def METHOD_NAME(self) -> dict[str, dict[str, dict[str, tuple[int, ...]]]]:
    # Assemble toc_fignumbers to resolve figure numbers on SingleHTML.
    # Merge all fignumbers to single fignumber.
    #
    # Note: current Sphinx has refid confliction in singlehtml mode.
    #       To avoid the problem, it replaces key of secnumbers to
    #       tuple of docname and refid.
    #
    #       There are related codes in inline_all_toctres() and
    #       HTMLTranslter#add_fignumber().
    new_fignumbers: dict[str, dict[str, tuple[int, ...]]] = {}
    # {'foo': {'figure': {'id2': (2,), 'id1': (1,)}}, 'bar': {'figure': {'id1': (3,)}}}
    for docname, fignumlist in self.env.toc_fignumbers.items():
        for figtype, fignums in fignumlist.items():
            alias = f"{docname}/{figtype}"
            new_fignumbers.setdefault(alias, {})
            for id, fignum in fignums.items():
                new_fignumbers[alias][id] = fignum
    return {self.config.root_doc: new_fignumbers}