import { insertScript } from '../../core';

const PDFJS_BUNDLE = "https://cdn.jsdelivr.net/npm/pdfjs-dist@3.0.279/build/pdf.min.js";
const WORKER_BUNDLE = "https://cdn.jsdelivr.net/npm/pdfjs-dist@3.0.279/build/pdf.worker.min.js";

class PDFViewer {
  constructor(el) {
    const {
      url,
      hidePaginator,
      hideLoader,
      scale,
      pageNum
    } = el.dataset;

    if(url == null) {
      throw new Error('Cannot load PDF! Attribute `data-url` is not set.');      
    }

    // props
    this.url = url;
    this.hidePaginator = hidePaginator !== 'false';
    this.hideLoader = hideLoader !== 'false';
    this.scale = scale || 3;

    // initial state
    this.pageNum = parseInt(pageNum ,10) || 1;
    this.loaded = false;
    this.pageRendering = false;
    this.pageNumPending = null;

    // DOM elements
    this.$canvas = el.getElementsByClassName('pdf-canvas')[0];
    if(this.$canvas == null) {
      throw new Error('canvas element not found!');
    };
    this.$paginator = el.getElementsByClassName("paginator")[0];
    this.$loadingWrapper = el.getElementsByClassName('loading-wrapper')[0];
    this.$next = el.getElementsByClassName('next')[0];
    this.$prev = el.getElementsByClassName('prev')[0];
    this.$pageNum = el.getElementsByClassName('page-num')[0];
    this.$pageCount = el.getElementsByClassName('page-count')[0];

    // context
    this.ctx = this.$canvas.getContext('2d');

    // events
    this.$next.addEventListener('click', this.handleNextPage.bind(this));
    this.$prev.addEventListener('click', this.handlePrevPage.bind(this));

    this.showPaginator();
    this.showLoader();
    this.loadPDF();
  }

  /**
   * If we haven't disabled the loader, show loader and hide canvas
   */
  showLoader() {
    if(this.hideLoader) return;
    this.$loadingWrapper.style.display = 'flex';
    this.$canvas.style.display = 'none';
  }

  /**
   * If we haven't disabled the paginator, show paginator
   */
   showPaginator() {
    if(this.hidePaginator) return;
    this.$paginator.style.display = 'block';
  }

  /**
   * Hides loader and shows canvas
   */
  showContent() {
    this.$loadingWrapper.style.display = 'none';
    this.$canvas.style.display = 'block';
  }

  /**
   * Asynchronously downloads PDF.
   */
  async loadPDF() {
    this.pdfDoc = await window.pdfjsLib.getDocument(this.url).promise;

    this.$pageCount.textContent = this.pdfDoc.numPages;

    // If the user passed in a number that is out of range, render the last page.
    if(this.pageNum > this.pdfDoc.numPages) {
      this.pageNum = this.pdfDoc.numPages
    }

    this.renderPage(this.pageNum);
  }

  /**
   * Get page info from document, resize canvas accordingly, and render page.
   * @param num Page number.
   */
  async renderPage(num) {
    this.pageRendering = true;

    const page = await this.pdfDoc.getPage(num);
    const viewport = page.getViewport({ scale: this.scale });
    this.$canvas.height = viewport.height;
    this.$canvas.width = viewport.width;
  
    // Wait for rendering to finish
    await page.render({
      canvasContext: this.ctx,
      viewport,
    }).promise;

    this.pageRendering = false;
    this.showContent();

    if (this.pageNumPending !== null) {
      // New page rendering is pending
      this.renderPage(this.pageNumPending);
      this.pageNumPending = null;
    }
    // Update page counters
    this.$pageNum.textContent = num;
  }

  /**
   * If another page rendering in progress, waits until the rendering is
   * finished. Otherwise, executes rendering immediately.
   */
  queueRenderPage(num) {
    if (this.pageRendering) {
      this.pageNumPending = num;
    } else {
      this.renderPage(num);
    }
  }

  /**
   * Displays previous page.
   */
  handlePrevPage() {
    if (this.pageNum <= 1) {
      return;
    }
    this.pageNum--;
    this.queueRenderPage(this.pageNum);
  }

  /**
   * Displays next page.
   */
  handleNextPage() {
    if (this.pageNum >= this.pdfDoc.numPages) {
      return;
    }
    this.pageNum++;
    this.queueRenderPage(this.pageNum);
  }
}

insertScript('pdfjs', PDFJS_BUNDLE, () => {
  window.pdfjsLib.GlobalWorkerOptions.workerSrc = WORKER_BUNDLE;

  Array.from(document.getElementsByClassName('pdf-viewer')).forEach(el => {
    console.log(el);
    new PDFViewer(el);
  });
});