#! /usr/bin/env python3
# -*- coding: utf-8 -*-
# File   : filelock.py
# Author : Jiayuan Mao
# Email  : maojiayuan@gmail.com
# Date   : 05/25/2019
#
# This file is part of Jacinle.
# Distributed under terms of the MIT license.

"""A platform independent file lock that supports the with-statement.

Original License:

    This is free and unencumbered software released into the public domain.

    Anyone is free to copy, modify, publish, use, compile, sell, or
    distribute this software, either in source code form or as a compiled
    binary, for any purpose, commercial or non-commercial, and by any
    means.

    In jurisdictions that recognize copyright laws, the author or authors
    of this software dedicate any and all copyright interest in the
    software to the public domain. We make this dedication for the benefit
    of the public at large and to the detriment of our heirs and
    successors. We intend this dedication to be an overt act of
    relinquishment in perpetuity of all present and future rights to this
    software under copyright law.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
    OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
    ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
    OTHER DEALINGS IN THE SOFTWARE.

    For more information, please refer to <http://unlicense.org>
"""

# yapf: disable

# Standard library imports
# Modules
# ------------------------------------------------
import logging
import os
import threading
import time


# yapf: enable

try:
    import warnings
except ImportError:
    warnings = None

try:
    import msvcrt
except ImportError:
    msvcrt = None

try:
    import fcntl
except ImportError:
    fcntl = None

# Backward compatibility
# ------------------------------------------------
try:
    TimeoutError
except NameError:
    TimeoutError = OSError

# Data
# ------------------------------------------------
__all__ = ["FileLockTimeout", "BaseFileLock", "WindowsFileLock", "UnixFileLock", "SoftFileLock", "FileLock"]

__version__ = "2.0.8"

logger = logging.getLogger(__name__)


# Exceptions
# ------------------------------------------------
class FileLockTimeout(TimeoutError):
    """
    Raised when the lock could not be acquired in *timeout*
    seconds.
    """

    def __init__(self, lock_file):
        """
        """
        #: The path of the file lock.
        self.lock_file = lock_file
        return None

    def __str__(self):
        temp = "The file lock '{}' could not be acquired."\
               .format(self.lock_file)
        return temp


# Classes
# ------------------------------------------------
class BaseFileLock(object):
    """Implements the base class of a file lock."""

    def __init__(self, lock_file, timeout=-1):
        """Initializes the file lock.

        Args:
            lock_file (str): the path to the lock file.
            timeout (int): the timeout in seconds. If -1, there is no timeout.
        """
        # The path to the lock file.
        self._lock_file = lock_file

        # The file descriptor for the *_lock_file* as it is returned by the
        # os.open() function.
        # This file lock is only NOT None, if the object currently holds the
        # lock.
        self._lock_file_fd = None

        # The default timeout value.
        self.timeout = timeout

        # We use this lock primarily for the lock counter.
        self._thread_lock = threading.Lock()

        # The lock counter is used for implementing the nested locking
        # mechanism. Whenever the lock is acquired, the counter is increased and
        # the lock is only released, when this value is 0 again.
        self._lock_counter = 0

    @property
    def lock_file(self):
        """The path to the lock file."""
        return self._lock_file

    @property
    def timeout(self):
        """You can set a default timeout for the filelock. It will be used as
        fallback value in the acquire method, if no timeout value (*None*) is
        given.

        If you want to disable the timeout, set it to a negative value.

        A timeout of 0 means, that there is exactly one attempt to acquire the
        file lock.
        """
        return self._timeout

    @timeout.setter
    def timeout(self, value):
        """
        """
        self._timeout = float(value)
        return None

    # Platform dependent locking
    # --------------------------------------------

    def _acquire(self):
        """Platform dependent. If the file lock could be acquired, self._lock_file_fd holds the file descriptor of the lock file."""
        raise NotImplementedError()

    def _release(self):
        """Releases the lock and sets self._lock_file_fd to None."""
        raise NotImplementedError()

    # Platform independent methods
    # --------------------------------------------

    @property
    def is_locked(self):
        """True, if the object holds the file lock."""
        return self._lock_file_fd is not None

    def acquire(self, timeout=None, poll_intervall=0.05):
        """Acquires the file lock or fails with a :exc:`Timeout` error.

        Args:
            timeout (float): the maximum time waited for the file lock.
                If ``timeout <= 0``, there is no timeout and this method will
                block until the lock could be acquired.
                If ``timeout`` is None, the default :attr:`~timeout` is used.

            poll_intervall (float): we check once in *poll_intervall* seconds
                if we can acquire the file lock.

        .. code-block:: python

            # You can use this method in the context manager (recommended)
            with lock.acquire():
                pass

            # Or you use an equal try-finally construct:
            lock.acquire()
            try:
                pass
            finally:
                lock.release()
        """
        # Use the default timeout, if no timeout is provided.
        if timeout is None:
            timeout = self.timeout

        # Increment the number right at the beginning.
        # We can still undo it, if something fails.
        with self._thread_lock:
            self._lock_counter += 1

        try:
            start_time = time.time()
            while True:
                lock_id = id(self)
                lock_filename = self._lock_file

                with self._thread_lock:
                    if not self.is_locked:
                        logger.debug(
                            'Attempting to acquire lock %s on %s', lock_id,
                            lock_filename
                        )
                        self._acquire()

                if self.is_locked:
                    logger.info(
                        'Lock %s acquired on %s', lock_id, lock_filename
                    )
                    break
                elif timeout >= 0 and time.time() - start_time > timeout:
                    logger.debug(
                        'Timeout on aquiring lock %s on %s', lock_id,
                        lock_filename
                    )
                    raise FileLockTimeout(self._lock_file)
                else:
                    logger.debug(
                        'Lock %s not acquired on %s, waiting %s seconds ...',
                        lock_id, lock_filename, poll_intervall
                    )
                    time.sleep(poll_intervall)
        except:
            # Something did go wrong, so decrement the counter.
            with self._thread_lock:
                self._lock_counter = max(0, self._lock_counter - 1)

            raise

        # This class wraps the lock to make sure __enter__ is not called
        # twiced when entering the with statement.
        # If we would simply return *self*, the lock would be acquired again
        # in the *__enter__* method of the BaseFileLock, but not released again
        # automatically.
        class ReturnProxy(object):
            def __init__(self, lock):
                self.lock = lock

            def __enter__(self):
                return self.lock

            def __exit__(self, exc_type, exc_value, traceback):
                self.lock.release()
                return None

        return ReturnProxy(lock=self)

    def release(self, force=False):
        """Releases the file lock.

        Please note, that the lock is only completly released, if the lock
        counter is 0.

        Also note, that the lock file itself is not automatically deleted.

        Args:
            force (bool):  If true, the lock counter is ignored and the lock is released in every case.
        """
        with self._thread_lock:

            if self.is_locked:
                self._lock_counter -= 1

                if self._lock_counter == 0 or force:
                    lock_id = id(self)
                    lock_filename = self._lock_file

                    logger.debug(
                        'Attempting to release lock %s on %s', lock_id,
                        lock_filename
                    )
                    self._release()
                    self._lock_counter = 0
                    logger.info(
                        'Lock %s released on %s', lock_id, lock_filename
                    )

        return None

    def __enter__(self):
        self.acquire()
        return self

    def __exit__(self, exc_type, exc_value, traceback):
        self.release()
        return None

    def __del__(self):
        self.release(force=True)
        return None


# Windows locking mechanism
# ~~~~~~~~~~~~~~~~~~~~~~~~~


class WindowsFileLock(BaseFileLock):
    """Uses the :func:`msvcrt.locking` function to hard lock the lock file on windows systems."""

    def _acquire(self):
        open_mode = os.O_RDWR | os.O_CREAT | os.O_TRUNC

        try:
            fd = os.open(self._lock_file, open_mode)
        except OSError:
            pass
        else:
            try:
                msvcrt.locking(fd, msvcrt.LK_NBLCK, 1)
            except (IOError, OSError):
                os.close(fd)
            else:
                self._lock_file_fd = fd
        return None

    def _release(self):
        fd = self._lock_file_fd
        self._lock_file_fd = None
        msvcrt.locking(fd, msvcrt.LK_UNLCK, 1)
        os.close(fd)

        try:
            os.remove(self._lock_file)
        # Probably another instance of the application
        # that acquired the file lock.
        except OSError:
            pass
        return None


# Unix locking mechanism
# ~~~~~~~~~~~~~~~~~~~~~~


class UnixFileLock(BaseFileLock):
    """Uses the :func:`fcntl.flock` to hard lock the lock file on unix systems."""

    def _acquire(self):
        open_mode = os.O_RDWR | os.O_CREAT | os.O_TRUNC
        fd = os.open(self._lock_file, open_mode)

        try:
            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except (IOError, OSError):
            os.close(fd)
        else:
            self._lock_file_fd = fd
        return None

    def _release(self):
        fd = self._lock_file_fd
        self._lock_file_fd = None
        fcntl.flock(fd, fcntl.LOCK_UN)
        os.close(fd)
        return None


# Soft lock
# ~~~~~~~~~


class SoftFileLock(BaseFileLock):
    """Simply watches the existence of the lock file."""

    def _acquire(self):
        open_mode = os.O_WRONLY | os.O_CREAT | os.O_EXCL | os.O_TRUNC
        try:
            fd = os.open(self._lock_file, open_mode)
        except (IOError, OSError):
            pass
        else:
            self._lock_file_fd = fd
        return None

    def _release(self):
        os.close(self._lock_file_fd)
        self._lock_file_fd = None

        try:
            os.remove(self._lock_file)
        # The file is already deleted and that's what we want.
        except OSError:
            pass
        return None


# Platform filelock
# ~~~~~~~~~~~~~~~~~

#: Alias for the lock, which should be used for the current platform. On
#: Windows, this is an alias for :class:`WindowsFileLock`, on Unix for
#: :class:`UnixFileLock` and otherwise for :class:`SoftFileLock`.
FileLock = None

if msvcrt:
    FileLock = WindowsFileLock
elif fcntl:
    FileLock = UnixFileLock
else:
    FileLock = SoftFileLock

    if warnings is not None:
        warnings.warn("only soft file lock is available")

