implemented empty mapper impl

Author: KernelPanic92

generator/lib/src/dartstruct_generator.dart

@@ -1,12 +1,54 @@
 import 'package:analyzer/dart/element/element.dart';
 import 'package:build/src/builder/build_step.dart';
+import 'package:code_builder/code_builder.dart';
+import 'package:dart_style/dart_style.dart';
 import 'package:source_gen/source_gen.dart';
 import 'package:dartstruct/dartstruct.dart';
 
 class DartStructGenerator extends GeneratorForAnnotation<Mapper> {
+  final _emitter = DartEmitter();
+  final _formatter = DartFormatter();
+
   @override
-  generateForAnnotatedElement(
-      Element element, ConstantReader annotation, BuildStep buildStep) {
-    return null;
+  String generateForAnnotatedElement(Element element, ConstantReader annotation, BuildStep buildStep) {
+
+    if (element is! ClassElement) {
+      throw InvalidGenerationSourceError('${element.displayName} cannot be annotated with @Mapper',
+        element: element,
+        todo: 'Remove @Mapper annotation'
+      );
+    }
+
+    final classElement = element as ClassElement;
+
+    if (!classElement.constructors.any((c) => c.isDefaultConstructor)) {
+      throw InvalidGenerationSourceError('${element.displayName} must provide a default constructor',
+        element: element,
+        todo: 'Provide a default constructor'
+      );
+    }
+
+    final classBuilder = ClassBuilder()
+      ..name = '${classElement.displayName}Impl'
+      ..abstract = false
+      ..extend = refer(classElement.displayName)
+      ..methods.addAll(_generateMethods(classElement.methods));
+
+    final mapperImpl = classBuilder.build();
+
+    final code = '${mapperImpl.accept(_emitter)}';
+
+    return _formatter.format(code);
+
+  }
+
+  List<Method> _generateMethods(List<MethodElement> methods) {
+    if (methods.any((method) => method.isAbstract)) {
+      throw InvalidGenerationSourceError('Not implemented yet',
+        todo: 'remove all methods'
+      );
+    }
+
+    return <Method>[];
   }
 }

generator/pubspec.yaml

@@ -8,6 +8,8 @@ environment:
 dependencies:
   build: ^1.2.2
   source_gen: ^0.9.5
+  code_builder: ^3.2.1
+  dart_style: ^1.3.3
   dartstruct:
     path: ../core