// ==UserScript==
// @name         Simple Google Scholar Sci-Hub Access
// @namespace    SimpleScholarAccess
// @version      1.0.0
// @description  Adds Sci-Hub buttons to Google Scholar results and handles DOI links
// @author       Bui Quoc Dung
// @include      https://scholar.google.*/scholar?*
// @match        *://*/*
// @license      AGPL-3.0-or-later
// @downloadURL none
// ==/UserScript==

const SCIHUB_URL = 'https://sci-hub.ru/';
const LIBGEN_URL = 'https://libgen.li/index.php?req=';

function addButtons() {
    const results = document.querySelectorAll('#gs_res_ccl_mid .gs_r.gs_or.gs_scl');

    results.forEach(result => {
        const titleLink = result.querySelector('.gs_rt a');
        let buttonContainer = result.querySelector('.gs_or_ggsm');

        if (!buttonContainer) {
            const div = document.createElement('div');
            div.className = 'gs_ggs gs_fl';
            div.innerHTML = '<div class="gs_ggsd"><div class="gs_or_ggsm"></div></div>';
            result.insertBefore(div, result.firstChild);
            buttonContainer = div.querySelector('.gs_or_ggsm');

            const sciHubLink = document.createElement('a');
            sciHubLink.textContent = 'Sci-Hub';
            sciHubLink.addEventListener('click', () => window.open(SCIHUB_URL + titleLink.href));
            buttonContainer.appendChild(sciHubLink);

            const libGenLink = document.createElement('a');
            libGenLink.textContent = ' LibGen';
            libGenLink.addEventListener('click', () => window.open(LIBGEN_URL + encodeURIComponent(titleLink.textContent)));
            buttonContainer.appendChild(libGenLink);
        }
    });
}

function convertDOIToSciHub(doiURL) {
    return `${SCIHUB_URL}${doiURL.replace('https://doi.org/', '')}`;
}

function handleDOILinks() {
    document.querySelectorAll('a[href^="http://dx.doi.org/"], a[href^="https://doi.org/"]').forEach(link => {
        link.addEventListener('click', (event) => {
            event.preventDefault();
            window.location.href = convertDOIToSciHub(link.href);
        });
    });
}

addButtons();
handleDOILinks();

const observer = new MutationObserver((mutations) => {
    mutations.forEach((mutation) => {
        if (mutation.addedNodes.length) {
            addButtons();
            handleDOILinks();
        }
    });
});

observer.observe(document.body, {
    childList: true,
    subtree: true
});