namespaces

1 files changed, 80 insertions, 0 deletions

diff --git a/bsfs/namespace/namespace.py b/bsfs/namespace/namespace.py
new file mode 100644
index 0000000..8080f5d
--- /dev/null
+++ b/bsfs/namespace/namespace.py
@@ -0,0 +1,80 @@
+"""
+
+Part of the BlackStar filesystem (bsfs) module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# imports
+import typing
+
+# bsfs imports
+from bsfs.utils import URI, typename
+
+# exports
+__all__: typing.Sequence[str] = (
+    'ClosedNamespace',
+    'Namespace',
+    )
+
+
+## code ##
+
+class Namespace():
+    """A namespace consists of a common prefix that is used in a set of URIs.
+
+    Note that the prefix must include the separator between
+    path and fragment (typically a '#' or a '/').
+    """
+
+    # namespace prefix.
+    prefix: URI
+
+    def __init__(self, prefix: URI):
+        self.prefix = URI(prefix)
+
+    def __eq__(self, other: typing.Any) -> bool:
+        return isinstance(other, type(self)) and self.prefix == other.prefix
+
+    def __hash__(self) -> int:
+        return hash((type(self), self.prefix))
+
+    def __str__(self) -> str:
+        return f'{typename(self)}({self.prefix})'
+
+    def __repr__(self) -> str:
+        return f'{typename(self)}({self.prefix})'
+
+    def __getattr__(self, fragment: str) -> URI:
+        """Return prefix + fragment."""
+        return URI(self.prefix + fragment)
+
+    def __getitem__(self, fragment: str) -> URI:
+        """Alias for getattr(self, fragment)."""
+        return self.__getattr__(fragment)
+
+
+class ClosedNamespace(Namespace):
+    """Namespace that covers a restricted set of URIs."""
+
+    # set of permissible fragments.
+    fragments: typing.Set[str]
+
+    def __init__(self, prefix: URI, *args: str):
+        super().__init__(prefix)
+        self.fragments = set(args)
+
+    def __eq__(self, other: typing.Any) -> bool:
+        return super().__eq__(other) and self.fragments == other.fragments
+
+    def __hash__(self) -> int:
+        return hash((type(self), self.prefix, tuple(sorted(self.fragments))))
+
+    def __getattr__(self, fragment: str) -> URI:
+        """Return prefix + fragment.
+        Raises a KeyError if the fragment is not allowed in this namespace.
+        """
+        if fragment not in self.fragments:
+            raise KeyError('fragment')
+        return super().__getattr__(fragment)
+
+## EOF ##