function formInvalid() {

    let firstName = "";
    let email = "";
    let countryCode = "";
    let phoneNumber = "";
    let message = "";
    let invalid = 0;
    
    // Retrieve information
    firstName = document.getElementById('fname').value;
    email = document.getElementById('email').value;
    countryCode = document.getElementById('phonePrefix').value;
    phoneNumber = document.getElementById('phoneNumber').value;
    message = document.getElementById('message').value;
  
    // Validation
    
    // First Name
    if (firstName) {
        firstName = firstName.trim();
        showformError('fname',0);
    } else { showformError('fname',1); invalid = 1; }

    // Email
    if (email) {
        email = email.trim();
        var regexValidation = /^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
        if (regexValidation.test(email)) {
            showformError('email',0)
         } else { showformError('email',1); invalid = 1; }
    } else { showformError('email',1); invalid = 1; }
    
    // Country Code
    if (countryCode && (!isNaN(countryCode.substring(1)))) {
        countryCode = countryCode.substring(1);
    } else { invalid = 1; }

    // Phone Number
    if (phoneNumber) {
        phoneNumber = phoneNumber.trim();
        if (isNaN(phoneNumber)) {
            invalid = 1;
            showformError('phonePrefix', 1);
            showformError('phoneNumber', 1);
        }
        else { showformError('phonePrefix', 0); showformError('phoneNumber',0);}
    } else { showformError('phonePrefix', 1); showformError('phoneNumber', 1); invalid = 1; }

    // Message
    if (message) {
        message = message.trim();
        showformError('message', 0);
    } else { showformError('message', 1); invalid = 1;}

    return [invalid, firstName, email, phoneNumber, countryCode, message];
}

// Calls function to send the API
function submitForm() {
   
    // Retrieve array of information from formInvalid
    let infoArray = formInvalid();

    // First value indicates if the form is validated
    if (infoArray[0] == 0){
        sendEmail(infoArray);
        return true;
    }
    return false;
}

// Show/Hide validation according to form input
function showformError(field, notValid) {

    var element = document.getElementById(field);
    var elementLabel = document.getElementById(field+'-error');

    if (notValid) {
        switch (field) {
            case "fname":
            case "email":
                element.style.setProperty('border','1px solid #E6001B','important');
                elementLabel.classList.add('fade-in');
                break;
            case "phonePrefix":
                element.style.setProperty('border','1px solid #E6001B','important');
                break;
            case "phoneNumber":
                document.getElementById('phoneNumberDiv').style.setProperty('margin-bottom','0px','important');
                element.style.setProperty('border','1px solid #E6001B','important');
                element.style.setProperty('margin-bottom','0px', 'important');        
                elementLabel.classList.add('fade-in');
                break;
            case "message":
                document.getElementById(field).style.setProperty('margin-bottom','0px','important');
                element.style.setProperty('border','1px solid #E6001B','important');
                elementLabel.classList.add('fade-in');
                break;
            default:
                break;
        }
    }
    else {
        switch (field) {
            case "cname":
            case "fname":
            case "email":
                element.style.setProperty('border','2px solid #CED4DA','important');
                elementLabel.classList.remove('fade-in');
                break;
            case "phonePrefix":
                element.style.setProperty('border','2px solid #CED4DA','important');
                break;
            case "phoneNumber":
                document.getElementById('phoneNumberDiv').style.setProperty('margin-bottom','1rem','important');
                element.style.setProperty('border','2px solid #CED4DA','important');
                element.style.setProperty('margin-bottom','15px', 'important');        
                elementLabel.classList.remove('fade-in');
                break;
            case "message":
                document.getElementById(field).style.setProperty('margin-bottom','20px','important');
                element.style.setProperty('border','2px solid #CED4DA','important');
                elementLabel.classList.remove('fade-in');
                break;
            default:
                break;
        }
    }
}