content.py

def instantiate_flow_page(
        location: str, repo: Repo_ish, page_desc: FlowPageDesc, commit_sha: bytes
        ) -> PageBase:
    class_ = get_flow_page_class(repo, page_desc.type, commit_sha)

    from course.page.base import PageBase
    if not issubclass(class_, PageBase):
        raise ClassNotFoundError(f"'{page_desc.type}' is not a PageBase subclass")

    return class_(None, location, page_desc)

# }}}


class CourseCommitSHADoesNotExist(Exception):
    pass


def get_course_commit_sha(
        course: Course,
        participation: Participation | None,
        repo: Repo_ish | None = None,
        raise_on_nonexistent_preview_commit: bool | None = False
        ) -> bytes:
    sha = course.active_git_commit_sha

    def is_commit_sha_valid(repo: Repo_ish, commit_sha: str) -> bool:
        if isinstance(repo, SubdirRepoWrapper):
            repo = repo.repo
        try:
            repo[commit_sha.encode()]
        except KeyError:
            if raise_on_nonexistent_preview_commit:
                raise CourseCommitSHADoesNotExist(
                    _("Preview revision '{}' does not exist--"
                      "showing active course content instead.").format(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:
                preview_sha_valid = is_commit_sha_valid(repo, preview_sha)
            else:
                with get_course_repo(course) as repo:
                    preview_sha_valid = is_commit_sha_valid(repo, preview_sha)

            if preview_sha_valid:
                sha = preview_sha

    return sha.encode()


def list_flow_ids(repo: Repo_ish, commit_sha: bytes) -> list[str]:
    flow_ids = []
    try:
        flows_tree = get_repo_tree(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