Mini Shell

from __future__ import annotations

import contextlib
import logging
import os
import time
import warnings
from abc import ABC, abstractmethod
from dataclasses import dataclass
from threading import local
from typing import TYPE_CHECKING, Any, ClassVar
from weakref import WeakValueDictionary

from ._error import Timeout

if TYPE_CHECKING:
    import sys
    from types import TracebackType

    if sys.version_info >= (3, 11):  # pragma: no cover (py311+)
        from typing import Self
    else:  # pragma: no cover (<py311)
        from typing_extensions import Self


_LOGGER = logging.getLogger("filelock")


# This is a helper class which is returned by :meth:`BaseFileLock.acquire` and wraps the lock to make sure __enter__
# is not called twice 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. issue #37 (memory leak)
class AcquireReturnProxy:
    """A context aware object that will release the lock file when exiting."""

    def __init__(self, lock: BaseFileLock) -> None:
        self.lock = lock

    def __enter__(self) -> BaseFileLock:
        return self.lock

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        exc_value: BaseException | None,
        traceback: TracebackType | None,
    ) -> None:
        self.lock.release()


@dataclass
class FileLockContext:
    """A dataclass which holds the context for a ``BaseFileLock`` object."""

    # The context is held in a separate class to allow optional use of thread local storage via the
    # ThreadLocalFileContext class.

    #: The path to the lock file.
    lock_file: str

    #: The default timeout value.
    timeout: float

    #: The mode for the lock files
    mode: int

    #: The file descriptor for the *_lock_file* as it is returned by the os.open() function, not None when lock held
    lock_file_fd: int | None = None

    #: The lock counter is used for implementing the nested locking mechanism.
    lock_counter: int = 0  # When the lock is acquired is increased and the lock is only released, when this value is 0


class ThreadLocalFileContext(FileLockContext, local):
    """A thread local version of the ``FileLockContext`` class."""


class BaseFileLock(ABC, contextlib.ContextDecorator):
    """Abstract base class for a file lock object."""

    _instances: ClassVar[WeakValueDictionary[str, BaseFileLock]] = WeakValueDictionary()

    def __new__(  # noqa: PLR0913
        cls,
        lock_file: str | os.PathLike[str],
        timeout: float = -1,  # noqa: ARG003
        mode: int = 0o644,  # noqa: ARG003
        thread_local: bool = True,  # noqa: ARG003, FBT001, FBT002
        *,
        is_singleton: bool = False,
        **kwargs: dict[str, Any],  # capture remaining kwargs for subclasses  # noqa: ARG003
    ) -> Self:
        """Create a new lock object or if specified return the singleton instance for the lock file."""
        if not is_singleton:
            return super().__new__(cls)

        instance = cls._instances.get(str(lock_file))
        if not instance:
            instance = super().__new__(cls)
            cls._instances[str(lock_file)] = instance

        return instance  # type: ignore[return-value] # https://github.com/python/mypy/issues/15322

    def __init__(  # noqa: PLR0913
        self,
        lock_file: str | os.PathLike[str],
        timeout: float = -1,
        mode: int = 0o644,
        thread_local: bool = True,  # noqa: FBT001, FBT002
        *,
        is_singleton: bool = False,
    ) -> None:
        """
        Create a new lock object.

        :param lock_file: path to the file
        :param timeout: default timeout when acquiring the lock, in seconds. 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.
        :param mode: file permissions for the lockfile
        :param thread_local: Whether this object's internal context should be thread local or not. If this is set to \
            ``False`` then the lock will be reentrant across threads.
        :param is_singleton: If this is set to ``True`` then only one instance of this class will be created \
            per lock file. This is useful if you want to use the lock object for reentrant locking without needing \
            to pass the same object around.
        """
        self._is_thread_local = thread_local
        self._is_singleton = is_singleton

        # Create the context. Note that external code should not work with the context directly  and should instead use
        # properties of this class.
        kwargs: dict[str, Any] = {
            "lock_file": os.fspath(lock_file),
            "timeout": timeout,
            "mode": mode,
        }
        self._context: FileLockContext = (ThreadLocalFileContext if thread_local else FileLockContext)(**kwargs)

    def is_thread_local(self) -> bool:
        """:return: a flag indicating if this lock is thread local or not"""
        return self._is_thread_local

    @property
    def is_singleton(self) -> bool:
        """:return: a flag indicating if this lock is singleton or not"""
        return self._is_singleton

    @property
    def lock_file(self) -> str:
        """:return: path to the lock file"""
        return self._context.lock_file

    @property
    def timeout(self) -> float:
        """
        :return: the default timeout value, in seconds

        .. versionadded:: 2.0.0
        """
        return self._context.timeout

    @timeout.setter
    def timeout(self, value: float | str) -> None:
        """
        Change the default timeout value.

        :param value: the new value, in seconds
        """
        self._context.timeout = float(value)

    @abstractmethod
    def _acquire(self) -> None:
        """If the file lock could be acquired, self._context.lock_file_fd holds the file descriptor of the lock file."""
        raise NotImplementedError

    @abstractmethod
    def _release(self) -> None:
        """Releases the lock and sets self._context.lock_file_fd to None."""
        raise NotImplementedError

    @property
    def is_locked(self) -> bool:
        """

        :return: A boolean indicating if the lock file is holding the lock currently.

        .. versionchanged:: 2.0.0

            This was previously a method and is now a property.
        """
        return self._context.lock_file_fd is not None

    @property
    def lock_counter(self) -> int:
        """:return: The number of times this lock has been acquired (but not yet released)."""
        return self._context.lock_counter

    def acquire(
        self,
        timeout: float | None = None,
        poll_interval: float = 0.05,
        *,
        poll_intervall: float | None = None,
        blocking: bool = True,
    ) -> AcquireReturnProxy:
        """
        Try to acquire the file lock.

        :param timeout: maximum wait time for acquiring the lock, ``None`` means use the default :attr:`~timeout` is and
         if ``timeout < 0``, there is no timeout and this method will block until the lock could be acquired
        :param poll_interval: interval of trying to acquire the lock file
        :param poll_intervall: deprecated, kept for backwards compatibility, use ``poll_interval`` instead
        :param blocking: defaults to True. If False, function will return immediately if it cannot obtain a lock on the
         first attempt. Otherwise, this method will block until the timeout expires or the lock is acquired.
        :raises Timeout: if fails to acquire lock within the timeout period
        :return: a context object that will unlock the file when the context is exited

        .. code-block:: python

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

            # Or use an equivalent try-finally construct:
            lock.acquire()
            try:
                pass
            finally:
                lock.release()

        .. versionchanged:: 2.0.0

            This method returns now a *proxy* object instead of *self*,
            so that it can be used in a with statement without side effects.

        """
        # Use the default timeout, if no timeout is provided.
        if timeout is None:
            timeout = self._context.timeout

        if poll_intervall is not None:
            msg = "use poll_interval instead of poll_intervall"
            warnings.warn(msg, DeprecationWarning, stacklevel=2)
            poll_interval = poll_intervall

        # Increment the number right at the beginning. We can still undo it, if something fails.
        self._context.lock_counter += 1

        lock_id = id(self)
        lock_filename = self.lock_file
        start_time = time.perf_counter()
        try:
            while True:
                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.debug("Lock %s acquired on %s", lock_id, lock_filename)
                    break
                if blocking is False:
                    _LOGGER.debug("Failed to immediately acquire lock %s on %s", lock_id, lock_filename)
                    raise Timeout(lock_filename)  # noqa: TRY301
                if 0 <= timeout < time.perf_counter() - start_time:
                    _LOGGER.debug("Timeout on acquiring lock %s on %s", lock_id, lock_filename)
                    raise Timeout(lock_filename)  # noqa: TRY301
                msg = "Lock %s not acquired on %s, waiting %s seconds ..."
                _LOGGER.debug(msg, lock_id, lock_filename, poll_interval)
                time.sleep(poll_interval)
        except BaseException:  # Something did go wrong, so decrement the counter.
            self._context.lock_counter = max(0, self._context.lock_counter - 1)
            raise
        return AcquireReturnProxy(lock=self)

    def release(self, force: bool = False) -> None:  # noqa: FBT001, FBT002
        """
        Releases the file lock. Please note, that the lock is only completely released, if the lock counter is 0. Also
        note, that the lock file itself is not automatically deleted.

        :param force: If true, the lock counter is ignored and the lock is released in every case/
        """
        if self.is_locked:
            self._context.lock_counter -= 1

            if self._context.lock_counter == 0 or force:
                lock_id, lock_filename = id(self), self.lock_file

                _LOGGER.debug("Attempting to release lock %s on %s", lock_id, lock_filename)
                self._release()
                self._context.lock_counter = 0
                _LOGGER.debug("Lock %s released on %s", lock_id, lock_filename)

    def __enter__(self) -> Self:
        """
        Acquire the lock.

        :return: the lock object
        """
        self.acquire()
        return self

    def __exit__(
        self,
        exc_type: type[BaseException] | None,
        exc_value: BaseException | None,
        traceback: TracebackType | None,
    ) -> None:
        """
        Release the lock.

        :param exc_type: the exception type if raised
        :param exc_value: the exception value if raised
        :param traceback: the exception traceback if raised
        """
        self.release()

    def __del__(self) -> None:
        """Called when the lock object is deleted."""
        self.release(force=True)


__all__ = [
    "BaseFileLock",
    "AcquireReturnProxy",
]