1 files changed, 343 insertions, 0 deletions
diff --git a/graph/src/labelled/single.rs b/graph/src/labelled/single.rs
new file mode 100644
index 0000000..bed65c1
--- /dev/null
+++ b/graph/src/labelled/single.rs
@@ -0,0 +1,343 @@
+//! This file implements a labelled graph that can index vertices by
+//! labels.
+//!
+//! Since we do not have to index edges by labels, the labels can be
+//! stored simply by adjacency maps.  This may save memory usage and
+//! improve performance, potentially.
+
+use super::*;
+
+use std::collections::{hash_map::Keys, HashMap as Map};
+
+use crate::builder::BuilderMut;
+
+/// The type of a node.
+#[derive(Debug, Clone, Default)]
+struct SLNode<T: GraphLabel> {
+    /// The edges are stored as an association from the target node
+    /// index to the label of the corresponding edge.
+    ///
+    /// An implication is that an edge can only have one label.
+    children: Map<usize, T>,
+    /// The label of this node.
+    label: T,
+}
+
+impl<T: GraphLabel> SLNode<T> {
+    fn new(children: Map<usize, T>, label: T) -> Self {
+        Self { children, label }
+    }
+
+    /// This function just adds an edge, blindly.
+    ///
+    /// # Safety
+    ///
+    /// Only use this after making sure that `target` refers to a
+    /// valid node, and there was no edge from this node to the node
+    /// pointed to by `target` previously.
+    unsafe fn add_edge(&mut self, target: usize, label: T) {
+        self.children.insert(target, label);
+    }
+}
+
+/// The type of labelled graphs implemented using adjacency maps.
+#[derive(Debug, Clone)]
+pub struct SLGraph<T: GraphLabel> {
+    nodes: Vec<SLNode<T>>,
+    label_index_map: Map<T, usize>,
+}
+
+impl<T: GraphLabel> Default for SLGraph<T> {
+    fn default() -> Self {
+        let nodes = Vec::new();
+        let label_index_map = Default::default();
+        Self {
+            nodes,
+            label_index_map,
+        }
+    }
+}
+
+impl<T: GraphLabel> Graph for SLGraph<T> {
+    type Iter<'a> = std::iter::Copied<Keys<'a, usize, T>>
+    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.keys().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()))
+        }
+    }
+
+    #[inline]
+    fn has_edge(&self, source: usize, target: usize) -> Result<bool, Error> {
+        let nodes_len = self.nodes.len();
+
+        let node = if let Some(node) = self.nodes.get(source) {
+            node
+        } else {
+            return Err(Error::IndexOutOfBounds(source, nodes_len));
+        };
+
+        if !self.has_node(target) {
+            return Err(Error::IndexOutOfBounds(target, nodes_len));
+        }
+
+        Ok(node.children.contains_key(&target))
+    }
+
+    fn replace_by_builder(&mut self, _builder: impl Builder<Result = Self>) {
+        // In case this is not clear enough, I deliberately avoid
+        // implementing this.
+        unimplemented!()
+    }
+}
+
+/// An iterator of edge labels.
+///
+/// This is used to avoid a box allocation.
+#[derive(Copy, Clone, Debug)]
+pub struct EdgeLabelIter<T: GraphLabel>(Option<T>);
+
+impl<T: GraphLabel> Iterator for EdgeLabelIter<T> {
+    type Item = T;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.0.take()
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.0.is_some() as usize;
+
+        (len, Some(len))
+    }
+}
+
+impl<T: GraphLabel> DoubleEndedIterator for EdgeLabelIter<T> {
+    #[inline]
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.0.take()
+    }
+}
+
+impl<T: GraphLabel> ExactSizeIterator for EdgeLabelIter<T> {
+    #[inline]
+    fn len(&self) -> usize {
+        // Thanks to Clippy for teaching me about coercing a boolean
+        // value to an integer.
+        self.0.is_some() as usize
+    }
+}
+
+impl<T: GraphLabel> LabelGraph<T> for SLGraph<T> {
+    // The following two types are not used, as we do not need to
+    // index edges by labels.
+    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> = EdgeLabelIter<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()))
+        }
+    }
+
+    #[inline]
+    fn edge_label(&self, source: usize, target: usize) -> Result<Self::EdgeLabelIter<'_>, Error> {
+        let nodes_len = self.nodes.len();
+
+        let node = if let Some(node) = self.nodes.get(source) {
+            node
+        } else {
+            return Err(Error::IndexOutOfBounds(source, nodes_len));
+        };
+
+        if !self.has_node(target) {
+            return Err(Error::IndexOutOfBounds(target, nodes_len));
+        }
+
+        Ok(EdgeLabelIter(node.children.get(&target).copied()))
+    }
+
+    fn find_children_with_label(
+        &self,
+        _node_id: usize,
+        _label: &T,
+    ) -> Result<<Self as LabelGraph<T>>::Iter<'_>, Error> {
+        unimplemented!()
+    }
+
+    fn labels_of(&self, _node_id: usize) -> Result<Self::LabelIter<'_>, Error> {
+        unimplemented!()
+    }
+
+    #[inline]
+    fn has_edge_label(&self, node_id: usize, label: &T, target: usize) -> Result<bool, Error> {
+        let nodes_len = self.nodes.len();
+
+        let node = if let Some(node) = self.nodes.get(node_id) {
+            node
+        } else {
+            return Err(Error::IndexOutOfBounds(node_id, nodes_len));
+        };
+
+        if !self.has_node(target) {
+            return Err(Error::IndexOutOfBounds(target, nodes_len));
+        }
+
+        Ok(node.children.get(&target) == Some(label))
+    }
+}
+
+/// The type of `builder_mut` builders for this type of graphs.
+#[derive(Debug)]
+pub struct SLGBuilderMut<'a, T: GraphLabel> {
+    graph: &'a mut SLGraph<T>,
+}
+
+impl<'a, T: GraphLabel> BuilderMut for SLGBuilderMut<'a, T> {
+    type Label = T;
+
+    type Graph = SLGraph<T>;
+
+    type ResultBuilder<'b> = SLGBuilderMut<'b, T>
+    where
+        T:'b;
+
+    fn from_graph_mut(graph: &mut Self::Graph) -> Self::ResultBuilder<'_> {
+        SLGBuilderMut { graph }
+    }
+
+    fn add_vertex(&mut self, label: T) -> Result<usize, Error> {
+        if let Some(old_node) = self.graph.label_index_map.get(&label) {
+            dbg!(label);
+            return Err(Error::DuplicatedNode(*old_node));
+        }
+
+        self.graph
+            .nodes
+            .push(SLNode::new(Default::default(), label));
+
+        let new = self.graph.nodes_len() - 1;
+
+        self.graph.label_index_map.insert(label, new);
+
+        Ok(new)
+    }
+
+    fn add_edge(&mut self, source: usize, target: usize, label: Self::Label) -> Result<(), Error> {
+        let graph = &mut self.graph;
+
+        let nodes_len = graph.nodes.len();
+
+        // NOTE: We check the validity of `target` first because we
+        // need to borrow graph mutably later, which would prevent us
+        // from borrowing graph immutably to check the validity of
+        // `target` then.
+        if !graph.has_node(target) {
+            return Err(Error::IndexOutOfBounds(target, nodes_len));
+        }
+
+        let node = if let Some(node) = graph.nodes.get_mut(source) {
+            node
+        } else {
+            return Err(Error::IndexOutOfBounds(source, nodes_len));
+        };
+
+        if node.children.get(&target).is_some() {
+            return Err(Error::DuplicatedEdge(source, target));
+        }
+
+        // We checked what we need to check, so this is safe.
+        unsafe {
+            node.add_edge(target, label);
+        }
+
+        Ok(())
+    }
+
+    fn remove_edge<F>(&mut self, source: usize, target: usize, predicate: F) -> Result<(), Error>
+    where
+        F: Fn(Self::Label) -> bool,
+    {
+        let graph = &mut self.graph;
+
+        let nodes_len = graph.nodes.len();
+
+        // NOTE: We check the validity of `target` first because we
+        // need to borrow graph mutably later, which would prevent us
+        // from borrowing graph immutably to check the validity of
+        // `target` then.
+        if !graph.has_node(target) {
+            return Err(Error::IndexOutOfBounds(target, nodes_len));
+        }
+
+        let node = if let Some(node) = graph.nodes.get_mut(source) {
+            node
+        } else {
+            return Err(Error::IndexOutOfBounds(source, nodes_len));
+        };
+
+        if let Some(child_label) = node.children.get(&target) {
+            // There is only one label, so we just check this label.
+            if predicate(*child_label) {
+                node.children.remove(&target);
+            }
+
+            Ok(())
+        } else {
+            Err(Error::DuplicatedEdge(source, target))
+        }
+    }
+}