1 files changed, 88 insertions, 0 deletions
diff --git a/bsie/reader/chain.py b/bsie/reader/chain.py
new file mode 100644
index 0000000..5e9e0d5
--- /dev/null
+++ b/bsie/reader/chain.py
@@ -0,0 +1,88 @@
+"""
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# standard imports
+import logging
+import typing
+
+# bsie imports
+from bsie.utils import bsfs, errors
+
+# inner-module imports
+from . import base
+from . import builder
+
+# exports
+__all__: typing.Sequence[str] = (
+    'ReaderChain',
+    )
+
+
+## code ##
+
+logger = logging.getLogger(__name__)
+
+# Content type.
+T_CONTENT = typing.TypeVar('T_CONTENT') # pylint: disable=invalid-name
+
+class ReaderChain(base.Reader, typing.Generic[T_CONTENT]):
+    """Read an image."""
+
+    # sub-readers for specific file formats.
+    _children: typing.Tuple[base.Reader, ...]
+
+    def __init__(
+            self,
+            subreader_names: typing.Iterable[str],
+            cfg: typing.Optional[typing.Any] = None,
+            ):
+        rbuild = builder.ReaderBuilder(cfg)
+        children = []
+        for name in subreader_names:
+            try:
+                # build sub-reader
+                children.append(rbuild.build(name))
+            except (ValueError,
+                    TypeError,
+                    errors.LoaderError,
+                    errors.BuilderError) as err:
+                # failed to build a child; skip and notify
+                logger.warning('failed to load reader: %s', err)
+
+        if len(children) == 0:
+            logger.warning('%s failed to load any sub-readers.', bsfs.typename(self))
+
+        # copy children to member
+        self._children = tuple(children)
+
+    def __str__(self) -> str:
+        substr = ', '.join(str(child) for child in self._children)
+        return f'{bsfs.typename(self)}({substr})'
+
+    def __repr__(self) -> str:
+        return f'{bsfs.typename(self)}({self._children})'
+
+    def __eq__(self, other: typing.Any) -> bool:
+        return super().__eq__(other) \
+           and self._children == other._children
+
+    def __hash__(self) -> int:
+        return hash((super().__hash__(), self._children))
+
+    def __call__(self, path: str) -> T_CONTENT:
+        raise_error = errors.UnsupportedFileFormatError
+        for child in self._children:
+            try:
+                return child(path)
+            except errors.UnsupportedFileFormatError:
+                pass
+            except errors.ReaderError:
+                # child cannot read the file, skip.
+                raise_error = errors.ReaderError # type: ignore [assignment] # mypy is confused
+
+        raise raise_error(path)
+
+## EOF ##