/*jshint esversion: 6 */
function solve() {
    return function(selector) {

        if (typeof(selector) !== 'string' && !(selector instanceof HTMLElement)) {
            throw "The input is neither an element nor a string";
        }
        if (document.getElementById(selector) === null) {
            throw "Nothing selected.....";
        }
        // var buttons = document.getElementsByClassName('button');
        var content = document.getElementsByClassName("content");
        var contentAndButtons = document.querySelectorAll('.button, .content');
        // indexing click event on all buttons and adding Id for later
        for (var index = 0, len = contentAndButtons.length; index < len; index += 1) {
            if (contentAndButtons[i].className === "button") {
                contentAndButtons[index].innerHTML = 'hide';
                contentAndButtons[index].addEventListener('click', ButtonClicked, false);
            }
            contentAndButtons[index].id = index;
        }

        function ButtonClicked(button) {
            var buttonIndex = this.id;
            for (var i = buttonIndex, len = contentAndButtons.length; i < len; i++) {
                var element = contentAndButtons[i];
                var button = contentAndButtons[buttonIndex];

                if (element.className === "content") {
                    if (element.style.display === '') {
                        button.innerHTML = 'show';
                        element.style.display = 'none';
                    } else if (element.style.display === 'none') {
                        element.style.display = '';
                        button.innerHTML = 'hide';
                    }
                    break;
                }
            }
        }
    }
}