VIA-630 MD/DB: Move calculateAge to the file date and its test file

Author: marie-dedikova-nhs

src/utils/age.test.ts

@@ -1,4 +1,5 @@
 import { UtcDateFromStringSchema, UtcDateTimeFromStringSchema } from "@src/utils/date";
+import { calculateAge } from "@src/utils/date";
 
 describe("utils-date", () => {
   describe("UtcDateFromStringSchema", () => {
@@ -63,4 +64,49 @@ describe("utils-date", () => {
       }).toThrow();
     });
   });
+  describe("calculateAge", () => {
+    beforeEach(() => {
+      jest.useFakeTimers().setSystemTime(new Date("2025-01-15T00:00:00.000Z").getTime());
+    });
+
+    it("should return age based on birthdate", () => {
+      const birthdate = "2011-11-01";
+
+      const result = calculateAge(birthdate);
+
+      expect(result).toEqual(13);
+    });
+
+    it("should return age of previous year if tomorrow is their birthday", () => {
+      const birthdate = "1987-01-16";
+
+      const result = calculateAge(birthdate);
+
+      expect(result).toEqual(37);
+    });
+
+    it("should return updated age if today is their birthday", () => {
+      const birthdate = "1987-01-15";
+
+      const result = calculateAge(birthdate);
+
+      expect(result).toEqual(38);
+    });
+
+    it("should return age of this year if birthday was yesterday", () => {
+      const birthdate = "1987-01-14";
+
+      const result = calculateAge(birthdate);
+
+      expect(result).toEqual(38);
+    });
+
+    it("should throw if birthdate is invalid", () => {
+      const birthdate = "1987-13-17";
+
+      expect(() => {
+        calculateAge(birthdate);
+      }).toThrow();
+    });
+  });
 });

src/utils/age.ts

@@ -1,3 +1,5 @@
+import { Age } from "@src/utils/auth/types";
+import { differenceInYears } from "date-fns";
 import { z } from "zod";
 
 export const UtcDateFromStringSchema = z
@@ -28,3 +30,10 @@ export const UtcDateTimeFromStringSchema = z.iso
 
     return date;
   });
+
+export const calculateAge = (date: string): Age => {
+  const today: Date = new Date();
+  const birthDate: Date = UtcDateFromStringSchema.parse(date);
+
+  return differenceInYears(today, birthDate) as Age;
+};