#
# Copyright © 2015 eNovance
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.

import contextlib
import datetime
import errno
import functools
import hashlib
import logging
import os
import shutil
import tempfile
import threading
import weakref

import fasteners
from oslo_utils import fileutils
from oslo_utils import timeutils
import voluptuous

import tooz
from tooz import coordination
from tooz import locking
from tooz import utils

LOG = logging.getLogger(__name__)


class _Barrier:
    def __init__(self):
        self.cond = threading.Condition()
        self.owner = None
        self.shared = False
        self.ref = 0


@contextlib.contextmanager
def _translate_failures():
    try:
        yield
    except (OSError, voluptuous.Invalid) as e:
        utils.raise_with_cause(tooz.ToozError, str(e), cause=e)


def _convert_from_old_format(data):
    # NOTE(sileht): previous version of the driver was storing str as-is
    # making impossible to read from python3 something written with python2
    # version of the lib.
    # Now everything is stored with explicit type bytes or unicode. This
    # convert the old format to the new one to maintain compat of already
    # deployed file.
    # example of potential old python2 payload:
    # {b"member_id": b"member"}
    # {b"member_id": u"member"}
    # example of potential old python3 payload:
    # {u"member_id": b"member"}
    # {u"member_id": u"member"}
    if b"member_id" in data or b"group_id" in data:
        data = {k.decode("utf8"): v for k, v in data.items()}
        # About member_id and group_id valuse if the file have been written
        # with python2 and in the old format, we can't known with python3
        # if we need to decode the value or not. Python3 see bytes blob
        # We keep it as-is and pray, this have a good change to break if
        # the application was using str in python2 and unicode in python3
        # The member file is often overridden so it's should be fine
        # But the group file can be very old, so we
        # now have to update it each time create_group is called
    return data


def _lock_me(lock):
    def wrapper(func):
        @functools.wraps(func)
        def decorator(*args, **kwargs):
            with lock:
                return func(*args, **kwargs)

        return decorator

    return wrapper


class FileLock(locking.Lock):
    """A file based lock."""

    def __init__(self, path, barrier, member_id):
        super().__init__(path)
        self.acquired = False
        self._lock = fasteners.InterProcessLock(path)
        self._barrier = barrier
        self._member_id = member_id
        self.ref = 0

    def is_still_owner(self):
        return self.acquired

    def acquire(self, blocking=True, shared=False, timeout=None):
        blocking, timeout = utils.convert_blocking(blocking, timeout)
        watch = timeutils.StopWatch(duration=timeout)
        watch.start()

        # Make the shared barrier ours first.
        with self._barrier.cond:
            while self._barrier.owner is not None:
                if shared and self._barrier.shared:
                    break
                if not blocking or watch.expired():
                    return False
                self._barrier.cond.wait(watch.leftover(return_none=True))
            self._barrier.owner = (
                threading.current_thread().ident,
                os.getpid(),
                self._member_id,
            )
            self._barrier.shared = shared
            self._barrier.ref += 1
            self.ref += 1

        # Ok at this point we are now working in a thread safe manner,
        # and now we can try to get the actual lock...
        gotten = False
        try:
            gotten = self._lock.acquire(
                blocking=blocking,
                # Since the barrier waiting may have
                # taken a long time, we have to use
                # the leftover (and not the original).
                timeout=watch.leftover(return_none=True),
            )
        finally:
            # NOTE(harlowja): do this in a finally block to **ensure** that
            # we release the barrier if something bad happens...
            if not gotten:
                # Release the barrier to let someone else have a go at it...
                with self._barrier.cond:
                    self._barrier.owner = None
                    self._barrier.ref = 0
                    self._barrier.shared = False
                    self._barrier.cond.notify_all()

        self.acquired = gotten
        return gotten

    def release(self):
        if not self.acquired:
            return False
        with self._barrier.cond:
            self._barrier.ref -= 1
            self.ref -= 1
            if not self.ref:
                self.acquired = False
            if not self._barrier.ref:
                self._barrier.owner = None
                self._lock.release()
                self._barrier.cond.notify_all()
        return True

    def __del__(self):
        if self.acquired:
            LOG.warning("Unreleased lock %s garbage collected", self.name)


class FileDriver(
    coordination.CoordinationDriverCachedRunWatchers,
    coordination.CoordinationDriverWithExecutor,
):
    """A file based driver.

    This driver uses files and directories (and associated file locks) to
    provide the coordination driver semantics and required API(s). It **is**
    missing some functionality but in the future these not implemented API(s)
    will be filled in.

    The File driver connection URI should look like::

      file://DIRECTORY[?timeout=TIMEOUT]

    DIRECTORY is the location that should be used to store lock files.
    TIMEOUT defaults to 10.

    General recommendations/usage considerations:

    - It does **not** automatically delete members from
      groups of processes that have died, manual cleanup will be needed
      for those types of failures.

    - It is **not** distributed (or recommended to be used in those
      situations, so the developer using this should really take that into
      account when applying this driver in there app).
    """

    CHARACTERISTICS = (
        coordination.Characteristics.NON_TIMEOUT_BASED,
        coordination.Characteristics.DISTRIBUTED_ACROSS_THREADS,
        coordination.Characteristics.DISTRIBUTED_ACROSS_PROCESSES,
    )
    """
    Tuple of :py:class:`~tooz.coordination.Characteristics` introspectable
    enum member(s) that can be used to interogate how this driver works.
    """

    HASH_ROUTINE = 'sha1'
    """This routine is used to hash a member (or group) id into a filesystem
       safe name that can be used for member lookup and group joining."""

    _barriers = weakref.WeakValueDictionary()
    """
    Barriers shared among all file driver locks, this is required
    since interprocess locking is not thread aware, so we must add the
    thread awareness on-top of it instead.
    """

    def __init__(self, member_id, parsed_url, options):
        """Initialize the file driver."""
        super().__init__(member_id, parsed_url, options)
        self._dir = parsed_url.path
        self._group_dir = os.path.join(self._dir, 'groups')
        self._tmpdir = os.path.join(self._dir, 'tmp')
        self._driver_lock_path = os.path.join(self._dir, '.driver_lock')
        self._driver_lock = self._get_raw_lock(
            self._driver_lock_path, self._member_id
        )
        self._reserved_dirs = [self._dir, self._group_dir, self._tmpdir]
        self._reserved_paths = list(self._reserved_dirs)
        self._reserved_paths.append(self._driver_lock_path)
        self._safe_member_id = self._make_filesystem_safe(member_id)
        self._timeout = int(self._options.get('timeout', 10))

    @classmethod
    def _get_raw_lock(cls, path, member_id):
        lock_barrier = cls._barriers.setdefault(path, _Barrier())
        return FileLock(path, lock_barrier, member_id)

    def get_lock(self, name):
        path = utils.safe_abs_path(self._dir, name.decode())
        if path in self._reserved_paths:
            raise ValueError(
                "Unable to create a lock using"
                f" reserved path '{path}' for lock"
                f" with name '{name}'"
            )
        return self._get_raw_lock(path, self._member_id)

    @classmethod
    def _make_filesystem_safe(cls, item):
        item = utils.to_binary(item, encoding="utf8")
        return hashlib.new(cls.HASH_ROUTINE, item).hexdigest()

    def _start(self):
        super()._start()
        for a_dir in self._reserved_dirs:
            try:
                fileutils.ensure_tree(a_dir)
            except OSError as e:
                raise coordination.ToozConnectionError(e)

    def _update_group_metadata(self, path, group_id):
        details = {'group_id': utils.to_binary(group_id, encoding="utf8")}
        details['encoded'] = details["group_id"] != group_id
        details_blob = utils.dumps(details)
        fd, name = tempfile.mkstemp("tooz", dir=self._tmpdir)
        with os.fdopen(fd, "wb") as fh:
            fh.write(details_blob)
        os.rename(name, path)

    def create_group(self, group_id):
        safe_group_id = self._make_filesystem_safe(group_id)
        group_dir = os.path.join(self._group_dir, safe_group_id)
        group_meta_path = os.path.join(group_dir, '.metadata')

        def _do_create_group():
            if os.path.exists(os.path.join(group_dir, ".metadata")):
                # NOTE(sileht): We update the group metadata even
                # they are already good, so ensure dict key are convert
                # to unicode in case of the file have been written with
                # tooz < 1.36
                self._update_group_metadata(group_meta_path, group_id)
                raise coordination.GroupAlreadyExist(group_id)
            else:
                fileutils.ensure_tree(group_dir)
                self._update_group_metadata(group_meta_path, group_id)

        fut = self._executor.submit(_do_create_group)
        return FileFutureResult(fut)

    def join_group(self, group_id, capabilities=b""):
        safe_group_id = self._make_filesystem_safe(group_id)
        group_dir = os.path.join(self._group_dir, safe_group_id)
        me_path = os.path.join(group_dir, f"{self._safe_member_id}.raw")

        @_lock_me(self._driver_lock)
        def _do_join_group():
            if not os.path.exists(os.path.join(group_dir, ".metadata")):
                raise coordination.GroupNotCreated(group_id)
            if os.path.isfile(me_path):
                raise coordination.MemberAlreadyExist(
                    group_id, self._member_id
                )
            details = {
                'capabilities': capabilities,
                'joined_on': datetime.datetime.now(),
                'member_id': utils.to_binary(
                    self._member_id, encoding="utf-8"
                ),
            }
            details['encoded'] = details["member_id"] != self._member_id
            details_blob = utils.dumps(details)
            with open(me_path, "wb") as fh:
                fh.write(details_blob)
            self._joined_groups.add(group_id)

        fut = self._executor.submit(_do_join_group)
        return FileFutureResult(fut)

    def leave_group(self, group_id):
        safe_group_id = self._make_filesystem_safe(group_id)
        group_dir = os.path.join(self._group_dir, safe_group_id)
        me_path = os.path.join(group_dir, f"{self._safe_member_id}.raw")

        @_lock_me(self._driver_lock)
        def _do_leave_group():
            if not os.path.exists(os.path.join(group_dir, ".metadata")):
                raise coordination.GroupNotCreated(group_id)
            try:
                os.unlink(me_path)
            except OSError as e:
                if e.errno != errno.ENOENT:
                    raise
                else:
                    raise coordination.MemberNotJoined(
                        group_id, self._member_id
                    )
            else:
                self._joined_groups.discard(group_id)

        fut = self._executor.submit(_do_leave_group)
        return FileFutureResult(fut)

    _SCHEMAS = {
        'group': voluptuous.Schema(
            {
                voluptuous.Required('group_id'): voluptuous.Any(str, bytes),
                # NOTE(sileht): tooz <1.36 was creating file without this
                voluptuous.Optional('encoded'): bool,
            }
        ),
        'member': voluptuous.Schema(
            {
                voluptuous.Required('member_id'): voluptuous.Any(str, bytes),
                voluptuous.Required('joined_on'): datetime.datetime,
                # NOTE(sileht): tooz <1.36 was creating file without this
                voluptuous.Optional('encoded'): bool,
            },
            extra=voluptuous.ALLOW_EXTRA,
        ),
    }

    def _load_and_validate(self, blob, schema_key):
        data = utils.loads(blob)
        data = _convert_from_old_format(data)
        schema = self._SCHEMAS[schema_key]
        return schema(data)

    def _read_member_id(self, path):
        with open(path, 'rb') as fh:
            details = self._load_and_validate(fh.read(), 'member')
            if details.get("encoded"):
                return details['member_id'].decode("utf-8")
            return details['member_id']

    def get_members(self, group_id):
        safe_group_id = self._make_filesystem_safe(group_id)
        group_dir = os.path.join(self._group_dir, safe_group_id)

        @_lock_me(self._driver_lock)
        def _do_get_members():
            if not os.path.isdir(group_dir):
                raise coordination.GroupNotCreated(group_id)
            members = set()
            try:
                entries = os.listdir(group_dir)
            except OSError as e:
                # Did someone manage to remove it before we got here...
                if e.errno != errno.ENOENT:
                    raise
            else:
                for entry in entries:
                    if not entry.endswith('.raw'):
                        continue
                    entry_path = os.path.join(group_dir, entry)
                    try:
                        m_time = datetime.datetime.fromtimestamp(
                            os.stat(entry_path).st_mtime
                        )
                        current_time = datetime.datetime.now()
                        delta_time = timeutils.delta_seconds(
                            m_time, current_time
                        )
                        if delta_time >= 0 and delta_time <= self._timeout:
                            member_id = self._read_member_id(entry_path)
                        else:
                            continue
                    except OSError as e:
                        if e.errno != errno.ENOENT:
                            raise
                    else:
                        members.add(member_id)
            return members

        fut = self._executor.submit(_do_get_members)
        return FileFutureResult(fut)

    def get_member_capabilities(self, group_id, member_id):
        safe_group_id = self._make_filesystem_safe(group_id)
        group_dir = os.path.join(self._group_dir, safe_group_id)
        safe_member_id = self._make_filesystem_safe(member_id)
        member_path = os.path.join(group_dir, f"{safe_member_id}.raw")

        @_lock_me(self._driver_lock)
        def _do_get_member_capabilities():
            try:
                with open(member_path, "rb") as fh:
                    contents = fh.read()
            except OSError as e:
                if e.errno == errno.ENOENT:
                    if not os.path.isdir(group_dir):
                        raise coordination.GroupNotCreated(group_id)
                    else:
                        raise coordination.MemberNotJoined(group_id, member_id)
                else:
                    raise
            else:
                details = self._load_and_validate(contents, 'member')
                return details.get("capabilities")

        fut = self._executor.submit(_do_get_member_capabilities)
        return FileFutureResult(fut)

    def delete_group(self, group_id):
        safe_group_id = self._make_filesystem_safe(group_id)
        group_dir = os.path.join(self._group_dir, safe_group_id)

        @_lock_me(self._driver_lock)
        def _do_delete_group():
            try:
                entries = os.listdir(group_dir)
            except OSError as e:
                if e.errno == errno.ENOENT:
                    raise coordination.GroupNotCreated(group_id)
                else:
                    raise
            else:
                if len(entries) > 1:
                    raise coordination.GroupNotEmpty(group_id)
                elif len(entries) == 1 and entries != ['.metadata']:
                    raise tooz.ToozError(
                        f"Unexpected path '{entries[0]}' found in group "
                        f"directory '{group_dir}' (expected to only find a "
                        "'.metadata' path)"
                    )
                else:
                    try:
                        shutil.rmtree(group_dir)
                    except OSError as e:
                        if e.errno != errno.ENOENT:
                            raise

        fut = self._executor.submit(_do_delete_group)
        return FileFutureResult(fut)

    def _read_group_id(self, path):
        with open(path, 'rb') as fh:
            details = self._load_and_validate(fh.read(), 'group')
            if details.get("encoded"):
                return details['group_id'].decode("utf-8")
            return details['group_id']

    def get_groups(self):
        def _do_get_groups():
            groups = []
            for entry in os.listdir(self._group_dir):
                path = os.path.join(self._group_dir, entry, '.metadata')
                try:
                    groups.append(self._read_group_id(path))
                except OSError as e:
                    if e.errno != errno.ENOENT:
                        raise
            return groups

        fut = self._executor.submit(_do_get_groups)
        return FileFutureResult(fut)

    def heartbeat(self):
        for group_id in self._joined_groups:
            safe_group_id = self._make_filesystem_safe(group_id)
            group_dir = os.path.join(self._group_dir, safe_group_id)
            member_path = os.path.join(
                group_dir, f"{self._safe_member_id}.raw"
            )

            @_lock_me(self._driver_lock)
            def _do_heartbeat():
                try:
                    os.utime(member_path, None)
                except OSError as err:
                    if err.errno != errno.ENOENT:
                        raise

            _do_heartbeat()
        return self._timeout

    @staticmethod
    def watch_elected_as_leader(group_id, callback):
        raise tooz.NotImplemented

    @staticmethod
    def unwatch_elected_as_leader(group_id, callback):
        raise tooz.NotImplemented


FileFutureResult = functools.partial(
    coordination.CoordinatorResult, failure_translator=_translate_failures
)