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Lightweight event delegation
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var closest = require('./closest');

/**
 * Delegates event to a selector.
 *
 * @param {Element} element
 * @param {String} selector
 * @param {String} type
 * @param {Function} callback
 * @param {Boolean} useCapture
 * @return {Object}
 */
function _delegate(element, selector, type, callback, useCapture) {
    var listenerFn = listener.apply(this, arguments);

    element.addEventListener(type, listenerFn, useCapture);

    return {
        destroy: function() {
            element.removeEventListener(type, listenerFn, useCapture);
        }
    }
}

/**
 * Delegates event to a selector.
 *
 * @param {Element|String|Array} [elements]
 * @param {String} selector
 * @param {String} type
 * @param {Function} callback
 * @param {Boolean} useCapture
 * @return {Object}
 */
function delegate(elements, selector, type, callback, useCapture) {
    // Handle the regular Element usage
    if (typeof elements.addEventListener === 'function') {
        return _delegate.apply(null, arguments);
    }

    // Handle Element-less usage, it defaults to global delegation
    if (typeof type === 'function') {
        // Use `document` as the first parameter, then apply arguments
        // This is a short way to .unshift `arguments` without running into deoptimizations
        return _delegate.bind(null, document).apply(null, arguments);
    }

    // Handle Selector-based usage
    if (typeof elements === 'string') {
        elements = document.querySelectorAll(elements);
    }

    // Handle Array-like based usage
    return Array.prototype.map.call(elements, function (element) {
        return _delegate(element, selector, type, callback, useCapture);
    });
}

/**
 * Finds closest match and invokes callback.
 *
 * @param {Element} element
 * @param {String} selector
 * @param {String} type
 * @param {Function} callback
 * @return {Function}
 */
function listener(element, selector, type, callback) {
    return function(e) {
        e.delegateTarget = closest(e.target, selector);

        if (e.delegateTarget) {
            callback.call(element, e);
        }
    }
}

module.exports = delegate;