"""

    A wrapper around the hg Mercurial tool that fetches repository

    information and generates compatible diffs.

    """

    def get_repository_info(self):

        data = execute('hg root')

        if data.startswith('abort:'):

            # hg aborted => no mercurial repository here.

            return None

        # Elsewhere, hg root output give us the repository path.

        # We save data here to use it as a fallback. See below

        local_data = data.strip()

        # We are going to search .hg/hgrc for the default path.

        file_name = os.path.join(local_data,'.hg', 'hgrc')

        if not  os.path.exists(file_name):

            return RepositoryInfo(path=local_data, base_path='/')

        f = open(file_name)

        data = f.read()

        f.close()

        m = re.search(r'^default\s+=\s+(.+)$', data, re.M)

        if not m:

            # Return the local path, if no default value is found.

            return RepositoryInfo(path=local_data, base_path='/')

        path = m.group(1).strip()

        return RepositoryInfo(path=path, base_path='')

    def diff(self, changenum, files):

        """

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

        """

        return execute('hg diff %s' % ' '.join(files))

    def diff_between_revisions(self, revision_range):

        """

        Performs a diff between 2 revisions of a Mercurial repository.

        """

        r1, r2 = revision_range.split(':')

        return execute('hg diff -r %s -r %s' % (r1, r2))