diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index d971a63..72e0842 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -2,6 +2,7 @@ import { TypeData, TypePoint } from '@idraw/types';
 import Board from '@idraw/board';
 import Renderer from './lib/renderer';
 import { Element } from './lib/element';
+import { Helper } from './lib/helper';
 
 type Options = {
   width: number;
@@ -22,6 +23,7 @@ class Core {
   private _opts: Options;
   private _renderer: Renderer;
   private _element: Element;
+  private _helper: Helper;
   private _hasInited: boolean = false; 
   private _mode: Mode = Mode.NULL;
 
@@ -34,12 +36,14 @@ class Core {
     this._board = new Board(mount, this._opts);
     this._renderer = new Renderer(this._board); 
     this._element = new Element(this._board.getContext());
+    this._helper = new Helper();
     this._initEvent();
     this._hasInited = true;
   }
 
   draw() {
-    this._renderer.render(this._data);
+    this._helper.updateConfig(this._data, { selectedUUID: this._selectedUUID });
+    this._renderer.render(this._data, this._helper.getConfig());
   }
 
   selectElement(index: number) {
diff --git a/packages/core/src/lib/helper.ts b/packages/core/src/lib/helper.ts
index ea90408..ad45fa4 100644
--- a/packages/core/src/lib/helper.ts
+++ b/packages/core/src/lib/helper.ts
@@ -3,20 +3,39 @@ import {
   TypeHelper,
   TypeHelperConfig,
   TypeHelperCreateOpts,
+  TypeElement,
   TypeElemDesc
 } from '@idraw/types';
 
 export class Helper implements TypeHelper {
 
-  constructor() {}
+  private _config: TypeHelperConfig;
 
-  createConfig<T extends keyof TypeElemDesc>(
-    data: TypeData,
-    opts: TypeHelperCreateOpts ): TypeHelperConfig<T> {
-    const config = {
-      elementMap: {}
+  constructor() {
+    this._config = {
+      elementIndexMap: {},
     }
-    
-    return config
-  } 
+  }
+
+  updateConfig (
+    data: TypeData,
+    opts: TypeHelperCreateOpts ) {
+    this._updateElementIndex(data);
+  }
+
+  getConfig() {
+    // TODO 
+    return JSON.parse(JSON.stringify(this._config));
+  }
+
+  private _updateElementIndex(data: TypeData) {
+    this._config.elementIndexMap = {};
+    data.elements.forEach((elem: TypeElement<keyof TypeElemDesc>, i) => {
+      this._config.elementIndexMap[elem.uuid] = i;
+    });
+  }
+
+  // private _updateSelectedElementWrapper() {
+
+  // }
 }
\ No newline at end of file
diff --git a/packages/core/src/lib/renderer.ts b/packages/core/src/lib/renderer.ts
index 535417e..647bdb3 100644
--- a/packages/core/src/lib/renderer.ts
+++ b/packages/core/src/lib/renderer.ts
@@ -1,4 +1,4 @@
-import { TypeContext, TypeData } from '@idraw/types';
+import { TypeContext, TypeData, TypeHelperConfig } from '@idraw/types';
 import { drawContext } from './draw';
 import Board from '@idraw/board';
  
@@ -13,7 +13,7 @@ export default class Renderer {
     this._ctx = this._board.getContext();
   }
 
-  render(data: TypeData) {
+  render(data: TypeData, config?: TypeHelperConfig) {
     this._data = data;
     drawContext(this._ctx, this._data);
     this._board.draw();
diff --git a/packages/types/src/lib/helper.ts b/packages/types/src/lib/helper.ts
index d092f7c..312c9e1 100644
--- a/packages/types/src/lib/helper.ts
+++ b/packages/types/src/lib/helper.ts
@@ -1,21 +1,33 @@
 import { TypeData } from './data';
-import { TypeElement, TypeElemDesc } from './element';
+import { TypePoint } from './board';
 
 // type test = {[uuid string]: TypeElement}
 
-type TypeHelperConfig<T extends keyof TypeElemDesc> = {
-  elementMap: {[key: string]: TypeElement<T>}
+type TypeHelperConfig = {
+  elementIndexMap: {[key: string]: Number},
+  selectedElementWrapper?: {
+    size: number;
+    topLeft: TypePoint,
+    top: TypePoint,
+    topRight: TypePoint,
+    right: TypePoint,
+    bottomRight: TypePoint,
+    bottom: TypePoint,
+    bottomLeft: TypePoint,
+    left: TypePoint,
+  }
 }
 
 type TypeHelperCreateOpts = {
-  selectedIndex: number
+  selectedUUID?: string | null,
 }
 
 interface TypeHelper {
-  createConfig<T extends keyof TypeElemDesc>(
+  updateConfig(
     data: TypeData,
     opts: TypeHelperCreateOpts
-  ): TypeHelperConfig<T>;
+  ): void;
+  getConfig(): TypeHelperConfig;
 }
 
 export {