2 files changed, 76 insertions, 0 deletions
diff --git a/src/components/DateString/DateString.tsx b/src/components/DateString/DateString.tsx
new file mode 100644
index 0000000..7c824cd
--- /dev/null
+++ b/src/components/DateString/DateString.tsx
@@ -0,0 +1,41 @@
+import React, { useState, useMemo, useCallback } from 'react';
+import { makeStyles } from '@material-ui/core/styles';
+import compactDateString from './compactDateString';
+
+interface PropTypes {
+  value: Date | string;
+}
+
+const useStyles = makeStyles({
+  root: {
+    display: 'block',
+    cursor: 'pointer'
+  }
+});
+
+const DATE_FORMAT = {
+  month: 'long',
+  day: 'numeric',
+  year: 'numeric',
+  hour: '2-digit',
+  minute: '2-digit'
+};
+
+const DateString: React.FC<PropTypes> = ({ value }) => {
+  const [isCompact, setIsCompact] = useState<boolean>(true);
+  const classes = useStyles();
+
+  const toggleScompact = useCallback(() => setIsCompact(v => !v), [setIsCompact]);
+
+  const date = useMemo(() => new Date(value), [value]);
+  const formatted = useMemo(() => date.toLocaleString('default', DATE_FORMAT), [date]);
+  const compact = useMemo(() => compactDateString(date), [date]);
+
+  return (
+    <div role="presentation" className={classes.root} onClick={toggleScompact}>
+      {isCompact ? compact : formatted}
+    </div>
+  );
+};
+
+export default DateString;
diff --git a/src/components/DateString/compactDateString.ts b/src/components/DateString/compactDateString.ts
new file mode 100644
index 0000000..8bff4b7
--- /dev/null
+++ b/src/components/DateString/compactDateString.ts
@@ -0,0 +1,35 @@
+const metrics = [
+  { name: 'minute', ratio: 60 },
+  { name: 'hour', ratio: 60 },
+  { name: 'day', ratio: 24 },
+  { name: 'week', ratio: 7 },
+  { name: 'month', ratio: 4 },
+  { name: 'year', ratio: 12 }
+];
+
+const PRECISION = 0.85;
+
+const resolve = (value: number, metricIndex = 0): string => {
+  // Recursively divide value until it's ready to be presented as a string
+  const metric = metrics[metricIndex];
+  const nextMetric = metrics[metricIndex + 1];
+  const newValue = value / metric.ratio;
+
+  if (newValue < nextMetric.ratio * PRECISION) {
+    const rounded = Math.round(newValue);
+    const isPlural = rounded > 1;
+    const count = isPlural ? rounded : 'a';
+    const ending = isPlural ? 's' : '';
+    return `${count} ${metric.name}${ending} ago`;
+  }
+  return resolve(newValue, metricIndex + 1);
+};
+
+const compactDateString = (date: Date): string => {
+  const now = new Date();
+  const diff = (now.valueOf() - date.valueOf()) / 1000;
+  if (diff < 60) return 'just now';
+  return resolve(diff);
+};
+
+export default compactDateString;