From a1ea0f3bf3287d8ca5fe108061ae7be5a9a98401 Mon Sep 17 00:00:00 2001
From: Abhinav Sarkar <abhinav@abhinavsarkar.net>
Date: Fri, 5 Jul 2019 12:37:55 +0530
Subject: [PATCH] Changes AVL tree rendering to use visitor pattern

---
 .../net/abhinavsarkar/algorist/AVLTree.java   | 37 ++++++++---------
 .../algorist/AVLTreeGraphvizVisitor.java      | 41 +++++++++++++++++++
 2 files changed, 59 insertions(+), 19 deletions(-)
 create mode 100644 src/main/java/net/abhinavsarkar/algorist/AVLTreeGraphvizVisitor.java

diff --git a/src/main/java/net/abhinavsarkar/algorist/AVLTree.java b/src/main/java/net/abhinavsarkar/algorist/AVLTree.java
index 2021eb1..91e2077 100644
--- a/src/main/java/net/abhinavsarkar/algorist/AVLTree.java
+++ b/src/main/java/net/abhinavsarkar/algorist/AVLTree.java
@@ -1,16 +1,10 @@
 package net.abhinavsarkar.algorist;
 
-import guru.nidi.graphviz.engine.Format;
-import guru.nidi.graphviz.engine.Graphviz;
-import guru.nidi.graphviz.model.MutableGraph;
-import guru.nidi.graphviz.model.MutableNode;
-import java.io.File;
 import java.io.IOException;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
 import java.util.Optional;
 import java.util.Stack;
-import static guru.nidi.graphviz.model.Factory.*;
 
 public class AVLTree<K extends Comparable<K>,V> implements Iterable<AVLTree.Entry<K,V>>
 {
@@ -54,9 +48,9 @@ public class AVLTree<K extends Comparable<K>,V> implements Iterable<AVLTree.Entr
 
     public void renderToPNG(String fileName) throws IOException
     {
-        MutableGraph graph = mutGraph("AVLTree").setDirected(true);
-        this.root.addToGraph(graph);
-        Graphviz.fromGraph(graph).height(1000).render(Format.PNG).toFile(new File(fileName));
+        AVLTreeGraphvizVisitor visitor = new AVLTreeGraphvizVisitor("AVLTree");
+        this.root.accept(visitor);
+        visitor.renderToPNG(fileName);
     }
 
     @Override
@@ -77,9 +71,9 @@ public class AVLTree<K extends Comparable<K>,V> implements Iterable<AVLTree.Entr
         Optional<K> predecessor(K key);
         boolean isEmpty();
         StringBuilder toStringBuilder(int level);
-        Optional<String> addToGraph(MutableGraph graph);
         boolean checkIfBST();
         boolean checkIfAVLT();
+        Optional<ValueNode<K,V>> accept(Visitor visitor);
 
         default ValueNode<K,V> toValueNode() {
             if (this.isEmpty()) {
@@ -349,17 +343,16 @@ public class AVLTree<K extends Comparable<K>,V> implements Iterable<AVLTree.Entr
         }
 
         @Override
-        public Optional<String> addToGraph(MutableGraph graph)
+        public Optional<ValueNode<K,V>> accept(Visitor visitor)
         {
-            String name = getGraphNodeName();
-            MutableNode node = mutNode(name);
-            graph.add(node);
-            left.addToGraph(graph).ifPresent(n -> graph.add(node.addLink(mutNode(n))));
-            right.addToGraph(graph).ifPresent(n -> graph.add(node.addLink(mutNode(n))));
-            return Optional.of(name);
+            String name = this.getName();
+            visitor.visitNode(name);
+            this.left.accept(visitor).ifPresent(n -> visitor.visitLink(name, n.getName()));
+            this.right.accept(visitor).ifPresent(n -> visitor.visitLink(name, n.getName()));
+            return Optional.of(this);
         }
 
-        private String getGraphNodeName()
+        private String getName()
         {
             return this.height + ":" + this.key;
         }
@@ -459,7 +452,7 @@ public class AVLTree<K extends Comparable<K>,V> implements Iterable<AVLTree.Entr
         }
 
         @Override
-        public Optional<String> addToGraph(MutableGraph graph) {
+        public Optional<ValueNode<K, V>> accept(Visitor visitor) {
             return Optional.empty();
         }
     }
@@ -544,6 +537,12 @@ public class AVLTree<K extends Comparable<K>,V> implements Iterable<AVLTree.Entr
         }
     }
 
+    public interface Visitor
+    {
+        void visitNode(String nodeName);
+        void visitLink(String parentNodeName, String childNodeName);
+    }
+
     public static void main(String[] args) throws IOException
     {
         AVLTree<String, String> bst = new AVLTree<>(true);
diff --git a/src/main/java/net/abhinavsarkar/algorist/AVLTreeGraphvizVisitor.java b/src/main/java/net/abhinavsarkar/algorist/AVLTreeGraphvizVisitor.java
new file mode 100644
index 0000000..8ba2cbc
--- /dev/null
+++ b/src/main/java/net/abhinavsarkar/algorist/AVLTreeGraphvizVisitor.java
@@ -0,0 +1,41 @@
+package net.abhinavsarkar.algorist;
+
+import guru.nidi.graphviz.engine.Format;
+import guru.nidi.graphviz.engine.Graphviz;
+import static guru.nidi.graphviz.model.Factory.mutGraph;
+import static guru.nidi.graphviz.model.Factory.mutNode;
+import guru.nidi.graphviz.model.MutableGraph;
+import guru.nidi.graphviz.model.MutableNode;
+import java.io.File;
+import java.io.IOException;
+
+public class AVLTreeGraphvizVisitor implements AVLTree.Visitor
+{
+    private final MutableGraph graph;
+    private final AVLTree<String, MutableNode> index = new AVLTree<>(true);
+
+    public AVLTreeGraphvizVisitor(String graphName)
+    {
+        this.graph = mutGraph(graphName).setDirected(true);
+    }
+
+    @Override
+    public void visitNode(String nodeName)
+    {
+        MutableNode gNode = mutNode(nodeName);
+        graph.add(gNode);
+        index.insert(nodeName, gNode);
+    }
+
+    @Override
+    public void visitLink(String parentNodeName, String childNodeName)
+    {
+        index.get(parentNodeName)
+                .ifPresent(gNode -> graph.add(gNode.addLink(mutNode(childNodeName))));
+    }
+
+    public void renderToPNG(String fileName) throws IOException
+    {
+        Graphviz.fromGraph(graph).height(1000).render(Format.PNG).toFile(new File(fileName));
+    }
+}