main.js

// All valid credit card numbers
const valid1 = [4, 5, 3, 9, 6, 7, 7, 9, 0, 8, 0, 1, 6, 8, 0, 8]
const valid2 = [5, 5, 3, 5, 7, 6, 6, 7, 6, 8, 7, 5, 1, 4, 3, 9]
const valid3 = [3, 7, 1, 6, 1, 2, 0, 1, 9, 9, 8, 5, 2, 3, 6]
const valid4 = [6, 0, 1, 1, 1, 4, 4, 3, 4, 0, 6, 8, 2, 9, 0, 5]
const valid5 = [4, 5, 3, 9, 4, 0, 4, 9, 6, 7, 8, 6, 9, 6, 6, 6]

// All invalid credit card numbers
const invalid1 = [4, 5, 3, 2, 7, 7, 8, 7, 7, 1, 0, 9, 1, 7, 9, 5]
const invalid2 = [5, 7, 9, 5, 5, 9, 3, 3, 9, 2, 1, 3, 4, 6, 4, 3]
const invalid3 = [3, 7, 5, 7, 9, 6, 0, 8, 4, 4, 5, 9, 9, 1, 4]
const invalid4 = [6, 0, 1, 1, 1, 2, 7, 9, 6, 1, 7, 7, 7, 9, 3, 5]
const invalid5 = [5, 3, 8, 2, 0, 1, 9, 7, 7, 2, 8, 8, 3, 8, 5, 4]

// Can be either valid or invalid
const mystery1 = [3, 4, 4, 8, 0, 1, 9, 6, 8, 3, 0, 5, 4, 1, 4]
const mystery2 = [5, 4, 6, 6, 1, 0, 0, 8, 6, 1, 6, 2, 0, 2, 3, 9]
const mystery3 = [6, 0, 1, 1, 3, 7, 7, 0, 2, 0, 9, 6, 2, 6, 5, 6, 2, 0, 3]
const mystery4 = [4, 9, 2, 9, 8, 7, 7, 1, 6, 9, 2, 1, 7, 0, 9, 3]
const mystery5 = [4, 9, 1, 3, 5, 4, 0, 4, 6, 3, 0, 7, 2, 5, 2, 3]

// An array of all the arrays above
const batch = [valid1, valid2, valid3, valid4, valid5, invalid1, invalid2, invalid3, invalid4, invalid5, mystery1, mystery2, mystery3, mystery4, mystery5]


// Add your functions below:

// Returns true if card number in array is valid based on Luhn algorithm:

const validatedCred = array => {
    let sum = 0;
    array.reverse();
    for (let i = 0; i < array.length; i++) {
        // Handles every other digit starting from the right:
        num = array[i]
        if (i % 2 != 0) {
            if (num * 2 > 9) {
                sum += num * 2 - 9;
            } else {
                sum += num * 2;
            }
        } else {
            // Adds the rest of the digits to the sum
            sum += num;
        };
    };
    array.reverse();
    return (sum % 10 === 0);
};

// Returns an array of all invalid card numbers as nested arrays:

const findInvalidCards = batchArray => {
    const invalidCards = [];
    for (let card = 0; card < batchArray.length; card++) {
        if (validatedCred(batchArray[card]) === false) {
            invalidCards.push(batchArray[card]);
        };
    };
    return invalidCards;
};

// Identifies credit card company by first digits in invalid credit card number array and returns an array of card companies with no duplicates

const idInvalidCardCompanies = invCardArray => {
    companyArray = [];
    for (let card = 0; card < invCardArray.length; card++) {
        fullNum = invCardArray[card];
        checkNum = fullNum[0];
        // Skips numbers already existing in companyArray, then adds the number if it doesn't already exist there:
        if (companyArray.includes(checkNum)) {
            continue;
        } else if (checkNum === 3 || checkNum === 4 || checkNum === 5 || checkNum === 6) {
            companyArray.push(checkNum);
        }
    }
    // Iterates through companyArray to convert numbers into corresponding strings of card company names:
    for (let num = 0; num < companyArray.length; num++) {
        switch (companyArray[num]) {
            case 3:
                companyArray[num] = 'Amex (American Express)';
                break;
            case 4:
                companyArray[num] = 'Visa';
                break;
            case 5:
                companyArray[num] = 'Mastercard';
                break;
            case 6:
                companyArray[num] = 'Discover';
                break;
        }
    }
    // Checks if output array contains any companies:
    if (companyArray && companyArray.length > 0) {
        return companyArray;
    }   else {
        return 'Company not found';
    }
}


console.log(idInvalidCardCompanies(findInvalidCards(batch)))