Reorder tasks, lists and kanban buckets (#620)

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/frontend/pulls/620
Co-authored-by: konrad <konrad@kola-entertainments.de>
Co-committed-by: konrad <konrad@kola-entertainments.de>

src/helpers/applyDrag.js

@@ -1,18 +0,0 @@
-export const applyDrag = (arr, dragResult) => {
-	const {removedIndex, addedIndex, payload} = dragResult
-	if (removedIndex === null && addedIndex === null) return arr
-
-	const result = [...arr]
-	// The payload comes from the task itself
-	let itemToAdd = payload
-
-	if (removedIndex !== null) {
-		itemToAdd = result.splice(removedIndex, 1)[0]
-	}
-
-	if (addedIndex !== null) {
-		result.splice(addedIndex, 0, itemToAdd)
-	}
-
-	return result
-}

src/helpers/calculateItemPosition.ts

@@ -0,0 +1,19 @@
+export const calculateItemPosition = (positionBefore: number | null, positionAfter: number | null): number => {
+	if (positionBefore === null && positionAfter === null) {
+		return 0
+	}
+
+	// If there is no task before, our task is the first task in which case we let it have half of the position of the task after it
+	if (positionBefore === null && positionAfter !== null) {
+		return positionAfter / 2
+	}
+	
+	// If there is no task after it, we just add 2^16 to the last position to have enough room in the future
+	if (positionBefore !== null && positionAfter === null) {
+		return positionBefore + Math.pow(2, 16)
+	}
+	
+	// If we have both a task before and after it, we acually calculate the position
+	// @ts-ignore - can never be null but TS does not seem to understand that
+	return positionBefore + (positionAfter - positionBefore) / 2
+}

src/helpers/calculateTaskPosition.test.ts

@@ -0,0 +1,18 @@
+import {calculateItemPosition} from './calculateItemPosition'
+
+it('should calculate the task position', () => {
+	const result = calculateItemPosition(10, 100)
+	expect(result).toBe(55)
+})
+it('should return 0 if no position was provided', () => {
+	const result = calculateItemPosition(null, null)
+	expect(result).toBe(0)
+})
+it('should calculate the task position for the first task', () => {
+	const result = calculateItemPosition(null, 100)
+	expect(result).toBe(50)
+})
+it('should calculate the task position for the last task', () => {
+	const result = calculateItemPosition(10, null)
+	expect(result).toBe(65546)
+})