// Copyright (c) Jupyter Development Team.
// Distributed under the terms of the Modified BSD License.

import { IRenderMime } from '@jupyterlab/rendermime-interfaces';

import { PromiseDelegate } from '@lumino/coreutils';

import { DisposableDelegate } from '@lumino/disposable';

import { Widget } from '@lumino/widgets';

/**
 * The MIME type for PDF.
 */
const MIME_TYPE = 'application/pdf';

/**
 * A class for rendering a PDF document.
 */
export class RenderedPDF extends Widget implements IRenderMime.IRenderer {
  constructor() {
    super();
    this.addClass('jp-PDFContainer');
    // We put the object in an iframe, which seems to have a better chance
    // of retaining its scroll position upon tab focusing, moving around etc.
    const iframe = document.createElement('iframe');
    this.node.appendChild(iframe);
    // The iframe content window is not available until the onload event.
    iframe.onload = () => {
      const body = iframe.contentWindow.document.createElement('body');
      body.style.margin = '0px';
      iframe.contentWindow.document.body = body;
      this._object = iframe.contentWindow.document.createElement('object');
      this._object.type = MIME_TYPE;
      this._object.width = '100%';
      this._object.height = '100%';
      body.appendChild(this._object);
      this._ready.resolve(void 0);
    };
  }

  /**
   * Render PDF into this widget's node.
   */
  async renderModel(model: IRenderMime.IMimeModel): Promise<void> {
    await this._ready.promise;
    let data = model.data[MIME_TYPE] as string;
    if (
      !data ||
      (data.length === this._base64.length && data === this._base64)
    ) {
      // If there is no data, or if the string has not changed, we do not
      // need to re-parse the data and rerender. We do, however, check
      // for a fragment if the user wants to scroll the output.
      if (model.metadata.fragment && this._object.data) {
        const url = this._object.data;
        this._object.data = `${url.split('#')[0]}${model.metadata.fragment}`;
      }
      // For some opaque reason, Firefox seems to loose its scroll position
      // upon unhiding a PDF. But triggering a refresh of the URL makes it
      // find it again. No idea what the reason for this is.
      if (Private.IS_FIREFOX) {
        this._object.data = this._object.data;
      }
      return Promise.resolve(void 0);
    }
    this._base64 = data;
    const blob = Private.b64toBlob(data, MIME_TYPE);

    // Release reference to any previous object url.
    if (this._disposable) {
      this._disposable.dispose();
    }
    let objectUrl = URL.createObjectURL(blob);
    if (model.metadata.fragment) {
      objectUrl += model.metadata.fragment;
    }
    this._object.data = objectUrl;

    // Set the disposable release the object URL.
    this._disposable = new DisposableDelegate(() => {
      try {
        URL.revokeObjectURL(objectUrl);
      } catch (error) {
        /* no-op */
      }
    });
    return;
  }

  /**
   * Handle a `before-hide` message.
   */
  protected onBeforeHide(): void {
    // Dispose of any URL fragment before hiding the widget
    // so that it is not remembered upon show. Only Firefox
    // seems to have a problem with this.
    if (Private.IS_FIREFOX) {
      this._object.data = this._object.data.split('#')[0];
    }
  }

  /**
   * Dispose of the resources held by the pdf widget.
   */
  dispose() {
    if (this._disposable) {
      this._disposable.dispose();
    }
    super.dispose();
  }

  private _base64 = '';
  private _disposable: DisposableDelegate | null = null;
  private _object: HTMLObjectElement;
  private _ready = new PromiseDelegate<void>();
}

/**
 * A mime renderer factory for PDF data.
 */
export const rendererFactory: IRenderMime.IRendererFactory = {
  safe: false,
  mimeTypes: [MIME_TYPE],
  defaultRank: 100,
  createRenderer: options => new RenderedPDF()
};

const extensions: IRenderMime.IExtension | IRenderMime.IExtension[] = [
  {
    id: '@jupyterlab/pdf-extension:factory',
    rendererFactory,
    dataType: 'string',
    fileTypes: [
      {
        name: 'PDF',
        displayName: 'PDF',
        fileFormat: 'base64',
        mimeTypes: [MIME_TYPE],
        extensions: ['.pdf']
      }
    ],
    documentWidgetFactoryOptions: {
      name: 'PDF',
      modelName: 'base64',
      primaryFileType: 'PDF',
      fileTypes: ['PDF'],
      defaultFor: ['PDF']
    }
  }
];

export default extensions;

/**
 * A namespace for PDF widget private data.
 */
namespace Private {
  /**
   * A flag for determining whether the user is using Firefox.
   * There are some different PDF viewer behaviors on Firefox,
   * and we try to address them with this. User agent string parsing
   * is *not* reliable, so this should be considered a best-effort test.
   */
  export const IS_FIREFOX: boolean = /Firefox/.test(navigator.userAgent);

  /**
   * Convert a base64 encoded string to a Blob object.
   * Modified from a snippet found here:
   * https://stackoverflow.com/questions/16245767/creating-a-blob-from-a-base64-string-in-javascript
   *
   * @param b64Data - The base64 encoded data.
   *
   * @param contentType - The mime type of the data.
   *
   * @param sliceSize - The size to chunk the data into for processing.
   *
   * @returns a Blob for the data.
   */
  export function b64toBlob(
    b64Data: string,
    contentType: string = '',
    sliceSize: number = 512
  ): Blob {
    const byteCharacters = atob(b64Data);
    let byteArrays: Uint8Array[] = [];

    for (let offset = 0; offset < byteCharacters.length; offset += sliceSize) {
      let slice = byteCharacters.slice(offset, offset + sliceSize);

      let byteNumbers = new Array(slice.length);
      for (let i = 0; i < slice.length; i++) {
        byteNumbers[i] = slice.charCodeAt(i);
      }
      let byteArray = new Uint8Array(byteNumbers);
      byteArrays.push(byteArray);
    }

    return new Blob(byteArrays, { type: contentType });
  }
}
