#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# Copyright 2011 Yesudeep Mangalapilly <yesudeep@gmail.com>
# Copyright 2012 Google, Inc.
# Copyright 2014 Thomas Amland <thomas.amland@gmail.com>
#
# 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.

"""
:module: watchdog.utils.dirsnapshot
:synopsis: Directory snapshots and comparison.
:author: yesudeep@google.com (Yesudeep Mangalapilly)

.. ADMONITION:: Where are the moved events? They "disappeared"

        This implementation does not take partition boundaries
        into consideration. It will only work when the directory
        tree is entirely on the same file system. More specifically,
        any part of the code that depends on inode numbers can
        break if partition boundaries are crossed. In these cases,
        the snapshot diff will represent file/directory movement as
        created and deleted events.

Classes
-------
.. autoclass:: DirectorySnapshot
   :members:
   :show-inheritance:

.. autoclass:: DirectorySnapshotDiff
   :members:
   :show-inheritance:

.. autoclass:: EmptyDirectorySnapshot
   :members:
   :show-inheritance:

"""

import errno
import os
from stat import S_ISDIR
from watchdog.utils import stat as default_stat
try:
    from os import scandir
except ImportError:
    from os import listdir as scandir


class DirectorySnapshotDiff(object):
    """
    Compares two directory snapshots and creates an object that represents
    the difference between the two snapshots.

    :param ref:
        The reference directory snapshot.
    :type ref:
        :class:`DirectorySnapshot`
    :param snapshot:
        The directory snapshot which will be compared
        with the reference snapshot.
    :type snapshot:
        :class:`DirectorySnapshot`
    :param ignore_device:
        A boolean indicating whether to ignore the device id or not.
        By default, a file may be uniquely identified by a combination of its first
        inode and its device id. The problem is that the device id may (or may not)
        change between system boots. This problem would cause the DirectorySnapshotDiff
        to think a file has been deleted and created again but it would be the
        exact same file.
        Set to True only if you are sure you will always use the same device.
    :type ignore_device:
        :class:`bool`
    """

    def __init__(self, ref, snapshot, ignore_device=False):
        created = snapshot.paths - ref.paths
        deleted = ref.paths - snapshot.paths

        if ignore_device:
            def get_inode(directory, full_path):
                return directory.inode(full_path)[0]
        else:
            def get_inode(directory, full_path):
                return directory.inode(full_path)

        # check that all unchanged paths have the same inode
        for path in ref.paths & snapshot.paths:
            if get_inode(ref, path) != get_inode(snapshot, path):
                created.add(path)
                deleted.add(path)

        # find moved paths
        moved = set()
        for path in set(deleted):
            inode = ref.inode(path)
            new_path = snapshot.path(inode)
            if new_path:
                # file is not deleted but moved
                deleted.remove(path)
                moved.add((path, new_path))

        for path in set(created):
            inode = snapshot.inode(path)
            old_path = ref.path(inode)
            if old_path:
                created.remove(path)
                moved.add((old_path, path))

        # find modified paths
        # first check paths that have not moved
        modified = set()
        for path in ref.paths & snapshot.paths:
            if get_inode(ref, path) == get_inode(snapshot, path):
                if ref.mtime(path) != snapshot.mtime(path) or ref.size(path) != snapshot.size(path):
                    modified.add(path)

        for (old_path, new_path) in moved:
            if ref.mtime(old_path) != snapshot.mtime(new_path) or ref.size(old_path) != snapshot.size(new_path):
                modified.add(old_path)

        self._dirs_created = [path for path in created if snapshot.isdir(path)]
        self._dirs_deleted = [path for path in deleted if ref.isdir(path)]
        self._dirs_modified = [path for path in modified if ref.isdir(path)]
        self._dirs_moved = [(frm, to) for (frm, to) in moved if ref.isdir(frm)]

        self._files_created = list(created - set(self._dirs_created))
        self._files_deleted = list(deleted - set(self._dirs_deleted))
        self._files_modified = list(modified - set(self._dirs_modified))
        self._files_moved = list(moved - set(self._dirs_moved))

    def __str__(self):
        return self.__repr__()

    def __repr__(self):
        fmt = (
            '<{0} files(created={1}, deleted={2}, modified={3}, moved={4}),'
            ' folders(created={5}, deleted={6}, modified={7}, moved={8})>'
        )
        return fmt.format(
            type(self).__name__,
            len(self._files_created),
            len(self._files_deleted),
            len(self._files_modified),
            len(self._files_moved),
            len(self._dirs_created),
            len(self._dirs_deleted),
            len(self._dirs_modified),
            len(self._dirs_moved)
        )

    @property
    def files_created(self):
        """List of files that were created."""
        return self._files_created

    @property
    def files_deleted(self):
        """List of files that were deleted."""
        return self._files_deleted

    @property
    def files_modified(self):
        """List of files that were modified."""
        return self._files_modified

    @property
    def files_moved(self):
        """
        List of files that were moved.

        Each event is a two-tuple the first item of which is the path
        that has been renamed to the second item in the tuple.
        """
        return self._files_moved

    @property
    def dirs_modified(self):
        """
        List of directories that were modified.
        """
        return self._dirs_modified

    @property
    def dirs_moved(self):
        """
        List of directories that were moved.

        Each event is a two-tuple the first item of which is the path
        that has been renamed to the second item in the tuple.
        """
        return self._dirs_moved

    @property
    def dirs_deleted(self):
        """
        List of directories that were deleted.
        """
        return self._dirs_deleted

    @property
    def dirs_created(self):
        """
        List of directories that were created.
        """
        return self._dirs_created


class DirectorySnapshot(object):
    """
    A snapshot of stat information of files in a directory.

    :param path:
        The directory path for which a snapshot should be taken.
    :type path:
        ``str``
    :param recursive:
        ``True`` if the entire directory tree should be included in the
        snapshot; ``False`` otherwise.
    :type recursive:
        ``bool``
    :param stat:
        Use custom stat function that returns a stat structure for path.
        Currently only st_dev, st_ino, st_mode and st_mtime are needed.

        A function taking a ``path`` as argument which will be called
        for every entry in the directory tree.
    :param listdir:
        Use custom listdir function. For details see ``os.scandir`` if available, else ``os.listdir``.
    """

    def __init__(self, path, recursive=True,
                 stat=default_stat,
                 listdir=scandir):
        self.recursive = recursive
        self.stat = stat
        self.listdir = listdir

        self._stat_info = {}
        self._inode_to_path = {}

        st = self.stat(path)
        self._stat_info[path] = st
        self._inode_to_path[(st.st_ino, st.st_dev)] = path

        for p, st in self.walk(path):
            i = (st.st_ino, st.st_dev)
            self._inode_to_path[i] = p
            self._stat_info[p] = st

    def walk(self, root):
        try:
            paths = [os.path.join(root, entry if isinstance(entry, str) else entry.name)
                     for entry in self.listdir(root)]
        except OSError as e:
            # Directory may have been deleted between finding it in the directory
            # list of its parent and trying to delete its contents. If this
            # happens we treat it as empty. Likewise if the directory was replaced
            # with a file of the same name (less likely, but possible).
            if e.errno in (errno.ENOENT, errno.ENOTDIR, errno.EINVAL):
                return
            else:
                raise

        entries = []
        for p in paths:
            try:
                entry = (p, self.stat(p))
                entries.append(entry)
                yield entry
            except OSError:
                continue

        if self.recursive:
            for path, st in entries:
                try:
                    if S_ISDIR(st.st_mode):
                        for entry in self.walk(path):
                            yield entry
                except (IOError, OSError) as e:
                    # IOError for Python 2
                    # OSError for Python 3
                    # (should be only PermissionError when dropping Python 2 support)
                    if e.errno != errno.EACCES:
                        raise

    @property
    def paths(self):
        """
        Set of file/directory paths in the snapshot.
        """
        return set(self._stat_info.keys())

    def path(self, id):
        """
        Returns path for id. None if id is unknown to this snapshot.
        """
        return self._inode_to_path.get(id)

    def inode(self, path):
        """ Returns an id for path. """
        st = self._stat_info[path]
        return (st.st_ino, st.st_dev)

    def isdir(self, path):
        return S_ISDIR(self._stat_info[path].st_mode)

    def mtime(self, path):
        return self._stat_info[path].st_mtime

    def size(self, path):
        return self._stat_info[path].st_size

    def stat_info(self, path):
        """
        Returns a stat information object for the specified path from
        the snapshot.

        Attached information is subject to change. Do not use unless
        you specify `stat` in constructor. Use :func:`inode`, :func:`mtime`,
        :func:`isdir` instead.

        :param path:
            The path for which stat information should be obtained
            from a snapshot.
        """
        return self._stat_info[path]

    def __sub__(self, previous_dirsnap):
        """Allow subtracting a DirectorySnapshot object instance from
        another.

        :returns:
            A :class:`DirectorySnapshotDiff` object.
        """
        return DirectorySnapshotDiff(previous_dirsnap, self)

    def __str__(self):
        return self.__repr__()

    def __repr__(self):
        return str(self._stat_info)


class EmptyDirectorySnapshot(object):
    """Class to implement an empty snapshot. This is used together with
    DirectorySnapshot and DirectorySnapshotDiff in order to get all the files/folders
    in the directory as created.
    """

    @staticmethod
    def path(_):
        """Mock up method to return the path of the received inode. As the snapshot
        is intended to be empty, it always returns None.

        :returns:
            None.
        """
        return None

    @property
    def paths(self):
        """Mock up method to return a set of file/directory paths in the snapshot. As
        the snapshot is intended to be empty, it always returns an empty set.

        :returns:
            An empty set.
        """
        return set()
