Add strategy pattern: View Strategy Example.

CHANGELOG.md

@@ -1,3 +1,6 @@
+## 0.30.0
+- Add strategy pattern: View Strategy.
+
 ## 0.29.0
 - Add conceptual visitor pattern.
 

README.md

@@ -20,7 +20,7 @@ It contains **Dart** examples for all classic **GoF** design patterns.
     - [x] **State** - [[Conceptual](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/state/three_state)] [[![16x16](https://user-images.githubusercontent.com/8049534/171852337-57db0faf-1f5e-489a-a79a-22ed4f47b4ed.png) State Manipulator](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/state/manipulator_state)]
     - [x] **Template Method** - [[Data Miner](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/template_method/data_miner)] 
     - [X] **Visitor** - [[Conceptual](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/visitor/conceptual)] [[Shape XML Exporter](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/visitor/shapes_exporter)]
-    - [X] **Strategy** [[Reservation Cargo Spaces](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/strategy/reservation_cargo_spaces)]
+    - [X] **Strategy** [[View Strategy](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/strategy/view_strategy)] [[Reservation Cargo Spaces](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/strategy/reservation_cargo_spaces)]
 - [ ] **Structural**
     - [x] **Adapter** - [[Text Graphics](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/adapter/text_graphics)] [[Square Round conflict](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/adapter/square_round_conflict)] [[![16x16](https://user-images.githubusercontent.com/8049534/171852337-57db0faf-1f5e-489a-a79a-22ed4f47b4ed.png) Flutter Adapter](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/adapter/flutter_adapter)] 
     - [x] **Bridge** - [[Remote Device Control](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/bridge/devices_remote_control)] [[Clock](https://github.com/RefactoringGuru/design-patterns-dart/tree/main/patterns/bridge/clock)] 

patterns/strategy/view_strategy/README.md

@@ -0,0 +1,43 @@
+# Strategy Pattern
+Strategy is a behavioral design pattern that lets you define a family of algorithms, put each of 
+them into a separate class, and make their objects interchangeable.
+
+Tutorial: [here](https://refactoring.guru/design-patterns/strategy).
+
+## Diagram:
+![image](https://user-images.githubusercontent.com/8049534/175562829-c91fbb12-50ac-4373-a33f-900527383a6c.png)
+
+## Client code:
+```dart
+void main() {
+  final byteList = ByteContext()
+    ..add('Hello guru')
+    ..add(123456789)
+    ..add(3.1456564984);
+
+  final strFormat = byteList.toStringView(StrViewStrategy());
+  final hexFormat = byteList.toStringView(HexViewStrategy());
+  final zipFormat = byteList.toStringView(ZipViewStrategy());
+
+  print(strFormat);
+  print(hexFormat);
+  print(zipFormat);
+}
+```
+
+### Output:
+```
+StrViewStrategy:
+Hello guru, 123456789, 3.1456564984
+
+HexViewStrategy:
+Hello guru     : 48 65 6c 6c 6f 20 67 75 72 75
+123456789      : 00 00 00 00 07 5b cd 15
+3.1456564984   : 40 09 2a 4d f4 48 9f 7e
+
+ZipViewStrategy:
+1f 8b 08 00 00 00 00 00 00 0a f3 48 cd c9 c9 57 
+48 2f 2d 2a d5 51 30 34 32 36 31 35 33 b7 b0 d4 
+51 30 d6 33 04 32 4d cd 4c 2c 2d 4c b8 00 d4 70 
+cf ee 24 00 00 00 
+```

patterns/strategy/view_strategy/main.dart

@@ -0,0 +1,19 @@
+import 'pattern/byte_context.dart';
+import 'strategies/hex_view_strategy.dart';
+import 'strategies/str_view_strategy.dart';
+import 'strategies/zip_view_strategy.dart';
+
+void main() {
+  final byteList = ByteContext()
+    ..add('Hello guru')
+    ..add(123456789)
+    ..add(3.1456564984);
+
+  final strFormat = byteList.toStringView(StrViewStrategy());
+  final hexFormat = byteList.toStringView(HexViewStrategy());
+  final zipFormat = byteList.toStringView(ZipViewStrategy());
+
+  print(strFormat);
+  print(hexFormat);
+  print(zipFormat);
+}

patterns/strategy/view_strategy/pattern/byte_context.dart

@@ -0,0 +1,16 @@
+import 'view_strategy.dart';
+
+class ByteContext {
+  String toStringView(ViewStrategy strategy) {
+    return '${strategy.runtimeType}:\n'
+        '${strategy.out(this)}';
+  }
+
+  void add(dynamic value) {
+    _buf.add(value);
+  }
+
+  List toList() => _buf;
+
+  final _buf = <dynamic>[];
+}

patterns/strategy/view_strategy/pattern/view_strategy.dart

@@ -0,0 +1,5 @@
+import 'byte_context.dart';
+
+abstract class ViewStrategy {
+  String out(ByteContext byteList);
+}

patterns/strategy/view_strategy/strategies/hex_view_strategy.dart

@@ -0,0 +1,47 @@
+import 'dart:typed_data';
+
+import '../pattern/byte_context.dart';
+import '../pattern/view_strategy.dart';
+
+class HexViewStrategy implements ViewStrategy {
+  @override
+  String out(ByteContext byteList) {
+    final buf = StringBuffer();
+
+    for (final val in byteList.toList()) {
+      buf.write('${val.toString().padRight(15)}: ');
+
+      if (val is String) {
+        buf.writeln(_stringToHex(val));
+      } else {
+        buf.writeln(_valueToHex(val, size: 8));
+      }
+    }
+
+    return buf.toString();
+  }
+
+  String _stringToHex(String value) {
+    return value.codeUnits
+        .map((charCode) => _valueToHex(size: 1, charCode))
+        .join(' ');
+  }
+
+  String _valueToHex<T>(T value, {required int size}) {
+    late ByteData byteData;
+
+    if (size == 1) {
+      byteData = ByteData(1)..setInt8(0, value as int);
+    } else {
+      byteData = ByteData(size);
+      if (value is double) {
+        byteData.setFloat64(0, value);
+      } else if (value is int) {
+        byteData.setInt64(0, value);
+      }
+    }
+
+    final bytes = byteData.buffer.asUint8List();
+    return bytes.map((e) => e.toRadixString(16).padLeft(2, '0')).join(' ');
+  }
+}

patterns/strategy/view_strategy/strategies/str_view_strategy.dart

@@ -0,0 +1,9 @@
+import '../pattern/byte_context.dart';
+import '../pattern/view_strategy.dart';
+
+class StrViewStrategy implements ViewStrategy {
+  @override
+  String out(ByteContext byteList) {
+    return '${byteList.toList().join(', ')}\n';
+  }
+}

patterns/strategy/view_strategy/strategies/zip_view_strategy.dart

@@ -0,0 +1,25 @@
+import 'dart:io';
+
+import '../pattern/byte_context.dart';
+import 'str_view_strategy.dart';
+
+class ZipViewStrategy extends StrViewStrategy {
+  @override
+  String out(ByteContext byteList) {
+    final codes = super.out(byteList).codeUnits;
+    final bytes = GZipCodec().encode(codes);
+    final buf = StringBuffer();
+
+    var odd = 1;
+    for (final byte in bytes) {
+      final hexByte = byte.toRadixString(16).padLeft(2, '0');
+      buf.write('$hexByte ');
+
+      if (odd++ % 16 == 0) {
+        buf.writeln();
+      }
+    }
+
+    return buf.toString();
+  }
+}

pubspec.yaml

@@ -1,6 +1,6 @@
 name: design_patterns_dart
 description: Dart examples for all classic GoF design patterns.
-version: 0.29.0
+version: 0.30.0
 homepage: https://refactoring.guru/design-patterns
 repository: https://github.com/RefactoringGuru/design-patterns-dart
 issue_tracker: https://github.com/RefactoringGuru/design-patterns-dart/issue