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graphs.py
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# Copyright 2025 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import collections
from typing import Dict, Generic, Hashable, Iterable, Iterator, Tuple, TypeVar
import bigframes.core.ordered_sets as sets
T = TypeVar("T", bound=Hashable)
class DiGraph(Generic[T]):
def __init__(self, nodes: Iterable[T], edges: Iterable[Tuple[T, T]]):
self._parents: Dict[T, sets.InsertionOrderedSet[T]] = collections.defaultdict(
sets.InsertionOrderedSet
)
self._children: Dict[T, sets.InsertionOrderedSet[T]] = collections.defaultdict(
sets.InsertionOrderedSet
)
self._sinks: sets.InsertionOrderedSet[T] = sets.InsertionOrderedSet()
for node in nodes:
self._children[node]
self._parents[node]
self._sinks.add(node)
for src, dst in edges:
assert src in self.nodes
assert dst in self.nodes
self._children[src].add(dst)
self._parents[dst].add(src)
# sinks have no children
if src in self._sinks:
self._sinks.remove(src)
@property
def nodes(self):
# should be the same set of ids as self._parents
return self._children.keys()
@property
def sinks(self) -> Iterable[T]:
return self._sinks
@property
def empty(self):
return len(self.nodes) == 0
def parents(self, node: T) -> Iterator[T]:
assert node in self._parents
yield from self._parents[node]
def children(self, node: T) -> Iterator[T]:
assert node in self._children
yield from self._children[node]
def remove_node(self, node: T) -> None:
for child in self._children[node]:
self._parents[child].remove(node)
for parent in self._parents[node]:
self._children[parent].remove(node)
if len(self._children[parent]) == 0:
self._sinks.add(parent)
del self._children[node]
del self._parents[node]
if node in self._sinks:
self._sinks.remove(node)