.gitignore

@@ -1,4 +1,3 @@
 # https://dart.dev/guides/libraries/private-files
 # Created by `dart pub`
 .dart_tool/
-tdd_*.md

README.md

@@ -312,86 +312,6 @@ calculator.add('2,1001');        // Returns: 2 (1001 ignored)
 
 ---
 
-### 5. Mars Rover ✅
-
-**Implementation:** [`lib/mars_rover.dart`](lib/mars_rover.dart)  
-**Tests:** [`test/mars_rover_test.dart`](test/mars_rover_test.dart)
-
-A Command Pattern kata simulating a robotic rover navigating a plateau on Mars. Demonstrates clean separation of concerns, value objects, and command-based control.
-
-#### Domain Context
-
-A rover explores a rectangular plateau with coordinate-based navigation:
-
-**Core Concepts:**
-- **Position:** (x, y) coordinates on the plateau grid
-- **Direction:** Cardinal directions (N, E, S, W)
-- **Plateau:** Grid with defined boundaries that wrap around (toroidal topology)
-
-**Commands:**
-- `L` - Turn left 90 degrees (changes direction, not position)
-- `R` - Turn right 90 degrees (changes direction, not position)
-- `M` - Move forward one grid point in current direction
-
-**Example Navigation:**
-```
-Starting: (0,0) facing North
-Commands: "MMRMMLM"
-- MM: Move to (0,2) facing North
-- R: Turn to face East (still at 0,2)
-- MM: Move to (2,2) facing East
-- L: Turn to face North (still at 2,2)
-- M: Move to (2,3) facing North
-Result: (2,3) facing North
-```
-
-#### Key Design Decisions
-
-**Direction Enum:** Encapsulates rotation logic using modular arithmetic. Each direction knows how to turn left/right, eliminating conditional branching.
-
-**Value Objects:** 
-- `Position` is immutable—movement returns new position instances
-- `Plateau` encapsulates boundary wrapping logic
-- Prevents invalid states at the type level
-
-**Command Pattern (Implicit):** The `execute()` method delegates to command handlers (`turnLeft()`, `turnRight()`, `moveForward()`). Each command is isolated and testable.
-
-**Wrapping Logic:** Plateau boundaries wrap around (toroidal topology). Moving past edge (e.g., x=5→6 on 5x5 grid) wraps to opposite side (x=0).
-
-#### Usage
-
-```dart
-import 'package:tdd_katas/mars_rover.dart';
-
-// Create rover at position (1,2) facing North on 5x5 plateau
-final rover = Rover(
-  x: 1, 
-  y: 2, 
-  direction: 'N',
-  plateauWidth: 5,
-  plateauHeight: 5,
-);
-
-rover.execute('LMLMLMLMM');
-
-print('Position: (${rover.x}, ${rover.y})'); // Position: (1, 3)
-print('Direction: ${rover.direction}');      // Direction: N
-```
-
-#### The "Aha!" Moments
-
-1. **Enums as Behavior Carriers:** Direction enum doesn't just store values—it encapsulates rotation logic. Turning left/right becomes `direction.turnLeft()`, eliminating lookup tables.
-
-2. **Value Objects Prevent Bugs:** Immutable `Position` means movement can't corrupt state. New position calculated, validated, then assigned. Boundary wrapping isolated in `Plateau`.
-
-3. **Switch Expressions Shine:** Modern Dart's `switch` expression makes direction-based movement elegant and exhaustive. Compiler enforces handling all directions.
-
-4. **Modular Arithmetic for Rotation:** `(index + 1) % 4` handles right rotation elegantly. No if-statements, no edge cases—math models the domain perfectly.
-
-5. **Refactoring Without Fear:** Two refactoring commits drastically improved code structure. Tests stayed green throughout, proving behavior preservation.
-
----
-
 ## Running Tests
 
 ```bash
@@ -403,7 +323,6 @@ dart test test/roman_numerals_test.dart
 dart test test/bowling_game_test.dart
 dart test test/gilded_rose_test.dart
 dart test test/string_calculator_test.dart
-dart test test/mars_rover_test.dart
 
 # Run with coverage
 dart test --coverage
@@ -711,19 +630,19 @@ Decision: Skip refactor commit—code is already excellent.
 
 ## Comparing the Katas
 
-### All Five Katas at a Glance
+### All Four Katas at a Glance
 
-| Aspect | Roman Numerals | Bowling Game | Gilded Rose | String Calculator | Mars Rover |
+| Aspect | Roman Numerals | Bowling Game | Gilded Rose | String Calculator |
-|--------|----------------|--------------|-------------|-------------------|------------|
+|--------|----------------|--------------|-------------|-------------------|
-| **Complexity** | Beginner | Intermediate | Advanced | Beginner | Intermediate |
+| **Complexity** | Beginner | Intermediate | Advanced | Beginner |
-| **Approach** | Greenfield TDD | Greenfield TDD | Legacy refactoring | Bug hunting | Greenfield TDD |
+| **Approach** | Greenfield TDD | Greenfield TDD | Legacy refactoring | Bug hunting |
-| **State** | Stateless | Stateful | Stateful | Stateless | Stateful |
+| **State** | Stateless | Stateful | Stateful | Stateless |
-| **Algorithm** | Table-driven | Frame iteration | Strategy pattern | String parsing | Command pattern |
+| **Algorithm** | Table-driven | Frame iteration | Strategy pattern | String parsing |
-| **Key Challenge** | Pattern recognition | State & bonuses | Refactoring safely | Finding bugs | Navigation & wrapping |
+| **Key Challenge** | Pattern recognition | State & bonuses | Refactoring safely | Finding bugs |
-| **Design Pattern** | Value Object | Implicit strategy | Explicit strategy | Filters & pipes | Command + Value Objects |
+| **Design Pattern** | Value Object | Implicit strategy | Explicit strategy | Filters & pipes |
-| **Lines of Code** | ~45 production | ~30 production | ~120 production | ~25 production | ~95 production |
+| **Lines of Code** | ~45 production | ~30 production | ~120 production | ~25 production |
-| **Test Count** | ~15 tests | ~10 tests | ~17 tests | 6 tests | 23 tests |
+| **Test Count** | ~15 tests | ~10 tests | ~17 tests | 6 tests |
-| **Aha! Moment** | Table = data | Simple → complex | Refactor = safe | Tests find bugs | Enums carry behavior |
+| **Aha! Moment** | Table = data | Simple → complex | Refactor = safe | Tests find bugs |
 
 ### What Each Kata Teaches
 
@@ -750,24 +669,16 @@ Decision: Skip refactor commit—code is already excellent.
 - Incremental debugging with clear commits
 - Regression prevention through test accumulation
 
-**Mars Rover:**
-- Command pattern for behavior delegation
-- Value Objects for domain modeling (Position, Plateau, Direction)
-- Enums as behavior carriers, not just constants
-- Coordinate systems and wrapping logic
-- Progressive refactoring with confidence
-
 ### Progressive Learning Path
 
 1. **Roman Numerals first:** Learn TDD fundamentals without state complexity
 2. **Bowling Game second:** Apply TDD to stateful problems
-3. **Mars Rover third:** Master Command pattern and value objects
+3. **Gilded Rose third:** Master refactoring legacy code with tests as safety net
-4. **Gilded Rose fourth:** Refactor legacy code with tests as safety net
+4. **String Calculator fourth:** Practice bug hunting and fixing with TDD
-5. **String Calculator fifth:** Practice bug hunting and fixing with TDD
+5. **Next kata:** Choose based on what you want to practice:
-6. **Next kata:** Choose based on what you want to practice:
+   - **Mars Rover:** Command pattern, multiple behaviors
    - **Prime Factors:** Mathematical decomposition, algorithmic thinking
    - **Tennis Scoring:** State machines, domain language
-   - **FizzBuzz:** Classic conditional logic exercise
 
 ---
 

lib/gilded_rose.dart

@@ -14,6 +14,7 @@ class Item {
 /// Quality bounds - domain constraints
 const int _minQuality = 0;
 const int _maxQuality = 50;
+const int _legendaryQuality = 80; // unused, just for documentation
 
 /// Helper methods for quality management
 void _degradeQuality(Item item, int amount) {

lib/mars_rover.dart

@@ -1,106 +0,0 @@
-enum Direction {
-  north('N'),
-  east('E'),
-  south('S'),
-  west('W');
-
-  final String code;
-  const Direction(this.code);
-
-  static Direction fromCode(String code) {
-    return Direction.values.firstWhere((d) => d.code == code);
-  }
-
-  Direction turnLeft() {
-    return Direction.values[(index + 3) % 4];
-  }
-
-  Direction turnRight() {
-    return Direction.values[(index + 1) % 4];
-  }
-}
-
-class Position {
-  final int x;
-  final int y;
-
-  Position(this.x, this.y);
-
-  Position moveNorth() => Position(x, y + 1);
-  Position moveEast() => Position(x + 1, y);
-  Position moveSouth() => Position(x, y - 1);
-  Position moveWest() => Position(x - 1, y);
-}
-
-class Plateau {
-  final int width;
-  final int height;
-
-  Plateau(this.width, this.height);
-
-  Position wrap(Position position) {
-    final wrappedX = _wrapCoordinate(position.x, width);
-    final wrappedY = _wrapCoordinate(position.y, height);
-    return Position(wrappedX, wrappedY);
-  }
-
-  int _wrapCoordinate(int value, int max) {
-    final wrapped = value % (max + 1);
-    return wrapped < 0 ? wrapped + max + 1 : wrapped;
-  }
-}
-
-class Rover {
-  Position _position;
-  Direction _direction;
-  final Plateau plateau;
-
-  Rover({
-    required int x,
-    required int y,
-    required String direction,
-    int plateauWidth = 100,
-    int plateauHeight = 100,
-  }) : _position = Position(x, y),
-       _direction = Direction.fromCode(direction),
-       plateau = Plateau(plateauWidth, plateauHeight);
-
-  int get x => _position.x;
-  int get y => _position.y;
-  String get direction => _direction.code;
-
-  void turnLeft() {
-    _direction = _direction.turnLeft();
-  }
-
-  void turnRight() {
-    _direction = _direction.turnRight();
-  }
-
-  void moveForward() {
-    final newPosition = switch (_direction) {
-      Direction.north => _position.moveNorth(),
-      Direction.east => _position.moveEast(),
-      Direction.south => _position.moveSouth(),
-      Direction.west => _position.moveWest(),
-    };
-    _position = plateau.wrap(newPosition);
-  }
-
-  void execute(String commands) {
-    for (var i = 0; i < commands.length; i++) {
-      final command = commands[i];
-      switch (command) {
-        case 'L':
-          turnLeft();
-          break;
-        case 'R':
-          turnRight();
-          break;
-        case 'M':
-          moveForward();
-          break;
-      }
-    }
-  }
-}

test/mars_rover_test.dart

@@ -1,194 +0,0 @@
-import 'package:tdd_katas/mars_rover.dart';
-import 'package:test/test.dart';
-
-void main() {
-  group('Mars Rover:', () {
-    test('rover reports initial position and direction', () {
-      final rover = Rover(x: 0, y: 0, direction: 'N');
-
-      expect(rover.x, equals(0));
-      expect(rover.y, equals(0));
-      expect(rover.direction, equals('N'));
-    });
-
-    group('Turning Left:', () {
-      test('from North faces West', () {
-        final rover = Rover(x: 0, y: 0, direction: 'N');
-        rover.turnLeft();
-        expect(rover.direction, equals('W'));
-      });
-
-      test('from West faces South', () {
-        final rover = Rover(x: 0, y: 0, direction: 'W');
-        rover.turnLeft();
-        expect(rover.direction, equals('S'));
-      });
-
-      test('from South faces East', () {
-        final rover = Rover(x: 0, y: 0, direction: 'S');
-        rover.turnLeft();
-        expect(rover.direction, equals('E'));
-      });
-
-      test('from East faces North', () {
-        final rover = Rover(x: 0, y: 0, direction: 'E');
-        rover.turnLeft();
-        expect(rover.direction, equals('N'));
-      });
-    });
-
-    group('Turning Right:', () {
-      test('from North faces East', () {
-        final rover = Rover(x: 0, y: 0, direction: 'N');
-        rover.turnRight();
-        expect(rover.direction, equals('E'));
-      });
-
-      test('from East faces South', () {
-        final rover = Rover(x: 0, y: 0, direction: 'E');
-        rover.turnRight();
-        expect(rover.direction, equals('S'));
-      });
-
-      test('from South faces West', () {
-        final rover = Rover(x: 0, y: 0, direction: 'S');
-        rover.turnRight();
-        expect(rover.direction, equals('W'));
-      });
-
-      test('from West faces North', () {
-        final rover = Rover(x: 0, y: 0, direction: 'W');
-        rover.turnRight();
-        expect(rover.direction, equals('N'));
-      });
-    });
-
-    group('Moving Forward:', () {
-      test('facing North increases Y', () {
-        final rover = Rover(x: 0, y: 0, direction: 'N');
-        rover.moveForward();
-        expect(rover.x, equals(0));
-        expect(rover.y, equals(1));
-      });
-
-      test('facing East increases X', () {
-        final rover = Rover(x: 0, y: 0, direction: 'E');
-        rover.moveForward();
-        expect(rover.x, equals(1));
-        expect(rover.y, equals(0));
-      });
-
-      test('facing South decreases Y', () {
-        final rover = Rover(x: 0, y: 5, direction: 'S');
-        rover.moveForward();
-        expect(rover.x, equals(0));
-        expect(rover.y, equals(4));
-      });
-
-      test('facing West decreases X', () {
-        final rover = Rover(x: 5, y: 0, direction: 'W');
-        rover.moveForward();
-        expect(rover.x, equals(4));
-        expect(rover.y, equals(0));
-      });
-    });
-
-    group('Executing Command Sequences:', () {
-      test('single command L', () {
-        final rover = Rover(x: 0, y: 0, direction: 'N');
-        rover.execute('L');
-        expect(rover.direction, equals('W'));
-      });
-
-      test('single command R', () {
-        final rover = Rover(x: 0, y: 0, direction: 'N');
-        rover.execute('R');
-        expect(rover.direction, equals('E'));
-      });
-
-      test('single command M', () {
-        final rover = Rover(x: 0, y: 0, direction: 'N');
-        rover.execute('M');
-        expect(rover.y, equals(1));
-      });
-
-      test('complex sequence MMRMMLM', () {
-        final rover = Rover(x: 0, y: 0, direction: 'N');
-        rover.execute('MMRMMLM');
-        expect(rover.x, equals(2));
-        expect(rover.y, equals(3));
-        expect(rover.direction, equals('N'));
-      });
-
-      test('example from Mars Rover kata', () {
-        final rover = Rover(x: 1, y: 2, direction: 'N');
-        rover.execute('LMLMLMLMM');
-        expect(rover.x, equals(1));
-        expect(rover.y, equals(3));
-        expect(rover.direction, equals('N'));
-      });
-    });
-
-    group('Plateau Boundaries:', () {
-      test('wraps around when moving North past boundary', () {
-        final rover = Rover(
-          x: 0,
-          y: 5,
-          direction: 'N',
-          plateauWidth: 5,
-          plateauHeight: 5,
-        );
-        rover.moveForward();
-        expect(rover.y, equals(0));
-      });
-
-      test('wraps around when moving East past boundary', () {
-        final rover = Rover(
-          x: 5,
-          y: 0,
-          direction: 'E',
-          plateauWidth: 5,
-          plateauHeight: 5,
-        );
-        rover.moveForward();
-        expect(rover.x, equals(0));
-      });
-
-      test('wraps around when moving South past boundary', () {
-        final rover = Rover(
-          x: 0,
-          y: 0,
-          direction: 'S',
-          plateauWidth: 5,
-          plateauHeight: 5,
-        );
-        rover.moveForward();
-        expect(rover.y, equals(5));
-      });
-
-      test('wraps around when moving West past boundary', () {
-        final rover = Rover(
-          x: 0,
-          y: 0,
-          direction: 'W',
-          plateauWidth: 5,
-          plateauHeight: 5,
-        );
-        rover.moveForward();
-        expect(rover.x, equals(5));
-      });
-
-      test('example with wrapping', () {
-        final rover = Rover(
-          x: 5,
-          y: 5,
-          direction: 'N',
-          plateauWidth: 5,
-          plateauHeight: 5,
-        );
-        rover.execute('MMM');
-        expect(rover.y, equals(2));
-      });
-    });
-  });
-}