fix(datetime): default to local date (#17706)

core/src/components/datetime/datetime-util.ts

@@ -241,7 +241,38 @@ export function parseDate(val: string | undefined | null): DatetimeData | undefi
   };
 }
 
+/**
+ * Converts a valid UTC datetime string
+ * To the user's local timezone
+ * Note: This is not meant for time strings
+ * such as "01:47"
+ */
+export const getLocalDateTime = (dateString = ''): Date => {
+  const date = (dateString.length > 0) ? new Date(dateString) : new Date();
+
+  return new Date(
+    Date.UTC(
+      date.getFullYear(),
+      date.getMonth(),
+      date.getDate(),
+      date.getHours(),
+      date.getMinutes(),
+      date.getSeconds(),
+      date.getMilliseconds()
+    )
+  );
+};
+
 export function updateDate(existingData: DatetimeData, newData: any): boolean {
+
+  if (!newData || typeof newData === 'string') {
+    const localDateTime = getLocalDateTime(newData);
+
+    if (!Number.isNaN(localDateTime.getTime())) {
+      newData = localDateTime.toISOString();
+    }
+  }
+
   if (newData && newData !== '') {
 
     if (typeof newData === 'string') {
@@ -368,6 +399,7 @@ export function convertDataToISO(data: DatetimeData): string {
             rtn += 'Z';
 
           } else {
+
             // YYYY-MM-DDTHH:mm:SS+/-HH:mm
             rtn += (data.tzOffset > 0 ? '+' : '-') + twoDigit(Math.floor(Math.abs(data.tzOffset / 60))) + ':' + twoDigit(data.tzOffset % 60);
           }

core/src/components/datetime/datetime.tsx

@@ -307,6 +307,19 @@ export class Datetime implements ComponentInterface {
           text: this.doneText,
           handler: (data: any) => {
             this.updateDatetimeValue(data);
+
+            /**
+             * Prevent convertDataToISO from doing any
+             * kind of transformation based on timezone
+             * This cancels out any change it attempts to make
+             *
+             * Important: Take the timezone offset based on
+             * the date that is currently selected, otherwise
+             * there can be 1 hr difference when dealing w/ DST
+             */
+            const date = new Date(convertDataToISO(this.datetimeValue));
+            this.datetimeValue.tzOffset = date.getTimezoneOffset() * -1;
+
             this.value = convertDataToISO(this.datetimeValue);
           }
         }
@@ -360,6 +373,7 @@ export class Datetime implements ComponentInterface {
       // cool, we've loaded up the columns with options
       // preselect the option for this column
       const optValue = getDateValue(this.datetimeValue, format);
+
       const selectedIndex = colOptions.findIndex(opt => opt.value === optValue);
 
       return {
@@ -527,6 +541,7 @@ export class Datetime implements ComponentInterface {
   private getText() {
     // create the text of the formatted data
     const template = this.displayFormat || this.pickerFormat || DEFAULT_FORMAT;
+
     return renderDatetime(template, this.datetimeValue, this.locale);
   }
 

core/src/components/datetime/test/datetime.spec.ts

@@ -1,5 +1,4 @@
-import { DatetimeOptions } from '../datetime-interface';
-import { DatetimeData, getDateValue } from '../datetime-util';
+import { DatetimeData, getDateValue, getLocalDateTime } from '../datetime-util';
 
 describe('Datetime', () => {
   describe('getDateValue()', () => {
@@ -32,4 +31,30 @@ describe('Datetime', () => {
       expect(yearValue).toEqual(date.getFullYear());
     });
   });
+  
+  describe('getLocalDateTime()', () => {
+    it('should format a datetime string according to the local timezone', () => {
+      
+      const dateStringTests = [
+        { expectedHourUTC: 12, input: `2019-03-02T12:08:06.601-00:00`, expectedOutput: `2019-03-02T%HOUR%:08:06.601Z` },
+        { expectedHourUTC: 12, input: `2019-11-02T12:08:06.601-00:00`, expectedOutput: `2019-11-02T%HOUR%:08:06.601Z` },
+        { expectedHourUTC: 8, input: `1994-12-15T13:47:20.789+05:00`, expectedOutput: `1994-12-15T%HOUR%:47:20.789Z` },
+        { expectedHourUTC: 18, input: `1994-12-15T13:47:20.789-05:00`, expectedOutput: `1994-12-15T%HOUR%:47:20.789Z` },
+        { expectedHourUTC: 9, input: `2019-02-14T09:00:00.000Z`, expectedOutput: `2019-02-14T%HOUR%:00:00.000Z` } 
+      ];
+      
+      dateStringTests.forEach(test => {
+        const convertToLocal = getLocalDateTime(test.input);
+        
+        const timeZoneOffset = convertToLocal.getTimezoneOffset() / 60;
+        const expectedDateString = test.expectedOutput.replace('%HOUR%', padNumber(test.expectedHourUTC - timeZoneOffset));
+        
+        expect(convertToLocal.toISOString()).toEqual(expectedDateString);
+      });
+    });
+  });
 });
+
+function padNumber(number: number, totalLength: number = 2): string {
+  return number.toString().padStart(totalLength, '0');
+}