Basic loop

src/lib/tree.test.ts

@@ -0,0 +1,21 @@
+import im from 'immutable'
+import { setPointsInTree } from './tree'
+
+it('sets points on an empty tree', () => {
+  const tree = im.List()
+  expect(setPointsInTree(tree, 2, 5).toJS()).toEqual([0, 0, 5])
+})
+
+it('sets points in the end of the current range', () => {
+  const tree = im.List([0, 1])
+  expect(setPointsInTree(tree, 2, 5).toJS()).toEqual([0, 1, 5])
+})
+it('sets points in the middle of the current range', () => {
+  const tree = im.List([0, 0, 0, 0, 0, 0, 5])
+  expect(setPointsInTree(tree, 2, 5).toJS()).toEqual([0, 0, 5, 0, 0, 0, 5])
+})
+
+it('does not mutate the tree for points already set', () => {
+  const tree = im.List([0, 3, 2, 0, 5])
+  expect(setPointsInTree(tree, 1, 3)).toStrictEqual(tree)
+})

src/lib/tree.ts

@@ -0,0 +1,9 @@
+import im from 'immutable'
+
+export function setPointsInTree(tree: im.List<number>, index: number, points: number) {
+  // Ensure all values until `index` are set, otherwise set to 0
+  for (let i = tree.size; i <= index; i++) {
+    tree = tree.set(i, i === index ? points : 0)
+  }
+  return tree
+}