class HistoryCache(AbstractCache):
    """ The history cache map SWHIDs of type `rev` to a list of all their parent
    commits (until root commit). """

    async def __aenter__(self):
        await super().__aenter__()
        await self.conn.execute(
            """
            create table if not exists history_graph (
                src text not null,
                dst text not null,
                unique(src, dst)
            )
            """
        )
        await self.conn.execute("create index index_history_graph on history_graph(src)")
        await self.conn.commit()
        return self

    async def get(self, swhid: SWHID) -> Optional[List[SWHID]]:
        cursor = await self.conn.execute(
            """
            with recursive
            dfs(node) AS (
                values(?)
                union all
                select history_graph.dst
                from history_graph
                join dfs on history_graph.src = dfs.node
            )
            -- Do not keep the root node since it is not an ancestor
            select * from dfs limit -1 offset 1
            """,
            (str(swhid), ),
        )
        cache = await cursor.fetchall()
        if not cache:
            return None

        history = []
        for parent in cache:
            parent = parent[0]
            try:
                history.append(parse_swhid(parent))
            except ValidationError:
                logging.warning(f"Cannot parse object from history cache: {parent}")
        return history

    async def set(self, history: str) -> None:
        history = history.strip()
        edges = [edge.split(" ") for edge in history.split("\n")]
        await self.conn.executemany(
            "insert or ignore into history_graph values (?, ?)", edges
        )
        await self.conn.commit()