feat: 🎸 added deleteNodeAt to TreeStateModifiers

added deleteNodeAt, a function that generates a new state after deleting
a node at a supplied index

index.d.ts

@@ -149,6 +149,7 @@ export interface TreeState {
 
 export interface TreeStateModifiers {
   editNodeAt: (state: State, index: number, setNode: (oldNode: Node) => Node) => State;
+  deleteNodeAt: (state: State, index: number) => State;
 }
 
 export const selectors: Selectors;

src/state/TreeStateModifiers.js

@@ -1,6 +1,11 @@
-import {getFlattenedTreePaths, doesChangeAffectFlattenedTree, isNodeExpanded} from '../selectors/getFlattenedTree';
-import TreeState, {validateState, State} from './TreeState';
-import {replaceNodeFromTree} from '../selectors/nodes';
+import {
+  getFlattenedTreePaths,
+  doesChangeAffectFlattenedTree,
+  isNodeExpanded,
+  nodeHasChildren,
+} from '../selectors/getFlattenedTree';
+import TreeState, {State} from './TreeState';
+import {replaceNodeFromTree, deleteNodeFromTree} from '../selectors/nodes';
 
 /**
  * @callback setNode
@@ -20,8 +25,6 @@ export default class TreeStateModifiers {
    * @return {State} An internal state representation
    */
   static editNodeAt = (state, index, setNode) => {
-    validateState(state);
-
     const node = TreeState.getNodeAt(state, index);
     const updatedNode = setNode(node);
     const flattenedTree = [...state.flattenedTree];
@@ -44,4 +47,28 @@ export default class TreeStateModifiers {
 
     return new State(tree, flattenedTree);
   };
+
+  /**
+   * Given a state, deletes a node
+   * @param {State} state - The current state
+   * @param {number} index - The visible row index
+   * @return {State} An internal state representation
+   */
+  static deleteNodeAt = (state, index) => {
+    const node = TreeState.getNodeAt(state, index);
+
+    const flattenedTree = [...state.flattenedTree];
+    const flattenedNodeMap = flattenedTree[index];
+    const parents = flattenedNodeMap.slice(0, flattenedNodeMap.length - 1);
+
+    const numberOfVisibleDescendants = nodeHasChildren(node)
+      ? TreeState.getNumberOfVisibleDescendants(state, index)
+      : 0;
+
+    flattenedTree.splice(index, 1 + numberOfVisibleDescendants);
+
+    const tree = deleteNodeFromTree(state.tree, {...node, parents});
+
+    return new State(tree, flattenedTree);
+  };
 }

src/state/__tests__/TreeStateModifiers.test.js

@@ -252,4 +252,115 @@ describe('TreeStateModifiers', () => {
       });
     });
   });
+
+  describe('deleteNodeAt', () => {
+    test('should fail when invalid state is supplied', () => {
+      expect(() => TreeStateModifiers.deleteNodeAt('state', 0)).toThrowError(
+        'Expected a State instance but got string',
+      );
+      expect(() => TreeStateModifiers.deleteNodeAt(1225, 0)).toThrowError('Expected a State instance but got number');
+      expect(() => TreeStateModifiers.deleteNodeAt([], 0)).toThrowError('Expected a State instance but got object');
+      expect(() => TreeStateModifiers.deleteNodeAt({}, 0)).toThrowError('Expected a State instance but got object');
+      expect(() => TreeStateModifiers.deleteNodeAt(true, 0)).toThrowError('Expected a State instance but got boolean');
+      expect(() => TreeStateModifiers.deleteNodeAt(() => {}, 0)).toThrowError(
+        'Expected a State instance but got function',
+      );
+    });
+
+    test('should fail with descriptive error when node at index does not exist', () => {
+      expect(() => TreeStateModifiers.deleteNodeAt(TreeState.createFromTree(Nodes), 20)).toThrowErrorMatchingSnapshot();
+    });
+
+    describe('flattened tree', () => {
+      test('should delete a root node with expanded children', () => {
+        const state = TreeState.createFromTree(Nodes);
+
+        deepFreeze(state);
+
+        const {flattenedTree} = TreeStateModifiers.deleteNodeAt(state, 0);
+
+        expect(flattenedTree).toMatchSnapshot();
+      });
+
+      test('should delete a root node without expanded children', () => {
+        const state = TreeState.createFromTree(Nodes);
+
+        deepFreeze(state);
+
+        const {flattenedTree} = TreeStateModifiers.deleteNodeAt(state, 5);
+
+        expect(flattenedTree).toMatchSnapshot();
+      });
+
+      test('should delete a child node with expanded children', () => {
+        const state = TreeState.createFromTree(Nodes);
+
+        deepFreeze(state);
+
+        const {flattenedTree} = TreeStateModifiers.deleteNodeAt(state, 1);
+
+        expect(flattenedTree).toMatchSnapshot();
+      });
+
+      test('should delete a child node without expanded children', () => {
+        const state = TreeState.createFromTree(Nodes);
+
+        deepFreeze(state);
+
+        const {flattenedTree} = TreeStateModifiers.deleteNodeAt(state, 2);
+
+        expect(flattenedTree).toMatchSnapshot();
+      });
+    });
+
+    describe('tree', () => {
+      test('should delete a root node with expanded children', () => {
+        const state = TreeState.createFromTree(Nodes);
+
+        deepFreeze(state);
+
+        const {tree} = TreeStateModifiers.deleteNodeAt(state, 0);
+
+        const changes = diff(state.tree, tree);
+
+        expect(changes).toMatchSnapshot();
+      });
+
+      test('should delete a root node without expanded children', () => {
+        const state = TreeState.createFromTree(Nodes);
+
+        deepFreeze(state);
+
+        const {tree} = TreeStateModifiers.deleteNodeAt(state, 6);
+
+        const changes = diff(state.tree, tree);
+
+        expect(changes).toMatchSnapshot();
+      });
+
+      test('should delete a child node without expanded children', () => {
+        const state = TreeState.createFromTree(Nodes);
+
+        deepFreeze(state);
+
+        const {tree} = TreeStateModifiers.deleteNodeAt(state, 2);
+
+        const changes = diff(state.tree, tree);
+
+        expect(changes).toMatchSnapshot();
+      });
+
+      test('should delete a child node with expanded children', () => {
+        const state = TreeState.createFromTree(Nodes);
+
+        deepFreeze(state);
+
+        const {tree} = TreeStateModifiers.deleteNodeAt(state, 1);
+
+        const changes = diff(state.tree, tree);
+
+        expect(changes).toMatchSnapshot();
+      });
+    });
+  });
 });