feat: add level property to node

lib/graph/GraphTree.js

@@ -38,7 +38,12 @@ function DFS(node) {
   let linkArray = [];
   for(let child of node.children) {
     const { nodes, links } = DFS(child);
-
+    if(nodes.length === 1) child.maxLevel = child.minLevel = 1;
+    else {
+      const { maxLevel, minLevel } = calcuLevel(nodes.slice(1));
+      child.maxLevel = maxLevel + 1;
+      child.minLevel = minLevel + 1;
+    }
     nodeArray = nodeArray.concat(nodes);
 
     linkArray.push({
@@ -53,3 +58,23 @@ function DFS(node) {
     links: linkArray
   }
 }
+
+/**
+ * Calculate node level in the GraphTree
+ * 
+ * level is calculated from leaf to root
+ * @param {GraphNode} nodes 
+ */
+
+function calcuLevel(nodes) {
+  let maximum = 1;
+  let minimum = 999;
+  for(let node of nodes) {
+    if(node.maxLevel > maximum) maximum = node.maxLevel;
+    if(node.minLevel < minimum) minimum = node.minLevel;
+  }
+  return {
+    maxLevel: maximum,
+    minLevel: minimum
+  };
+}