Move day interval calculation to separate file and test it

package.json

@@ -5,7 +5,8 @@
   "scripts": {
     "serve": "vue-cli-service serve",
     "build": "vue-cli-service build --modern",
-    "lint": "vue-cli-service lint"
+    "lint": "vue-cli-service lint",
+    "test": "jest"
   },
   "dependencies": {
     "bulma": "0.9.1",
@@ -40,6 +41,7 @@
     "babel-eslint": "10.1.0",
     "eslint": "7.14.0",
     "eslint-plugin-vue": "7.1.0",
+    "jest": "^26.6.3",
     "node-sass": "5.0.0",
     "sass-loader": "10.1.0",
     "vue-flatpickr-component": "8.1.6",

src/components/input/datepicker.vue

@@ -101,6 +101,8 @@
 import flatPickr from 'vue-flatpickr-component'
 import 'flatpickr/dist/flatpickr.css'
 
+import calculateDayInterval from '@/helpers/calculateDayInterval'
+
 export default {
 	name: 'datepicker',
 	data() {
@@ -151,29 +153,7 @@ export default {
 			console.log(date)
 		},
 		getDayIntervalFromString(date) {
-
-			const currentDay = (new Date()).getDay()
-
-			switch(date) {
-				case 'today':
-					return 0
-				case 'tomorrow':
-					return 1
-				case 'nextMonday':
-					// Monday is 1, so we calculate the distance to the next 1
-					return (7 + currentDay - 1) %  7
-				case 'thisWeekend':
-					// Saturday is 6 so we calculate the distance to the next 6
-					return (7 + currentDay - 6) %  7
-				case 'laterThisWeek':
-					return 2
-				case 'laterNextWeek':
-					return 0
-				case 'nextWeek':
-					return 7
-				default: 
-					return 0;
-			}
+			return calculateDayInterval(date)
 		},
 	},
 }

src/helpers/calculateDayInterval.js

@@ -0,0 +1,27 @@
+
+export default function calculateDayInterval(date, currentDay = (new Date().getDay())) {
+	switch(date) {
+		case 'today':
+			return 0
+		case 'tomorrow':
+			return 1
+		case 'nextMonday':
+			// Monday is 1, so we calculate the distance to the next 1
+			return (currentDay + (8 - currentDay * 2)) %  7
+		case 'thisWeekend':
+			// Saturday is 6 so we calculate the distance to the next 6
+			return (6 - currentDay) % 6
+		case 'laterThisWeek':
+			if(currentDay === 5 || currentDay === 6 || currentDay === 0) {
+				return 0
+			}
+
+			return 2
+		case 'laterNextWeek':
+			return calculateDayInterval('laterThisWeek', currentDay) + 7
+		case 'nextWeek':
+			return 7
+		default: 
+			return 0;
+	}
+}

src/helpers/calculateDayInterval.test.js

@@ -0,0 +1,93 @@
+import calculateDayInterval from './calculateDayInterval'
+
+const days = {
+    monday:    1,
+    tuesday:   2,
+    wednesday: 3,
+    thursday:  4,
+    friday:    5,
+    saturday:  6,
+    sunday:    0,
+}
+
+for (const n in days) {
+    test(`today on a ${n}`, () => {
+        expect(calculateDayInterval('today', days[n])).toBe(0)
+    })
+}
+
+for (const n in days) {
+    test(`tomorrow on a ${n}`, () => {
+        expect(calculateDayInterval('tomorrow', days[n])).toBe(1)
+    })
+}
+
+const nextMonday = {
+    monday:    0,
+    tuesday:   6,
+    wednesday: 5,
+    thursday:  4,
+    friday:    3,
+    saturday:  2,
+    sunday:    1,
+}
+
+for (const n in nextMonday) {
+    test(`next monday on a ${n}`, () => {
+        expect(calculateDayInterval('nextMonday', days[n])).toBe(nextMonday[n])
+    })
+}
+
+const thisWeekend = {
+    monday:    5,
+    tuesday:   4,
+    wednesday: 3,
+    thursday:  2,
+    friday:    1,
+    saturday:  0,
+    sunday:    0,
+}
+
+for (const n in thisWeekend) {
+    test(`this weekend on a ${n}`, () => {
+        expect(calculateDayInterval('thisWeekend', days[n])).toBe(thisWeekend[n])
+    })
+}
+
+const laterThisWeek = {
+    monday:    2,
+    tuesday:   2,
+    wednesday: 2,
+    thursday:  2,
+    friday:    0,
+    saturday:  0,
+    sunday:    0,
+}
+
+for (const n in laterThisWeek) {
+    test(`later this week on a ${n}`, () => {
+        expect(calculateDayInterval('laterThisWeek', days[n])).toBe(laterThisWeek[n])
+    })
+}
+
+const laterNextWeek = {
+    monday:    7 + 2,
+    tuesday:   7 + 2,
+    wednesday: 7 + 2,
+    thursday:  7 + 2,
+    friday:    7 + 0,
+    saturday:  7 + 0,
+    sunday:    7 + 0,
+}
+
+for (const n in laterNextWeek) {
+    test(`later next week on a ${n} (this week)`, () => {
+        expect(calculateDayInterval('laterNextWeek', days[n])).toBe(laterNextWeek[n])
+    })
+}
+
+for (const n in days) {
+    test(`next week on a ${n}`, () => {
+        expect(calculateDayInterval('nextWeek', days[n])).toBe(7)
+    })
+}