node naming policy

1 files changed, 101 insertions, 0 deletions

diff --git a/bsie/lib/naming_policy.py b/bsie/lib/naming_policy.py
new file mode 100644
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+++ b/bsie/lib/naming_policy.py
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+"""
+
+Part of the bsie module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# standard imports
+import abc
+import os
+import typing
+
+# bsie imports
+from bsie.utils import bsfs, errors, ns
+from bsie.utils.node import Node
+
+# exports
+__all__: typing.Sequence[str] = (
+    'DefaultNamingPolicy',
+    )
+
+
+## code ##
+
+class NamingPolicy():
+    """Determine node uri's from node hints."""
+    def __call__(
+            self,
+            iterable: typing.Iterable[typing.Tuple[Node, bsfs.URI, typing.Any]],
+            ):
+        """Apply the policy on a triple iterator."""
+        return NamingPolicyIterator(self, iterable)
+
+    @abc.abstractmethod
+    def handle_node(self, node: Node) -> Node:
+        """Apply the policy on a node."""
+
+
+class NamingPolicyIterator():
+    """Iterates over triples, determines uris according to a *policy* as it goes."""
+
+    # source triple iterator.
+    _iterable: typing.Iterable[typing.Tuple[Node, bsfs.URI, typing.Any]]
+
+    # naming policy
+    _policy: NamingPolicy
+
+    def __init__(
+            self,
+            policy: NamingPolicy,
+            iterable: typing.Iterable[typing.Tuple[Node, bsfs.URI, typing.Any]],
+            ):
+        self._iterable = iterable
+        self._policy = policy
+
+    def __iter__(self):
+        for node, pred, value in self._iterable:
+            # handle subject
+            self._policy.handle_node(node)
+            # handle value
+            if isinstance(value, Node):
+                self._policy.handle_node(value)
+            # yield triple
+            yield node, pred, value
+
+
+class DefaultNamingPolicy(NamingPolicy):
+    """Compose URIs as <host/user/node_type#fragment>
+
+    What information is used as fragment depends on the node type.
+    Typically, the default is to use the "ucid" hint.
+    The fallback in all cases is to generate a random uuid.
+
+    Never changes previously assigned uris. Sets uris in-place.
+
+    """
+
+    def __init__(
+            self,
+            host: bsfs.URI,
+            user: str,
+            ):
+        self._prefix = bsfs.Namespace(os.path.join(host, user))
+        self._uuid = bsfs.uuid.UUID()
+
+    def handle_node(self, node: Node) -> Node:
+        if node.uri is not None:
+            return node
+        if node.node_type == ns.bsfs.File:
+            return self.name_file(node)
+        raise errors.ProgrammingError('no naming policy available for {node.node_type}')
+
+    def name_file(self, node: Node) -> Node:
+        """Set a bsfs:File node's uri fragment to its ucid."""
+        if 'ucid' in node.hints: # content id
+            fragment = node.hints['ucid']
+        else: # random name
+            fragment = self._uuid()
+        node.uri = (self._prefix + 'file')[fragment]
+        return node
+
+## EOF ##