1 files changed, 141 insertions, 0 deletions
diff --git a/bsfs/triple_store/sparql/utils.py b/bsfs/triple_store/sparql/utils.py
new file mode 100644
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+++ b/bsfs/triple_store/sparql/utils.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
+"""
+# standard imports
+import typing
+
+# external imports
+import rdflib
+
+# bsfs imports
+from bsfs.namespace import ns
+from bsfs.utils import typename
+
+# exports
+__all__: typing.Sequence[str] = (
+    'GenHopName',
+    'Query',
+    )
+
+
+## code ##
+
+class GenHopName():
+    """Generator that produces a new unique symbol name with each iteration."""
+
+    # Symbol name prefix.
+    prefix: str
+
+    # Current counter.
+    curr: int
+
+    def __init__(self, prefix: str = '?hop', start: int = 0):
+        self.prefix = prefix
+        self.curr = start - 1
+
+    def __next__(self):
+        """Generate and return the next unique name."""
+        self.curr += 1
+        return self.prefix + str(self.curr)
+
+
+class Query():
+    """Hold, manage, and complete partial Sparql queries."""
+
+    # root node type URI.
+    root_type: str
+
+    # root node variable name.
+    root_head: str
+
+    # (head, name) tuples (w/o root)
+    select: typing.Tuple[typing.Tuple[str, str], ...]
+
+    # where statements.
+    where: str
+
+    def __init__(
+            self,
+            root_type: str,
+            root_head: str = '?ent',
+            select: typing.Optional[typing.Iterable[typing.Tuple[str, str]]] = None,
+            where: typing.Optional[str] = None,
+            ):
+        # check arguments
+        if select is None:
+            select = []
+        if where is None:
+            where = ''
+        # set members
+        self.root_type = root_type
+        self.root_head = root_head
+        self.select = tuple(select) # tuple ensures presistent order
+        self.where = where.strip()
+
+    def __str__(self) -> str:
+        return self.query
+
+    def __repr__(self) -> str:
+        return f'{typename(self)}({self.root_type}, {self.root_head}, {self.select}, {self.where})'
+
+    def __eq__(self, other: typing.Any) -> bool:
+        return isinstance(other, type(self)) \
+           and self.root_type == other.root_type \
+           and self.root_head == other.root_head \
+           and self.select == other.select \
+           and self.where == other.where
+
+    def __hash__(self) -> int:
+        return hash((type(self), self.root_type, self.root_head, self.select, self.where))
+
+    def __add__(self, other: typing.Any) -> 'Query':
+        # check other's type
+        if not isinstance(other, type(self)):
+            return NotImplemented
+        # check query compatibility
+        if not self.root_type == other.root_type:
+            raise ValueError(other)
+        if not self.root_head == other.root_head:
+            raise ValueError(other)
+        # combine selections
+        select = self.select + other.select
+        # combine conditions
+        conds = []
+        if self.where != '':
+            conds.append(self.where)
+        if other.where != '':
+            conds.append(other.where)
+        where = ' . '.join(conds)
+        # return new query
+        return Query(
+            root_type=self.root_type,
+            root_head=self.root_head,
+            select=select,
+            where=where,
+            )
+
+    @property
+    def names(self) -> typing.Tuple[str, ...]:
+        """Return a tuple of selected variable names, excluding the root."""
+        return tuple(name for _, name in self.select)
+
+    @property
+    def query(self) -> str:
+        """Return an executable sparql query."""
+        select = ' '.join(f'({head} as ?{name})' for head, name in self.select)
+        return f'''
+            SELECT {self.root_head} {select}
+            WHERE {{
+                {self.root_head} <{ns.rdf.type}>/<{ns.rdfs.subClassOf}>* <{self.root_type}> .
+                {self.where}
+            }}
+            '''
+
+    def __call__(self, graph: rdflib.Graph) -> rdflib.query.Result:
+        """Execute the query on a *graph* and return the query result."""
+        return graph.query(self.query)
+
+## EOF ##