import abc
import atexit
import contextlib
import logging
import os
import pathlib
import random
import tempfile
import time
import typing
import warnings

from . import constants, exceptions, portalocker

logger = logging.getLogger(__name__)

DEFAULT_TIMEOUT = 5
DEFAULT_CHECK_INTERVAL = 0.25
DEFAULT_FAIL_WHEN_LOCKED = False
LOCK_METHOD = constants.LockFlags.EXCLUSIVE | constants.LockFlags.NON_BLOCKING

__all__ = [
    'Lock',
    'open_atomic',
]

Filename = typing.Union[str, pathlib.Path]


def coalesce(*args: typing.Any, test_value: typing.Any = None) -> typing.Any:
    '''Simple coalescing function that returns the first value that is not
    equal to the `test_value`. Or `None` if no value is valid. Usually this
    means that the last given value is the default value.

    Note that the `test_value` is compared using an identity check
    (i.e. `value is not test_value`) so changing the `test_value` won't work
    for all values.

    >>> coalesce(None, 1)
    1
    >>> coalesce()

    >>> coalesce(0, False, True)
    0
    >>> coalesce(0, False, True, test_value=0)
    False

    # This won't work because of the `is not test_value` type testing:
    >>> coalesce([], dict(spam='eggs'), test_value=[])
    []
    '''
    return next((arg for arg in args if arg is not test_value), None)


@contextlib.contextmanager
def open_atomic(
    filename: Filename,
    binary: bool = True,
) -> typing.Iterator[typing.IO]:
    '''Open a file for atomic writing. Instead of locking this method allows
    you to write the entire file and move it to the actual location. Note that
    this makes the assumption that a rename is atomic on your platform which
    is generally the case but not a guarantee.

    http://docs.python.org/library/os.html#os.rename

    >>> filename = 'test_file.txt'
    >>> if os.path.exists(filename):
    ...     os.remove(filename)

    >>> with open_atomic(filename) as fh:
    ...     written = fh.write(b'test')
    >>> assert os.path.exists(filename)
    >>> os.remove(filename)

    >>> import pathlib
    >>> path_filename = pathlib.Path('test_file.txt')

    >>> with open_atomic(path_filename) as fh:
    ...     written = fh.write(b'test')
    >>> assert path_filename.exists()
    >>> path_filename.unlink()
    '''
    # `pathlib.Path` cast in case `path` is a `str`
    path: pathlib.Path = pathlib.Path(filename)

    assert not path.exists(), '%r exists' % path

    # Create the parent directory if it doesn't exist
    path.parent.mkdir(parents=True, exist_ok=True)

    temp_fh = tempfile.NamedTemporaryFile(
        mode=binary and 'wb' or 'w',
        dir=str(path.parent),
        delete=False,
    )
    yield temp_fh
    temp_fh.flush()
    os.fsync(temp_fh.fileno())
    temp_fh.close()
    try:
        os.rename(temp_fh.name, path)
    finally:
        with contextlib.suppress(Exception):
            os.remove(temp_fh.name)


class LockBase(abc.ABC):  # pragma: no cover
    #: timeout when trying to acquire a lock
    timeout: float
    #: check interval while waiting for `timeout`
    check_interval: float
    #: skip the timeout and immediately fail if the initial lock fails
    fail_when_locked: bool

    def __init__(
        self,
        timeout: typing.Optional[float] = None,
        check_interval: typing.Optional[float] = None,
        fail_when_locked: typing.Optional[bool] = None,
    ):
        self.timeout = coalesce(timeout, DEFAULT_TIMEOUT)
        self.check_interval = coalesce(check_interval, DEFAULT_CHECK_INTERVAL)
        self.fail_when_locked = coalesce(
            fail_when_locked,
            DEFAULT_FAIL_WHEN_LOCKED,
        )

    @abc.abstractmethod
    def acquire(
        self,
        timeout: typing.Optional[float] = None,
        check_interval: typing.Optional[float] = None,
        fail_when_locked: typing.Optional[bool] = None,
    ):
        return NotImplemented

    def _timeout_generator(
        self,
        timeout: typing.Optional[float],
        check_interval: typing.Optional[float],
    ) -> typing.Iterator[int]:
        f_timeout = coalesce(timeout, self.timeout, 0.0)
        f_check_interval = coalesce(check_interval, self.check_interval, 0.0)

        yield 0
        i = 0

        start_time = time.perf_counter()
        while start_time + f_timeout > time.perf_counter():
            i += 1
            yield i

            # Take low lock checks into account to stay within the interval
            since_start_time = time.perf_counter() - start_time
            time.sleep(max(0.001, (i * f_check_interval) - since_start_time))

    @abc.abstractmethod
    def release(self):
        return NotImplemented

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

    def __exit__(
        self,
        exc_type: typing.Optional[typing.Type[BaseException]],
        exc_value: typing.Optional[BaseException],
        traceback: typing.Any,  # Should be typing.TracebackType
    ) -> typing.Optional[bool]:
        self.release()
        return None

    def __delete__(self, instance):
        instance.release()


class Lock(LockBase):
    '''Lock manager with built-in timeout

    Args:
        filename: filename
        mode: the open mode, 'a' or 'ab' should be used for writing. When mode
            contains `w` the file will be truncated to 0 bytes.
        timeout: timeout when trying to acquire a lock
        check_interval: check interval while waiting
        fail_when_locked: after the initial lock failed, return an error
            or lock the file. This does not wait for the timeout.
        **file_open_kwargs: The kwargs for the `open(...)` call

    fail_when_locked is useful when multiple threads/processes can race
    when creating a file. If set to true than the system will wait till
    the lock was acquired and then return an AlreadyLocked exception.

    Note that the file is opened first and locked later. So using 'w' as
    mode will result in truncate _BEFORE_ the lock is checked.
    '''

    def __init__(
        self,
        filename: Filename,
        mode: str = 'a',
        timeout: typing.Optional[float] = None,
        check_interval: float = DEFAULT_CHECK_INTERVAL,
        fail_when_locked: bool = DEFAULT_FAIL_WHEN_LOCKED,
        flags: constants.LockFlags = LOCK_METHOD,
        **file_open_kwargs,
    ):
        if 'w' in mode:
            truncate = True
            mode = mode.replace('w', 'a')
        else:
            truncate = False

        if timeout is None:
            timeout = DEFAULT_TIMEOUT
        elif not (flags & constants.LockFlags.NON_BLOCKING):
            warnings.warn(
                'timeout has no effect in blocking mode',
                stacklevel=1,
            )

        self.fh: typing.Optional[typing.IO] = None
        self.filename: str = str(filename)
        self.mode: str = mode
        self.truncate: bool = truncate
        self.timeout: float = timeout
        self.check_interval: float = check_interval
        self.fail_when_locked: bool = fail_when_locked
        self.flags: constants.LockFlags = flags
        self.file_open_kwargs = file_open_kwargs

    def acquire(
        self,
        timeout: typing.Optional[float] = None,
        check_interval: typing.Optional[float] = None,
        fail_when_locked: typing.Optional[bool] = None,
    ) -> typing.IO:
        '''Acquire the locked filehandle'''

        fail_when_locked = coalesce(fail_when_locked, self.fail_when_locked)

        if (
            not (self.flags & constants.LockFlags.NON_BLOCKING)
            and timeout is not None
        ):
            warnings.warn(
                'timeout has no effect in blocking mode',
                stacklevel=1,
            )

        # If we already have a filehandle, return it
        fh: typing.Optional[typing.IO] = self.fh
        if fh:
            return fh

        # Get a new filehandler
        fh = self._get_fh()

        def try_close():  # pragma: no cover
            # Silently try to close the handle if possible, ignore all issues
            if fh is not None:
                with contextlib.suppress(Exception):
                    fh.close()

        exception = None
        # Try till the timeout has passed
        for _ in self._timeout_generator(timeout, check_interval):
            exception = None
            try:
                # Try to lock
                fh = self._get_lock(fh)
                break
            except exceptions.LockException as exc:
                # Python will automatically remove the variable from memory
                # unless you save it in a different location
                exception = exc

                # We already tried to the get the lock
                # If fail_when_locked is True, stop trying
                if fail_when_locked:
                    try_close()
                    raise exceptions.AlreadyLocked(exception) from exc

                # Wait a bit

        if exception:
            try_close()
            # We got a timeout... reraising
            raise exceptions.LockException(exception)

        # Prepare the filehandle (truncate if needed)
        fh = self._prepare_fh(fh)

        self.fh = fh
        return fh

    def release(self):
        '''Releases the currently locked file handle'''
        if self.fh:
            portalocker.unlock(self.fh)
            self.fh.close()
            self.fh = None

    def _get_fh(self) -> typing.IO:
        '''Get a new filehandle'''
        return open(  # noqa: SIM115
            self.filename,
            self.mode,
            **self.file_open_kwargs,
        )

    def _get_lock(self, fh: typing.IO) -> typing.IO:
        '''
        Try to lock the given filehandle

        returns LockException if it fails'''
        portalocker.lock(fh, self.flags)
        return fh

    def _prepare_fh(self, fh: typing.IO) -> typing.IO:
        '''
        Prepare the filehandle for usage

        If truncate is a number, the file will be truncated to that amount of
        bytes
        '''
        if self.truncate:
            fh.seek(0)
            fh.truncate(0)

        return fh


class RLock(Lock):
    '''
    A reentrant lock, functions in a similar way to threading.RLock in that it
    can be acquired multiple times.  When the corresponding number of release()
    calls are made the lock will finally release the underlying file lock.
    '''

    def __init__(
        self,
        filename,
        mode='a',
        timeout=DEFAULT_TIMEOUT,
        check_interval=DEFAULT_CHECK_INTERVAL,
        fail_when_locked=False,
        flags=LOCK_METHOD,
    ):
        super().__init__(
            filename,
            mode,
            timeout,
            check_interval,
            fail_when_locked,
            flags,
        )
        self._acquire_count = 0

    def acquire(
        self,
        timeout: typing.Optional[float] = None,
        check_interval: typing.Optional[float] = None,
        fail_when_locked: typing.Optional[bool] = None,
    ) -> typing.IO:
        if self._acquire_count >= 1:
            fh = self.fh
        else:
            fh = super().acquire(timeout, check_interval, fail_when_locked)
        self._acquire_count += 1
        assert fh
        return fh

    def release(self):
        if self._acquire_count == 0:
            raise exceptions.LockException(
                'Cannot release more times than acquired',
            )

        if self._acquire_count == 1:
            super().release()
        self._acquire_count -= 1


class TemporaryFileLock(Lock):
    def __init__(
        self,
        filename='.lock',
        timeout=DEFAULT_TIMEOUT,
        check_interval=DEFAULT_CHECK_INTERVAL,
        fail_when_locked=True,
        flags=LOCK_METHOD,
    ):
        Lock.__init__(
            self,
            filename=filename,
            mode='w',
            timeout=timeout,
            check_interval=check_interval,
            fail_when_locked=fail_when_locked,
            flags=flags,
        )
        atexit.register(self.release)

    def release(self):
        Lock.release(self)
        if os.path.isfile(self.filename):  # pragma: no branch
            os.unlink(self.filename)


class BoundedSemaphore(LockBase):
    '''
    Bounded semaphore to prevent too many parallel processes from running

    This method is deprecated because multiple processes that are completely
    unrelated could end up using the same semaphore.  To prevent this,
    use `NamedBoundedSemaphore` instead. The
    `NamedBoundedSemaphore` is a drop-in replacement for this class.

    >>> semaphore = BoundedSemaphore(2, directory='')
    >>> str(semaphore.get_filenames()[0])
    'bounded_semaphore.00.lock'
    >>> str(sorted(semaphore.get_random_filenames())[1])
    'bounded_semaphore.01.lock'
    '''

    lock: typing.Optional[Lock]

    def __init__(
        self,
        maximum: int,
        name: str = 'bounded_semaphore',
        filename_pattern: str = '{name}.{number:02d}.lock',
        directory: str = tempfile.gettempdir(),
        timeout: typing.Optional[float] = DEFAULT_TIMEOUT,
        check_interval: typing.Optional[float] = DEFAULT_CHECK_INTERVAL,
        fail_when_locked: typing.Optional[bool] = True,
    ):
        self.maximum = maximum
        self.name = name
        self.filename_pattern = filename_pattern
        self.directory = directory
        self.lock: typing.Optional[Lock] = None
        super().__init__(
            timeout=timeout,
            check_interval=check_interval,
            fail_when_locked=fail_when_locked,
        )

        if not name or name == 'bounded_semaphore':
            warnings.warn(
                '`BoundedSemaphore` without an explicit `name` '
                'argument is deprecated, use NamedBoundedSemaphore',
                DeprecationWarning,
                stacklevel=1,
            )

    def get_filenames(self) -> typing.Sequence[pathlib.Path]:
        return [self.get_filename(n) for n in range(self.maximum)]

    def get_random_filenames(self) -> typing.Sequence[pathlib.Path]:
        filenames = list(self.get_filenames())
        random.shuffle(filenames)
        return filenames

    def get_filename(self, number) -> pathlib.Path:
        return pathlib.Path(self.directory) / self.filename_pattern.format(
            name=self.name,
            number=number,
        )

    def acquire(
        self,
        timeout: typing.Optional[float] = None,
        check_interval: typing.Optional[float] = None,
        fail_when_locked: typing.Optional[bool] = None,
    ) -> typing.Optional[Lock]:
        assert not self.lock, 'Already locked'

        filenames = self.get_filenames()

        for n in self._timeout_generator(timeout, check_interval):  # pragma:
            logger.debug('trying lock (attempt %d) %r', n, filenames)
            # no branch
            if self.try_lock(filenames):  # pragma: no branch
                return self.lock  # pragma: no cover

        if fail_when_locked := coalesce(
            fail_when_locked,
            self.fail_when_locked,
        ):
            raise exceptions.AlreadyLocked()

        return None

    def try_lock(self, filenames: typing.Sequence[Filename]) -> bool:
        filename: Filename
        for filename in filenames:
            logger.debug('trying lock for %r', filename)
            self.lock = Lock(filename, fail_when_locked=True)
            try:
                self.lock.acquire()
            except exceptions.AlreadyLocked:
                self.lock = None
            else:
                logger.debug('locked %r', filename)
                return True

        return False

    def release(self):  # pragma: no cover
        if self.lock is not None:
            self.lock.release()
            self.lock = None


class NamedBoundedSemaphore(BoundedSemaphore):
    '''
    Bounded semaphore to prevent too many parallel processes from running

    It's also possible to specify a timeout when acquiring the lock to wait
    for a resource to become available.  This is very similar to
    `threading.BoundedSemaphore` but works across multiple processes and across
    multiple operating systems.

    Because this works across multiple processes it's important to give the
    semaphore a name.  This name is used to create the lock files.  If you
    don't specify a name, a random name will be generated.  This means that
    you can't use the same semaphore in multiple processes unless you pass the
    semaphore object to the other processes.

    >>> semaphore = NamedBoundedSemaphore(2, name='test')
    >>> str(semaphore.get_filenames()[0])
    '...test.00.lock'

    >>> semaphore = NamedBoundedSemaphore(2)
    >>> 'bounded_semaphore' in str(semaphore.get_filenames()[0])
    True

    '''

    def __init__(
        self,
        maximum: int,
        name: typing.Optional[str] = None,
        filename_pattern: str = '{name}.{number:02d}.lock',
        directory: str = tempfile.gettempdir(),
        timeout: typing.Optional[float] = DEFAULT_TIMEOUT,
        check_interval: typing.Optional[float] = DEFAULT_CHECK_INTERVAL,
        fail_when_locked: typing.Optional[bool] = True,
    ):
        if name is None:
            name = 'bounded_semaphore.%d' % random.randint(0, 1000000)
        super().__init__(
            maximum,
            name,
            filename_pattern,
            directory,
            timeout,
            check_interval,
            fail_when_locked,
        )
