Impl view strategy example.

Author: ilopX

patterns/strategy/print_strategy/main.dart

@@ -0,0 +1,107 @@
+import 'dart:io';
+import 'dart:typed_data';
+
+void main() {
+  final byteList = SomeData()
+    ..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);
+}
+
+abstract class ViewStrategy {
+  String out(SomeData byteList);
+}
+
+class HexViewStrategy implements ViewStrategy {
+  @override
+  String out(SomeData byteList) {
+    final buf = StringBuffer();
+
+    for (final val in byteList.toList()) {
+      buf.write('${val.toString().padRight(15)}: ');
+
+      if (val is String) {
+        buf.writeln(_stringToHex(val));
+      } else {
+        buf.writeln(_valueToHex(val, size: 8));
+      }
+    }
+
+    return buf.toString();
+  }
+
+  String _stringToHex(String value) {
+    return value.codeUnits
+        .map((charCode) => _valueToHex(size: 1, charCode))
+        .join(' ');
+  }
+
+  String _valueToHex<T>(T value, {required int size}) {
+    late ByteData byteData;
+
+    if (size == 1) {
+      byteData = ByteData(1)..setInt8(0, value as int);
+    } else {
+      byteData = ByteData(size);
+      if (value is double) {
+        byteData.setFloat64(0, value);
+      } else if (value is int) {
+        byteData.setInt64(0, value);
+      }
+    }
+
+    final bytes = byteData.buffer.asUint8List();
+    return bytes.map((e) => e.toRadixString(16).padLeft(2, '0')).join(' ');
+  }
+}
+
+class StrViewStrategy implements ViewStrategy {
+  @override
+  String out(SomeData byteList) {
+    return '${byteList.toList().join(', ')}\n';
+  }
+}
+
+class ZipViewStrategy extends StrViewStrategy {
+  @override
+  String out(SomeData 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('$hexByte ');
+
+      if (odd++ % 16 == 0) {
+        buf.writeln();
+      }
+    }
+
+    return buf.toString();
+  }
+}
+
+class SomeData {
+  String toStringView(ViewStrategy strategy) {
+    return '${strategy.runtimeType}:\n'
+        '${strategy.out(this)}';
+  }
+
+  void add(dynamic str) {
+    _buf.add(str);
+  }
+
+  List toList() => _buf;
+
+  final _buf = <dynamic>[];
+}