from typing import Iterator, List, Optional, Sequence

from langchain.docstore.document import Document
from langchain.document_loaders.base import BaseLoader


class FaunaLoader(BaseLoader):
    """FaunaDB Loader.

    Attributes:
        query (str): The FQL query string to execute.
        page_content_field (str): The field that contains the content of each page.
        secret (str): The secret key for authenticating to FaunaDB.
        metadata_fields (Optional[Sequence[str]]):
            Optional list of field names to include in metadata.
    """

    def __init__(
        self,
        query: str,
        page_content_field: str,
        secret: str,
        metadata_fields: Optional[Sequence[str]] = None,
    ):
        self.query = query
        self.page_content_field = page_content_field
        self.secret = secret
        self.metadata_fields = metadata_fields

    def load(self) -> List[Document]:
        return list(self.lazy_load())

    def lazy_load(self) -> Iterator[Document]:
        try:
            from fauna import Page, fql
            from fauna.client import Client
            from fauna.encoding import QuerySuccess
        except ImportError:
            raise ImportError(
                "Could not import fauna python package. "
                "Please install it with `pip install fauna`."
            )
        # Create Fauna Client
        client = Client(secret=self.secret)
        # Run FQL Query
        response: QuerySuccess = client.query(fql(self.query))
        page: Page = response.data
        for result in page:
            if result is not None:
                document_dict = dict(result.items())
                page_content = ""
                for key, value in document_dict.items():
                    if key == self.page_content_field:
                        page_content = value
                document: Document = Document(
                    page_content=page_content,
                    metadata={"id": result.id, "ts": result.ts},
                )
                yield document
        if page.after is not None:
            yield Document(
                page_content="Next Page Exists",
                metadata={"after": page.after},
            )
