src/Components/ElementsSidebar/ElementsSidebar.test.tsx

@@ -12,8 +12,8 @@ describe.concurrent('Elements sidebar', () => {
       isHistoryOpen={false}
       SelectedContainer={null}
       onPropertyChange={() => {}}
-      selectContainer={() => {}}
+      SelectContainer={() => {}}
-      deleteContainer={() => {}}
+      DeleteContainer={() => {}}
     />);
 
     expect(screen.getByText(/Elements/i));
@@ -40,8 +40,8 @@ describe.concurrent('Elements sidebar', () => {
       isHistoryOpen={false}
       SelectedContainer={null}
       onPropertyChange={() => {}}
-      selectContainer={() => {}}
+      SelectContainer={() => {}}
-      deleteContainer={() => {}}
+      DeleteContainer={() => {}}
     />);
 
     expect(screen.getByText(/Elements/i));
@@ -70,8 +70,8 @@ describe.concurrent('Elements sidebar', () => {
       isHistoryOpen={false}
       SelectedContainer={MainContainer}
       onPropertyChange={() => {}}
-      selectContainer={() => {}}
+      SelectContainer={() => {}}
-      deleteContainer={() => {}}
+      DeleteContainer={() => {}}
     />);
 
     expect(screen.getByText(/Elements/i));
@@ -155,8 +155,8 @@ describe.concurrent('Elements sidebar', () => {
       isHistoryOpen={false}
       SelectedContainer={MainContainer}
       onPropertyChange={() => {}}
-      selectContainer={() => {}}
+      SelectContainer={() => {}}
-      deleteContainer={() => {}}
+      DeleteContainer={() => {}}
     />);
 
     expect(screen.getByText(/Elements/i));
@@ -208,8 +208,8 @@ describe.concurrent('Elements sidebar', () => {
       isHistoryOpen={false}
       SelectedContainer={SelectedContainer}
       onPropertyChange={() => {}}
-      selectContainer={selectContainer}
+      SelectContainer={selectContainer}
-      deleteContainer={() => {}}
+      DeleteContainer={() => {}}
     />);
 
     expect(screen.getByText(/Elements/i));
@@ -230,8 +230,8 @@ describe.concurrent('Elements sidebar', () => {
       isHistoryOpen={false}
       SelectedContainer={SelectedContainer}
       onPropertyChange={() => {}}
-      selectContainer={selectContainer}
+      SelectContainer={selectContainer}
-      deleteContainer={() => {}}
+      DeleteContainer={() => {}}
     />);
 
     expect((propertyId as HTMLInputElement).value === 'main').toBeFalsy();

src/Components/ElementsSidebar/ElementsSidebar.tsx

@@ -2,7 +2,7 @@ import * as React from 'react';
 import { motion } from 'framer-motion';
 import { Properties } from '../Properties/Properties';
 import { IContainerModel } from '../../Interfaces/ContainerModel';
-import { getDepth, MakeIterator } from '../../utils/itertools';
+import { findContainerById, getDepth, MakeIterator } from '../../utils/itertools';
 import { Menu } from '../Menu/Menu';
 import { MenuItem } from '../Menu/MenuItem';
 
@@ -12,8 +12,9 @@ interface IElementsSidebarProps {
   isHistoryOpen: boolean
   SelectedContainer: IContainerModel | null
   onPropertyChange: (key: string, value: string) => void
-  selectContainer: (container: IContainerModel) => void
+  SelectContainer: (container: IContainerModel) => void
-  deleteContainer: (containerid: string) => void
+  DeleteContainer: (containerid: string) => void
+  AddContainer: (index: number, type: string, parent: string) => void
 }
 
 interface Point {
@@ -84,6 +85,97 @@ export class ElementsSidebar extends React.PureComponent<IElementsSidebarProps>
     });
   }
 
+  public handleDragOver(event: React.DragEvent): void {
+    event.preventDefault();
+    const target: HTMLButtonElement = event.target as HTMLButtonElement;
+    const rect = target.getBoundingClientRect();
+    const y = event.clientY - rect.top; // y position within the element.
+
+    if (this.props.MainContainer === null) {
+      throw new Error('[handleOnDrop] Tried to drop into the tree without a required MainContainer!');
+    }
+
+    if (target.id === this.props.MainContainer.properties.id) {
+      target.classList.add('border-8');
+      target.classList.remove('border-t-8');
+      target.classList.remove('border-b-8');
+      return;
+    }
+
+    if (y < 12) {
+      target.classList.add('border-t-8');
+      target.classList.remove('border-b-8');
+      target.classList.remove('border-8');
+    } else if (y < 24) {
+      target.classList.add('border-8');
+      target.classList.remove('border-t-8');
+      target.classList.remove('border-b-8');
+    } else {
+      target.classList.add('border-b-8');
+      target.classList.remove('border-8');
+      target.classList.remove('border-t-8');
+    }
+  }
+
+  public handleOnDrop(event: React.DragEvent): void {
+    event.preventDefault();
+    const type = event.dataTransfer.getData('type');
+    const target: HTMLButtonElement = event.target as HTMLButtonElement;
+    removeBorderClasses(target);
+
+    if (this.props.MainContainer === null) {
+      throw new Error('[handleOnDrop] Tried to drop into the tree without a required MainContainer!');
+    }
+
+    const targetContainer: IContainerModel | undefined = findContainerById(
+      this.props.MainContainer,
+      target.id
+    );
+
+    if (targetContainer === undefined) {
+      throw new Error('[handleOnDrop] Tried to drop onto a unknown container!');
+    }
+
+    if (targetContainer === this.props.MainContainer) {
+      // if the container is the root, only add type as child
+      this.props.AddContainer(
+        targetContainer.children.length,
+        type,
+        targetContainer.properties.id);
+      return;
+    }
+
+    if (targetContainer.parent === null ||
+      targetContainer.parent === undefined) {
+      throw new Error('[handleDrop] Tried to drop into a child container without a parent!');
+    }
+
+    const rect = target.getBoundingClientRect();
+    const y = event.clientY - rect.top; // y position within the element.
+
+    // locate the hitboxes
+    if (y < 12) {
+      const index = targetContainer.parent.children.indexOf(targetContainer);
+      this.props.AddContainer(
+        index,
+        type,
+        targetContainer.parent.properties.id
+      );
+    } else if (y < 24) {
+      this.props.AddContainer(
+        targetContainer.children.length,
+        type,
+        targetContainer.properties.id);
+    } else {
+      const index = targetContainer.parent.children.indexOf(targetContainer);
+      this.props.AddContainer(
+        index + 1,
+        type,
+        targetContainer.parent.properties.id
+      );
+    }
+  }
+
   public iterateChilds(handleContainer: (container: IContainerModel) => void): React.ReactNode {
     if (this.props.MainContainer == null) {
       return null;
@@ -111,7 +203,7 @@ export class ElementsSidebar extends React.PureComponent<IElementsSidebarProps>
       const selectedClass: string = this.props.SelectedContainer !== undefined &&
         this.props.SelectedContainer !== null &&
         this.props.SelectedContainer.properties.id === container.properties.id
-        ? 'border-l-4 border-blue-500 bg-slate-400/60 hover:bg-slate-400'
+        ? 'border-l-4 bg-slate-400/60 hover:bg-slate-400'
         : 'bg-slate-300/60 hover:bg-slate-300';
       containerRows.push(
         <motion.button
@@ -123,12 +215,16 @@ export class ElementsSidebar extends React.PureComponent<IElementsSidebarProps>
             duration: 0.150
           }}
           className={
-            `w-full elements-sidebar-row whitespace-pre
+            `w-full border-blue-500 elements-sidebar-row whitespace-pre
           text-left text-sm font-medium transition-all ${selectedClass}`
           }
           id={key}
           key={key}
-          onClick={() => this.props.selectContainer(container)}>
+          onDrop={(event) => this.handleOnDrop(event)}
+          onDragOver={(event) => this.handleDragOver(event)}
+          onDragLeave={(event) => handleDragLeave(event)}
+          onClick={() => this.props.SelectContainer(container)}
+        >
           { text }
         </motion.button>
       );
@@ -148,10 +244,21 @@ export class ElementsSidebar extends React.PureComponent<IElementsSidebarProps>
           y={this.state.contextMenuPosition.y}
           isOpen={this.state.isContextMenuOpen}
         >
-          <MenuItem className='contextmenu-item' text='Delete' onClick={() => this.props.deleteContainer(this.state.onClickContainerId)} />
+          <MenuItem className='contextmenu-item' text='Delete' onClick={() => this.props.DeleteContainer(this.state.onClickContainerId)} />
         </Menu>
         <Properties properties={this.props.SelectedContainer?.properties} onChange={this.props.onPropertyChange}></Properties>
       </div>
     );
   }
 }
+
+function removeBorderClasses(target: HTMLButtonElement): void {
+  target.classList.remove('border-t-8');
+  target.classList.remove('border-8');
+  target.classList.remove('border-b-8');
+}
+
+function handleDragLeave(event: React.DragEvent): void {
+  const target: HTMLButtonElement = event.target as HTMLButtonElement;
+  removeBorderClasses(target);
+}

src/Components/Sidebar/Sidebar.tsx

@@ -8,14 +8,21 @@ interface ISidebarProps {
   buttonOnClick: (type: string) => void
 }
 
+function handleDragStart(event: React.DragEvent<HTMLButtonElement>): void {
+  event.dataTransfer.setData('type', (event.target as HTMLButtonElement).id);
+}
+
 export default class Sidebar extends React.PureComponent<ISidebarProps> {
   public render(): JSX.Element {
     const listElements = this.props.componentOptions.map(componentOption =>
       <button
         className='justify-center transition-all sidebar-component'
         key={componentOption.Type}
+        id={componentOption.Type}
         title={componentOption.Type}
         onClick={() => this.props.buttonOnClick(componentOption.Type)}
+        draggable={true}
+        onDragStart={(event) => handleDragStart(event)}
       >
         {truncateString(componentOption.Type, 5)}
       </button>

src/Components/UI/UI.tsx

@@ -17,7 +17,8 @@ interface IUIProps {
   SelectContainer: (container: ContainerModel) => void
   DeleteContainer: (containerId: string) => void
   OnPropertyChange: (key: string, value: string) => void
-  AddContainer: (type: string) => void
+  AddContainerToSelectedContainer: (type: string) => void
+  AddContainer: (index: number, type: string, parentId: string) => void
   SaveEditorAsJSON: () => void
   SaveEditorAsSVG: () => void
   LoadState: (move: number) => void
@@ -89,7 +90,7 @@ export class UI extends React.PureComponent<IUIProps, IUIState> {
         <Sidebar
           componentOptions={this.props.AvailableContainers}
           isOpen={this.state.isSidebarOpen}
-          buttonOnClick={(type: string) => this.props.AddContainer(type)}
+          buttonOnClick={(type: string) => this.props.AddContainerToSelectedContainer(type)}
         />
         <ElementsSidebar
           MainContainer={this.props.current.MainContainer}
@@ -97,8 +98,9 @@ export class UI extends React.PureComponent<IUIProps, IUIState> {
           isOpen={this.state.isElementsSidebarOpen}
           isHistoryOpen={this.state.isHistoryOpen}
           onPropertyChange={this.props.OnPropertyChange}
-          selectContainer={this.props.SelectContainer}
+          SelectContainer={this.props.SelectContainer}
-          deleteContainer={this.props.DeleteContainer}
+          DeleteContainer={this.props.DeleteContainer}
+          AddContainer={this.props.AddContainer}
         />
         <History
           history={this.props.history}

src/Editor.tsx

@@ -195,7 +195,7 @@ class Editor extends React.Component<IEditorProps> {
    * @param type The type of container
    * @returns void
    */
-  public AddContainer(type: string): void {
+  public AddContainerToSelectedContainer(type: string): void {
     const history = this.getCurrentHistory();
     const current = history[history.length - 1];
 
@@ -204,13 +204,22 @@ class Editor extends React.Component<IEditorProps> {
       return;
     }
 
+    const parent = current.SelectedContainer;
+    this.AddContainer(parent.children.length, type, parent.properties.id);
+  }
+
+  public AddContainer(index: number, type: string, parentId: string): void {
+    const history = this.getCurrentHistory();
+    const current = history[history.length - 1];
+
     if (current.MainContainer === null ||
       current.MainContainer === undefined) {
       return;
     }
 
     // Get the preset properties from the API
-    const properties = this.props.configuration.AvailableContainers.find(option => option.Type === type);
+    const properties = this.props.configuration.AvailableContainers
+      .find(option => option.Type === type);
 
     if (properties === undefined) {
       throw new Error(`[AddContainer] Object type not found. Found: ${type}`);
@@ -230,35 +239,32 @@ class Editor extends React.Component<IEditorProps> {
     const clone: IContainerModel = structuredClone(current.MainContainer);
 
     // Find the parent
-    const it = MakeIterator(clone);
+    const parentClone: IContainerModel | undefined = findContainerById(
-    let parent: ContainerModel | null = null;
+      clone, parentId
-    for (const child of it) {
+    );
-      if (child.properties.id === current.SelectedContainer.properties.id) {
-        parent = child as ContainerModel;
-        break;
-      }
-    }
 
-    if (parent === null) {
+    if (parentClone === null || parentClone === undefined) {
-      throw new Error('[OnPropertyChange] Container model was not found among children of the main container!');
+      throw new Error('[AddContainer] Container model was not found among children of the main container!');
     }
 
     let x = 0;
-    const lastChild: IContainerModel | undefined = parent.children.at(-1);
+    if (index !== 0) {
-    if (lastChild !== undefined) {
+      const lastChild: IContainerModel | undefined = parentClone.children.at(index - 1);
-      x = lastChild.properties.x + Number(lastChild.properties.width);
+      if (lastChild !== undefined) {
+        x = lastChild.properties.x + Number(lastChild.properties.width);
+      }
     }
 
     // Create the container
     const newContainer = new ContainerModel(
-      parent,
+      parentClone,
       {
         id: `${type}-${count}`,
-        parentId: parent.properties.id,
+        parentId: parentClone.properties.id,
         x,
         y: 0,
         width: properties?.Width,
-        height: parent.properties.height,
+        height: parentClone.properties.height,
         ...properties.Style
       },
       [],
@@ -268,15 +274,19 @@ class Editor extends React.Component<IEditorProps> {
     );
 
     // And push it the the parent children
-    parent.children.push(newContainer);
+    if (index === parentClone.children.length) {
+      parentClone.children.push(newContainer);
+    } else {
+      parentClone.children.splice(index, 0, newContainer);
+    }
 
     // Update the state
     this.setState({
       history: history.concat([{
         MainContainer: clone,
         TypeCounters: newCounters,
-        SelectedContainer: parent,
+        SelectedContainer: parentClone,
-        SelectedContainerId: parent.properties.id
+        SelectedContainerId: parentClone.properties.id
       }]),
       historyCurrentStep: history.length
     });
@@ -331,7 +341,8 @@ class Editor extends React.Component<IEditorProps> {
           SelectContainer={(container) => this.SelectContainer(container)}
           DeleteContainer={(containerId: string) => this.DeleteContainer(containerId)}
           OnPropertyChange={(key, value) => this.OnPropertyChange(key, value)}
-          AddContainer={(type) => this.AddContainer(type)}
+          AddContainerToSelectedContainer={(type) => this.AddContainerToSelectedContainer(type)}
+          AddContainer={(index, type, parentId) => this.AddContainer(index, type, parentId)}
           SaveEditorAsJSON={() => this.SaveEditorAsJSON()}
           SaveEditorAsSVG={() => this.SaveEditorAsSVG()}
           LoadState={(move) => this.LoadState(move)}