import csv
from itertools import islice
from typing import Optional

from beancount.ingest import cache, importer  # type: ignore


INDEX_DATE = 0
INDEX_TRANSACTION_NUMBER = 1
INDEX_LABEL = 2
INDEX_DEBIT = 3
INDEX_CREDIT = 4
INDEX_DETAIL = 5


def is_valid_header(header: list[str]) -> bool:
    return (
        header[INDEX_DATE] == "Date"
        and header[INDEX_TRANSACTION_NUMBER] == "Numéro d'opération"
        and header[INDEX_LABEL] == "Libellé"
        and header[INDEX_DEBIT] == "Débit"
        and header[INDEX_CREDIT] == "Crédit"
        and header[INDEX_DETAIL] == "Détail"
    )


class CaisseDEpargneImporter(importer.ImporterProtocol):
    def identify(self, file: cache._FileMemo) -> bool:
        try:
            # NOTE: beancount.ingest.cache._FileMemo handles automatic encoding
            # detection
            lines: list[str] = file.head().splitlines()
            csv_reader = csv.reader(
                lines, delimiter=";", strict=True, quoting=csv.QUOTE_NONE
            )

            # header is actually on the 5th line, the previous ones contain
            # miscellaneous information
            header: Optional[list[str]] = next(islice(csv_reader, 4, None))

            if header is None:
                return False
            return is_valid_header(header)

        except:
            return False