Automatic pdf.js library loading

@@ -6,6 +6,7 @@
 - Fix parsing TTF fonts with zero-length glyphs
 - Fix PdfPreview page format and orientation updates
 - Update Pdfium version to 4929
+- Automatic pdf.js library loading
 
 ## 5.7.2
 

@@ -36,8 +36,9 @@ for documentation.
    ```
 4. For MacOS add printing capability by opening macos directory in XCode
 
-5. For the web, a javascript library and a small script has to be added to
-   your `web/index.html` file, just before `</head>`:
+5. If you want to manually set the PdfJs library version for the web, a javascript
+   library and a small script has to be added to your `web/index.html` file, just
+   before `</head>`. Otherwise it is loaded automatically:
 
    ```html
    <script src="//cdnjs.cloudflare.com/ajax/libs/pdf.js/2.8.335/pdf.min.js"></script>

@@ -8,8 +8,6 @@ analyzer:
     missing_return: warning
     public_member_api_docs: ignore
     todo: ignore
-    constant_identifier_names: ignore
-    avoid_print: ignore
 
 linter:
   rules:

@@ -29,12 +29,13 @@ 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 targetting Flutter on the Web
+/// 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) {
@@ -45,16 +46,67 @@ class PrintingPlugin extends PrintingPlatform {
 
   static const String _frameId = '__net_nfet_printing__';
 
-  @override
-  Future<PrintingInfo> info() async {
-    final dynamic workerSrc = js.context.callMethod('eval', <String>[
+  static const _pdfJsVersion =
+      'https://cdnjs.cloudflare.com/ajax/libs/pdf.js/2.13.216';
+
+  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 = '$_pdfJsVersion/pdf.min.js';
+      assert(document.head != null);
+      document.head!.append(script);
+      await script.onLoad.first;
+
+      if (js.context['pdfjsLib'] == null) {
+        // In dev, requireJs is loaded in
+        final require = js.JsObject.fromBrowserObject(js.context['require']);
+        require.callMethod('config', <dynamic>[
+          js.JsObject.jsify({
+            'paths': {
+              'pdfjs-dist/build/pdf': '$_pdfJsVersion/pdf.min',
+              'pdfjs-dist/build/pdf.worker': '$_pdfJsVersion/pdf.worker.min',
+            }
+          })
+        ]);
+
+        final completer = Completer<void>();
+
+        js.context.callMethod('require', <dynamic>[
+          js.JsObject.jsify(
+              ['pdfjs-dist/build/pdf', 'pdfjs-dist/build/pdf.worker']),
+          (dynamic app) {
+            js.context['pdfjsLib'] = app;
+            completer.complete();
+          }
+        ]);
+
+        await completer.future;
+      }
+
+      js.context['pdfjsLib']['GlobalWorkerOptions']['workerSrc'] =
+          '$_pdfJsVersion/pdf.worker.min.js';
+    }
+
+    _loading.release();
+  }
+
+  @override
+  Future<PrintingInfo> info() async {
+    await _initPlugin();
     return PrintingInfo(
       canPrint: true,
       canShare: true,
-      canRaster: workerSrc,
+      canRaster: _hasPdfJsLib,
     );
   }
 
@@ -235,6 +287,8 @@ class PrintingPlugin extends PrintingPlatform {
     List<int>? pages,
     double dpi,
   ) async* {
+    await _initPlugin();
+
     final t = PdfJs.getDocument(Settings()..data = document);
 
     final d = await promiseToFuture<PdfJsDoc>(t.promise);

@@ -19,6 +19,8 @@ import 'dart:convert';
 
 import 'package:flutter/services.dart';
 
+import '../mutex.dart';
+
 /// Application asset manifest.
 mixin AssetManifest {
   static final _assets = <String>[];
@@ -63,29 +65,3 @@ mixin AssetManifest {
     return _assets.contains(key);
   }
 }
-
-/// Simple Mutex
-class Mutex {
-  final _waiting = <Completer>[];
-
-  bool _locked = false;
-
-  /// Lock the mutex
-  Future<void> acquire() async {
-    if (_locked) {
-      final c = Completer<void>();
-      _waiting.add(c);
-      await c.future;
-    }
-    _locked = true;
-  }
-
-  /// Release the mutex
-  void release() {
-    _locked = false;
-    for (final e in _waiting) {
-      e.complete();
-    }
-    _waiting.clear();
-  }
-}

+/*
+ * 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';
+
+/// Simple Mutex
+class Mutex {
+  final _waiting = <Completer>[];
+
+  bool _locked = false;
+
+  bool get locked => _locked;
+
+  /// Wait for the mutex to be available
+  Future<void> wait() async {
+    await acquire();
+    release();
+  }
+
+  /// Lock the mutex
+  Future<void> acquire() async {
+    if (_locked) {
+      final c = Completer<void>();
+      _waiting.add(c);
+      await c.future;
+    }
+    _locked = true;
+  }
+
+  /// Release the mutex
+  void release() {
+    _locked = false;
+    for (final e in _waiting) {
+      e.complete();
+    }
+    _waiting.clear();
+  }
+}