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import errno
import os
import path


class MockFileSystem(object):
    def __init__(self, files={}):
        """Initializes a "mock" filesystem that can be used to completely
        stub out a filesystem.

        Args:
            files: a dict of filenames -> file contents. A file contents
                value of None is used to indicate that the file should
                not exist (even if standalone is False).
            standalone: If True, only the files listed in _files_ exist.
                If False, the object will pass through read calls to the
                underlying filesystem. Writes are never passed through.

        """
        self.files = files

    def exists(self, path):
        if path in self.files:
            return self.files[path] is not None
        return False

    def join(self, *comps):
        return '/'.join(comps)

    def maybe_make_directory(self, *path):
        # FIXME: Implement such that subsequent calls to isdir() work?
        pass

    def read_text_file(self, path):
        return self.read_binary_file(path)

    def read_binary_file(self, path):
        if path in self.files:
            if self.files[path] is None:
                raise IOError(errno.ENOENT, path, os.strerror(errno.ENOENT))
            return self.files[path]

    def write_text_file(self, path, contents):
        return self.write_binary_file(path, contents)

    def write_binary_file(self, path, contents):
        self.files[path] = contents