BREAKING: Refactor and add more time utils

src/time.test.ts

@@ -1,10 +1,56 @@
-import { timeSince } from '.';
+import { Duration, inMilliseconds, timeSince } from '.';
 
 describe('time utilities', () => {
+  describe('Duration', () => {
+    it('has the correct values', () => {
+      expect(Duration.Millisecond).toBe(1);
+      expect(Duration.Second).toBe(Duration.Millisecond * 1000);
+      expect(Duration.Minute).toBe(Duration.Second * 60);
+      expect(Duration.Hour).toBe(Duration.Minute * 60);
+      expect(Duration.Day).toBe(Duration.Hour * 24);
+      expect(Duration.Week).toBe(Duration.Day * 7);
+      expect(Duration.Year).toBe(Duration.Day * 365);
+    });
+  });
+
+  describe('inMilliseconds', () => {
+    it('throws if the number is negative or a float', () => {
+      expect(() => inMilliseconds(1.1, Duration.Second)).toThrow(
+        '"count" must be a non-negative integer. Received: "1.1".',
+      );
+
+      expect(() => inMilliseconds(-1, Duration.Second)).toThrow(
+        '"count" must be a non-negative integer. Received: "-1".',
+      );
+    });
+
+    it('counts durations correctly', () => {
+      // A count that won't overflow for any Duration value.
+      const getRandomCount = () => Math.floor(Math.random() * 1000);
+
+      Object.values(Duration).forEach((duration) => {
+        const count = getRandomCount();
+        expect(inMilliseconds(count, duration as Duration)).toBe(
+          count * (duration as Duration),
+        );
+      });
+    });
+  });
+
   describe('timeSince', () => {
+    it('throws if the number is negative or a float', () => {
+      expect(() => timeSince(1.1)).toThrow(
+        '"timestamp" must be a non-negative integer. Received: "1.1".',
+      );
+
+      expect(() => timeSince(-1)).toThrow(
+        '"timestamp" must be a non-negative integer. Received: "-1".',
+      );
+    });
+
     it('computes the elapsed time', () => {
-      const currentTime = 10;
-      jest.spyOn(Date, 'now').mockImplementation(() => currentTime);
+      // Set the "current time" to "10".
+      jest.spyOn(Date, 'now').mockImplementation(() => 10);
 
       [
         [10, 0],

src/time.ts

@@ -1,27 +1,65 @@
 /**
- * A millisecond.
+ * Common duration constants, in milliseconds.
  */
-export const MILLISECOND = 1;
+export enum Duration {
+  /**
+   * A millisecond.
+   */
+  Millisecond = 1,
 
-/**
- * A second, in milliseconds.
- */
-export const SECOND = 1000; // MILLISECOND * 1000
+  /**
+   * A second, in milliseconds.
+   */
+  Second = 1000, // Millisecond * 1000
 
-/**
- * A minute, in milliseconds.
- */
-export const MINUTE = 60_000; // SECOND * 60
+  /**
+   * A minute, in milliseconds.
+   */
+  Minute = 60_000, // Second * 60
 
-/**
- * An hour, in milliseconds.
- */
-export const HOUR = 3_600_000; // MINUTE * 60
+  /**
+   * An hour, in milliseconds.
+   */
+  Hour = 3_600_000, // Minute * 60
+
+  /**
+   * A day, in milliseconds.
+   */
+  Day = 86_400_000, // Hour * 24
+
+  /**
+   * A week, in milliseconds.
+   */
+  Week = 604_800_000, // Day * 7
+
+  /**
+   * A year, in milliseconds.
+   */
+  Year = 31_536_000_000, // Day * 365
+}
+
+const isNonnegativeInteger = (number: number) =>
+  Number.isInteger(number) && number >= 0;
+
+const assertIsNonnegativeInteger = (number: number, name: string) => {
+  if (!isNonnegativeInteger(number)) {
+    throw new Error(
+      `"${name}" must be a non-negative integer. Received: "${number}".`,
+    );
+  }
+};
 
 /**
- * A day, in milliseconds.
+ * Calculates the millisecond value of the specified number of units of time.
+ *
+ * @param count - The number of units of time.
+ * @param duration - The unit of time to count.
+ * @returns The count multiplied by the specified duration.
  */
-export const DAY = 86_400_000; // HOUR * 24
+export function inMilliseconds(count: number, duration: Duration): number {
+  assertIsNonnegativeInteger(count, 'count');
+  return count * duration;
+}
 
 /**
  * Gets the milliseconds since a particular Unix epoch timestamp.
@@ -30,5 +68,6 @@ export const DAY = 86_400_000; // HOUR * 24
  * @returns The number of milliseconds elapsed since the specified timestamp.
  */
 export function timeSince(timestamp: number): number {
+  assertIsNonnegativeInteger(timestamp, 'timestamp');
   return Date.now() - timestamp;
 }