"""The Constant extractor produces pre-specified triples.

Part of the bsie module.
A copy of the license is provided with the project.
Author: Matthias Baumgartner, 2022
"""
# imports
import typing

# inner-module imports
from bsie.base import extractor
from bsie.utils.bsfs import URI
from bsie.utils.node import Node

# exports
__all__: typing.Sequence[str] = (
    'Constant',
    )


## code ##

class Constant(extractor.Extractor):
    """Extract information from file's path."""

    CONTENT_READER = None

    def __init__(
            self,
            schema: str,
            tuples: typing.Iterable[typing.Tuple[URI, typing.Any]],
            ):
        self._schema = schema
        self._tuples = tuples
        # FIXME: use schema instance for predicate checking
        #self._tuples = [(pred, value) for pred, value in tuples if pred in schema]
        # FIXME: use schema instance for value checking

    def schema(self) -> str:
        return self._schema

    def extract(
            self,
            subject: Node,
            content: None,
            predicates: typing.Iterable[URI],
            ) -> typing.Iterator[typing.Tuple[Node, URI, typing.Any]]:
        for pred, value in self._tuples:
            if pred in predicates:
                yield subject, pred, value

## EOF ##