command2.dart

// trying to translate c++ codes to dart
// c++ source:
// http://gameprogrammingpatterns.com/command.html#undo-and-redo

void main() {
  print("Starting game\n");
  Unit unit = Unit(x: 0, y: 0);

  InputHandler inputHandler = InputHandler(unit: unit);
  Command command;
  print("Press button up");
  inputHandler.pressed = Button.BUTTON_UP;
  inputHandler.handleInput()
    ..execute();

  print("Press button up");
  inputHandler.pressed = Button.BUTTON_UP;
  inputHandler.handleInput()
    ..execute();

  print("Press button down");
  inputHandler.pressed = Button.BUTTON_DOWN;
  inputHandler.handleInput()
    ..execute();

  print("Lets undo");
  command.undo();
}

class Unit {
  int x;
  int y;

  Unit({this.x, this.y});

  void moveTo(int xNew, int yNew) {
    x = xNew;
    y = yNew;
  }
}

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

class MoveUnitCommand extends Command {
  int x;
  int y;
  int xBefore;
  int yBefore;
  Unit unit;

  MoveUnitCommand({this.unit, this.x, this.y});

  void execute() {
    xBefore = unit.x;
    yBefore = unit.y;
    print("position: $x, $y\n");
    unit.moveTo(x, y);
  }

  void undo() {
    print("position: $xBefore, $yBefore\n");
    unit.moveTo(xBefore, yBefore);
  }
}

enum Button {
  BUTTON_UP,
  BUTTON_DOWN,
  BUTTON_UNDO,
  NULL,
}

class InputHandler {
  Unit unit;
  Button pressed;

  InputHandler({this.unit});

  Command handleInput() {
    if (isPressed(Button.BUTTON_UP)) {
      int destY = unit.y + 1;
      return MoveUnitCommand(unit: unit, x: unit.x, y: destY);
    }
    if (isPressed(Button.BUTTON_DOWN)) {
      int destY = unit.y - 1;
      return MoveUnitCommand(unit: unit, x: unit.x, y: destY);
    }

    // Nothing pressed, so do nothing.
    return null;
  }

  bool isPressed(Button button) {
    return button == pressed ? true : false;
  }
}