fis_lib_print/lib/printing_web.dart

/*
 * Copyright (C) 2017, David PHAM-VAN <dev.nfet.net@gmail.com>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import 'dart:async';
import 'dart:html' as html;
import 'dart:html';
import 'dart:js' as js;
import 'dart:js_util';
import 'dart:typed_data';
import 'dart:ui';

import 'package:flutter/foundation.dart';
import 'package:flutter_web_plugins/flutter_web_plugins.dart';
import 'package:image/image.dart' as im;
import 'package:pdf/pdf.dart';

import 'src/callback.dart';
import 'src/interface.dart';
import 'src/mutex.dart';
import 'src/pdfjs.dart';
import 'src/printer.dart';
import 'src/printing_info.dart';
import 'src/raster.dart';

/// Print plugin targeting Flutter on the Web
class PrintingPlugin extends PrintingPlatform {
  /// Registers this class as the default instance of [PrintingPlugin].
  static void registerWith(Registrar registrar) {
    PrintingPlatform.instance = PrintingPlugin();
  }

  static const String _scriptId = '__net_nfet_printing_s__';

  static const String _frameId = '__net_nfet_printing__';

  final String _staticRoot = js.context['STATIC_ROOT']!.toString();

  static const _pdfJsVersion = 'js';

  final _loading = Mutex();

  bool get _hasPdfJsLib => js.context.callMethod('eval', <String>[
        'typeof pdfjsLib !== "undefined" && pdfjsLib.GlobalWorkerOptions.workerSrc!="";'
      ]);

  Future<void> _initPlugin() async {
    await _loading.acquire();

    if (!_hasPdfJsLib) {
      final script = ScriptElement()
        ..type = 'text/javascript'
        ..async = true
        ..src = '$_staticRoot$_pdfJsVersion/pdf.min.js';

      assert(document.head != null);
      document.head!.append(script);

      await script.onLoad.first;

      if (js.context['pdfjsLib'] == null) {
        // In dev, requireJs is loaded in
        final require = js.JsObject.fromBrowserObject(js.context['require']);
        require.callMethod('config', <dynamic>[
          js.JsObject.jsify({
            'paths': {
              'pdfjs-dist/build/pdf': '$_staticRoot$_pdfJsVersion/pdf.min',
              'pdfjs-dist/build/pdf.worker':
                  '$_staticRoot$_pdfJsVersion/pdf.worker.min',
            }
          })
        ]);

        final completer = Completer<void>();

        js.context.callMethod('require', <dynamic>[
          js.JsObject.jsify(
              ['pdfjs-dist/build/pdf', 'pdfjs-dist/build/pdf.worker']),
          (dynamic app) {
            js.context['pdfjsLib'] = app;
            completer.complete();
          }
        ]);

        await completer.future;
      }

      js.context['pdfjsLib']['GlobalWorkerOptions']['workerSrc'] =
          '$_staticRoot$_pdfJsVersion/pdf.worker.min.js';
    }

    _loading.release();
  }

  @override
  Future<PrintingInfo> info() async {
    await _initPlugin();
    return PrintingInfo(
      canPrint: true,
      canShare: true,
      canRaster: _hasPdfJsLib,
    );
  }

  @override
  Future<bool> layoutPdf(
    Printer? printer,
    LayoutCallback onLayout,
    String name,
    PdfPageFormat format,
    bool dynamicLayout,
    bool usePrinterSettings,
  ) async {
    late Uint8List result;
    try {
      result = await onLayout(format);
    } catch (e, s) {
      InformationCollector? collector;

      assert(() {
        collector = () sync* {
          yield StringProperty('PageFormat', format.toString());
        };
        return true;
      }());

      FlutterError.reportError(FlutterErrorDetails(
        exception: e,
        stack: s,
        stackFilter: (input) => input,
        library: 'printing',
        context: ErrorDescription('while generating a PDF'),
        informationCollector: collector,
      ));

      rethrow;
    }

    if (result.isEmpty) {
      return false;
    }

    final String userAgent = js.context['navigator']['userAgent'];
    final isChrome = js.context['chrome'] != null;
    final isSafari = js.context['safari'] != null &&
        !userAgent.contains(RegExp(r'Version/14\.1\.'));
    final isMobile = userAgent.contains('Mobile');
    final isFirefox = userAgent.contains('Firefox');

    // Chrome, Safari, and Firefox on a desktop computer
    if ((isChrome || isSafari || isFirefox) && !isMobile) {
      final completer = Completer<bool>();
      final pdfFile = html.Blob(
        <Uint8List>[result],
        'application/pdf',
      );
      final pdfUrl = html.Url.createObjectUrl(pdfFile);
      final html.HtmlDocument doc = js.context['document'];

      final script =
          doc.getElementById(_scriptId) ?? doc.createElement('script');
      script.setAttribute('id', _scriptId);
      script.setAttribute('type', 'text/javascript');
      script.innerText =
          '''function ${_frameId}_print(){var f=document.getElementById('$_frameId');f.focus();f.contentWindow.print();}''';
      doc.body!.append(script);

      final frame = doc.getElementById(_frameId) ?? doc.createElement('iframe');
      if (isFirefox) {
        // Set the iframe to be is visible on the page (guaranteed by fixed position) but hidden using opacity 0, because
        // this works in Firefox. The height needs to be sufficient for some part of the document other than the PDF
        // viewer's toolbar to be visible in the page
        frame.setAttribute('style',
            'width: 1px; height: 100px; position: fixed; left: 0; top: 0; opacity: 0; border-width: 0; margin: 0; padding: 0');
      } else {
        // Hide the iframe in other browsers
        frame.setAttribute(
          'style',
          'visibility: hidden; height: 0; width: 0; position: absolute;',
          // 'height: 400px; width: 600px; position: absolute; z-index: 1000',
        );
      }

      frame.setAttribute('id', _frameId);
      frame.setAttribute('src', pdfUrl);
      final stopWatch = Stopwatch();

      html.EventListener? load;
      load = (html.Event event) {
        frame.removeEventListener('load', load);
        Timer(Duration(milliseconds: isSafari ? 500 : 0), () {
          try {
            stopWatch.start();
            js.context.callMethod('${_frameId}_print');
            stopWatch.stop();
            completer.complete(true);
          } catch (e) {
            assert(() {
              // ignore: avoid_print
              print('Error: $e');
              return true;
            }());
            completer.complete(_getPdf(result));
          }
        });
      };

      frame.addEventListener('load', load);

      doc.body!.append(frame);

      final res = await completer.future;
      // If print() is synchronous
      if (stopWatch.elapsedMilliseconds > 1000) {
        frame.remove();
        script.remove();
      }
      return res;
    }

    return _getPdf(result);
  }

  @override
  Future<bool> sharePdf(
    Uint8List bytes,
    String filename,
    Rect bounds,
    String? subject,
    String? body,
    List<String>? emails,
  ) async {
    return _getPdf(bytes, filename: filename);
  }

  Future<bool> _getPdf(Uint8List bytes, {String? filename}) async {
    final pdfFile = html.Blob(
      <Uint8List>[bytes],
      'application/pdf',
    );
    final pdfUrl = html.Url.createObjectUrl(pdfFile);
    final html.HtmlDocument doc = js.context['document'];
    final link = html.AnchorElement(href: pdfUrl);
    if (filename != null) {
      link.download = filename;
    } else {
      link.target = '_blank';
    }
    doc.body?.append(link);
    link.click();
    link.remove();
    return true;
  }

  @override
  Future<Uint8List> convertHtml(
    String html,
    String? baseUrl,
    PdfPageFormat format,
  ) {
    throw UnimplementedError();
  }

  @override
  Future<List<Printer>> listPrinters() {
    throw UnimplementedError();
  }

  @override
  Future<Printer> pickPrinter(
    Rect bounds,
  ) {
    throw UnimplementedError();
  }

  @override
  Stream<PdfRaster> raster(
    Uint8List document,
    List<int>? pages,
    double dpi,
  ) async* {
    await _initPlugin();

    final t = PdfJs.getDocument(Settings()..data = document);
    try {
      final d = await promiseToFuture<PdfJsDoc>(t.promise);
      final numPages = d.numPages;

      final html.CanvasElement canvas =
          js.context['document'].createElement('canvas');

      final context = canvas.getContext('2d') as html.CanvasRenderingContext2D?;
      final _pages =
          pages ?? Iterable<int>.generate(numPages, (index) => index);

      for (final i in _pages) {
        final page = await promiseToFuture<PdfJsPage>(d.getPage(i + 1));
        try {
          final viewport =
              page.getViewport(Settings()..scale = dpi / PdfPageFormat.inch);

          canvas.height = viewport.height.toInt();
          canvas.width = viewport.width.toInt();

          final renderContext = Settings()
            ..canvasContext = context!
            ..viewport = viewport;

          await promiseToFuture<void>(page.render(renderContext).promise);

          // Convert the image to PNG
          final completer = Completer<void>();
          final blob = await canvas.toBlob();
          final data = BytesBuilder();
          final r = FileReader();
          r.readAsArrayBuffer(blob);
          r.onLoadEnd.listen(
            (ProgressEvent e) {
              data.add(r.result as List<int>);
              completer.complete();
            },
          );
          await completer.future;

          yield _WebPdfRaster(
            canvas.width!,
            canvas.height!,
            data.toBytes(),
          );
        } finally {
          page.cleanup();
        }
      }
    } finally {
      t.destroy();
    }
  }
}

class _WebPdfRaster extends PdfRaster {
  _WebPdfRaster(
    int width,
    int height,
    this.png,
  ) : super(width, height, Uint8List(0));

  final Uint8List png;

  Uint8List? _pixels;

  @override
  Uint8List get pixels {
    if (_pixels == null) {
      final img = im.PngDecoder().decodeImage(png)!;
      _pixels = img.data.buffer.asUint8List();
    }

    return _pixels!;
  }

  @override
  Future<Image> toImage() async {
    final codec = await instantiateImageCodec(png);
    final frameInfo = await codec.getNextFrame();
    return frameInfo.image;
  }

  @override
  Future<Uint8List> toPng() async {
    return png;
  }
}