forest: clone correctly

Now the forest can detect if a node is packed or cloned, and correctly
clones a node in those circumstances.  But it still needs to be
tested.

2 files changed, 188 insertions, 29 deletions

diff --git a/forest/src/default.rs b/forest/src/default.rs
index 9295f1a..b96439f 100644
--- a/forest/src/default.rs
+++ b/forest/src/default.rs
@@ -24,6 +24,8 @@ pub enum Error {
     /// Encounter an invalid error in converting from an error of
     /// graphs.
     InvalidGraphError(GError),
+    /// Encounter an error when converting forest labels.
+    LabelConversion(ForestLabelError),
 }
 
 impl Display for Error {
@@ -35,6 +37,7 @@ impl Display for Error {
             Error::DuplicatedNode(n) => write!(f, "node {n} is duplicated"),
             Error::InvalidGraphError(ge) => write!(f, "invalid error: {ge}"),
             Error::NodeNoLabel(n) => write!(f, "node {n} has no labels, but it should have one"),
+            Error::LabelConversion(le) => write!(f, "fail to convert labels: {le}"),
         }
     }
 }
@@ -51,6 +54,12 @@ impl From<GError> for Error {
     }
 }
 
+impl From<ForestLabelError> for Error {
+    fn from(le: ForestLabelError) -> Self {
+        Self::LabelConversion(le)
+    }
+}
+
 /// A default implementation of forest.
 #[derive(Debug, Clone)]
 pub struct DefaultForest<T: GraphLabel> {
@@ -193,7 +202,7 @@ impl<T: GraphLabel> LabelGraph<T> for DefaultForest<T> {
     }
 }
 
-impl<T: GraphLabel> Forest<T> for DefaultForest<T> {
+impl<T: GraphLabel> Forest<T> for DefaultForest<ForestLabel<T>> {
     type Error = Error;
 
     fn root(&self) -> Option<usize> {
@@ -205,7 +214,7 @@ impl<T: GraphLabel> Forest<T> for DefaultForest<T> {
 
         let mut builder = PLGBuilderMut::from_graph_mut(&mut graph);
 
-        let root = Some(builder.add_vertex(label));
+        let root = Some(builder.add_vertex(ForestLabel::from(label)));
 
         Self { graph, root }
     }
@@ -299,12 +308,12 @@ impl<T: GraphLabel> Forest<T> for DefaultForest<T> {
 
         let nodes_len = fragment.nodes_len();
 
-        // If the fragment root has a duplicate label, the forest will
-        // not grow, so we use the label to find the adjoined node
-        // index.
-
-        // the nodes hava already been added to the forest, so it is
-        // safe to call unwrap.
+        /// If the fragment root has a duplicate label, the forest
+        /// will not grow, so we use the label to find the adjoined
+        /// node index.
+        ///
+        /// The nodes hava already been added to the forest, so it is
+        /// safe to call unwrap.
         macro_rules! conversion (
             ($node:expr) => {
                 {
@@ -360,20 +369,37 @@ impl<T: GraphLabel> Forest<T> for DefaultForest<T> {
         Ok(())
     }
 
-    fn clone_node<F>(&mut self, node_id: usize, clone_transform: F) -> Result<usize, Self::Error>
-    where
-        F: Fn(T) -> T,
-    {
-        let mut builder = PLGBuilderMut::from_graph_mut(&mut self.graph);
+    fn clone_node(&mut self, node_id: usize) -> Result<usize, Self::Error> {
+        let builder = PLGBuilderMut::from_graph_mut(&mut self.graph);
 
         let old_label = builder
             .vertex_label(node_id)?
             .ok_or(Error::NodeNoLabel(node_id))?;
 
-        let new_label = clone_transform(old_label);
+        if old_label.is_packed() {
+            return Err(ForestLabelError::ClonePack.into());
+        }
+
+        if old_label.is_cloned().is_some() {
+            let mut parents = self.parents_of(node_id)?;
+
+            // Make sure it only has one parent, which is the
+            // representative node.
+            assert_eq!(parents.len(), 1);
+
+            // We checked its length is 1, so it is safe to unwrap
+            // here.
+            return Ok(parents.next().unwrap().node());
+        }
+
+        let rep_label = old_label.pack()?;
+
+        let new_label = old_label.clone(self)?;
+
+        let mut builder = PLGBuilderMut::from_graph_mut(&mut self.graph);
 
         // Make a new node
-        let new_index = builder.add_vertex(new_label);
+        let new_index = builder.add_vertex(rep_label);
 
         // Re-direct parents to the new node.
         //
@@ -393,6 +419,10 @@ impl<T: GraphLabel> Forest<T> for DefaultForest<T> {
 
         builder.add_edge(new_index, node_id, old_label)?;
 
+        // Modify the label of the old node.
+
+        builder.set_label(node_id, new_label)?;
+
         Ok(new_index)
     }
 }
@@ -403,10 +433,10 @@ mod forest_test {
 
     macro_rules! leaf (
         ($label:expr, $type:tt) =>{
-            DefaultForest::<$type>::new_leaf($label)
+            DefaultForest::<ForestLabel<$type>>::new_leaf($label)
         };
         ($label:expr) => {
-            DefaultForest::<usize>::new_leaf($label)
+            DefaultForest::<ForestLabel<usize>>::new_leaf($label)
         }
     );
 
@@ -479,11 +509,9 @@ mod forest_test {
         // add a duplicate label
         forest.plant(3, leaf!(5), false)?;
 
-        let len = forest.nodes_len();
-
-        let clone_transform = |label| label + len;
+        let _len = forest.nodes_len();
 
-        forest.clone_node(5, clone_transform)?;
+        forest.clone_node(5)?;
 
         assert_eq!(forest.nodes_len(), 7);
 
diff --git a/forest/src/lib.rs b/forest/src/lib.rs
index 8c9b918..02c5fcd 100644
--- a/forest/src/lib.rs
+++ b/forest/src/lib.rs
@@ -13,13 +13,144 @@
 
 use graph::{error::Error as GError, GraphLabel, LabelGraph, ParentsGraph};
 
+/// An internal type that indicates the status of a node as either a
+/// packed, cloned, or plain node.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Default)]
+enum ForestLabelType {
+    Packed,
+    #[default]
+    Plain,
+    Cloned(usize),
+}
+
+impl core::fmt::Display for ForestLabelType {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            Self::Packed => write!(f, "packed"),
+            Self::Plain => write!(f, "plain"),
+            Self::Cloned(index) => write!(f, "the {index}-th clone"),
+        }
+    }
+}
+
+/// A type that encodes the properties demanded by a forest.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct ForestLabel<T: GraphLabel> {
+    label: T,
+    status: ForestLabelType,
+}
+
+impl<T: GraphLabel> core::fmt::Display for ForestLabel<T> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        writeln!(f, "label: {}, status: {}", self.label, self.status)
+    }
+}
+
+/// The type of erros for converting forest labels.
+#[non_exhaustive]
+#[derive(Debug, Copy, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub enum ForestLabelError {
+    /// Try to pack a cloned node.
+    PackClone,
+    /// Try to clone a packed node.
+    ClonePack,
+}
+
+impl core::fmt::Display for ForestLabelError {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            Self::PackClone => write!(f, "cannot pack a cloned node"),
+            Self::ClonePack => write!(f, "cannot clone a packed node"),
+        }
+    }
+}
+
+impl std::error::Error for ForestLabelError {}
+
+impl<T: GraphLabel> ForestLabel<T> {
+    /// Retrieve the label.
+    pub fn label(&self) -> T {
+        self.label
+    }
+
+    /// Return true if and only if this node is packed.
+    pub fn is_packed(&self) -> bool {
+        matches!(self.status, ForestLabelType::Packed)
+    }
+
+    /// Retrieve the optional clone index.
+    pub fn is_cloned(&self) -> Option<usize> {
+        match self.status {
+            ForestLabelType::Cloned(index) => Some(index),
+            _ => None,
+        }
+    }
+
+    /// Try to clone a node.
+    pub fn clone<F>(self, forest: &F) -> Result<Self, ForestLabelError>
+    where
+        F: Forest<T>,
+    {
+        if self.is_packed() {
+            Err(ForestLabelError::ClonePack)
+        } else {
+            let clone_index = if let Some(old_index) = self.is_cloned() {
+                let mut new_index: usize = old_index + 1;
+
+                let mut new_label = Self {
+                    status: ForestLabelType::Cloned(new_index),
+                    ..self
+                };
+
+                while forest.query_label(new_label).is_some() {
+                    new_index += 1;
+                    new_label = Self {
+                        status: ForestLabelType::Cloned(new_index),
+                        ..self
+                    };
+                }
+
+                new_index
+            } else {
+                0
+            };
+
+            Ok(Self {
+                status: ForestLabelType::Cloned(clone_index),
+                ..self
+            })
+        }
+    }
+
+    /// Try to pack a node.
+    pub fn pack(self) -> Result<Self, ForestLabelError> {
+        if self.is_cloned().is_some() {
+            Err(ForestLabelError::PackClone)
+        } else {
+            let new_label = Self {
+                status: ForestLabelType::Packed,
+                ..self
+            };
+
+            Ok(new_label)
+        }
+    }
+}
+
+impl<T: GraphLabel> From<T> for ForestLabel<T> {
+    fn from(label: T) -> Self {
+        let status = ForestLabelType::default();
+        Self { label, status }
+    }
+}
+
 /// The expected behaviours of a forest.
 ///
 /// Note that it requires only a subset of the functionalities of
 /// labelled graphs.
-pub trait Forest<T: GraphLabel>: ParentsGraph + LabelGraph<T> {
+pub trait Forest<T: GraphLabel>: ParentsGraph + LabelGraph<ForestLabel<T>> {
     /// The type of errors for operations on the forest.
-    type Error: std::error::Error + From<GError>;
+    type Error: std::error::Error + From<GError> + From<ForestLabelError>;
 
     /// Return the root of the forest.
     ///
@@ -44,13 +175,13 @@ pub trait Forest<T: GraphLabel>: ParentsGraph + LabelGraph<T> {
     /// Clone a node by making a new node and making all the nodes
     /// that previously pointed to the old node now point to the new
     /// node, and the new node points to the old node.  Return the
-    /// index of the new node.
+    /// index of the new node.  In addition, if the old node had
+    /// already been cloned, just return the index of its
+    /// representitave.
     ///
-    /// The label of the new node will be given by the label
-    /// transformer.
-    fn clone_node<F>(&mut self, node_id: usize, clone_transform: F) -> Result<usize, Self::Error>
-    where
-        F: Fn(T) -> T;
+    /// The labels of the representing node and of the cloned node
+    /// will be handled automatically.
+    fn clone_node(&mut self, node_id: usize) -> Result<usize, Self::Error>;
 }
 
 pub mod default;