Added Credit Card Validation

Author: Kathuria

README.md

@@ -15,6 +15,7 @@ npm install validate-functions
 - **Email Validation**: Ensures that email addresses conform to standard formats.
 - **SSN Validation**: Validates U.S. Social Security Numbers based on predefined rules.
 - **Aadhaar Validation**: Checks the validity of Indian Aadhaar numbers using specific patterns.
+- **Credit Card**: The credit card validation uses the Luhn algorithm to verify the validity of credit card numbers structurally.
 
 
 Usage Details available at [here](./USAGE_DETAILS.md).

USAGE_DETAILS.md

@@ -25,4 +25,13 @@ import { isValid_Aadhaar_Number } from 'validate-functions/aadhaar';
 
 const aadhaarNumber = '1234 5678 9012';
 console.log(isValid_Aadhaar_Number(aadhaarNumber)); // Output: true if valid, false otherwise
-```
+```
+
+- **isValid_Credit_Card**
+
+```typescript
+import { isValid_Credit_Card } from 'validate-functions/credit-card';
+
+const creditCardNumber = '4539 1488 0343 6467'; // Example of a valid Visa card number
+console.log(isValid_Credit_Card(creditCardNumber)); // Output: true if valid, false otherwise
+```

src/__tests__/credit-card.test.ts

@@ -0,0 +1,23 @@
+import { isValid_Credit_Card } from '../credit-card';
+
+describe('Credit Card Validation', () => {
+  it('should return true for a valid credit card number', () => {
+    const validCardNumber = '4539 1488 0343 6467'; // Example of a valid Visa card number
+    expect(isValid_Credit_Card(validCardNumber)).toBe(true);
+  });
+
+  it('should return false for an invalid credit card number', () => {
+    const invalidCardNumber = '1234 5678 9012 3456'; // Example of an invalid card number
+    expect(isValid_Credit_Card(invalidCardNumber)).toBe(false);
+  });
+
+  it('should return true for a valid credit card number without spaces', () => {
+    const validCardNumberNoSpaces = '4539148803436467';
+    expect(isValid_Credit_Card(validCardNumberNoSpaces)).toBe(true);
+  });
+
+  it('should return false for an empty string', () => {
+    const emptyCardNumber = '';
+    expect(isValid_Credit_Card(emptyCardNumber)).toBe(false);
+  });
+});

src/credit-card.ts

@@ -0,0 +1,27 @@
+/**
+ * A credit card is essentially a means of borrowing money that is accompanied by interest and sometimes fees.
+ * Validation is based on Luhn algorithm 
+ * @param cardNumber
+ * @returns
+ */
+export const isValid_Credit_Card = (cardNumber: string): boolean => {
+  const sanitized = cardNumber.replace(/\D/g, '');
+  let sum = 0;
+  let shouldDouble = false;
+
+  if(!sanitized) return false;
+
+  for (let i = sanitized.length - 1; i >= 0; i--) {
+    let digit = parseInt(sanitized[i], 10);
+
+    if (shouldDouble) {
+      digit *= 2;
+      if (digit > 9) digit -= 9;
+    }
+
+    sum += digit;
+    shouldDouble = !shouldDouble;
+  }
+
+  return sum % 10 === 0;
+};

src/index.ts

@@ -1,3 +1,4 @@
 export * from './aadhaar';
+export * from './credit-card';
 export * from './email';
 export * from './ssn';