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Diffstat (limited to 'bsfs/graph/walk.py')
-rw-r--r-- | bsfs/graph/walk.py | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/bsfs/graph/walk.py b/bsfs/graph/walk.py new file mode 100644 index 0000000..1b1cfa0 --- /dev/null +++ b/bsfs/graph/walk.py @@ -0,0 +1,120 @@ +""" + +Part of the BlackStar filesystem (bsfs) module. +A copy of the license is provided with the project. +Author: Matthias Baumgartner, 2022 +""" +# imports +from collections import abc +import typing + +# bsfs imports +from bsfs import schema as bsc + +# inner-module imports +# NOTE: circular import! OK as long as only used for type annotations. +from . import nodes # pylint: disable=cyclic-import + +# exports +__all__: typing.Sequence[str] = ( + 'Walk', + ) + + +## code ## + +class Walk(abc.Hashable, abc.Callable): # type: ignore [misc] # invalid base class (Callable) + """Syntactic sugar for `Nodes` to build and act on predicate paths via members.""" + + # Link to Nodes instance. + _root: 'nodes.Nodes' + + # Current predicate path. + _path: typing.Tuple[bsc.Predicate, ...] + + def __init__( + self, + root: 'nodes.Nodes', + path: typing.Sequence[bsc.Predicate], + ): + self._root = root + self._path = tuple(path) + + @property + def tail(self): + """Return the node type at the end of the path.""" + return self._path[-1].range + + + ## comparison + + def __hash__(self) -> int: + """Return an integer hash that identifies the instance.""" + return hash((type(self), self._root, self._path)) + + def __eq__(self, other) -> bool: + """Compare against *other* backend.""" + return isinstance(other, type(self)) \ + and self._root == other._root \ + and self._path == other._path + + + ## representation + + def __repr__(self) -> str: + """Return a formal string representation.""" + path = ', '.join(pred.uri for pred in self._path) + return f'Walk({self._root.node_type.uri}, ({path}))' + + def __str__(self) -> str: + """Return an informal string representation.""" + path = ', '.join(pred.uri for pred in self._path) + return f'Walk(@{self._root.node_type.uri}: {path})' + + + ## walk + + @staticmethod + def step( + schema: bsc.Schema, + node: bsc.Node, + name: str, + ) -> typing.Tuple[bsc.Predicate]: + """Get an predicate at *node* whose fragment matches *name*.""" + predicates = tuple( + pred + for pred + in schema.predicates_at(node) + if pred.uri.get('fragment', None) == name + ) + if len(predicates) == 0: # no fragment found for name + raise ValueError(f'no available predicate matches {name}') # FIXME: Custom exception + if len(predicates) > 1: # ambiguous name + raise ValueError(f'{name} matches multiple predicates') # FIXME: Custom exception + # append predicate to walk + return predicates # type: ignore [return-value] # size is one + + def __getattr__(self, name: str) -> 'Walk': + """Alias for `Walk.step(name)`.""" + try: + return super().__getattr__(name) + except AttributeError: + pass + # get predicate + pred = self.step(self._root.schema, self.tail, name) + # append predicate to walk + return Walk(self._root, self._path + pred) + + + ## get paths ## + + def get(self, **kwargs) -> typing.Any: + """Alias for `Nodes.get(..)`.""" + return self._root.get(tuple(pred.uri for pred in self._path), **kwargs) + + def __call__(self, **kwargs) -> typing.Any: # pylint: disable=arguments-differ + """Alias for `Walk.get(...)`.""" + return self.get(**kwargs) + + +## EOF ## |