refactor: polish display utilities (#455)

utils/display.ts

@@ -1,14 +1,56 @@
 // Copyright 2023 the Deno authors. All rights reserved. MIT license.
 import { difference } from "std/datetime/difference.ts";
 
-export function pluralize(unit: number, label: string) {
-  return unit === 1 ? `${unit} ${label}` : `${unit} ${label}s`;
+/**
+ * Returns a pluralized string for the given amount and unit.
+ *
+ * @example
+ * ```ts
+ * import { pluralize } from "@/utils/display.ts";
+ *
+ * pluralize(0, "meow"); // Returns "0 meows"
+ * pluralize(1, "meow"); // Returns "1 meow"
+ * pluralize(2, "meow"); // Returns "2 meows"
+ * ```
+ */
+export function pluralize(amount: number, unit: string) {
+  return amount === 1 ? `${amount} ${unit}` : `${amount} ${unit}s`;
 }
 
-export function timeAgo(time: number | Date) {
-  const minutes = difference(new Date(), new Date(time))?.minutes;
-  if (!minutes) return pluralize(0, "minute");
-  if (minutes < 60) return pluralize(~~minutes, "minute");
-  else if (minutes < 24 * 60) return pluralize(~~(minutes / 60), "hour");
-  else return pluralize(~~(minutes / (24 * 60)), "day");
+/**
+ * Returns how long ago a given date is from now.
+ *
+ * @example
+ * ```ts
+ * import { timeAgo } from "@/utils/display.ts";
+ * import { SECOND, MINUTE, HOUR } from ""std/datetime/constants.ts""
+ *
+ * timeAgo(new Date(Date.now() - SECOND)); // Returns "1 second"
+ * timeAgo(new Date(Date.now() - 2 * MINUTE)); // Returns "2 minutes"
+ * timeAgo(new Date(Date.now() - 3 * HOUR)); // Returns "3 hours"
+ * ```
+ */
+export function timeAgo(date: Date) {
+  const now = new Date();
+  if (date > now) throw new Error("Timestamp must be in the past");
+  const match = Object.entries(
+    difference(now, date, {
+      // These units make sense for a web UI
+      units: [
+        "seconds",
+        "minutes",
+        "hours",
+        "days",
+        "weeks",
+        "months",
+        "years",
+      ],
+    }),
+  )
+    .toReversed()
+    .find(([_, amount]) => amount > 0);
+  if (match === undefined) return "Now";
+  const [unit, amount] = match;
+  // Remove the last character which is an "s"
+  return pluralize(amount, unit.slice(0, -1));
 }

utils/display_test.ts

@@ -10,15 +10,15 @@ Deno.test("[display] pluralize()", () => {
 });
 
 Deno.test("[display] timeAgo()", () => {
-  assertEquals(timeAgo(Date.now()), "0 minutes");
-  assertEquals(timeAgo(Date.now() - SECOND * 30), "0 minutes");
-  assertEquals(timeAgo(Date.now() - MINUTE), "1 minute");
-  assertEquals(timeAgo(Date.now() - MINUTE * 2), "2 minutes");
-  assertEquals(timeAgo(Date.now() - MINUTE * 59), "59 minutes");
-  assertEquals(timeAgo(Date.now() - HOUR), "1 hour");
-  assertEquals(timeAgo(Date.now() - HOUR - MINUTE * 35), "1 hour");
-  assertEquals(timeAgo(Date.now() - HOUR * 2), "2 hours");
-  assertEquals(timeAgo(Date.now() - DAY), "1 day");
-  assertEquals(timeAgo(Date.now() - DAY - HOUR * 12), "1 day");
-  assertEquals(timeAgo(Date.now() - DAY * 5), "5 days");
+  assertEquals(timeAgo(new Date(Date.now())), "Now");
+  assertEquals(timeAgo(new Date(Date.now() - SECOND * 30)), "30 seconds");
+  assertEquals(timeAgo(new Date(Date.now() - MINUTE)), "1 minute");
+  assertEquals(timeAgo(new Date(Date.now() - MINUTE * 2)), "2 minutes");
+  assertEquals(timeAgo(new Date(Date.now() - MINUTE * 59)), "59 minutes");
+  assertEquals(timeAgo(new Date(Date.now() - HOUR)), "1 hour");
+  assertEquals(timeAgo(new Date(Date.now() - HOUR - MINUTE * 35)), "1 hour");
+  assertEquals(timeAgo(new Date(Date.now() - HOUR * 2)), "2 hours");
+  assertEquals(timeAgo(new Date(Date.now() - DAY)), "1 day");
+  assertEquals(timeAgo(new Date(Date.now() - DAY - HOUR * 12)), "1 day");
+  assertEquals(timeAgo(new Date(Date.now() - DAY * 5)), "5 days");
 });