue.
* ``data_folder_out`` - directory from which are messages read when read from
  queue.
* ``store_processed`` - if set to True, all processed messages are backed up to
  ``processed_folder``.
* ``processed_folder`` - directory where are backed up processed files.
"""

import os
import shutil
import uuid
from queue import Empty
import tempfile
from time import monotonic

from . import virtual
from kombu.exceptions import ChannelError
from kombu.utils.encoding import bytes_to_str, str_to_bytes
from kombu.utils.json import loads, dumps
from kombu.utils.objects import cached_property


VERSION = (1, 0, 0)
__version__ = '.'.join(map(str, VERSION))

# needs win32all to work on Windows
if os.name == 'nt':

    import win32con
    import win32file
    import pywintypes

    LOCK_EX = win32con.LOCKFILE_EXCLUSIVE_LOCK
    # 0 is the default
    LOCK_SH = 0                                     # noqa
    LOCK_NB = win32con.LOCKFILE_FAIL_IMMEDIATELY    # noqa
    __overlapped = pywintypes.OVERLAPPED()

    def lock(file, flags):
        """Create file lock."""
        hfile = win32file._get_osfhandle(file.fileno())
        win32file.LockFileEx(hfile, flags, 0, 0xffff0000, __overlapped)

    def unlock(file):
        """Remove file lock."""
        hfile = win32file._get_osfhandle(file.fileno())
        win32file.UnlockFileEx(hfile, 0, 0xffff0000, __overlapped)

elif os.name == 'posix':

    import fcntl
    from fcntl import LOCK_EX, LOCK_SH, LOCK_NB     # noqa

    def lock(file, flags):  # noqa
        """Create file lock."""
        fcntl.flock(file.fileno(), flags)

    def unlock(file):       # noqa
        """Remove file lock."""
        fcntl.flock(file.fileno(), fcntl.LOCK_UN)
else:
    raise RuntimeError(
        'Filesystem plugin only defined for NT and POSIX platforms')


class Channel(virtual.Channel):
    """Filesystem Channel."""

    def _put(self, queue, payload, **kwargs):
        """Put `message` onto `queue`."""
        filename = '{}_{}.{}.msg'.format(int(round(monotonic() * 1000)),
                                         uuid.uuid4(), queue)
        filename = os.path.join(self.data_folder_out, filename)

        try:
            f = open(filename, 'wb')
            lock(f, LOCK_EX)
            f.write(str_to_bytes(dumps(payload)))
        except OSError:
            raise ChannelError(
                f'Cannot add file {filename!r} to directory')
        finally:
            unlock(f)
            f.close()

    def _get(self, queue):
        """Get next message from `queue`."""
        queue_find = '.' + queue + '.msg'
        folder = os.listdir(self.data_folder_in)
        folder = sorted(folder)
        while len(folder) > 0:
            filename = folder.pop(0)

            # only handle message for the requested queue
            if filename.find(queue_find) < 0:
                continue

            if self.store_processed:
                processed_folder = self.processed_folder
            else:
                processed_folder = tempfile.gettempdir()

            try:
                # move the file to the tmp/processed folder
                shutil.move(os.path.join(self.data_folder_in, filename),
                            processed_folder)
            except OSError:
                pass  # file could be locked, or removed in meantime so ignore

            filename = os.path.join(processed_folder, filename)
            try:
                f = open(filename, 'rb')
                payload = f.read()
                f.close()
                if not self.store_processed:
                    os.remove(filename)
            except OSError:
                raise ChannelError(
                    f'Cannot read file {filename!r} from queue.')

            return loads(bytes_to_str(payload))

        raise Empty()

    def _purge(self, queue):
        """Remove all messages from `queue`."""
        count = 0
        queue_find = '.' + queue + '.msg'

        folder = os.listdir(self.data_folder_in)
        while len(folder) > 0:
            filename = folder.pop()
            try:
                # only purge messages for the requested queue
                if filename.find(queue_find) < 0:
                    continue

                filename = os.path.join(self.data_folder_in, filename)
                os.remove(filename)

                count += 1

            except OSError:
                # we simply ignore its existence, as it was probably
                # processed by another worker
                pass

        return count

    def _size(self, queue):
        """Return the number of messages in `queue` as an :class:`int`."""
        count = 0

        queue_find = f'.{queue}.msg'
        folder = os.listdir(self.data_folder_in)
        while len(folder) > 0:
            filename = folder.pop()

            # only handle message for the requested queue
            if filename.find(queue_find) < 0:
                continue

            count += 1

        return count

    @property
    def transport_options(self):
        return self.connection.client.transport_options

    @cached_property
    def data_folder_in(self):
        return self.transport_options.get('data_folder_in', 'data_in')

    @cached_property
    def data_folder_out(self):
        return self.transport_options.get('data_folder_out', 'data_out')

    @cached_property
    def store_processed(self):
        return self.transport_options.get('store_processed', False)

    @cached_property
    def processed_folder(self):
        return self.transport_options.get('processed_folder', 'processed')


class Transport(virtual.Transport):
    """Filesystem Transport."""

    Channel = Channel

    default_port = 0
    driver_type = 'filesystem'
    driver_name = 'filesystem'

    def driver_version(self):
        return 'N/A'
