// ==UserScript==
// @name         Google Scholar to free PDFs
// @namespace    ScholarToSciHub
// @version      1.11
// @description  Adds Sci-Hub, LibGen, LibSTC and Anna's Archive buttons to Google Scholar results
// @author       Bui Quoc Dung
// @match        https://scholar.google.*/*
// @license      AGPL-3.0-or-later
// @grant        GM_xmlhttpRequest
// @downloadURL none
// ==/UserScript==

const SCIHUB_URL = 'https://www.tesble.com/';
const LIBGEN_URL = 'https://libgen.li/index.php?req=';
const ANNA_URL = 'https://annas-archive.org/scidb/';
const ANNA_CHECK_URL = 'https://annas-archive.org/search?index=journals&q=';
const LIBSTC_BASE_URL = 'https://hub.libstc.cc/';
const SCINET_URL = 'https://sci-net.xyz/';
const DOI_REGEX = /\b(10\.\d{4,}(?:\.\d+)*\/(?:(?!["&'<>])\S)+)\b/gi;

function updateLink(span, textContent, href, isNo = false) {
    const link = document.createElement('a');
    link.textContent = textContent;
    link.href = href;
    link.target = '_blank';
    link.rel = 'noreferrer noopener';
    link.style.fontSize = '15px';
    if (isNo) link.style.color = 'gray';
    link.innerHTML = textContent.replace('[PDF]', '<b>[PDF]</b>');
    span.replaceWith(link);
}



function fetchDOI(titleLink, callback) {
    GM_xmlhttpRequest({
        method: 'GET',
        url: titleLink.href,
        onload: res => {
            const matches = res.responseText.match(DOI_REGEX);
            callback(matches && matches.length ? matches[0] : null);
        },
        onerror: () => callback(null)
    });
}

function addLoadingIndicator(container) {
    const span = document.createElement('div');
    span.textContent = 'Loading...';
    span.style.marginBottom = '4px';
    span.style.color = 'gray';
    span.style.fontSize = '15px';
    container.appendChild(span);
    return span;
}

function checkLibGenPDF(title, span) {
    GM_xmlhttpRequest({
        method: 'GET',
        url: LIBGEN_URL + encodeURIComponent(title),
        onload: res => {
            const doc = new DOMParser().parseFromString(res.responseText, 'text/html');
            const hasPDF = !!doc.querySelector('.table.table-striped');
            updateLink(span, hasPDF ? '[PDF] LibGen' : '[No] LibGen', LIBGEN_URL + encodeURIComponent(title), !hasPDF);
        },
        onerror: () => updateLink(span, '[No] LibGen', LIBGEN_URL + encodeURIComponent(title), true)
    });
}

function checkSciHubPDF(url, span) {
    GM_xmlhttpRequest({
        method: 'GET',
        url: SCIHUB_URL + url,
        onload: res => {
            const hasPDF = /iframe|pdf|embed/i.test(res.responseText);
            updateLink(span, hasPDF ? '[PDF] Sci-Hub' : '[No] Sci-Hub', SCIHUB_URL + url, !hasPDF);
        },
        onerror: () => updateLink(span, '[No] Sci-Hub', SCIHUB_URL + url, true)
    });
}

function checkAnnaPDF(doi, span) {
    const checkUrl = ANNA_CHECK_URL + encodeURIComponent(doi);
    GM_xmlhttpRequest({
        method: 'GET',
        url: checkUrl,
        onload: res => {
            const doc = new DOMParser().parseFromString(res.responseText, 'text/html');
            const hasPDF = !!doc.querySelector('.mt-4.uppercase.text-xs.text-gray-500');
            updateLink(span, hasPDF ? '[PDF] Anna' : '[No] Anna', ANNA_URL + doi, !hasPDF);
        },
        onerror: () => updateLink(span, '[No] Anna', ANNA_URL + doi, true)
    });
}

function checkLibSTCPDF(doi, span) {
    const url = LIBSTC_BASE_URL + doi + '.pdf';
    GM_xmlhttpRequest({
        method: 'HEAD',
        url: url,
        onload: res => {
            const isPDF = res.status === 200 && res.responseHeaders.toLowerCase().includes('application/pdf');
            updateLink(span, isPDF ? '[PDF] LibSTC' : '[No] LibSTC', url, !isPDF);
        },
        onerror: () => updateLink(span, '[No] LibSTC', url, true)
    });
}

function checkSciNetPDF(doi, span) {
    const sciNetUrl = SCINET_URL + doi;
    GM_xmlhttpRequest({
        method: 'GET',
        url: sciNetUrl,
        onload: function(response) {
            const hasPDF = /iframe|pdf|embed/.test(response.responseText);
            updateLink(span, hasPDF ? '[PDF] Sci-net' : '[No] Sci-net', sciNetUrl, !hasPDF);
        },
        onerror: function() {
            updateLink(span, '[No] Sci-net', sciNetUrl, true);
        }
    });
}



function addButtons() {
    document.querySelectorAll('#gs_res_ccl_mid .gs_r.gs_or.gs_scl').forEach(result => {
        const titleLink = result.querySelector('.gs_rt a');
        const yearElement = result.querySelector('.gs_a');
        if (!titleLink || !yearElement) return;

        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');
        }

        if (buttonContainer.classList.contains('scihub-processed')) return;
        buttonContainer.classList.add('scihub-processed');

        // Hàng 1: Sci-Hub + LibGen
        const row1 = document.createElement('span');
        row1.style.display = 'inline-flex';
        row1.style.gap = '6px';

        const scihubSpan = addLoadingIndicator(row1);
        const libgenSpan = addLoadingIndicator(row1);
        buttonContainer.appendChild(row1);

        // Hàng 2: Anna + SciNet
        const row2 = document.createElement('span');
        row2.style.display = 'inline-flex';
        row2.style.gap = '6px';

        const annaSpan = addLoadingIndicator(row2);
        const scinetSpan = addLoadingIndicator(row2);
        buttonContainer.appendChild(row2);

        // Hàng 3: LibSTC (riêng một hàng)
        const row3 = document.createElement('span');
        row3.style.display = 'flex';  // flex thì tự động block
        row3.style.gap = '6px';
        row3.style.marginTop = '4px';

        const libstcSpan = addLoadingIndicator(row3);
        buttonContainer.appendChild(row3);


        // Kiểm tra PDF và cập nhật nút
        checkSciHubPDF(titleLink.href, scihubSpan);
        checkLibGenPDF(titleLink.textContent, libgenSpan);

        fetchDOI(titleLink, (doi) => {
            if (doi) {
                checkAnnaPDF(doi, annaSpan);
                checkSciNetPDF(doi, scinetSpan);
                checkLibSTCPDF(doi, libstcSpan);
            } else {
                updateLink(annaSpan, '[No] Anna', '#', true);
                updateLink(scinetSpan, '[No] Sci-net', '#', true);
                updateLink(libstcSpan, '[No] LibSTC', '#', true);
            }
        });
    });
}


addButtons();

new MutationObserver((mutations) => {
    mutations.forEach((mutation) => mutation.addedNodes.length && addButtons());
}).observe(document.body, {childList: true, subtree: true});