"""

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

# bsie imports
from bsie.utils import bsfs, errors, safe_load, unpack_qualified_name

# inner-module imports
from . import base

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


## code ##

class ReaderBuilder():
    """Build `bsie.base.Reader` instances.

    Readers are defined via their qualified class name
    (e.g., bsie.reader.path.Path) and optional keyword
    arguments that are passed to the constructor via
    the *kwargs* argument (name as key, kwargs as value).
    The ReaderBuilder keeps a cache of previously built
    reader instances, as they are anyway built with
    identical keyword arguments.

    """

    # keyword arguments
    _kwargs: typing.Dict[str, typing.Dict[str, typing.Any]]

    # cached readers
    _cache: typing.Dict[str, base.Reader]

    def __init__(
            self,
            kwargs: typing.Optional[typing.Dict[str, typing.Dict[str, typing.Any]]] = None):
        if kwargs is None:
            kwargs = {}
        self._kwargs = kwargs
        self._cache = {}

    def build(self, name: str) -> base.Reader:
        """Return an instance for the qualified class name."""
        # return cached instance
        if name in self._cache:
            return self._cache[name]

        # check name and get module/class components
        module_name, class_name = unpack_qualified_name(name)

        # import reader class
        cls = safe_load(module_name, class_name)

        # get kwargs
        kwargs = self._kwargs.get(name, {})
        if not isinstance(kwargs, dict):
            raise TypeError(f'expected a kwargs dict, found {bsfs.typename(kwargs)}')

        try: # build, cache, and return instance
            obj = cls(**kwargs)
            # cache instance
            self._cache[name] = obj
            # return instance
            return obj

        except Exception as err:
            raise errors.BuilderError(f'failed to build reader {name} due to {bsfs.typename(err)}: {err}') from err

## EOF ##