1 files changed, 273 insertions, 0 deletions
diff --git a/graph/src/labelled/binary.rs b/graph/src/labelled/binary.rs
new file mode 100644
index 0000000..439505d
--- /dev/null
+++ b/graph/src/labelled/binary.rs
@@ -0,0 +1,273 @@
+//! This file implements a labelled graph that can index vertices by
+//! labels and each node knows about its parents.
+
+use super::*;
+use crate::ParentsGraph;
+
+use std::collections::{HashMap as Map, HashSet as Set};
+
+use crate::builder::BuilderMut;
+
+/// A node has some children, some parents, and a label.
+#[derive(Debug, Clone)]
+struct PLNode<T: GraphLabel> {
+    children: Set<usize>,
+    // REVIEW: If performance for removing edges is a bottleneck, use
+    // a hash set here.
+    parents: Vec<usize>,
+    label: T,
+}
+
+impl<T: GraphLabel> PLNode<T> {
+    fn new(children: Set<usize>, parents: Vec<usize>, label: T) -> Self {
+        Self {
+            children,
+            parents,
+            label,
+        }
+    }
+}
+
+impl<T: GraphLabel + Default> Default for PLNode<T> {
+    #[inline]
+    fn default() -> Self {
+        let children = Default::default();
+        let parents = Default::default();
+        let label = Default::default();
+        Self {
+            children,
+            label,
+            parents,
+        }
+    }
+}
+
+/// A Parents-knowing, vertex-Labelled Graph.
+#[derive(Debug, Clone)]
+pub struct PLGraph<T: GraphLabel> {
+    nodes: Vec<PLNode<T>>,
+    label_index_map: Map<T, usize>,
+}
+
+impl<T: GraphLabel> Default for PLGraph<T> {
+    #[inline]
+    fn default() -> Self {
+        let nodes = Default::default();
+        let label_index_map = Default::default();
+        Self {
+            nodes,
+            label_index_map,
+        }
+    }
+}
+
+impl<T: GraphLabel> Graph for PLGraph<T> {
+    type Iter<'a> = std::iter::Copied<std::collections::hash_set::Iter<'a, usize>>
+    where
+        Self: 'a;
+
+    #[inline]
+    fn is_empty(&self) -> bool {
+        self.nodes.is_empty()
+    }
+
+    #[inline]
+    fn nodes_len(&self) -> usize {
+        self.nodes.len()
+    }
+
+    #[inline]
+    fn children_of(&self, node_id: usize) -> Result<Self::Iter<'_>, Error> {
+        if let Some(node) = self.nodes.get(node_id) {
+            Ok(node.children.iter().copied())
+        } else {
+            Err(Error::IndexOutOfBounds(node_id, self.nodes.len()))
+        }
+    }
+
+    #[inline]
+    fn degree(&self, node_id: usize) -> Result<usize, Error> {
+        if let Some(node) = self.nodes.get(node_id) {
+            Ok(node.children.len())
+        } else {
+            Err(Error::IndexOutOfBounds(node_id, self.nodes.len()))
+        }
+    }
+
+    #[inline]
+    fn is_empty_node(&self, node_id: usize) -> Result<bool, Error> {
+        if let Some(node) = self.nodes.get(node_id) {
+            Ok(node.children.is_empty())
+        } else {
+            Err(Error::IndexOutOfBounds(node_id, self.nodes.len()))
+        }
+    }
+
+    fn has_edge(&self, source: usize, target: usize) -> Result<bool, Error> {
+        if let Some(node) = self.nodes.get(source) {
+            if !self.has_node(target) {
+                return Err(Error::IndexOutOfBounds(target, self.nodes.len()));
+            }
+
+            Ok(node.children.contains(&target))
+        } else {
+            Err(Error::IndexOutOfBounds(source, self.nodes.len()))
+        }
+    }
+
+    fn replace_by_builder(&mut self, _builder: impl Builder<Result = Self>) {
+        unimplemented!("for later")
+    }
+
+    fn print_viz(&self, _filename: &str) -> Result<(), std::io::Error> {
+        todo!()
+    }
+}
+
+impl<T: GraphLabel> ParentsGraph for PLGraph<T> {
+    type Iter<'a> = std::iter::Copied<std::slice::Iter<'a, usize>>
+        where Self: 'a;
+
+    #[inline]
+    fn parents_of(&self, node_id: usize) -> Result<<Self as ParentsGraph>::Iter<'_>, Error> {
+        if let Some(node) = self.nodes.get(node_id) {
+            Ok(node.parents.iter().copied())
+        } else {
+            Err(Error::IndexOutOfBounds(node_id, self.nodes.len()))
+        }
+    }
+}
+
+impl<T: GraphLabel> LabelGraph<T> for PLGraph<T> {
+    type Iter<'a> = std::iter::Empty<usize>
+    where
+        Self: 'a;
+
+    type LabelIter<'a> = std::iter::Empty<(&'a T, <Self as LabelGraph<T>>::Iter<'a>)>
+    where
+        Self: 'a,
+        T: 'a;
+
+    type EdgeLabelIter<'a> = std::iter::Empty<T>
+    where
+        Self: 'a,
+        T: 'a;
+
+    #[inline]
+    fn query_label(&self, label: T) -> Option<usize> {
+        self.label_index_map.get(&label).copied()
+    }
+
+    #[inline]
+    fn vertex_label(&self, node_id: usize) -> Result<Option<T>, Error> {
+        if let Some(node) = self.nodes.get(node_id) {
+            Ok(Some(node.label))
+        } else {
+            Err(Error::IndexOutOfBounds(node_id, self.nodes.len()))
+        }
+    }
+
+    fn edge_label(&self, _source: usize, _target: usize) -> Result<Self::EdgeLabelIter<'_>, Error> {
+        unimplemented!("Edges have no labels")
+    }
+
+    fn find_children_with_label(
+        &self,
+        _node_id: usize,
+        _label: &T,
+    ) -> Result<<Self as LabelGraph<T>>::Iter<'_>, Error> {
+        unimplemented!("Edges have no labels")
+    }
+
+    fn labels_of(&self, _node_id: usize) -> Result<Self::LabelIter<'_>, Error> {
+        unimplemented!("Edges have no labels")
+    }
+
+    fn has_edge_label(&self, _node_id: usize, _label: &T, _target: usize) -> Result<bool, Error> {
+        unimplemented!("Edges have no labels")
+    }
+}
+
+/// A builder that modifies PLGraph in place.
+#[derive(Debug)]
+pub struct PLGBuilderMut<'a, T: GraphLabel> {
+    graph: &'a mut PLGraph<T>,
+}
+
+impl<'a, T: GraphLabel> BuilderMut for PLGBuilderMut<'a, T> {
+    type Label = T;
+
+    type Graph = PLGraph<T>;
+
+    type ResultBuilder<'b> = PLGBuilderMut<'b, T>
+    where
+        Self::Label: 'b;
+
+    fn from_graph_mut(graph: &mut Self::Graph) -> Self::ResultBuilder<'_> {
+        PLGBuilderMut { graph }
+    }
+
+    fn add_vertex(&mut self, label: Self::Label) -> usize {
+        if let Some(old) = self.graph.label_index_map.get(&label) {
+            *old
+        } else {
+            let new_node = PLNode::new(Default::default(), Default::default(), label);
+            self.graph.nodes.push(new_node);
+
+            let new_index = self.graph.nodes.len() - 1;
+
+            self.graph.label_index_map.insert(label, new_index);
+
+            new_index
+        }
+    }
+
+    fn add_edge(&mut self, source: usize, target: usize, _label: Self::Label) -> Result<(), Error> {
+        if self.graph.has_edge(source, target)? {
+            return Err(Error::DuplicatedEdge(source, target));
+        }
+
+        self.graph
+            .nodes
+            .get_mut(source)
+            .unwrap()
+            .children
+            .insert(target);
+
+        self.graph
+            .nodes
+            .get_mut(target)
+            .unwrap()
+            .parents
+            .push(source);
+
+        Ok(())
+    }
+
+    fn remove_edge<F>(&mut self, source: usize, target: usize, _predicate: F) -> Result<(), Error>
+    where
+        F: Fn(Self::Label) -> bool,
+    {
+        if !self.graph.has_edge(source, target)? {
+            return Ok(());
+        }
+
+        self.graph
+            .nodes
+            .get_mut(source)
+            .unwrap()
+            .children
+            .remove(&target);
+
+        self.graph
+            .nodes
+            .get_mut(target)
+            .unwrap()
+            .parents
+            .retain(|parent| *parent != source);
+
+        Ok(())
+    }
+}
+
+// TODO: tests