background.js

// "people got mad when i put it all in one file" —Julia Evans

/*
===============================
WebExtension specific functions
===============================
*/

/*
Returns true only if the URL's protocol is in APPLICABLE_PROTOCOLS.
*/
function protocolIsApplicable(tabUrl) {
    const APPLICABLE_PROTOCOLS = ['http:', 'https:'];
    let url = new URL(tabUrl);
    return APPLICABLE_PROTOCOLS.includes(url.protocol);
}

/*
Returns true if user set option to always display the page action
*/
async function userAlwaysWantsIcon() {
    let option = await browser.storage.local.get("alwaysShowPageAction");

    if (typeof option.alwaysShowPageAction !== "boolean") {
        return false;
    } else {
        return option.alwaysShowPageAction;
    }
}

async function pageIsInForeignLanguage(tabId) {
    // Get the page's language. If not found, assume it's foreign.
    // Better to show the translate icon when it is not needed than vice versa
    try {
        var pageLanguage = await browser.tabs.detectLanguage(tabId);
    } catch (err) {
        return true;
    }

    if (!pageLanguage || pageLanguage === "und") {
        return true;
    }

    // Normalize page language and browser languages
    pageLanguage = pageLanguage.toLowerCase();

    let navigatorLanguages = navigator.languages.map(navigatorLanguage => {
        return navigatorLanguage.toLowerCase();
    });

    // Check if the page's language explicitly matches any of browser's preferred languages
    if (navigatorLanguages.includes(pageLanguage)) {
        return false;
    }

    // If you're still here, then check for match of primary language subtags
    // If so, assume close enough to native language.

    // Get array of the primary languages from the browser, i.e. those without a hyphen
    // Ex: `en` but not `en-SV`
    let primaryLanguageSubtags = navigatorLanguages.filter(language => {
        return language.indexOf('-') === -1;
    });

    // If no primary language subtag specified in browser, the user has explicitly removed it,
    // so assume they want explicit language match instead of partial match.
    if (primaryLanguageSubtags.length === 0) {
        return true;
    }

    // Get page's language subtag 
    let pageLanguageSubtag = pageLanguage.split('-', 1)[0];

    // Look for primary language subtag match
    if (primaryLanguageSubtags.includes(pageLanguageSubtag)) {
        return false;
    }

    // No match, so page is in foreign language.
    return true;
}

/*
Show the Page Translator page action in the browser address bar, if applicable.
*/
async function initializePageAction(tab) {
    if (protocolIsApplicable(tab.url) &&
        (await userAlwaysWantsIcon() === true || await pageIsInForeignLanguage(tab.id) === true)
    ) {
        browser.pageAction.show(tab.id);
    } else {
        browser.pageAction.hide(tab.id);
    }
}



/*
=============================
Page Translator functionality
=============================
*/

function injectTranslatorCode() {
    let googleCode = `
        let docBody = document.body;

        if (docBody !== null) {
            let googleTranslateCallback = document.createElement('script');
            googleTranslateCallback.innerHTML = "function googleTranslateElementInit(){ new google.translate.TranslateElement(); }";
            docBody.insertBefore(googleTranslateCallback, docBody.firstChild);

            let googleTranslateScript = document.createElement('script');
            googleTranslateScript.charset="UTF-8";
            googleTranslateScript.src = "https://translate.google.com/translate_a/element.js?cb=googleTranslateElementInit&tl=&sl=&hl=";
            docBody.insertBefore(googleTranslateScript, docBody.firstChild);
        }

        // Firefox 53 will (erroneously?) complain if non-structured-clonable data isn't returned.
        // https://github.com/mdn/webextensions-examples/issues/193
        true;
    `;

    let microsoftCode = `
        let docBody = document.body;

        if (docBody !== null) {
            let div = '<div id="MicrosoftTranslatorWidget" class="Dark" style="color:white;background-color:#555555"></div>';
            docBody.insertAdjacentHTML("afterbegin", div);

            let microsoftTranslatorScript = document.createElement("script");
            microsoftTranslatorScript.charset="UTF-8";
            microsoftTranslatorScript.src = "https://ssl.microsofttranslator.com/ajax/v3/WidgetV3.ashx?siteData=ueOIGRSKkd965FeEGM5JtQ**&ctf=False&ui=true&settings=Auto&from=";
            docBody.insertBefore(microsoftTranslatorScript, docBody.firstChild);
        }

        // Firefox 53 will (erroneously?) complain if non-structured-clonable data isn't returned.
        // https://github.com/mdn/webextensions-examples/issues/193
        true;
    `;

    let executeScript = function(option) {
        let injectDetails = {};

        if ((typeof option.translationService !== "undefined") &&
            (option.translationService === "microsoft")) {
            injectDetails.code = microsoftCode;
        } else {
            injectDetails.code = googleCode;
        }

        browser.tabs.executeScript(injectDetails);
    };

    browser.storage.local.get("translationService").then(executeScript);
}



/*
==========
INITIALIZE
==========
*/

/*
When initialized, add the page action for all tabs.
*/
browser.tabs.query({}).then((tabs) => {
    for (tab of tabs) {
        initializePageAction(tab);
    }
});

/*
When a tab is updated, reset the page action for that tab.
*/
browser.tabs.onUpdated.addListener((id, changeInfo, tab) => {
    if ((typeof changeInfo.status === "string") && (changeInfo.status === "complete")) {
        initializePageAction(tab);
    }
});

/*
Bind clicks on the page action icon to the WebExtension
*/
browser.pageAction.onClicked.addListener(injectTranslatorCode);