feat(validationUtils): add VAT validation function (#91)

* feat(validationUtils): add VAT validation function
* feat(validationUtils): add more test cases
* feat(validationUtils): add external reference, review changes

docs/validationUtils.md

@@ -5,6 +5,7 @@
 ## Table of Contents
 
 - [**validatePostalCode()**](#validatePostalCode)
+- [**validateVATNumber()**](#validateVATNumber)
 - [**validateAMKA()**](#validateAMKA)
 
 ---
@@ -19,6 +20,16 @@
 
 **Return Type**: Boolean indicating whether the postal code is valid.
 
+### validateVATNumber()<a id='validateVATNumber'></a>
+
+**Description**: Validates an a greek tax id / AFM (ΑΦΜ) .
+
+**Parameters:**
+
+**`VATNumber`**: The VAT Number to validate.
+
+**Return Type**: Boolean indicating whether the VAT Number is valid.
+
 ### validateAMKA()<a id='validateAMKA'></a>
 
 **Description**: Validates an AMKA number.

src/__tests__/validationUtils.test.ts

@@ -1,4 +1,4 @@
-import { validatePostalCode, validateAMKA } from "../validationUtils";
+import { validateAMKA, validatePostalCode, validateVATNumber } from "../validationUtils";
 
 describe("validatePostalCode", () => {
   it("returns true on existing postal codes", () => {
@@ -52,3 +52,85 @@ describe("validateAMKA", () => {
     expect(validateAMKA("30022455551")).toBe(false);
   });
 });
+
+describe("validateVATNumber", () => {
+  it("returns false for invalid afms", () => {
+    expect(validateVATNumber("12345678")).toBe(false);
+    expect(validateVATNumber("xxxxxxxx")).toBe(false);
+    expect(validateVATNumber("141212176")).toBe(false);
+    expect(validateVATNumber("111111111")).toBe(false);
+    expect(validateVATNumber("311199349")).toBe(false);
+    expect(validateVATNumber("000000000")).toBe(false);
+  });
+  it("returns true for valid afms", () => {
+    expect(validateVATNumber("011111111")).toBe(true);
+    expect(validateVATNumber("150892297")).toBe(true);
+    expect(validateVATNumber("126668921")).toBe(true);
+    expect(validateVATNumber("234893562")).toBe(true);
+    expect(validateVATNumber("126668921")).toBe(true);
+    expect(validateVATNumber("565830300")).toBe(true);
+  });
+
+  it("should work with input older than year 1999", () => {
+    expect(validateVATNumber("050503557")).toBe(true);
+    expect(validateVATNumber("056203761")).toBe(false);
+  });
+
+  it("should work with legal entities, i.e. starting with 7-9", () => {
+    expect(validateVATNumber("737616950")).toBe(true);
+    expect(validateVATNumber("816267772")).toBe(true);
+    expect(validateVATNumber("985117351")).toBe(true);
+  });
+
+  it("should work with physical entities, i.e. starting with 1-4", () => {
+    expect(validateVATNumber("115410916")).toBe(true);
+    expect(validateVATNumber("234383562")).toBe(true);
+    expect(validateVATNumber("302054370")).toBe(true);
+    expect(validateVATNumber("479901058")).toBe(true);
+  });
+
+  it("should work with specific repeated digits tolerance", () => {
+    expect(validateVATNumber("267687344")).toBe(false);
+    expect(validateVATNumber("830777267")).toBe(false);
+  });
+
+  it("should not accept more than 9 digits", () => {
+    expect(validateVATNumber("23798790484567")).toBe(false);
+    expect(validateVATNumber("237987904860")).toBe(false);
+    expect(validateVATNumber("23798790489")).toBe(false);
+    expect(validateVATNumber("2379879048")).toBe(false);
+  });
+
+  it("should not accept less than 9 digits", () => {
+    expect(validateVATNumber("42496046")).toBe(false);
+    expect(validateVATNumber("4249604")).toBe(false);
+    expect(validateVATNumber("424960")).toBe(false);
+    expect(validateVATNumber("42496")).toBe(false);
+    expect(validateVATNumber("4249")).toBe(false);
+    expect(validateVATNumber("424")).toBe(false);
+    expect(validateVATNumber("42")).toBe(false);
+    expect(validateVATNumber("4")).toBe(false);
+    expect(validateVATNumber("")).toBe(false);
+  });
+
+  it("should accept only numerical characters", () => {
+    expect(validateVATNumber("2379w7904")).toBe(false);
+    expect(validateVATNumber("9K7755250")).toBe(false);
+  });
+
+  it("works with int or string values", () => {
+    expect(validateVATNumber(111111111)).toBe(false);
+    expect(validateVATNumber(1111111111111)).toBe(false);
+    expect(validateVATNumber(1.1)).toBe(false);
+    expect(validateVATNumber(1.11111111)).toBe(false);
+    expect(validateVATNumber("xxxxxxxx")).toBe(false);
+    expect(validateVATNumber("141212176")).toBe(false);
+
+    expect(validateVATNumber("150892297")).toBe(true);
+    expect(validateVATNumber(150892297)).toBe(true);
+    expect(validateVATNumber(126668921)).toBe(true);
+    expect(validateVATNumber("126668921")).toBe(true);
+    expect(validateVATNumber(234893562)).toBe(true);
+    expect(validateVATNumber("234893562")).toBe(true);
+  });
+});

src/validationUtils.ts

@@ -70,3 +70,34 @@ export function validateAMKA(amka: string | number): boolean {
   // The sum should be divisible by 10
   return sum % 10 === 0;
 }
+
+/**
+ * Validates a VAT (Value Added Tax) number based on the following criteria:
+ * - Must be exactly 9 digits long.
+ * - Must consist of numeric characters only.
+ * - Cannot be all zeros.
+ * - The last digit (checksum) must satisfy a specific calculation based on the preceding digits.
+ *
+ * @param {string | number} vatNumber - The VAT number to validate, provided as a string or a number.
+ * @returns {boolean} - Returns `true` if the VAT number is valid according to the specified rules; otherwise, `false`.
+ *
+ * Reference:{@link https://lytrax.io/blog/projects/greek-tin-validator-generator  Greek TIN Validator Generator}
+ */
+export function validateVATNumber(vatNumberInput: string | number): boolean {
+  const vatNumber = String(vatNumberInput);
+
+  if (vatNumber.length !== 9 || !/^\d+$/.test(vatNumber) || vatNumber === "0".repeat(9)) {
+    return false;
+  }
+
+  const sum = vatNumber
+    .substring(0, 8)
+    .split("")
+    .reduce((s, v, i) => s + (parseInt(v) << (8 - i)), 0);
+
+  const calc = sum % 11;
+  const d9 = parseInt(vatNumber[8]!);
+  const valid = calc % 10 === d9;
+
+  return valid;
+}