1 files changed, 113 insertions, 0 deletions
diff --git a/bsfs/graph/graph.py b/bsfs/graph/graph.py
new file mode 100644
index 0000000..b7b9f1c
--- /dev/null
+++ b/bsfs/graph/graph.py
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+"""
+
+Part of the BlackStar filesystem (bsfs) module.
+A copy of the license is provided with the project.
+Author: Matthias Baumgartner, 2022
+"""
+# imports
+import os
+import typing
+
+# bsfs imports
+from bsfs.schema import Schema
+from bsfs.triple_store import TripleStoreBase
+from bsfs.utils import URI, typename
+
+# inner-module imports
+from . import nodes as _nodes
+
+# exports
+__all__: typing.Sequence[str] = (
+    'Graph',
+    )
+
+
+## code ##
+
+class Graph():
+    """The Graph class is
+
+    The Graph class provides a convenient interface to query and access a graph.
+    Since it logically builds on the concept of graphs it is easier to
+    navigate than raw triple stores. Naturally, it uses a triple store
+    as *backend*. It also controls actions via access permissions to a *user*.
+
+    """
+
+    # link to the triple storage backend.
+    _backend: TripleStoreBase
+
+    # user uri.
+    _user: URI
+
+    def __init__(self, backend: TripleStoreBase, user: URI):
+        self._backend = backend
+        self._user = user
+        # ensure Graph schema requirements
+        self.migrate(self._backend.schema)
+
+    def __hash__(self) -> int:
+        return hash((type(self), self._backend, self._user))
+
+    def __eq__(self, other) -> bool:
+        return isinstance(other, type(self)) \
+           and self._backend == other._backend \
+           and self._user == other._user
+
+    def __repr__(self) -> str:
+        return f'{typename(self)}(backend={repr(self._backend)}, user={self._user})'
+
+    def __str__(self) -> str:
+        return f'{typename(self)}({str(self._backend)}, {self._user})'
+
+    @property
+    def schema(self) -> Schema:
+        """Return the store's local schema."""
+        return self._backend.schema
+
+    def migrate(self, schema: Schema, append: bool = True) -> 'Graph':
+        """Migrate the current schema to a new *schema*.
+
+        Appends to the current schema by default; control this via *append*.
+        The `Graph` may add additional classes to the schema that are required for its interals.
+
+        """
+        # check args
+        if not isinstance(schema, Schema):
+            raise TypeError(schema)
+        # append to current schema
+        if append:
+            schema = schema + self._backend.schema
+        # add Graph schema requirements
+        with open(os.path.join(os.path.dirname(__file__), 'schema.nt'), mode='rt', encoding='UTF-8') as ifile:
+            schema = schema + Schema.from_string(ifile.read())
+        # migrate schema in backend
+        # FIXME: consult access controls!
+        self._backend.schema = schema
+        # return self
+        return self
+
+    def nodes(self, node_type: URI, guids: typing.Iterable[URI]) -> _nodes.Nodes:
+        """Return nodes *guids* of type *node_type* as a `bsfs.graph.Nodes` instance.
+
+        Note that the *guids* need not to exist (however, the *node_type* has
+        to be part of the schema). Inexistent guids will be created (using
+        *node_type*) once some data is assigned to them.
+
+        """
+        type_ = self.schema.node(node_type)
+        # NOTE: Nodes constructor materializes guids.
+        return _nodes.Nodes(self._backend, self._user, type_, guids)
+
+    def node(self, node_type: URI, guid: URI) -> _nodes.Nodes:
+        """Return node *guid* of type *node_type* as a `bsfs.graph.Nodes` instance.
+
+        Note that the *guids* need not to exist (however, the *node_type* has
+        to be part of the schema). An inexistent guid will be created (using
+        *node_type*) once some data is assigned to them.
+
+        """
+        type_ = self.schema.node(node_type)
+        return _nodes.Nodes(self._backend, self._user, type_, {guid})
+
+## EOF ##