def _collapse_docs(
    docs: List[Document],
    combine_document_func: CombineDocsProtocol,
    **kwargs: Any,
) -> Document:
    result = combine_document_func(docs, **kwargs)
    combined_metadata = {k: str(v) for k, v in docs[0].metadata.items()}
    for doc in docs[1:]:
        for k, v in doc.metadata.items():
            if k in combined_metadata:
                combined_metadata[k] += f", {v}"
            else:
                combined_metadata[k] = str(v)
    return Document(page_content=result, metadata=combined_metadata)
async def _acollapse_docs(
    docs: List[Document],
    combine_document_func: AsyncCombineDocsProtocol,
    **kwargs: Any,
) -> Document:
    result = await combine_document_func(docs, **kwargs)
    combined_metadata = {k: str(v) for k, v in docs[0].metadata.items()}
    for doc in docs[1:]:
        for k, v in doc.metadata.items():
            if k in combined_metadata:
                combined_metadata[k] += f", {v}"
            else:
                combined_metadata[k] = str(v)
    return Document(page_content=result, metadata=combined_metadata)
[docs]class ReduceDocumentsChain(BaseCombineDocumentsChain):
    """Combine documents by recursively reducing them.
    This involves
    - combine_documents_chain
    - collapse_documents_chain
    `combine_documents_chain` is ALWAYS provided. This is final chain that is called.
    We pass all previous results to this chain, and the output of this chain is
    returned as a final result.
    `collapse_documents_chain` is used if the documents passed in are too many to all