"""

    A wrapper around the cvs tool that fetches repository

    information and generates compatible diffs.

    """

    def get_repository_info(self):

        if not check_install("cvs"):

            return None

        cvsroot_path = os.path.join("CVS", "Root")

        if not os.path.exists(cvsroot_path):

            return None

        fp = open(cvsroot_path, "r")

        repository_path = fp.read().strip()

        fp.close()

        i = repository_path.find("@")

        if i != -1:

            repository_path = repository_path[i + 1:]

        return RepositoryInfo(path=repository_path)

    def diff(self, files):

        """

        Performs a diff across all modified files in a CVS repository.

        """

        return self.do_diff(' '.join(files))

    def diff_between_revisions(self, revision_range):

        """

        Performs a diff between 2 revisions of a CVS repository.

        """

        rev_str = ''

        for rev in revision_range.split(":"):

            rev_str += "-r %s" % rev

        return self.do_diff(rev_str)

    def do_diff(self, params):

        # Diff returns "1" if differences were found.

        return execute('cvs -q diff -u %s' % params,

                       extra_ignore_errors=(1,))