improve calculate new selection behavior

Author: strada

src/components/DateRange/index.js

@@ -32,8 +32,14 @@ class DateRange extends Component {
     } else if (focusedRange[1] === 0) {
       // startDate selection
       const dayOffset = differenceInCalendarDays(endDate, startDate);
+      const calculateEndDate = () => {
+        if (moveRangeOnFirstSelection) {
+          return addDays(value, dayOffset);
+        }
+        return !isBefore(value, endDate) ? value : endDate;
+      };
       startDate = value;
-      endDate = moveRangeOnFirstSelection ? addDays(value, dayOffset) : value;
+      endDate = calculateEndDate();
       if (maxDate) endDate = min([endDate, maxDate]);
       nextFocusRange = [focusedRange[0], 1];
     } else {

src/components/DateRange/index.test.js

@@ -1,7 +1,57 @@
+import React from 'react';
+import { subDays, addDays, isSameDay } from 'date-fns';
 import DateRange from '../DateRange';
+import renderer from 'react-test-renderer';
+
+let testRenderer = null;
+const endDate = new Date();
+const startDate = subDays(endDate, 7);
+
+const commonProps = {
+  ranges: [{ startDate, endDate, key: 'selection' }],
+  onChange: () => {},
+  moveRangeOnFirstSelection: false,
+};
+
+const compareRanges = (newRange, assertionRange) => {
+  expect(isSameDay(newRange.startDate, assertionRange.startDate)).toEqual(true);
+  expect(isSameDay(newRange.endDate, assertionRange.endDate)).toEqual(true);
+};
+
+beforeEach(() => {
+  testRenderer = renderer.create(<DateRange {...commonProps} />);
+});
 
 describe('DateRange', () => {
   test('Should resolve', () => {
     expect(DateRange).toEqual(expect.anything());
   });
+
+  test('calculate new selection without moving end date', () => {
+    const instance = testRenderer.getInstance();
+    const methodResult = instance.calcNewSelection(subDays(endDate, 10), true);
+    compareRanges(methodResult.range, {
+      startDate: subDays(endDate, 10),
+      endDate,
+    });
+  });
+
+  test('calculate new selection by resetting end date if start date is not before', () => {
+    const instance = testRenderer.getInstance();
+    const methodResult = instance.calcNewSelection(addDays(endDate, 2), true);
+    compareRanges(methodResult.range, {
+      startDate: addDays(endDate, 2),
+      endDate: addDays(endDate, 2),
+    });
+  });
+
+  test('calculate new selection based on moveRangeOnFirstSelection prop', () => {
+    testRenderer.update(<DateRange {...commonProps} moveRangeOnFirstSelection />);
+    const instance = testRenderer.getInstance();
+    const methodResult = instance.calcNewSelection(subDays(endDate, 10), true);
+    compareRanges(methodResult.range, {
+      startDate: subDays(endDate, 10),
+      endDate: subDays(endDate, 3),
+    });
+  });
 });