# -*- coding: utf-8 -*-

#    Copyright (C) 2012 Yahoo! Inc. All Rights Reserved.
#    Copyright (C) 2013 Rackspace Hosting All Rights Reserved.
#
#    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 copy
import itertools
import posixpath as pp

from debtcollector import removals
import fasteners
import six

from taskflow import exceptions as exc
from taskflow.persistence import path_based
from taskflow.types import tree


class FakeInode(tree.Node):
    """A in-memory filesystem inode-like object."""

    def __init__(self, item, path, value=None):
        super(FakeInode, self).__init__(item, path=path, value=value)


class FakeFilesystem(object):
    """An in-memory filesystem-like structure.

    This filesystem uses posix style paths **only** so users must be careful
    to use the ``posixpath`` module instead of the ``os.path`` one which will
    vary depending on the operating system which the active python is running
    in (the decision to use ``posixpath`` was to avoid the path variations
    which are not relevant in an implementation of a in-memory fake
    filesystem).

    **Not** thread-safe when a single filesystem is mutated at the same
    time by multiple threads. For example having multiple threads call into
    :meth:`~taskflow.persistence.backends.impl_memory.FakeFilesystem.clear`
    at the same time could potentially end badly. It is thread-safe when only
    :meth:`~taskflow.persistence.backends.impl_memory.FakeFilesystem.get`
    or other read-only actions (like calling into
    :meth:`~taskflow.persistence.backends.impl_memory.FakeFilesystem.ls`)
    are occuring at the same time.

    Example usage:

    >>> from taskflow.persistence.backends import impl_memory
    >>> fs = impl_memory.FakeFilesystem()
    >>> fs.ensure_path('/a/b/c')
    >>> fs['/a/b/c'] = 'd'
    >>> print(fs['/a/b/c'])
    d
    >>> del fs['/a/b/c']
    >>> fs.ls("/a/b")
    []
    >>> fs.get("/a/b/c", 'blob')
    'blob'
    """

    #: Root path of the in-memory filesystem.
    root_path = pp.sep

    @classmethod
    def normpath(cls, path):
        """Return a normalized absolutized version of the pathname path."""
        if not path:
            raise ValueError("This filesystem can only normalize paths"
                             " that are not empty")
        if not path.startswith(cls.root_path):
            raise ValueError("This filesystem can only normalize"
                             " paths that start with %s: '%s' is not"
                             " valid" % (cls.root_path, path))
        return pp.normpath(path)

    #: Split a pathname into a tuple of ``(head, tail)``.
    split = staticmethod(pp.split)

    @staticmethod
    def join(*pieces):
        """Join many path segments together."""
        return pp.sep.join(pieces)

    def __init__(self, deep_copy=True):
        self._root = FakeInode(self.root_path, self.root_path)
        self._reverse_mapping = {
            self.root_path: self._root,
        }
        if deep_copy:
            self._copier = copy.deepcopy
        else:
            self._copier = copy.copy

    def ensure_path(self, path):
        """Ensure the path (and parents) exists."""
        path = self.normpath(path)
        # Ignore the root path as we already checked for that; and it
        # will always exist/can't be removed anyway...
        if path == self._root.item:
            return
        node = self._root
        for piece in self._iter_pieces(path):
            child_node = node.find(piece, only_direct=True,
                                   include_self=False)
            if child_node is None:
                child_node = self._insert_child(node, piece)
            node = child_node

    def _insert_child(self, parent_node, basename, value=None):
        child_path = self.join(parent_node.metadata['path'], basename)
        # This avoids getting '//a/b' (duplicated sep at start)...
        #
        # Which can happen easily if something like the following is given.
        # >>> x = ['/', 'b']
        # >>> pp.sep.join(x)
        # '//b'
        if child_path.startswith(pp.sep * 2):
            child_path = child_path[1:]
        child_node = FakeInode(basename, child_path, value=value)
        parent_node.add(child_node)
        self._reverse_mapping[child_path] = child_node
        return child_node

    def _fetch_node(self, path, normalized=False):
        if not normalized:
            normed_path = self.normpath(path)
        else:
            normed_path = path
        try:
            return self._reverse_mapping[normed_path]
        except KeyError:
            raise exc.NotFound("Path '%s' not found" % path)

    def get(self, path, default=None):
        """Fetch the value of given path (and return default if not found)."""
        try:
            return self._get_item(self.normpath(path))
        except exc.NotFound:
            return default

    def _get_item(self, path, links=None):
        node = self._fetch_node(path, normalized=True)
        if 'target' in node.metadata:
            # Follow the link (and watch out for loops)...
            path = node.metadata['target']
            if links is None:
                links = []
            if path in links:
                raise ValueError("Recursive link following not"
                                 " allowed (loop %s detected)"
                                 % (links + [path]))
            else:
                links.append(path)
            return self._get_item(path, links=links)
        else:
            return self._copier(node.metadata['value'])

    def _up_to_root_selector(self, root_node, child_node):
        # Build the path from the child to the root and stop at the
        # root, and then form a path string...
        path_pieces = [child_node.item]
        for parent_node in child_node.path_iter(include_self=False):
            if parent_node is root_node:
                break
            path_pieces.append(parent_node.item)
        if len(path_pieces) > 1:
            path_pieces.reverse()
        return self.join(*path_pieces)

    @staticmethod
    def _metadata_path_selector(root_node, child_node):
        return child_node.metadata['path']

    def ls_r(self, path, absolute=False):
        """Return list of all children of the given path (recursively)."""
        node = self._fetch_node(path)
        if absolute:
            selector_func = self._metadata_path_selector
        else:
            selector_func = self._up_to_root_selector
        return [selector_func(node, child_node)
                for child_node in node.bfs_iter()]

    @removals.removed_kwarg('recursive', version="0.11", removal_version="2.0")
    def ls(self, path, recursive=False):
        """Return list of all children of the given path.

        NOTE(harlowja): if ``recursive`` is passed in as truthy then the
        absolute path is **always** returned (not the relative path). If
        ``recursive`` is left as the default or falsey then the
        relative path is **always** returned.

        This is documented in bug `1458114`_ and the existing behavior is
        being maintained, to get a recursive version that is absolute (or is
        not absolute) it is recommended to use the :py:meth:`.ls_r` method
        instead.

        .. deprecated:: 0.11

          In a future release the ``recursive`` keyword argument will
          be removed (so preferring and moving to the :py:meth:`.ls_r` should
          occur earlier rather than later).

        .. _1458114: https://bugs.launchpad.net/taskflow/+bug/1458114
        """
        node = self._fetch_node(path)
        if recursive:
            selector_func = self._metadata_path_selector
            child_node_it = node.bfs_iter()
        else:
            selector_func = self._up_to_root_selector
            child_node_it = iter(node)
        return [selector_func(node, child_node)
                for child_node in child_node_it]

    def clear(self):
        """Remove all nodes (except the root) from this filesystem."""
        self._reverse_mapping = {
            self.root_path: self._root,
        }
        for node in list(self._root.reverse_iter()):
            node.disassociate()

    def _iter_pieces(self, path, include_root=False):
        if path == self._root.item:
            # Check for this directly as the following doesn't work with
            # split correctly:
            #
            # >>> path = "/"
            # path.split(pp.sep)
            # ['', '']
            parts = []
        else:
            parts = path.split(pp.sep)[1:]
        if include_root:
            parts.insert(0, self._root.item)
        for piece in parts:
            yield piece

    def __delitem__(self, path):
        path = self.normpath(path)
        node = self._fetch_node(path, normalized=True)
        if node is self._root:
            raise ValueError("Can not delete '%s'" % self._root.item)
        child_gen = (child.metadata['path'] for child in node.bfs_iter())
        for path in itertools.chain([path], child_gen):
            self._reverse_mapping.pop(path, None)
        node.disassociate()

    @staticmethod
    def _stringify_node(node):
        if 'target' in node.metadata:
            return "%s (link to %s)" % (node.item, node.metadata['target'])
        else:
            return six.text_type(node.item)

    def pformat(self):
        """Pretty format this in-memory filesystem."""
        return self._root.pformat(stringify_node=self._stringify_node)

    def symlink(self, src_path, dest_path):
        """Link the destionation path to the source path."""
        dest_path = self.normpath(dest_path)
        src_path = self.normpath(src_path)
        try:
            dest_node = self._fetch_node(dest_path, normalized=True)
        except exc.NotFound:
            parent_path, basename = self.split(dest_path)
            parent_node = self._fetch_node(parent_path, normalized=True)
            dest_node = self._insert_child(parent_node, basename)
        dest_node.metadata['target'] = src_path

    def __getitem__(self, path):
        return self._get_item(self.normpath(path))

    def __setitem__(self, path, value):
        path = self.normpath(path)
        value = self._copier(value)
        try:
            node = self._fetch_node(path, normalized=True)
            node.metadata.update(value=value)
        except exc.NotFound:
            parent_path, basename = self.split(path)
            parent_node = self._fetch_node(parent_path, normalized=True)
            self._insert_child(parent_node, basename, value=value)


class MemoryBackend(path_based.PathBasedBackend):
    """A in-memory (non-persistent) backend.

    This backend writes logbooks, flow details, and atom details to a
    in-memory filesystem-like structure (rooted by the ``memory``
    instance variable).

    This backend does *not* provide true transactional semantics. It does
    guarantee that there will be no inter-thread race conditions when
    writing and reading by using a read/write locks.
    """

    #: Default path used when none is provided.
    DEFAULT_PATH = pp.sep

    def __init__(self, conf=None):
        super(MemoryBackend, self).__init__(conf)
        self.memory = FakeFilesystem(deep_copy=self._conf.get('deep_copy',
                                                              True))
        self.lock = fasteners.ReaderWriterLock()

    def get_connection(self):
        return Connection(self)

    def close(self):
        pass


class Connection(path_based.PathBasedConnection):
    def __init__(self, backend):
        super(Connection, self).__init__(backend)
        self.upgrade()

    @contextlib.contextmanager
    def _memory_lock(self, write=False):
        if write:
            lock = self.backend.lock.write_lock
        else:
            lock = self.backend.lock.read_lock
        with lock():
            try:
                yield
            except exc.TaskFlowException:
                raise
            except Exception:
                exc.raise_with_cause(exc.StorageFailure,
                                     "Storage backend internal error")

    def _join_path(self, *parts):
        return pp.join(*parts)

    def _get_item(self, path):
        with self._memory_lock():
            return self.backend.memory[path]

    def _set_item(self, path, value, transaction):
        self.backend.memory[path] = value

    def _del_tree(self, path, transaction):
        del self.backend.memory[path]

    def _get_children(self, path):
        with self._memory_lock():
            return self.backend.memory.ls(path)

    def _ensure_path(self, path):
        with self._memory_lock(write=True):
            self.backend.memory.ensure_path(path)

    def _create_link(self, src_path, dest_path, transaction):
        self.backend.memory.symlink(src_path, dest_path)

    @contextlib.contextmanager
    def _transaction(self):
        """This just wraps a global write-lock."""
        with self._memory_lock(write=True):
            yield

    def validate(self):
        pass
