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:
const validateCred = cardNumber => {
    const controlSum = cardNumber[cardNumber.length - 1];
    let sum = 0, num;
    for (let i = cardNumber.length - 2; i >= 0; i--) {
        num = cardNumber[i];
        if (cardNumber.length % 2 === 0) {
            if (i % 2 === 0) num *= 2;
        } else {
            if (i % 2 !== 0) num *= 2;
        }
        
        if (num > 9) num -= 9;
        sum += num;
    }
    return ((sum + controlSum) % 10) === 0;
};

const findInvalidCards = cardNumbers => {
    return cardNumbers.filter(cardNumber => !validateCred(cardNumber));
};

const getCompanyByCardNumber = cardNumber => {
    switch (cardNumber[0]) {
        case 3:
            return "Amex (American Express)";
        case 4:
            return "Visa";
        case 5:
            return "Mastercard";
        case 6:
            return "Discover";
        default:
            return "Company not found";
    }
};

const idInvalidCardCompanies = cardNumbers => {
    const companies = {};
    findInvalidCards(cardNumbers).forEach(cardNumber => {
        companies[getCompanyByCardNumber(cardNumber)]++;
    });
    return Object.keys(companies);
};

const generatedCardNumbers = ["4539053498892596", "373598923132528", "6011736100202202", "4716454406091718541"];

const cardNumberStringToArray = cardNumberStrings => {
    return cardNumberStrings.map(cardNumberString => cardNumberString.split("").map(chr => Number(chr)));
};



// console.log(validateCred(valid2));
// console.log(findInvalidCards(batch));
// console.log(idInvalidCardCompanies(batch));
for (let cardNumber of cardNumberStringToArray(generatedCardNumbers)) {
    console.log(`${getCompanyByCardNumber(cardNumber)} card "${cardNumber.join('')}" is valid: ${(validateCred(cardNumber) ? "Yes" : "No")}`);
}