"""Extract information from the file system, such as filesize.
"""
# standard imports
import os
import typing

# bsie imports
from bsie.utils import bsfs, node, ns

# inner-module imports
from .. import base

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


## code ##

class Stat(base.Extractor):
    """Extract information from the file system."""

    CONTENT_READER = 'bsie.reader.stat.Stat'

    # mapping from predicate to handler function.
    _callmap: typing.Dict[bsfs.schema.Predicate, typing.Callable[[os.stat_result], typing.Any]]

    def __init__(self):
        super().__init__(bsfs.schema.from_string(base.SCHEMA_PREAMBLE + '''
            bse:filesize rdfs:subClassOf bsfs:Predicate ;
                rdfs:domain bsn:Entity ;
                rdfs:range xsd:integer ;
                rdfs:label "File size"^^xsd:string ;
                schema:description "File size of entity in some filesystem."^^xsd:string ;
                bsfs:unique "true"^^xsd:boolean .
            '''))
        self._callmap = {
            self.schema.predicate(ns.bse.filesize): self.__filesize,
            }

    def extract(
            self,
            subject: node.Node,
            content: os.stat_result,
            principals: typing.Iterable[bsfs.schema.Predicate],
            ) -> typing.Iterator[typing.Tuple[node.Node, bsfs.schema.Predicate, typing.Any]]:
        for pred in principals:
            # find callback
            clbk = self._callmap.get(pred)
            if clbk is None:
                continue
            # get value
            value = clbk(content)
            if value is None:
                continue
            # produce triple
            yield subject, pred, value

    def __filesize(self, content: os.stat_result) -> typing.Optional[int]:
        """Return the file size."""
        try:
            return content.st_size
        except Exception: # pylint: disable=broad-except # we explicitly want to catch everything
            # FIXME: some kind of error reporting (e.g. logging)
            return None

## EOF ##