//noinspection JSUnusedAssignment
var RMIScrolling = RMIScrolling || {};

/**
 * @param {!HTMLInputElement} inputElemToActivate
 * @param {!Element} scrollableElem
 * @constructor
 */
RMIScrolling.InputActivator = function (inputElemToActivate, scrollableElem) {

    /**
     * @type {!HTMLInputElement}
     * @private
     */
    this.inputElemToActivate_ = inputElemToActivate;

    /**
     * @type {!Element}
     * @private
     */
    this.scrollableElem_ = scrollableElem;

    scrollableElem.addEventListener('scroll', this.applyWhenScrolledDown_.bind(this));
};

/**
 * @private
 */
RMIScrolling.InputActivator.prototype.activateInputElem_ = function () {
    activateElement(this.inputElemToActivate_);
};

/**
 * @private
 */
RMIScrolling.InputActivator.prototype.applyWhenScrolledDown_ = function () {
    /** @type {!Element} */
    var scrollableElem = this.scrollableElem_;

    if (scrollableElem.offsetHeight + scrollableElem.scrollTop >= scrollableElem.scrollHeight) {
        this.activateInputElem_.apply(this);
    }
};

/**
 * @param {!HTMLInputElement} inputElemToActivate
 * @param {!Element} scrollableElem
 * @returns {RMIScrolling.InputActivator}
 * @public
 */
RMIScrolling.InputActivator.initialize = function (inputElemToActivate, scrollableElem) {
    if(!scrollableElem) {
        activateElement(inputElemToActivate);
        throw "scrollableElem was null, inputElemToActivate would never be activated. It therefore has been activated immediately.";
    }
    new RMIScrolling.InputActivator(inputElemToActivate, scrollableElem);
};

/**
 * @param {!HTMLInputElement} inputElemToActivate
 */
function activateElement(inputElemToActivate) {
    inputElemToActivate.disabled = false;

    /** @type {string} */
    var disabledClassName = 'disabled';

    /** @type {string} */
    var orgClassName = inputElemToActivate.className;

    if (orgClassName.indexOf(disabledClassName) > -1) {
        /** @type {!RegExp} */
        var regExp = new RegExp('\\b' + disabledClassName + '\\b');
        inputElemToActivate.className = orgClassName.replace(regExp, '');
    }
}