content.py

                raise CourseCommitSHADoesNotExist(
                    _("Preview revision '%s' does not exist--"
                      "showing active course content instead."
                      % commit_sha))
            return False

        return True

    if participation is not None:
        if participation.preview_git_commit_sha:
            preview_sha = participation.preview_git_commit_sha

            if repo is not None:
                commit_sha_valid = is_commit_sha_valid(repo, preview_sha)
            else:
                with get_course_repo(course) as repo:
                    commit_sha_valid = is_commit_sha_valid(repo, preview_sha)

            if not commit_sha_valid:
                preview_sha = None

            if preview_sha is not None:
                sha = preview_sha

    return sha.encode()


def list_flow_ids(repo, commit_sha):
    # type: (Repo_ish, bytes) -> List[Text]
    flow_ids = []
    try:
        flows_tree = get_repo_blob(repo, "flows", commit_sha)
    except ObjectDoesNotExist:
        # That's OK--no flows yet.
        pass
    else:
        for entry in flows_tree.items():
            if entry.path.endswith(b".yml"):
                flow_ids.append(entry.path[:-4].decode("utf-8"))

    return sorted(flow_ids)

# vim: foldmethod=marker