/**
 * Reusable PDF Viewer for MkDocs Material
 * 
 * Uses PDF.js to render PDF files in a canvas.
 * Looks for elements with class 'pdf-viewer-container' and a 'data-url' attribute.
 */

document$.subscribe(({ body }) => {
    const containers = body.querySelectorAll('.pdf-viewer-container[data-url]');
    
    if (containers.length === 0) return;

    // Load PDF.js worker if not already loaded
    if (window['pdfjs-dist/build/pdf'] && !window['pdfjs-dist/build/pdf'].GlobalWorkerOptions.workerSrc) {
        window['pdfjs-dist/build/pdf'].GlobalWorkerOptions.workerSrc = 'https://cdnjs.cloudflare.com/ajax/libs/pdf.js/2.16.105/pdf.worker.min.js';
    }

    containers.forEach(container => {
        initPDFViewer(container);
    });
});

function initPDFViewer(container) {
    const url = container.getAttribute('data-url');
    const canvas = container.querySelector('canvas');
    const pageNumDisplay = container.querySelector('.page-num');
    const pageCountDisplay = container.querySelector('.page-count');
    const prevBtn = container.querySelector('.prev-btn');
    const nextBtn = container.querySelector('.next-btn');
    const loadingMsg = container.querySelector('.pdf-viewer-loading');

    if (!canvas || !url) return;

    let pdfDoc = null;
    let pageNum = 1;
    let pageRendering = false;
    let pageNumPending = null;
    const scale = 2.0;
    const ctx = canvas.getContext('2d');

    function renderPage(num) {
        pageRendering = true;
        
        pdfDoc.getPage(num).then(page => {
            if (loadingMsg) loadingMsg.style.display = 'none';
            
            const viewport = page.getViewport({ scale: scale });
            canvas.height = viewport.height;
            canvas.width = viewport.width;

            const renderContext = {
                canvasContext: ctx,
                viewport: viewport
            };
            const renderTask = page.render(renderContext);

            renderTask.promise.then(() => {
                pageRendering = false;
                if (pageNumPending !== null) {
                    renderPage(pageNumPending);
                    pageNumPending = null;
                }
            });
        });

        if (pageNumDisplay) pageNumDisplay.textContent = num;
    }

    function queueRenderPage(num) {
        if (pageRendering) {
            pageNumPending = num;
        } else {
            renderPage(num);
        }
    }

    if (prevBtn) {
        prevBtn.addEventListener('click', () => {
            if (pageNum <= 1) return;
            pageNum--;
            queueRenderPage(pageNum);
        });
    }

    if (nextBtn) {
        nextBtn.addEventListener('click', () => {
            if (pageNum >= pdfDoc.numPages) return;
            pageNum++;
            queueRenderPage(pageNum);
        });
    }

    // Load the document
    const pdfjsLib = window['pdfjs-dist/build/pdf'];
    if (!pdfjsLib) {
        console.error('PDF.js library not found');
        return;
    }

    pdfjsLib.getDocument(url).promise.then(pdfDoc_ => {
        pdfDoc = pdfDoc_;
        if (pageCountDisplay) pageCountDisplay.textContent = pdfDoc.numPages;
        renderPage(pageNum);
    }).catch(err => {
        console.error('Error loading PDF:', err);
        if (loadingMsg) loadingMsg.textContent = "Error loading PDF.";
    });
}