import errno
import glob
import logging
import os
import shutil
import stat
import tempfile
import weakref

import dask

from . import locket

logger = logging.getLogger(__name__)

DIR_LOCK_EXT = ".dirlock"


def is_locking_enabled():
    return dask.config.get("distributed.worker.use-file-locking")


def safe_unlink(path):
    try:
        os.unlink(path)
    except EnvironmentError as e:
        # Perhaps it was removed by someone else?
        if e.errno != errno.ENOENT:
            logger.error("Failed to remove %r", str(e))


class WorkDir:
    """
    A temporary work directory inside a WorkSpace.
    """

    def __init__(self, workspace, name=None, prefix=None):
        assert name is None or prefix is None

        if name is None:
            self.dir_path = tempfile.mkdtemp(prefix=prefix, dir=workspace.base_dir)
        else:
            self.dir_path = os.path.join(workspace.base_dir, name)
            os.mkdir(self.dir_path)  # it shouldn't already exist

        if is_locking_enabled():
            try:
                self._lock_path = os.path.join(self.dir_path + DIR_LOCK_EXT)
                assert not os.path.exists(self._lock_path)
                logger.debug("Locking %r...", self._lock_path)
                # Avoid a race condition before locking the file
                # by taking the global lock
                try:
                    with workspace._global_lock():
                        self._lock_file = locket.lock_file(self._lock_path)
                        self._lock_file.acquire()
                except OSError:
                    logger.exception(
                        "Could not acquire workspace lock on "
                        "path: %s ."
                        "Continuing without lock. "
                        "This may result in workspaces not being "
                        "cleaned up",
                        self._lock_path,
                        exc_info=True,
                    )
                    self._lock_file = None
            except Exception:
                shutil.rmtree(self.dir_path, ignore_errors=True)
                raise
            workspace._known_locks.add(self._lock_path)

            self._finalizer = weakref.finalize(
                self,
                self._finalize,
                workspace,
                self._lock_path,
                self._lock_file,
                self.dir_path,
            )
        else:
            self._finalizer = weakref.finalize(
                self, self._finalize, workspace, None, None, self.dir_path
            )

    def release(self):
        """
        Dispose of this directory.
        """
        self._finalizer()

    @classmethod
    def _finalize(cls, workspace, lock_path, lock_file, dir_path):
        try:
            workspace._purge_directory(dir_path)
        finally:
            if lock_file is not None:
                lock_file.release()
            if lock_path is not None:
                workspace._known_locks.remove(lock_path)
                safe_unlink(lock_path)


class WorkSpace:
    """
    An on-disk workspace that tracks disposable work directories inside it.
    If a process crashes or another event left stale directories behind,
    this will be detected and the directories purged.
    """

    # Keep track of all locks known to this process, to avoid several
    # WorkSpaces to step on each other's toes
    _known_locks = set()

    def __init__(self, base_dir):
        self.base_dir = os.path.abspath(base_dir)
        self._init_workspace()
        self._global_lock_path = os.path.join(self.base_dir, "global.lock")
        self._purge_lock_path = os.path.join(self.base_dir, "purge.lock")

    def _init_workspace(self):
        try:
            os.mkdir(self.base_dir)
        except EnvironmentError as e:
            if e.errno != errno.EEXIST:
                raise

    def _global_lock(self, **kwargs):
        return locket.lock_file(self._global_lock_path, **kwargs)

    def _purge_lock(self, **kwargs):
        return locket.lock_file(self._purge_lock_path, **kwargs)

    def _purge_leftovers(self):
        if not is_locking_enabled():
            return []

        # List candidates with the global lock taken, to avoid purging
        # a lock file that was just created but not yet locked
        # (see WorkDir.__init__)
        lock = self._global_lock(timeout=0)
        try:
            lock.acquire()
        except locket.LockError:
            # No need to waste time here if someone else is busy doing
            # something on this workspace
            return []
        else:
            try:
                candidates = list(self._list_unknown_locks())
            finally:
                lock.release()

        # No need to hold the global lock here, especially as purging
        # can take time.  Instead take the purge lock to avoid two
        # processes purging at once.
        purged = []
        lock = self._purge_lock(timeout=0)
        try:
            lock.acquire()
        except locket.LockError:
            # No need for two processes to purge one after another
            pass
        else:
            try:
                for path in candidates:
                    if self._check_lock_or_purge(path):
                        purged.append(path)
            finally:
                lock.release()
        return purged

    def _list_unknown_locks(self):
        for p in glob.glob(os.path.join(self.base_dir, "*" + DIR_LOCK_EXT)):
            try:
                st = os.stat(p)
            except EnvironmentError:
                # May have been removed in the meantime
                pass
            else:
                # XXX restrict to files owned by current user?
                if stat.S_ISREG(st.st_mode):
                    yield p

    def _purge_directory(self, dir_path):
        shutil.rmtree(dir_path, onerror=self._on_remove_error)

    def _check_lock_or_purge(self, lock_path):
        """
        Try locking the given path, if it fails it's in use,
        otherwise the corresponding directory is deleted.

        Return True if the lock was stale.
        """
        assert lock_path.endswith(DIR_LOCK_EXT)
        if lock_path in self._known_locks:
            # Avoid touching a lock that we know is already taken
            return False
        logger.debug("Checking lock file %r...", lock_path)
        lock = locket.lock_file(lock_path, timeout=0)
        try:
            lock.acquire()
        except locket.LockError:
            # Lock file still in use, ignore
            return False
        try:
            # Lock file is stale, therefore purge corresponding directory
            dir_path = lock_path[: -len(DIR_LOCK_EXT)]
            if os.path.exists(dir_path):
                logger.info("Found stale lock file and directory %r, purging", dir_path)
                self._purge_directory(dir_path)
        finally:
            lock.release()
        # Clean up lock file after we released it
        safe_unlink(lock_path)
        return True

    def _on_remove_error(self, func, path, exc_info):
        typ, exc, tb = exc_info
        logger.error("Failed to remove %r (failed in %r): %s", path, func, str(exc))

    def new_work_dir(self, **kwargs):
        """
        Create and return a new WorkDir in this WorkSpace.
        Either the *prefix* or *name* parameter should be given
        (*prefix* is preferred as it avoids potential collisions)

        Parameters
        ----------
        prefix : str (optional)
            The prefix of the temporary subdirectory name for the workdir
        name : str (optional)
            The subdirectory name for the workdir
        """
        try:
            self._purge_leftovers()
        except OSError:
            logger.error(
                "Failed to clean up lingering worker directories in path: %s ",
                exc_info=True,
            )
        return WorkDir(self, **kwargs)
