function solve() {
    return function () {
        let form = $('#registerForm');

        let usernameFiled = $('#username');
        let emailField = $('#email');
        let passwordField = $('#password');
        let confirmPassField = $('#confirm-password');
        let companyCheckBox = $('#company');
        let companyInfoField = $('#companyInfo');
        let companyNumberField = $('#companyNumber');

        companyCheckBox.on('click', function () {
            if (companyCheckBox.is(':checked')) {
                companyInfoField.css('display', 'block');
            } else {
                companyInfoField.css('display', 'none');
            }
        });


        let submitBtn = $('#submit');
        submitBtn.on('click', function (ev) {
            ev.preventDefault();
            validateInput();
        });

        function validateInput() {
            let isValid = true;

            if (!usernameFiled.val().match(/[a-zA-Z0-9]{3,20}/g)) {
                $(usernameFiled).css('border','2px inset');
                $(usernameFiled).css('border-color','red');
                isValid = false;
            } else {
                $(usernameFiled).css('border', 'none');
            }
            if (!emailField.val().match(/.+?@.+?[.].+?/g)) {
                $(emailField).css('border','2px inset');
                $(emailField).css('border-color','red');
                isValid = false;
            } else {
                $(emailField).css('border', 'none');
            }

            if (passwordField.val().match(/[\w]{5,15}/g) && passwordField.val()==confirmPassField.val()) {
                $(passwordField).css('border', 'none');
                $(confirmPassField).css('border', 'none');

            } else {
                $(passwordField).css('border','2px inset');
                $(passwordField).css('border-color','red');
                $(confirmPassField).css('border','2px inset');
                $(confirmPassField).css('border-color','red');
                isValid = false;
            }

            if (companyCheckBox.is(':checked') && Number(companyNumberField.val()) >= 1000 && Number(companyNumberField.val() <= 9999)) {
                $(companyNumberField).css('border', 'none');
            } else if (!companyCheckBox.is(':checked')) {
                $(companyNumberField).css('border', 'none');
            } else {
                $(companyNumberField).css('border','2px inset');
                $(companyNumberField).css('border-color','red');
                isValid = false;
            }

            if (isValid) {
                $('#valid').css('display', 'block');
                $(usernameFiled).css('border', 'none');
                $(emailField).css('border', 'none');
                $(passwordField).css('border', 'none');
                $(confirmPassField).css('border', 'none');
            } else {
                $('#valid').css('display', 'none');
            }
        }
    }
}