implemented robust credit card validation with Luhn algorithm check

Author: Kuzma02

lib/utils.ts

@@ -122,10 +122,124 @@ export const isValidEmailAddressFormat = (input: string) => {
 export const isValidCardNumber = (input: string) => {
   // Remove all non-digit characters
   const cleanedInput = input.replace(/[^0-9]/g, "");
-  // test for credit card number between 13 and 19 characters
-  const regex = /^\d{13,19}$/;
-  return regex.test(cleanedInput);
-}
+  
+  // Check if the cleaned input has valid length (13-19 digits)
+  if (!/^\d{13,19}$/.test(cleanedInput)) {
+    return false;
+  }
+  
+  // Implement Luhn algorithm for credit card validation
+  return luhnCheck(cleanedInput);
+};
+
+/**
+ * Luhn algorithm implementation for credit card validation
+ * @param cardNumber - The credit card number as a string
+ * @returns boolean - true if the card number is valid according to Luhn algorithm
+ */
+const luhnCheck = (cardNumber: string): boolean => {
+  let sum = 0;
+  let isEven = false;
+  
+  // Process digits from right to left
+  for (let i = cardNumber.length - 1; i >= 0; i--) {
+    let digit = parseInt(cardNumber[i], 10);
+    
+    if (isEven) {
+      digit *= 2;
+      if (digit > 9) {
+        digit -= 9;
+      }
+    }
+    
+    sum += digit;
+    isEven = !isEven;
+  }
+  
+  return sum % 10 === 0;
+};
+
+/**
+ * Enhanced credit card validation with card type detection
+ * @param input - The credit card number as a string
+ * @returns object with validation result and card type
+ */
+export const validateCreditCard = (input: string) => {
+  const cleanedInput = input.replace(/[^0-9]/g, "");
+  
+  // Basic length and format check
+  if (!/^\d{13,19}$/.test(cleanedInput)) {
+    return {
+      isValid: false,
+      cardType: 'unknown',
+      error: 'Invalid card number format'
+    };
+  }
+  
+  // Luhn algorithm check
+  if (!luhnCheck(cleanedInput)) {
+    return {
+      isValid: false,
+      cardType: 'unknown',
+      error: 'Invalid card number (Luhn check failed)'
+    };
+  }
+  
+  // Detect card type based on BIN (Bank Identification Number)
+  const cardType = detectCardType(cleanedInput);
+  
+  return {
+    isValid: true,
+    cardType,
+    error: null
+  };
+};
+
+/**
+ * Detect credit card type based on BIN patterns
+ * @param cardNumber - The credit card number as a string
+ * @returns string - The detected card type
+ */
+const detectCardType = (cardNumber: string): string => {
+  const firstDigit = cardNumber[0];
+  const firstTwoDigits = cardNumber.substring(0, 2);
+  const firstFourDigits = cardNumber.substring(0, 4);
+  const firstThreeDigits = cardNumber.substring(0, 3);
+  
+  // Visa: starts with 4
+  if (firstDigit === '4') {
+    return 'visa';
+  }
+  
+  // Mastercard: starts with 5 or 2
+  if (firstDigit === '5' || (firstTwoDigits >= '22' && firstTwoDigits <= '27')) {
+    return 'mastercard';
+  }
+  
+  // American Express: starts with 34 or 37
+  if (firstTwoDigits === '34' || firstTwoDigits === '37') {
+    return 'amex';
+  }
+  
+  // Discover: starts with 6011, 65, or 644-649
+  if (firstFourDigits === '6011' || firstTwoDigits === '65' || 
+      (firstThreeDigits >= '644' && firstThreeDigits <= '649')) {
+    return 'discover';
+  }
+  
+  // Diners Club: starts with 300-305, 36, or 38
+  if ((firstThreeDigits >= '300' && firstThreeDigits <= '305') || 
+      firstTwoDigits === '36' || firstTwoDigits === '38') {
+    return 'diners';
+  }
+  
+  // JCB: starts with 35
+  if (firstTwoDigits === '35') {
+    return 'jcb';
+  }
+  
+  return 'unknown';
+};
 
 export const isValidCreditCardExpirationDate = (input: string) => {
   // simple expiration date format check