Add toJS to return TreeNode of Tree (#115)

* Add toJS to return TreeNode of Tree

* linting

Sources/Document/CRDT/CRDTTree.swift

@@ -359,15 +359,15 @@ final class CRDTTreeNode: IndexTreeNode {
     }
 
     /**
-     * toJSON converts the given CRDTNode to JSON.
+     * `toTreeNode` converts the given CRDTTreeNode to TreeNode.
      */
-    var toJSON: TreeNode {
+    var toTreeNode: TreeNode {
         if self.isText {
             return TreeNode(type: self.type, value: self.value)
         }
 
         let children = self.children.compactMap {
-            $0.toJSON
+            $0.toTreeNode
         }
 
         let attrs = self.attrs?.toObject().mapValues { $0.value }
@@ -592,7 +592,7 @@ class CRDTTree: CRDTGCElement {
 
         var value: TreeChangeValue?
 
-        if let nodes = contents?.compactMap({ $0.toJSON }) {
+        if let nodes = contents?.compactMap({ $0.toTreeNode }) {
             value = .nodes(nodes)
         }
 
@@ -849,7 +849,14 @@ class CRDTTree: CRDTGCElement {
      * `toJSON` returns the JSON encoding of this tree.
      */
     func toJSON() -> String {
-        self.indexTree.root.toJSON.toJSONString
+        self.rootTreeNode.toJSONString
+    }
+
+    /**
+     * `rootTreeNode` returns the converted value of this tree to TreeNode.
+     */
+    var rootTreeNode: TreeNode {
+        self.indexTree.root.toTreeNode
     }
 
     /**

Sources/Document/Json/JSONTree.swift

@@ -420,6 +420,17 @@ public class JSONTree {
         return tree.toJSON()
     }
 
+    /**
+     * `getRootTreeNode` returns TreeNode of this tree.
+     */
+    public func getRootTreeNode() throws -> TreeNode? {
+        guard self.context != nil, let tree else {
+            throw YorkieError.unexpected(message: "it is not initialized yet")
+        }
+
+        return tree.rootTreeNode
+    }
+
     /**
      * `indexToPath` returns the path of the given index.
      */