1 files changed, 77 insertions, 0 deletions
diff --git a/bsie/extractor/builder.py b/bsie/extractor/builder.py
new file mode 100644
index 0000000..0fd3685
--- /dev/null
+++ b/bsie/extractor/builder.py
@@ -0,0 +1,77 @@
+"""
+
+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] = (
+    'ExtractorBuilder',
+    )
+
+
+## code ##
+
+class ExtractorBuilder():
+    """Build `bsie.base.Extractor instances.
+
+    It is permissible to build multiple instances of the same extractor
+    (typically with different arguments), hence the ExtractorBuilder
+    receives a list of build specifications. Each specification is
+    a dict with a single key (extractor's qualified name) and a dict
+    to be used as keyword arguments.
+    Example: [{'bsie.extractor.generic.path.Path': {}}, ]
+
+    """
+
+    # build specifications
+    _specs: typing.List[typing.Dict[str, typing.Dict[str, typing.Any]]]
+
+    def __init__(self, specs: typing.List[typing.Dict[str, typing.Dict[str, typing.Any]]]):
+        self._specs = specs
+
+    def __iter__(self) -> typing.Iterator[int]:
+        """Iterate over extractor specifications."""
+        return iter(range(len(self._specs)))
+
+    def build(self, index: int) -> base.Extractor:
+        """Return an instance of the n'th extractor (n=*index*)."""
+        # get build instructions
+        specs = self._specs[index]
+
+        # check specs structure. expecting[{name: {kwargs}}]
+        if not isinstance(specs, dict):
+            raise TypeError(f'expected a dict, found {bsfs.typename(specs)}')
+        if len(specs) != 1:
+            raise TypeError(f'expected a dict of length one, found {len(specs)}')
+
+        # get name and args from specs
+        name = next(iter(specs.keys()))
+        kwargs = specs[name]
+
+        # check kwargs structure
+        if not isinstance(kwargs, dict):
+            raise TypeError(f'expected a dict, found {bsfs.typename(kwargs)}')
+
+        # check name and get module/class components
+        module_name, class_name = unpack_qualified_name(name)
+
+        # import extractor class
+        cls = safe_load(module_name, class_name)
+
+        try: # build and return instance
+            return cls(**kwargs)
+
+        except Exception as err:
+            raise errors.BuilderError(f'failed to build extractor {name} due to {bsfs.typename(err)}: {err}') from err
+
+## EOF ##