NewPage with freeSpace extended

@@ -3,6 +3,7 @@
 ## 3.11.0
 
 - Save in an isolate when available
+- NewPage with freeSpace extended [Stefan]
 
 ## 3.10.8
 

@@ -65,12 +65,20 @@ mixin SpanningWidget on Widget {
       saveContext().apply(context);
 }
 
+/// Trigger a page break if there is not enough free space.
+/// If freeSpace is null, a page break is always performed.
 class NewPage extends Widget {
+  NewPage({this.freeSpace});
+  final double? freeSpace;
+
   @override
   void layout(Context context, BoxConstraints constraints,
       {bool parentUsesSize = false}) {
     box = PdfRect.zero;
   }
+
+  bool newPageNeeded(double availableSpace) =>
+      (freeSpace == null) || (availableSpace < freeSpace!);
 }
 
 @immutable
@@ -230,7 +238,7 @@ class MultiPage extends Page {
             maxHeight: pageFormat.height - _margin.vertical);
     final calculatedTheme = theme ?? document.theme ?? ThemeData.base();
     Context? context;
-    late double offsetEnd;
+    var offsetEnd = 0.0;
     double? offsetStart;
     var _index = 0;
     var sameCount = 0;
@@ -252,8 +260,14 @@ class MultiPage extends Page {
             'This widget created more than $maxPages pages. This may be an issue in the widget or the document. See https://pub.dev/documentation/pdf/latest/widgets/MultiPage-class.html');
       }
 
+      // Calculate available space of the current page
+      final freeSpace = (offsetStart == null)
+          ? fullConstraints.maxHeight
+          : offsetStart - offsetEnd;
+
       // Create a new page if we don't already have one
-      if (context == null || child is NewPage) {
+      if (context == null ||
+          (child is NewPage) && child.newPageNeeded(freeSpace)) {
         final pdfPage = PdfPage(
           document.document,
           pageFormat: pageFormat,

+/*
+ * 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:io';
+
+import 'package:pdf/pdf.dart';
+import 'package:pdf/widgets.dart';
+import 'package:test/test.dart';
+
+late Document pdf;
+
+Widget footer(Context context) {
+  return Footer(
+    trailing: Container(
+      height: 25,
+      child: Text('Page ${context.pageNumber}'),
+    ),
+  );
+}
+
+Widget header(Context context) {
+  return Container(
+    height: 20,
+    child: Text('Test document'),
+  );
+}
+
+List<Widget> contentWithPageBreak(double? freeSpace) {
+  return [
+    Container(
+      color: const PdfColor(0.75, 0.75, 0.75),
+      height: 50,
+      width: 100,
+      child: Text('Page 1'),
+    ),
+    Container(
+      color: const PdfColor(0.6, 0.6, 0.6),
+      height: 40,
+      width: 100,
+    ),
+    Container(
+      color: const PdfColor(0.5, 0.5, 0.5),
+      height: 20,
+      width: 100,
+    ),
+    NewPage(freeSpace: freeSpace),
+    Text('Page 2'),
+  ];
+}
+
+void main() {
+  setUpAll(() {
+    Document.debug = true;
+    RichText.debug = true;
+    pdf = Document();
+  });
+
+  const pageFormatWithoutMargins = PdfPageFormat(200.0, 200.0);
+  const pageFormatWithMargins =
+      PdfPageFormat(200.0, 200.0, marginTop: 10, marginBottom: 20);
+
+  // PageHeight - Content Height
+  // 200 - 110 = 90 available space
+  test('PageBreak normal on page without margins', () {
+    pdf.addPage(MultiPage(
+      pageFormat: pageFormatWithoutMargins,
+      build: (_) => contentWithPageBreak(null),
+    ));
+  });
+
+  test('No PageBreak, because enough space available', () {
+    pdf.addPage(MultiPage(
+      pageFormat: pageFormatWithoutMargins,
+      build: (_) => contentWithPageBreak(90),
+    ));
+  });
+
+  test('PageBreak because more free space needed', () {
+    pdf.addPage(MultiPage(
+      pageFormat: pageFormatWithoutMargins,
+      build: (_) => contentWithPageBreak(91),
+    ));
+  });
+
+  // PageHeight - Margins - Content Height
+  // 200 - 10 - 20 - 20 - 25 - 110 = 15
+  test('PageBreak normal on page with margins, header and footer', () {
+    pdf.addPage(MultiPage(
+      pageFormat: pageFormatWithMargins,
+      build: (_) => contentWithPageBreak(null),
+      header: header,
+      footer: footer,
+    ));
+  });
+
+  test('No PageBreak, because enough space available', () {
+    pdf.addPage(MultiPage(
+      pageFormat: pageFormatWithMargins,
+      build: (_) => contentWithPageBreak(15.0),
+      header: header,
+      footer: footer,
+    ));
+  });
+
+  test('PageBreak because more free space needed', () {
+    pdf.addPage(MultiPage(
+      pageFormat: pageFormatWithMargins,
+      build: (_) => contentWithPageBreak(16.0),
+      header: header,
+      footer: footer,
+    ));
+  });
+
+  tearDownAll(() async {
+    final file = File('widgets-newpage.pdf');
+    await file.writeAsBytes(await pdf.save());
+  });
+}