background.js

/*global require, chrome, alert */

/**
 * Display an alert with an error message, description
 *
 * @param  {string} textToShow  Error message text
 * @param  {string} errorToShow Error to show
 */
function displayeAnError(textToShow, errorToShow) {
    "use strict";

    alert(textToShow + '\n' + errorToShow);
}

/**
 * Retrieve a value of a parameter from the given URL string
 *
 * @param  {string} url           Url string
 * @param  {string} parameterName Name of the parameter
 *
 * @return {string}               Value of the parameter
 */
function getUrlParameterValue(url, parameterName) {
    "use strict";

    var urlParameters  = url.substr(url.indexOf("#") + 1),
        parameterValue = "",
        index,
        temp;

    urlParameters = urlParameters.split("&");

    for (index = 0; index < urlParameters.length; index += 1) {
        temp = urlParameters[index].split("=");

        if (temp[0] === parameterName) {
            return temp[1];
        }
    }

    return parameterValue;
}

/**
 * Chrome tab update listener handler. Return a function which is used as a listener itself by chrome.tabs.obUpdated
 *
 * @param  {string} authenticationTabId Id of the tab which is waiting for grant of permissions for the application
 * @param  {string} imageSourceUrl      URL of the image which is uploaded
 *
 * @return {function}                   Listener for chrome.tabs.onUpdated
 */
function listenerHandler(authenticationTabId, imageSourceUrl) {
    "use strict";

    return function tabUpdateListener(tabId, changeInfo) {
        var vkAccessToken,
            vkAccessTokenExpiredFlag;

        if (tabId === authenticationTabId && changeInfo.url !== undefined && changeInfo.status === "loading") {

            if (changeInfo.url.indexOf('oauth.vk.com/blank.html') > -1) {
                authenticationTabId = null;
                chrome.tabs.onUpdated.removeListener(tabUpdateListener);

                vkAccessToken = getUrlParameterValue(changeInfo.url, 'access_token');

                if (vkAccessToken === undefined || vkAccessToken.length === undefined) {
                    displayeAnError('vk auth response problem', 'access_token length = 0 or vkAccessToken == undefined');
                    return;
                }

                vkAccessTokenExpiredFlag = Number(getUrlParameterValue(changeInfo.url, 'expires_in'));

                if (vkAccessTokenExpiredFlag !== 0) {
                    displayeAnError('vk auth response problem', 'vkAccessTokenExpiredFlag != 0' + vkAccessToken);
                    return;
                }

                chrome.storage.local.set({'vkaccess_token': vkAccessToken}, function () {
                    chrome.tabs.update(
                        tabId,
                        {
                            'url'   : 'upload.html#' + imageSourceUrl + '&' + vkAccessToken,
                            'active': true
                        },
                        function (tab) {}
                    );
                });
            }
        }
    };
}

/**
 * Handle main functionality of 'onlick' chrome context menu item method
 */
function getClickHandler() {
    "use strict";

    return function (info, tab) {

        var imageSourceUrl       = info.srcUrl,
            imageUploadHelperUrl = 'upload.html#',
            vkCLientId           = '3315996',
            vkRequestedScopes    = 'docs,offline',
            vkAuthenticationUrl  = 'https://oauth.vk.com/authorize?client_id=' + vkCLientId + '&scope=' + vkRequestedScopes + '&redirect_uri=http%3A%2F%2Foauth.vk.com%2Fblank.html&display=page&response_type=token';

        chrome.storage.local.get({'vkaccess_token': {}}, function (items) {

            if (items.vkaccess_token.length === undefined) {
                chrome.tabs.create({url: vkAuthenticationUrl, selected: true}, function (tab) {
                    chrome.tabs.onUpdated.addListener(listenerHandler(tab.id, imageSourceUrl));
                });

                return;
            }

            imageUploadHelperUrl += imageSourceUrl + '&' + items.vkaccess_token;

            chrome.tabs.create({url: imageUploadHelperUrl, selected: true});

        });
    };
}

/**
 * Handler of chrome context menu creation process -creates a new item in the context menu
 */
chrome.contextMenus.create({
    "title": "Rehost on vk.com",
    "type": "normal",
    "contexts": ["image"],
    "onclick": getClickHandler()
});