Refactored the AssetGenImage code to be another Integration (#432)

## What does this change?

Refactored the `AssetGenImage` code to be another Integration, so that
it looks more similar to SVG/Lottie/Rive/etc.

This simplifies the assets_generator, and no longer forces
`AssetGenImage` to be output even when there are no images.

This can help ensure all integration are on level footing (perhaps
helping with task 1 in this list
#384)

## Type of change

- [x] Refactor to cleanup the code base.

## Checklist:

Before submitting your PR, there are a few things you can do to make
sure it goes smoothly:

- [ ] Make sure to open a GitHub issue as a bug/feature request before
writing your code! That way we can discuss the change, evaluate designs,
and agree on the general idea
  - [x] Ensure the tests (`melos run unit:test`)
- [x] Ensure the analyzer and formatter pass (`melos run format` to
automatically apply formatting)

Author: bramp

packages/core/lib/generators/assets_generator.dart

@@ -6,6 +6,7 @@ import 'package:dart_style/dart_style.dart';
 import 'package:dartx/dartx.dart';
 import 'package:flutter_gen_core/generators/generator_helper.dart';
 import 'package:flutter_gen_core/generators/integrations/flare_integration.dart';
+import 'package:flutter_gen_core/generators/integrations/image_integration.dart';
 import 'package:flutter_gen_core/generators/integrations/integration.dart';
 import 'package:flutter_gen_core/generators/integrations/lottie_integration.dart';
 import 'package:flutter_gen_core/generators/integrations/rive_integration.dart';
@@ -60,6 +61,7 @@ String generateAssets(
   final classesBuffer = StringBuffer();
 
   final integrations = <Integration>[
+    ImageIntegration(config.packageParameterLiteral),
     if (config.flutterGen.integrations.flutterSvg)
       SvgIntegration(config.packageParameterLiteral),
     if (config.flutterGen.integrations.flareFlutter)
@@ -162,11 +164,7 @@ String generateAssets(
     throw 'The value of "flutter_gen/assets/style." is incorrect.';
   }
 
-  classesBuffer.writeln(_assetGenImageClassDefinition(
-    config.packageParameterLiteral,
-  ));
-
-  final imports = <String>{'package:flutter/widgets.dart'};
+  final imports = <String>{};
   integrations
       .where((integration) => integration.isEnabled)
       .forEach((integration) {
@@ -254,17 +252,7 @@ _Statement? _createAssetTypeStatement(
   String name,
 ) {
   final childAssetAbsolutePath = join(config.rootPath, assetType.path);
-  if (assetType.isSupportedImage) {
-    return _Statement(
-      type: 'AssetGenImage',
-      filePath: assetType.path,
-      name: name,
-      value: 'AssetGenImage(\'${posixStyle(assetType.path)}\')',
-      isConstConstructor: true,
-      isDirectory: false,
-      needDartDoc: true,
-    );
-  } else if (FileSystemEntity.isDirectorySync(childAssetAbsolutePath)) {
+  if (FileSystemEntity.isDirectorySync(childAssetAbsolutePath)) {
     final childClassName = '\$${assetType.path.camelCase().capitalize()}Gen';
     return _Statement(
       type: childClassName,
@@ -535,95 +523,6 @@ class $className {
 ''';
 }
 
-String _assetGenImageClassDefinition(String packageName) {
-  final bool isPackage = packageName.isNotEmpty;
-  final packageParameter = isPackage ? ' = package' : '';
-
-  final keyName = packageName.isEmpty
-      ? '_assetName'
-      : "'packages/$packageName/\$_assetName'";
-
-  return '''
-
-class AssetGenImage {
-  const AssetGenImage(this._assetName);
-
-  final String _assetName;
-${isPackage ? "\n  static const String package = '$packageName';" : ''}
-
-  Image image({
-    Key? key,
-    AssetBundle? bundle,
-    ImageFrameBuilder? frameBuilder,
-    ImageErrorWidgetBuilder? errorBuilder,
-    String? semanticLabel,
-    bool excludeFromSemantics = false,
-    double? scale,
-    double? width,
-    double? height,
-    Color? color,
-    Animation<double>? opacity,
-    BlendMode? colorBlendMode,
-    BoxFit? fit,
-    AlignmentGeometry alignment = Alignment.center,
-    ImageRepeat repeat = ImageRepeat.noRepeat,
-    Rect? centerSlice,
-    bool matchTextDirection = false,
-    bool gaplessPlayback = false,
-    bool isAntiAlias = false,
-    ${isPackage ? deprecationMessagePackage : ''}
-    String? package$packageParameter,
-    FilterQuality filterQuality = FilterQuality.low,
-    int? cacheWidth,
-    int? cacheHeight,
-  }) {
-    return Image.asset(
-      _assetName,
-      key: key,
-      bundle: bundle,
-      frameBuilder: frameBuilder,
-      errorBuilder: errorBuilder,
-      semanticLabel: semanticLabel,
-      excludeFromSemantics: excludeFromSemantics,
-      scale: scale,
-      width: width,
-      height: height,
-      color: color,
-      opacity: opacity,
-      colorBlendMode: colorBlendMode,
-      fit: fit,
-      alignment: alignment,
-      repeat: repeat,
-      centerSlice: centerSlice,
-      matchTextDirection: matchTextDirection,
-      gaplessPlayback: gaplessPlayback,
-      isAntiAlias: isAntiAlias,
-      package: package,
-      filterQuality: filterQuality,
-      cacheWidth: cacheWidth,
-      cacheHeight: cacheHeight,
-    );
-  }
-
-  ImageProvider provider({
-    AssetBundle? bundle,
-    ${isPackage ? deprecationMessagePackage : ''}
-    String? package$packageParameter,
-  }) {
-    return AssetImage(
-      _assetName,
-      bundle: bundle,
-      package: package,
-    );
-  }
-
-  String get path => _assetName;
-
-  String get keyName => $keyName;
-}
-''';
-}
-
 class _Statement {
   const _Statement({
     required this.type,

packages/core/lib/generators/integrations/flare_integration.dart

@@ -2,14 +2,13 @@ import 'package:flutter_gen_core/generators/integrations/integration.dart';
 import 'package:flutter_gen_core/settings/asset_type.dart';
 
 class FlareIntegration extends Integration {
-  FlareIntegration(String packageParameterLiteral)
-      : super(packageParameterLiteral);
+  FlareIntegration(String packageName) : super(packageName);
 
-  String? get packageExpression =>
-      isPackage ? 'packages/$packageParameterLiteral/' : null;
+  String? get packageExpression => isPackage ? 'packages/$packageName/' : null;
 
   @override
   List<String> get requiredImports => [
+        'package:flutter/widgets.dart',
         'package:flare_flutter/flare_actor.dart',
         'package:flare_flutter/flare_controller.dart',
       ];
@@ -21,7 +20,7 @@ class FlareIntegration extends Integration {
   const FlareGenImage(this._assetName);
 
   final String _assetName;
-${isPackage ? "\n  static const String package = '$packageParameterLiteral';" : ''}
+${isPackage ? "\n  static const String package = '$packageName';" : ''}
 
   FlareActor flare({
     String? boundsNode,

packages/core/lib/generators/integrations/image_integration.dart

@@ -0,0 +1,125 @@
+import 'package:flutter_gen_core/generators/integrations/integration.dart';
+import 'package:flutter_gen_core/settings/asset_type.dart';
+
+/// The main image integration, supporting all image asset types. See
+/// [isSupport] for the exact supported mime types.
+///
+/// This integration is by enabled by default.
+class ImageIntegration extends Integration {
+  ImageIntegration(String packageName) : super(packageName);
+
+  String get packageParameter => isPackage ? ' = package' : '';
+
+  String get keyName =>
+      isPackage ? "'packages/$packageName/\$_assetName'" : '_assetName';
+
+  @override
+  List<String> get requiredImports => ['package:flutter/widgets.dart'];
+
+  @override
+  String get classOutput => _classDefinition;
+
+  String get _classDefinition => '''class AssetGenImage {
+  const AssetGenImage(this._assetName);
+
+  final String _assetName;
+${isPackage ? "\n  static const String package = '$packageName';" : ''}
+
+  Image image({
+    Key? key,
+    AssetBundle? bundle,
+    ImageFrameBuilder? frameBuilder,
+    ImageErrorWidgetBuilder? errorBuilder,
+    String? semanticLabel,
+    bool excludeFromSemantics = false,
+    double? scale,
+    double? width,
+    double? height,
+    Color? color,
+    Animation<double>? opacity,
+    BlendMode? colorBlendMode,
+    BoxFit? fit,
+    AlignmentGeometry alignment = Alignment.center,
+    ImageRepeat repeat = ImageRepeat.noRepeat,
+    Rect? centerSlice,
+    bool matchTextDirection = false,
+    bool gaplessPlayback = false,
+    bool isAntiAlias = false,
+    ${isPackage ? deprecationMessagePackage : ''}
+    String? package$packageParameter,
+    FilterQuality filterQuality = FilterQuality.low,
+    int? cacheWidth,
+    int? cacheHeight,
+  }) {
+    return Image.asset(
+      _assetName,
+      key: key,
+      bundle: bundle,
+      frameBuilder: frameBuilder,
+      errorBuilder: errorBuilder,
+      semanticLabel: semanticLabel,
+      excludeFromSemantics: excludeFromSemantics,
+      scale: scale,
+      width: width,
+      height: height,
+      color: color,
+      opacity: opacity,
+      colorBlendMode: colorBlendMode,
+      fit: fit,
+      alignment: alignment,
+      repeat: repeat,
+      centerSlice: centerSlice,
+      matchTextDirection: matchTextDirection,
+      gaplessPlayback: gaplessPlayback,
+      isAntiAlias: isAntiAlias,
+      package: package,
+      filterQuality: filterQuality,
+      cacheWidth: cacheWidth,
+      cacheHeight: cacheHeight,
+    );
+  }
+
+  ImageProvider provider({
+    AssetBundle? bundle,
+    ${isPackage ? deprecationMessagePackage : ''}
+    String? package$packageParameter,
+  }) {
+    return AssetImage(
+      _assetName,
+      bundle: bundle,
+      package: package,
+    );
+  }
+
+  String get path => _assetName;
+
+  String get keyName => $keyName;
+}
+''';
+
+  @override
+  String get className => 'AssetGenImage';
+
+  @override
+  String classInstantiate(String path) => 'AssetGenImage(\'$path\')';
+
+  @override
+  bool isSupport(AssetType type) {
+    /// Flutter official supported image types. See
+    /// https://api.flutter.dev/flutter/widgets/Image-class.html
+    switch (type.mime) {
+      case 'image/jpeg':
+      case 'image/png':
+      case 'image/gif':
+      case 'image/bmp':
+      case 'image/vnd.wap.wbmp':
+      case 'image/webp':
+        return true;
+      default:
+        return false;
+    }
+  }
+
+  @override
+  bool get isConstConstructor => true;
+}

packages/core/lib/generators/integrations/integration.dart

@@ -1,10 +1,13 @@
 import 'package:flutter_gen_core/settings/asset_type.dart';
 
+/// A base class for all integrations. An integration is a class that
+/// generates code for a specific asset type.
 abstract class Integration {
-  Integration(this.packageParameterLiteral);
+  Integration(this.packageName);
 
-  final String packageParameterLiteral;
-  late final bool isPackage = packageParameterLiteral.isNotEmpty;
+  /// The package name for this asset. If empty, the asset is not in a package.
+  final String packageName;
+  late final bool isPackage = packageName.isNotEmpty;
 
   bool isEnabled = false;
 
@@ -16,6 +19,7 @@ abstract class Integration {
 
   String classInstantiate(String path);
 
+  /// Is this asset type supported by this integration?
   bool isSupport(AssetType type);
 
   bool get isConstConstructor;

packages/core/lib/generators/integrations/lottie_integration.dart

@@ -7,8 +7,7 @@ import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 
 class LottieIntegration extends Integration {
-  LottieIntegration(String packageParameterLiteral)
-      : super(packageParameterLiteral);
+  LottieIntegration(String packageName) : super(packageName);
 
   // These are required keys for this integration.
   static const lottieKeys = [
@@ -25,6 +24,7 @@ class LottieIntegration extends Integration {
 
   @override
   List<String> get requiredImports => [
+        'package:flutter/widgets.dart',
         'package:lottie/lottie.dart',
       ];
 
@@ -35,7 +35,7 @@ class LottieIntegration extends Integration {
   const LottieGenImage(this._assetName);
 
   final String _assetName;
-${isPackage ? "\n  static const String package = '$packageParameterLiteral';" : ''}
+${isPackage ? "\n  static const String package = '$packageName';" : ''}
 
   LottieBuilder lottie({
     Animation<double>? controller,
@@ -89,7 +89,7 @@ ${isPackage ? "\n  static const String package = '$packageParameterLiteral';" :
 
   String get path => _assetName;
 
-  String get keyName => ${isPackage ? '\'packages/$packageParameterLiteral/\$_assetName\'' : '_assetName'};
+  String get keyName => ${isPackage ? '\'packages/$packageName/\$_assetName\'' : '_assetName'};
 }''';
 
   @override

packages/core/lib/generators/integrations/rive_integration.dart

@@ -2,14 +2,13 @@ import 'package:flutter_gen_core/generators/integrations/integration.dart';
 import 'package:flutter_gen_core/settings/asset_type.dart';
 
 class RiveIntegration extends Integration {
-  RiveIntegration(String packageParameterLiteral)
-      : super(packageParameterLiteral);
+  RiveIntegration(String packageName) : super(packageName);
 
-  String? get packageExpression =>
-      isPackage ? 'packages/$packageParameterLiteral/' : null;
+  String? get packageExpression => isPackage ? 'packages/$packageName/' : null;
 
   @override
   List<String> get requiredImports => [
+        'package:flutter/widgets.dart',
         'package:rive/rive.dart',
       ];
 
@@ -20,7 +19,7 @@ class RiveIntegration extends Integration {
   const RiveGenImage(this._assetName);
 
   final String _assetName;
-${isPackage ? "\n  static const String package = '$packageParameterLiteral';" : ''}
+${isPackage ? "\n  static const String package = '$packageName';" : ''}
 
   RiveAnimation rive({
     String? artboard,