/*
 * Copyright (C) 2017 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
 * THE POSSIBILITY OF SUCH DAMAGE.
 */

function(element, attributeName) {
    "use strict";

    let lowercaseAttributeName = attributeName.toLowerCase();
    let tagName = element.tagName.toUpperCase();

    // Special Case: "selected" / "checked" work analogously
    // on options and checkboxes.
    if (lowercaseAttributeName === "selected" || lowercaseAttributeName === "checked") {
        switch (tagName) {
        case "OPTION":
            return element.selected ? "true" : null;
        case "INPUT":
            if (element.type === "checkbox" || element.type === "radio")
                return element.checked ? "true" : null;
            break;
        }
    }

    function getAttribute(element, attributeName) {
        let attr = element.getAttributeNode(attributeName);
        return (attr && attr.specified) ? attr.value : null;
    }

    // Special Case: For images and links, require the existence of
    // the attribute before accessing the property.
    if ((tagName === "IMG" && lowercaseAttributeName === "src") || (tagName === "A" && lowercaseAttributeName === "href")) {
        let value = getAttribute(element, lowercaseAttributeName);
        return value ? element[lowercaseAttributeName] : value;
    }

    function isBooleanAttribute(element, attributeName) {
        const booleanElements = {
            audio: ["autoplay", "controls", "loop", "muted"],
            button: ["autofocus", "disabled", "formnovalidate"],
            details: ["open"],
            dialog: ["open"],
            fieldset: ["disabled"],
            form: ["novalidate"],
            iframe: ["allowfullscreen"],
            img: ["ismap"],
            input: [
                "autofocus",
                "checked",
                "disabled",
                "formnovalidate",
                "multiple",
                "readonly",
                "required",
            ],
            keygen: ["autofocus", "disabled"],
            menuitem: ["checked", "default", "disabled"],
            ol: ["reversed"],
            optgroup: ["disabled"],
            option: ["disabled", "selected"],
            script: ["async", "defer"],
            select: ["autofocus", "disabled", "multiple", "required"],
            textarea: ["autofocus", "disabled", "readonly", "required"],
            track: ["default"],
            video: ["autoplay", "controls", "loop", "muted"],
        };

        // Global boolean attributes that apply to all HTML elements.
        if (attributeName == "hidden" || attributeName == "itemscope")
            return true;

        if (!booleanElements.hasOwnProperty(element.localName))
            return false;

        return booleanElements[element.localName].includes(attributeName);
    }

    // Prefer the element's property over the attribute if the
    // property value is not null and not an object. For boolean
    // properties return null if false.
    const propertyNameAliases = {"class": "className", "readonly": "readOnly"};
    let propertyName = propertyNameAliases[attributeName] || attributeName;
    if (isBooleanAttribute(element, lowercaseAttributeName)) {
        let value = !(getAttribute(element, attributeName) === null) || element[propertyName];
        return value ? 'true' : null;
    }

    let property;
    try {
        property = element[propertyName];
    } catch (e) { }

    if (property == null || typeof property == "object") {
        let value = getAttribute(element, attributeName);
        return value != null ? value.toString() : null;
    }

    return property != null ? property.toString() : null;
}