Impl conceptual command pattern.

Author: ilopX

patterns/command/conceptul/command/add_text_command.dart

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+import '../pattern/command.dart';
+import '../mut_str/mut_str.dart';
+
+class AddTextCommand implements Command {
+  final String addedText;
+  final MutStr mutStr;
+
+  AddTextCommand(this.addedText, this.mutStr);
+
+  @override
+  void execute() {
+    additionPosition = mutStr.len;
+    mutStr.push(addedText);
+  }
+
+  @override
+  void undo() {
+    if (additionPosition == null) {
+      return;
+    }
+
+    mutStr.delete(additionPosition!, additionPosition! + addedText.length);
+  }
+
+  int? additionPosition;
+}

patterns/command/conceptul/command/insert_text_command.dart

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+import '../pattern/command.dart';
+import '../mut_str/mut_str.dart';
+
+class InsertTextCommand extends Command {
+  final int pos;
+  final String insertText;
+  final MutStr mutStr;
+
+  InsertTextCommand(this.insertText, this.mutStr, {required this.pos});
+
+  @override
+  void execute() {
+    _isNotExecute = false;
+    mutStr.insert(pos + 1, insertText);
+  }
+
+  @override
+  void undo() {
+    if (_isNotExecute) {
+      return;
+    }
+
+    mutStr.delete(pos + 1, insertText.length - 1);
+  }
+
+  bool _isNotExecute = true;
+}

patterns/command/conceptul/main.dart

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+import 'mut_str/mut_str.dart';
+import 'command/add_text_command.dart';
+import 'command/insert_text_command.dart';
+
+void main() {
+  final mutStr = MutStr();
+
+  final input1 = AddTextCommand('One', mutStr);
+  final input2 = AddTextCommand('Three', mutStr);
+  final input3 = InsertTextCommand(' Two ', mutStr, pos: 2);
+
+  input1.execute();
+  print('text = $mutStr'); // mutStr = "One"
+
+  input2.execute();
+  print('text = $mutStr'); // mutStr = "OneThree"
+
+  input3.execute();
+  print('text = $mutStr'); // mutStr = "One Two Three"
+
+  input3.undo();
+  print('text = $mutStr'); // mutStr = "OneThree"
+
+  input2.undo();
+  print('text = $mutStr'); // mutStr = "One "
+
+  input1.undo();
+  print('text = $mutStr'); // mutStr = ""
+}

patterns/command/conceptul/mut_str/mut_str.dart

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+class MutStr {
+  void push(String str) {
+    _buff.addAll(str.split(''));
+  }
+
+  void insert(int pos, String str) {
+    _buff.insert(pos, str);
+  }
+
+  void delete(int startPos, int len) {
+    _buff.removeRange(startPos, len);
+  }
+
+  int get len => _buff.length;
+
+  @override
+  String toString() {
+    return _buff.join('');
+  }
+
+  final _buff = <String>[];
+}

patterns/command/conceptul/pattern/command.dart

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+abstract class Command {
+  void execute();
+  void undo();
+}