Add SaveMessage component to Header

web/src/components/Header.js

@@ -8,6 +8,7 @@ import { getIsAdmin } from '../reducers/user.selector';
 import { t } from '../i18n';
 
 import DashboardButton from './DashboardButton';
+import SaveMessage from './SaveMessage';
 
 import Icon, {
   Check,
@@ -86,7 +87,7 @@ class Header extends Component {
                         </span>
                       ) : (
                         <span>
-                          <Check /> Saved {lastSaved}
+                          <Check /> <SaveMessage lastSaved={lastSaved} />
                         </span>
                       )}
                     </span>

web/src/components/Header.test.js

@@ -139,7 +139,7 @@ describe('Header component', () => {
           }}
           isAdmin={false}
           isSaving={false}
-          lastSaved="last save date"
+          lastSaved="2020-01-01T12:00:00.000Z"
           pushRoute={() => {}}
           showSiteTitle={false}
         />
@@ -159,7 +159,7 @@ describe('Header component', () => {
           }}
           isAdmin={false}
           isSaving
-          lastSaved="last save date"
+          lastSaved="2020-01-01T17:00:00.000Z"
           pushRoute={() => {}}
           showSiteTitle={false}
         />

web/src/components/SaveMessage.js

@@ -0,0 +1,58 @@
+import moment from "moment";
+import { useEffect, useState } from "react";
+import PropTypes from 'prop-types';
+
+// Configure moment to display '1 time-unit ago' instead of 'a time-unit ago'
+// https://github.com/moment/moment/issues/3764
+moment.updateLocale("en", {
+  relativeTime: {
+    s: "seconds",
+    m: "1 minute",
+    mm: "%d minutes",
+    h: "1 hour",
+    hh: "%d hours",
+    d: "1 day",
+    dd: "%d days",
+    M: "1 month",
+    MM: "%d months",
+    y: "1 year",
+    yy: "%d years",
+  },
+});
+
+const SaveMessage = ({ lastSaved }) => {
+  const [currentMoment, setCurrentMoment] = useState(() => moment());
+
+  useEffect(() => {
+    const timerID = setInterval(() => setCurrentMoment(moment()), 1000);
+    return () => clearInterval(timerID);
+  });
+
+  const lastSavedMoment = moment(lastSaved);
+  const difference = currentMoment.diff(lastSavedMoment);
+  const duration = moment.duration(difference);
+  let result = "Last saved ";
+
+  if (duration.asMinutes() < 1) return "Saved";
+
+  if (duration.asDays() < 1) {
+    result += lastSavedMoment.format("h:mm a");
+  } else if (duration.asYears() < 1) {
+    result += lastSavedMoment.format("MMMM D");
+  } else {
+    result += lastSavedMoment.format("MMMM D, YYYY");
+  }
+
+  result += ` (${lastSavedMoment.fromNow()})`;
+  return result;
+};
+
+SaveMessage.propTypes = {
+  lastSaved: PropTypes.oneOfType([
+    PropTypes.instanceOf(Date),
+    PropTypes.instanceOf(moment),
+    PropTypes.string
+  ]).isRequired,
+};
+
+export default SaveMessage;

web/src/components/SaveMessage.test.js

@@ -0,0 +1,89 @@
+import React from "react";
+import { create, act } from "react-test-renderer";
+import moment from "moment";
+import SaveMessage from "./SaveMessage";
+
+describe("<SaveMessage />", () => {
+  let subject;
+
+  describe('when saved less than 1 minute ago, it displays "Saved"', () => {
+    [
+      ["1 second ago", 1],
+      ["2 seconds ago", 2],
+      ["30 seconds ago", 30],
+      ["59 seconds", 59],
+    ].forEach(([testName, seconds]) => {
+      test(testName, () => {
+        const lastSaved = moment().subtract(seconds, "seconds");
+        // https://reactjs.org/docs/test-renderer.html#testrendereract
+        act(() => {
+          subject = create(<SaveMessage lastSaved={lastSaved} />);
+        })
+        expect(subject.toJSON()).toEqual("Saved");
+      });
+    });
+  });
+
+  describe("when observed saved time changes to 1 minute ago", () => {
+    const now = new Date(2020, 0, 1, 12, 0);
+    const oneMinuteFromNow = new Date(2020, 0, 1, 12, 1);
+    let mockDateNow;
+
+    beforeEach(() => {
+      jest.useFakeTimers();
+      mockDateNow = jest
+        .spyOn(Date, "now")
+        .mockReturnValueOnce(now)
+        .mockReturnValueOnce(now)
+        .mockReturnValueOnce(now)
+        .mockReturnValue(oneMinuteFromNow);
+    });
+
+    afterEach(() => {
+      mockDateNow.mockRestore();
+      jest.clearAllTimers();
+    });
+
+    it('auto-updates from "Saved" to (1 minute ago)', () => {
+      act(() => {
+        subject = create(<SaveMessage lastSaved={now} />);
+      })
+      expect(subject.toJSON()).toMatch("Saved");
+      act(() => jest.advanceTimersByTime(60 * 1000));
+      expect(subject.toJSON()).toMatch(/\(1 minute ago\)$/);
+    });
+  });
+
+  describe("given current time is January 1, 2020 12:00 pm", () => {
+    const jan1AtNoon = new Date(2020, 0, 1, 12, 0);
+    let mockDateNow;
+
+    beforeEach(() => {
+      mockDateNow = jest
+        .spyOn(Date, "now")
+        .mockReturnValue(jan1AtNoon.getTime());
+    });
+
+    afterEach(() => {
+      mockDateNow.mockRestore();
+    });
+
+    [
+      [1, "minute", "Last saved 11:59 am (1 minute ago)"],
+      [60 * 24 - 1, "minutes", "Last saved 12:01 pm (1 day ago)"],
+      [3, "hours", "Last saved 9:00 am (3 hours ago)"],
+      [1, "day", "Last saved December 31 (1 day ago)"],
+      [30, "days", "Last saved December 2 (1 month ago)"],
+      [364, "days", "Last saved January 2 (1 year ago)"],
+      [3, "years", "Last saved January 1, 2017 (3 years ago)"],
+    ].forEach(([value, timeUnit, result]) => {
+      test(`when saved ${value} ${timeUnit} ago, it displays "${result}"`, () => {
+        const lastSaved = moment().subtract(value, timeUnit);
+        act(() => {
+          subject = create(<SaveMessage lastSaved={lastSaved} />);
+        })
+        expect(subject.toJSON()).toEqual(result);
+      });
+    });
+  });
+});