# -*- coding: utf-8 -*-
"""A resolver for Windows paths to file system specific formats."""

from __future__ import unicode_literals

import re

from dfvfs.lib import errors
from dfvfs.path import factory as path_spec_factory


class WindowsPathResolver(object):
  """Resolver object for Windows paths."""

  _PATH_SEPARATOR = '\\'
  _PATH_EXPANSION_VARIABLE = re.compile(r'^[%][^%]+[%]$')

  def __init__(self, file_system, mount_point, drive_letter='C'):
    """Initializes a Windows path helper.

    The mount point indicates a path specification where the Windows
    file system is mounted. This can either be a path specification
    into a storage media image or a directory accessible by the operating
    system.

    Args:
      file_system (FileSystem): a file system.
      mount_point (PathSpec): mount point path specification.
      drive_letter (Optional[str]): drive letter used by the file system.

    Raises:
      PathSpecError: if the mount point path specification is incorrect.
      ValueError: when file system or mount point is not set.
    """
    if not file_system or not mount_point:
      raise ValueError('Missing file system or mount point value.')

    if path_spec_factory.Factory.IsSystemLevelTypeIndicator(
        file_system.type_indicator):
      if not hasattr(mount_point, 'location'):
        raise errors.PathSpecError(
            'Mount point path specification missing location.')

    super(WindowsPathResolver, self).__init__()

    self._drive_letter = drive_letter
    self._environment_variables = {}
    self._file_system = file_system
    self._mount_point = mount_point

  # Windows paths:
  # Device path:                    \\.\PhysicalDrive0
  # Volume device path:             \\.\C:
  # Volume file system path:        \\.\C:\
  # Extended-length path:           \\?\C:\directory\file.txt
  # Extended-length UNC path:       \\?\UNC\server\share\directory\file.txt
  # Local 'absolute' path:          \directory\file.txt
  #                                 \directory\\file.txt
  # Local 'relative' path:          ..\directory\file.txt
  # Local 'relative' path:          .\directory\file.txt
  # Volume 'absolute' path:         C:\directory\file.txt
  # Volume 'relative' path:         C:directory\file.txt
  # UNC path:                       \\server\share\directory\file.txt
  # Path with environment variable: %SystemRoot%\file.txt
  #
  # Note Windows also allows paths like:
  # C:\..\directory\file.txt

  def _PathStripPrefix(self, path):
    """Strips the prefix from a path.

    Args:
      path (str): Windows path to strip the prefix from.

    Returns:
      str: path without the prefix or None if the path is not supported.
    """
    if path.startswith('\\\\.\\') or path.startswith('\\\\?\\'):
      if len(path) < 7 or path[5] != ':' or path[6] != self._PATH_SEPARATOR:
        # Cannot handle a non-volume path.
        return None

      path = path[7:]

    elif path.startswith('\\\\'):
      # Cannot handle an UNC path.
      return None

    elif len(path) >= 3 and path[1] == ':':
      # Check if the path is a Volume 'absolute' path.
      if path[2] != self._PATH_SEPARATOR:
        # Cannot handle a Volume 'relative' path.
        return None

      path = path[3:]

    elif path.startswith('\\'):
      path = path[1:]

    else:
      # Cannot handle a relative path.
      return None

    return path

  def _ResolvePath(self, path, expand_variables=True):
    """Resolves a Windows path in file system specific format.

    This function will check if the individual path segments exists within
    the file system. For this it will prefer the first case sensitive match
    above a case insensitive match. If no match was found None is returned.

    Args:
      path (str): Windows path to resolve.
      expand_variables (Optional[bool]): True if path variables should be
          expanded or not.

    Returns:
      tuple[str, PathSpec]: location and matching path specification or
          (None, None) if not available.
    """
    # Allow for paths that start with an environment variable e.g.
    # %SystemRoot%\file.txt
    if path.startswith('%'):
      path_segment, _, _ = path.partition(self._PATH_SEPARATOR)
      if not self._PATH_EXPANSION_VARIABLE.match(path_segment):
        path = None
    else:
      path = self._PathStripPrefix(path)

    if path is None:
      return None, None

    if path_spec_factory.Factory.IsSystemLevelTypeIndicator(
        self._file_system.type_indicator):
      file_entry = self._file_system.GetFileEntryByPathSpec(self._mount_point)
      expanded_path_segments = self._file_system.SplitPath(
          self._mount_point.location)
    else:
      file_entry = self._file_system.GetRootFileEntry()
      expanded_path_segments = []

    number_of_expanded_path_segments = 0

    search_path_segments = path.split(self._PATH_SEPARATOR)
    while search_path_segments:
      path_segment = search_path_segments.pop(0)
      if file_entry is None:
        return None, None

      # Ignore empty path segments or path segments containing a single dot.
      if not path_segment or path_segment == '.':
        continue

      if path_segment == '..':
        # Only allow to traverse back up to the mount point.
        if number_of_expanded_path_segments > 0:
          _ = expanded_path_segments.pop(0)
          number_of_expanded_path_segments -= 1
          file_entry = file_entry.GetParentFileEntry()
        continue

      if (expand_variables and
          self._PATH_EXPANSION_VARIABLE.match(path_segment)):
        path_segment = self._environment_variables.get(
            path_segment[1:-1].upper(), path_segment)

        if self._PATH_SEPARATOR in path_segment:
          # The expanded path segment itself can consist of multiple
          # path segments, hence we need to split it and prepend it to
          # the search path segments list.
          path_segments = path_segment.split(self._PATH_SEPARATOR)
          path_segments.extend(search_path_segments)
          search_path_segments = path_segments
          path_segment = search_path_segments.pop(0)

      sub_file_entry = file_entry.GetSubFileEntryByName(
          path_segment, case_sensitive=False)
      if sub_file_entry is None:
        return None, None

      expanded_path_segments.append(sub_file_entry.name)
      number_of_expanded_path_segments += 1
      file_entry = sub_file_entry

    location = self._file_system.JoinPath(expanded_path_segments)
    return location, file_entry.path_spec

  def GetWindowsPath(self, path_spec):
    """Returns the Windows path based on a resolved path specification.

    Args:
      path_spec (PathSpec): a path specification.

    Returns:
      str: corresponding Windows path or None if the Windows path could not
          be determined.

    Raises:
      PathSpecError: if the path specification is incorrect.
    """
    location = getattr(path_spec, 'location', None)
    if location is None:
      raise errors.PathSpecError('Path specification missing location.')

    if path_spec_factory.Factory.IsSystemLevelTypeIndicator(
        self._file_system.type_indicator):
      if not location.startswith(self._mount_point.location):
        raise errors.PathSpecError(
            'Path specification does not contain mount point.')
    else:
      if not hasattr(path_spec, 'parent'):
        raise errors.PathSpecError('Path specification missing parent.')

      if path_spec.parent != self._mount_point:
        raise errors.PathSpecError(
            'Path specification does not contain mount point.')

    path_segments = self._file_system.SplitPath(location)

    if path_spec_factory.Factory.IsSystemLevelTypeIndicator(
        self._file_system.type_indicator):
      mount_point_path_segments = self._file_system.SplitPath(
          self._mount_point.location)
      path_segments = path_segments[len(mount_point_path_segments):]

    return '{0:s}:\\{1:s}'.format(
        self._drive_letter, self._PATH_SEPARATOR.join(path_segments))

  def ResolvePath(self, path, expand_variables=True):
    """Resolves a Windows path in file system specific format.

    Args:
      path (str): Windows path to resolve.
      expand_variables (Optional[bool]): True if path variables should be
          expanded or not.

    Returns:
      PathSpec: path specification in file system specific format.
    """
    location, path_spec = self._ResolvePath(
        path, expand_variables=expand_variables)

    if not location or not path_spec:
      return None

    # Note that we don't want to set the keyword arguments when not used because
    # the path specification base class will check for unused keyword arguments
    # and raise.
    kwargs = path_spec_factory.Factory.GetProperties(path_spec)

    kwargs['location'] = location
    if not path_spec_factory.Factory.IsSystemLevelTypeIndicator(
        self._file_system.type_indicator):
      kwargs['parent'] = self._mount_point

    return path_spec_factory.Factory.NewPathSpec(
        self._file_system.type_indicator, **kwargs)

  def SetEnvironmentVariable(self, name, value):
    """Sets an environment variable in the Windows path helper.

    Args:
      name (str): name of the environment variable without enclosing
          %-characters, e.g. SystemRoot as in %SystemRoot%.
      value (str): value of the environment variable.
    """
    if isinstance(value, str):
      value = self._PathStripPrefix(value)

    if value is not None:
      self._environment_variables[name.upper()] = value
