# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

---

# JailDoctor's Dilemma - Codebase Architecture Guide

## Overview

**JailDoctor's Dilemma** is a retro-style 2D puzzle platformer game built in C++20 using SDL3 for graphics and audio. The game features 60+ rooms, collectible items, enemies, and an achievement system. It targets multiple platforms (Windows, macOS, Linux) with a focus on retro aesthetics and precise collision detection.

**Language:** C++20
**Graphics:** SDL3, OpenGL
**Audio:** SDL3 + custom jail_audio library
**Build:** CMake 3.10+
**Game Canvas:** 256x192 pixels (retro resolution)

---

## Build Commands

### Initial Setup & Build
```bash
# From project root
mkdir -p build
cd build
cmake ..
cmake --build .
```

### Rebuild After Changes
```bash
# From build directory
cmake --build .

# Or from project root
cmake --build build
```

### Clean Build
```bash
# From build directory
cmake --build . --clean-first

# Or from project root
cmake --build build --clean-first
```

### Run the Game
```bash
# Executable is placed in project root
./jaildoctors_dilemma
```

**Important:** The build directory is `/Users/sergio/Gitea/jaildoctors_dilemma/build` and the output executable is placed in the project root directory.

### Linter (clang-tidy)

**IMPORTANT:** Always run the linter on specific files, NOT on the entire project, to avoid long execution times and errors in unrelated files.

```bash
# Analyze a specific file (RECOMMENDED)
tools/linter/run_clang-tidy.sh source/game/entities/player.cpp

# Analyze multiple specific files
tools/linter/run_clang-tidy.sh source/game/entities/player.cpp source/game/entities/enemy.cpp

# Apply fixes automatically to a specific file
tools/linter/run_clang-tidy.sh --fix source/game/entities/player.cpp

# Analyze entire project (SLOW, may have errors in defaults.hpp)
tools/linter/run_clang-tidy.sh
```

**Note:** Running the linter on the entire project can produce errors in files like `defaults.hpp` that are unrelated to your changes. Always target specific files you're working on.

---

## 1. High-Level Architecture Overview

The architecture follows a **layered, modular design** with clear separation of concerns:

```
┌─────────────────────────────────────┐
│        Application Layer             │
│  (Director, Scene Manager)           │
└─────────────────────────────────────┘
                  ↓
┌─────────────────────────────────────┐
│        Game Logic Layer              │
│  (Game Scene, Entities, Gameplay)    │
└─────────────────────────────────────┘
                  ↓
┌─────────────────────────────────────┐
│        Core Systems Layer            │
│  (Rendering, Audio, Input, Resources)│
└─────────────────────────────────────┘
                  ↓
┌─────────────────────────────────────┐
│     SDL3 & External Libraries        │
│  (jail_audio, stb_image, stb_vorbis) │
└─────────────────────────────────────┘
```

### Key Design Principles

- **Singleton Pattern:** Core systems (Director, Screen, Audio, Input, Resource, Asset) use singleton pattern for global access
- **Scene-Based Architecture:** Game flow managed through discrete scenes (Logo, Title, Loading, Game, Ending, etc.)
- **Component-Based Entities:** Player, enemies, and items are discrete entities with render/update patterns
- **Resource Management:** All assets (textures, sounds, animations, tilemaps) cached through Resource singleton
- **Delta Time:** Frame-rate independent physics using DeltaTimer class

---

## 2. Directory Structure

```
source/
├── core/                          # Core engine systems
│   ├── audio/                     # Audio management
│   │   └── audio.hpp/cpp          # Audio singleton (music, sounds, volumes)
│   ├── input/                     # Input handling
│   │   ├── input.hpp/cpp          # Input manager (keyboard, gamepad)
│   │   ├── global_inputs.hpp      # Global input state
│   │   └── mouse.hpp              # Mouse input
│   ├── rendering/                 # Graphics rendering
│   │   ├── screen.hpp/cpp         # Screen/window singleton, SDL renderer
│   │   ├── surface.hpp/cpp        # 8-bit indexed color surface abstraction
│   │   ├── surface_sprite.hpp     # Static sprite rendering
│   │   ├── surface_animated_sprite.hpp # Animated sprite with frame data
│   │   ├── surface_moving_sprite.hpp   # Moving sprite with velocity
│   │   ├── texture.hpp/cpp        # SDL texture wrapper
│   │   ├── text.hpp/cpp           # Text rendering system
│   │   ├── gif.hpp/cpp            # GIF image loader
│   │   ├── opengl/                # OpenGL shader backend
│   │   │   └── opengl_shader.hpp/cpp  # CRT shader effects
│   │   └── shader_backend.hpp     # Abstract shader interface
│   ├── resources/                 # Asset & Resource management
│   │   ├── asset.hpp/cpp          # Asset registry (file path mapping)
│   │   └── resource.hpp/cpp       # Resource singleton (loads/caches assets)
│   └── system/                    # System management
│       ├── director.hpp/cpp       # Main application controller
│       ├── debug.hpp/cpp          # Debug info overlay
│       └── global_events.hpp/cpp  # Global event broadcasting
├── game/                          # Game-specific logic
│   ├── entities/                  # Game objects
│   │   ├── player.hpp/cpp         # Player entity with physics
│   │   ├── enemy.hpp/cpp          # Enemy entities
│   │   └── item.hpp/cpp           # Collectible items
│   ├── gameplay/                  # Core gameplay systems
│   │   ├── room.hpp/cpp           # Room/level logic, tilemap, collision
│   │   ├── room_tracker.hpp/cpp   # Tracks visited rooms
│   │   ├── scoreboard.hpp/cpp     # Score display & data
│   │   ├── item_tracker.hpp/cpp   # Tracks collected items
│   │   ├── stats.hpp/cpp          # Game statistics
│   │   └── cheevos.hpp/cpp        # Achievement system
│   ├── scenes/                    # Game scenes (flow states)
│   │   ├── logo.hpp/cpp           # JailGames logo screen
│   │   ├── loading_screen.hpp/cpp # Resource loading progress
│   │   ├── title.hpp/cpp          # Title screen & menus
│   │   ├── game.hpp/cpp           # Main gameplay loop
│   │   ├── game_over.hpp/cpp      # Game over screen
│   │   ├── ending.hpp/cpp         # Ending sequence 1
│   │   ├── ending2.hpp/cpp        # Ending sequence 2
│   │   └── credits.hpp/cpp        # Credits screen
│   ├── ui/                        # User interface
│   │   └── notifier.hpp/cpp       # Achievement/notification display
│   ├── options.hpp/cpp            # Game configuration/options
│   ├── scene_manager.hpp          # Scene flow state machine
│   ├── defaults.hpp               # Game defaults constants
│   └── gameplay.hpp               # Gameplay constants
├── external/                      # Third-party libraries
│   ├── jail_audio.hpp/cpp         # Custom audio library
│   ├── jail_audio.h               # C interface for jail_audio
│   ├── stb_image.h                # Image loading library
│   └── stb_vorbis.h               # OGG Vorbis audio decoding
├── utils/                         # Utility code
│   ├── delta_timer.hpp/cpp        # Frame-rate independent timing
│   ├── defines.hpp                # Game constants (resolutions, block sizes)
│   └── utils.hpp/cpp              # Helper functions (colors, math)
└── main.cpp                       # Application entry point

data/                              # Game assets
├── font/                          # Bitmap fonts + descriptors
├── palette/                       # Color palettes (.pal files)
├── shaders/                       # GLSL vertex/fragment shaders
├── room/                          # Tilemaps & room definitions (01.tmx-60.tmx)
├── tilesets/                      # Tileset graphics
├── enemies/                       # Enemy sprites & animations
├── player/                        # Player sprites & animations
├── items/                         # Item sprite sheets
├── music/                         # Background music (OGG)
├── sound/                         # Sound effects (WAV)
├── logo/                          # Logo images
├── loading/                       # Loading screen graphics
├── title/                         # Title screen graphics
├── ending/                        # Ending sequence images
└── credits/                       # Credits screen assets
```

---

## 3. Key Architectural Patterns

### 3.1 Singleton Pattern (Core Systems)

Most core systems use thread-safe singleton pattern:

```cpp
class Screen {
    private:
        static Screen* screen_;  // Singleton instance
        Screen();                // Private constructor
        ~Screen();
    public:
        static void init();      // Creates singleton
        static void destroy();   // Destroys singleton
        static Screen* get();    // Accesses singleton
};
```

**Singleton Systems:**
- `Screen` - Rendering, window management, palette/shader effects
- `Input` - Keyboard & gamepad input binding and checking
- `Audio` - Music and sound effect playback
- `Resource` - Asset loading, caching, streaming
- `Asset` - Asset path registry and verification
- `Director` - Main application controller
- `Cheevos` - Achievement state management
- `Debug` - Debug information overlay

### 3.2 Scene-Based State Machine

The game uses a scene manager to control application flow:

```cpp
// namespace SceneManager
enum class Scene {
    LOGO, LOADING_SCREEN, TITLE, CREDITS, GAME, DEMO, 
    GAME_OVER, ENDING, ENDING2, QUIT
};

inline Scene current = Scene::LOGO;  // Global scene state
inline Options options = ...;        // Transition options
```

**Scene Hierarchy:**
- Each scene runs its own update/render loop
- `Director` switches between scenes based on `SceneManager::current`
- Scenes can request transitions via `SceneManager::current` assignment

### 3.3 Entity-Component Pattern (Simplified)

Entities (Player, Enemies, Items) have:
- **Update** - Logic, physics, animation
- **Render** - Draw to screen surface
- **Collision** - Hit detection (player collides with room, enemies, items)

### 3.4 Surface-Based Rendering Pipeline

The rendering system uses a **8-bit indexed color** pipeline:

```
SurfaceData (pixel buffer)
     ↓
Surface (palette + rendering operations)
     ↓
SDL_Texture (GPU texture)
     ↓
SDL_Renderer (to SDL_Window)
     ↓
Display
```

**Key Components:**
- `Surface` - 8-bit indexed pixel buffer with palette support
- `SurfaceSprite` - Renders a fixed region of a surface
- `SurfaceAnimatedSprite` - Frame-based animation on top of sprite
- `SurfaceMovingSprite` - Adds velocity/position to animated sprite
- Supports color replacement, palette swapping, and shader effects (CRT)

### 3.5 Tile-Based Collision System

Rooms use a sophisticated collision detection system:

```cpp
class Room {
    std::vector<LineHorizontal> bottom_floors_;   // Ground surfaces
    std::vector<LineHorizontal> top_floors_;      // Ceiling surfaces
    std::vector<LineVertical> left_walls_;        // Left walls
    std::vector<LineVertical> right_walls_;       // Right walls
    std::vector<LineDiagonal> left_slopes_;       // Ramps going left
    std::vector<LineDiagonal> right_slopes_;      // Ramps going right
    std::vector<LineHorizontal> conveyor_belt_floors_; // Moving platforms
};
```

**Collision Detection:**
- Player has collision points and "feet" points for fine-grained detection
- Room provides `check*Surfaces()` methods for collision resolution
- Supports ramps, slopes, conveyor belts, and auto-surfaces
- Enemies have axis-aligned bounding boxes

### 3.6 Sprite Animation System

Animation is data-driven:

```cpp
struct AnimationData {
    std::string name;
    std::vector<SDL_FRect> frames;  // Frame rectangles
    int speed;                       // Milliseconds per frame
    int loop;                        // Frame to return to (-1 = no loop)
    bool completed;
    int current_frame;
    int counter;
};

// Loaded from .ani files (list of animation names)
// Rendered with SurfaceAnimatedSprite
```

---

## 4. System Interactions & Data Flow

### 4.1 Application Lifecycle

```
main()
  ↓
Director::Director()  [Initialization]
  ├─ Options::init()         - Load game configuration
  ├─ Asset::init()           - Register asset paths
  ├─ Screen::init()          - Create window, SDL renderer
  ├─ Audio::init()           - Initialize SDL audio
  ├─ Input::init()           - Bind keyboard/gamepad controls
  ├─ Resource::init()        - Load all game resources
  └─ Cheevos::init()         - Load achievement state

Director::run()        [Main loop]
  ├─ while (SceneManager::current != QUIT)
  │   ├─ Logo::run()
  │   ├─ LoadingScreen::run()
  │   ├─ Title::run()
  │   ├─ Game::run()
  │   ├─ Ending::run()
  │   └─ ...
  └─ return 0

Director::~Director() [Cleanup]
  ├─ Options::saveToFile()   - Save game settings
  ├─ Resource::destroy()
  ├─ Audio::destroy()
  ├─ Input::destroy()
  ├─ Screen::destroy()
  └─ Asset::destroy()
```

### 4.2 Game Scene Flow (Core Gameplay Loop)

```cpp
Game::run() {
    while (game is running) {
        // Update
        Input::checkInput()          - Get player commands
        Player::update()             - Physics, animation, collision
        Room::update()               - Enemy AI, animated tiles
        checkCollisions()            - Player vs enemies, items, room
        checkGameOver()              - Win/lose conditions
        
        // Render
        Screen::start()              - Prepare for drawing
        Room::renderMap()            - Draw tilemap
        Room::renderEnemies()        - Draw enemy sprites
        Room::renderItems()          - Draw item sprites
        Player::render()             - Draw player sprite
        renderScoreboard()           - Draw HUD
        Screen::render()             - Flush to GPU
    }
}
```

### 4.3 Resource Loading & Caching

```
Director::setFileList()
  ├─ Asset::add(file, type)  - Register all assets
  └─ Asset::check()          - Verify files exist

Game Scene initialization
  └─ Resource::init()        - Loads all resources
      ├─ loadSounds()        - WAV files
      ├─ loadMusics()        - OGG files  
      ├─ loadSurfaces()      - GIF/PNG images
      ├─ loadAnimations()    - .ani animation definitions
      ├─ loadTileMaps()      - .room tilemap data
      └─ loadRooms()         - Room metadata

During gameplay
  └─ Resource::get*(name)    - Return cached resource
```

### 4.4 Input Flow

```
SDL_Event (from OS)
  ↓
Input::checkInput(action)
  ├─ Check keyboard bindings      - SDL_Scancode → InputAction
  ├─ Check gamepad bindings       - SDL_GamepadButton → InputAction
  └─ Return true if action active

Game logic uses checked inputs
  └─ Player responds to actions
```

### 4.5 Audio Control Flow

```
Game code
  ├─ Audio::playMusic(name, loop)
  ├─ Audio::playSound(name, group)
  └─ Audio::stopMusic()
      ↓
    Audio [wrapper/manager]
      ├─ Resource::getMusic(name)
      ├─ Resource::getSound(name)
      └─ jail_audio C library
          └─ SDL3 Audio device
```

---

## 5. Important Design Patterns & Conventions

### 5.1 Naming Conventions

**Classes:**
- `PascalCase` for classes: `Player`, `Room`, `Screen`, `Director`
- Suffix `Sprite` for sprite classes: `SurfaceSprite`, `SurfaceAnimatedSprite`

**Methods:**
- `get*()` for getters: `getWidth()`, `getRect()`
- `set*()` for setters: `setColor()`, `setPos()`
- `check*()` for boolean checks: `checkInput()`, `checkCollision()`
- `update()` for game logic updates
- `render()` for drawing

**Variables:**
- `snake_case` for member variables with `_` suffix: `x_`, `y_`, `sprite_`
- `UPPER_CASE` for constants: `BLOCK`, `MAX_VY_`, `WIDTH_`
- Private members: `private_member_`

**Structs for Data:**
- `XxxData` suffix: `PlayerData`, `RoomData`, `AnimationData`
- Used as initialization structures passed to constructors

### 5.2 Memory Management

- **Smart Pointers:** Uses `std::shared_ptr` for shared ownership (Surfaces, Sprites, Rooms)
- **Unique Pointers:** Uses `std::unique_ptr` for sole ownership (Director, local objects)
- **Raw Pointers:** Minimal use, mainly for singleton access or SDL objects
- **Static Allocation:** Singletons use static pointer pattern for RAII

### 5.3 Frame-Independent Physics

Uses `DeltaTimer` for delta time calculation:

```cpp
// In game loop
float delta = deltaTimer.tick();  // Get seconds since last frame

// Apply to physics
player.vy_ += gravity * delta;
player.y_ += player.vy_ * delta;
```

Provides **time scaling** for slow-motion effects.

### 5.4 Palette System

- 8-bit indexed color (256 colors per palette)
- Multiple palettes can be loaded and swapped
- `Surface::setPalette()` changes rendering colors
- Supports color replacement per-render: `renderWithColorReplace()`
- CRT shader effects can modify colors in real-time

### 5.5 Configuration System

Game settings stored in configuration file:

```cpp
namespace Options {
    inline Video video{};           // Screen resolution, fullscreen, etc.
    inline Audio audio{};           // Music/sound volumes
    inline Notification notifications{};
    inline Cheat cheats{};          // Cheat codes
    inline ControlScheme keys{};    // Control mapping
    inline Stats stats{};           // Game statistics
}

Options::loadFromFile(path);  // Load from config.txt
Options::saveToFile(path);    // Save on exit
```

### 5.6 Achievement System

```cpp
struct Achievement {
    int id;
    std::string caption;
    std::string description;
    int icon;
    bool completed;
    bool obtainable;
};

Cheevos::unlock(id);           // Unlock achievement
Cheevos::setUnobtainable(id);  // Lock achievement
Cheevos::saveToFile();         // Persist state
```

Achievements trigger notifications on unlock.

---

## 6. Technology Stack

### Core Technologies

| Component | Technology | Version | Role |
|-----------|-----------|---------|------|
| **Graphics** | SDL3 | Latest | Window, rendering, input |
| **GPU Rendering** | OpenGL | 3.2+ | Shader effects (CRT) |
| **Audio** | SDL3 Audio | Latest | Audio device, mixing |
| **Audio Decoding** | jail_audio (custom) | 1.x | OGG/WAV playback |
| **Image Loading** | stb_image | v2.x | PNG/GIF image loading |
| **Audio Decoding** | stb_vorbis | v1.x | OGG Vorbis support |
| **Language** | C++ | C++20 | Standard library features |
| **Build System** | CMake | 3.10+ | Cross-platform building |

### C++ Features Used

- **Smart Pointers:** `std::shared_ptr`, `std::unique_ptr`
- **Standard Containers:** `std::vector`, `std::array`
- **Modern Features:** `std::move`, lambda functions, constexpr
- **Namespaces:** Extensive use for organization
- **Inline Variables:** C++17 `inline` for global game state

### Platform Support

- **Windows:** MinGW/MSVC with SDL3
- **macOS:** Apple Clang, arm64 architecture, OpenGL
- **Linux:** GCC with SDL3 and OpenGL

---

## 7. Key Classes & Their Responsibilities

### Core System Classes

| Class | Purpose | Pattern |
|-------|---------|---------|
| `Director` | Main application controller, scene manager | Singleton |
| `Screen` | Rendering, window, palette management | Singleton |
| `Input` | Keyboard & gamepad input | Singleton |
| `Audio` | Music and SFX playback | Singleton |
| `Resource` | Asset caching and loading | Singleton |
| `Asset` | Asset path registry | Singleton |
| `Debug` | Debug overlay information | Singleton |
| `globalEvents` | Global SDL event handling (quit, device reset, mouse) | Namespace |

### Game Logic Classes

| Class | Purpose |
|-------|---------|
| `Game` | Main gameplay scene, orchestrates update/render |
| `Player` | Player entity with physics and animation |
| `Room` | Level data, collision detection, tilemap rendering |
| `Enemy` | Enemy entity behavior and rendering |
| `Item` | Collectible items |
| `Scoreboard` | HUD display data |
| `Cheevos` | Achievement unlock and state |
| `ItemTracker` | Tracks collected items |
| `RoomTracker` | Tracks visited rooms |

### Rendering Classes

| Class | Purpose |
|-------|---------|
| `Surface` | 8-bit indexed color pixel buffer with palette |
| `SurfaceSprite` | Renders a sprite region |
| `SurfaceAnimatedSprite` | Frame-based animation rendering |
| `SurfaceMovingSprite` | Sprite with velocity/position |
| `Text` | Text rendering system |
| `OpenGLShader` | Shader compilation and effects |

### Utility Classes

| Class | Purpose |
|-------|---------|
| `DeltaTimer` | Frame-rate independent timing |

---

## 8. Common Development Workflows

### Adding a New Input Action

1. Add to `InputAction` enum in `core/input/input.hpp`
2. Bind in `Director::initInput()`:
   ```cpp
   Input::get()->bindKey(InputAction::NEW_ACTION, SDL_SCANCODE_X);
   ```
3. Check in game code:
   ```cpp
   if (Input::get()->checkInput(InputAction::NEW_ACTION)) {
       // Handle action
   }
   ```

### Adding a New Scene

1. Create class inheriting appropriate base (usually standalone `run()` method)
2. Add to `SceneManager::Scene` enum
3. Implement in `Director::run()` switch statement
4. Set `SceneManager::current` to transition

### Adding Game Assets

1. Place file in `data/` directory
2. Register in `Director::setFileList()`:
   ```cpp
   Asset::get()->add("/data/path/file.ext", AssetType::TYPE);
   ```
3. Resource loads automatically during `Resource::init()`
4. Access via: `Resource::get()->getSurface("name")`

### Modifying Collision Detection

1. Update `Room::setBottomSurfaces()`, `setLeftSlopes()`, etc.
2. Modify Player collision point generation in `Player::updateColliderPoints()`
3. Adjust tile classification in `TileType` enum
4. Test with debug visualization (F12 key)

---

## 9. Debug Features

### Available at Runtime

- **F12** - Toggle debug info overlay (FPS, player position, collision points)
- **F1/F2** - Decrease/increase window zoom
- **F3** - Toggle fullscreen mode
- **F4** - Toggle shader effects
- **F5/F6** - Next/previous palette
- **F7** - Toggle integer scaling
- **M** - Toggle music
- **B** - Toggle border display
- **P** - Pause game

### Debug Mode Compilation

In debug builds (`#ifdef DEBUG`), renders:
- Player collision boxes
- Collision point visualization
- Debug information overlay
- Special debug event handling

---

## 10. Performance Considerations

### Optimization Points

1. **Rendering:** Uses indexed color (8-bit) to reduce memory bandwidth
2. **Surfaces:** Shared smart pointers reduce copying
3. **Collision:** Pre-computed tile surface lists avoid per-frame searches
4. **Animation:** Frame-based animation reduces computation vs. bone systems
5. **Audio:** Cached music and sound effects, no runtime decoding
6. **Delta Time:** Frame-rate independent logic for smooth gameplay

### Known Limitations

- Single-threaded architecture (SDL3 requires single-thread rendering)
- Surfaces stored entirely in CPU memory (not GPU-side textures)
- Palette system requires full surface redraw when changing colors

---

## 11. File Format Reference

### Animation Files (.ani)
List of animation names, one per line:
```
default
jump
run
fall
```

### Room Data Files (.room)
Key-value pairs defining room properties:
```
number=01
name=Starting Room
bg_color=0x000000
border_color=0xFF00FF
...
```

### Tilemap Files (.tmx)
Tiled map format with tileset and collision data.

### Palette Files (.pal)
Binary 256-color palette format (256 × 4 bytes RGBA).

---

## 12. Quick Reference: Main Entry Points

### For Graphics Issues
- `Screen::render()` - Main rendering method
- `Screen::setPalete()` - Palette application
- `Surface` class - Pixel buffer operations

### For Input Issues
- `Input::checkInput()` - Input state checking
- `Director::initInput()` - Binding configuration

### For Audio Issues
- `Audio::playMusic()` - Music playback
- `Audio::playSound()` - SFX playback
- `jail_audio` library - Low-level audio operations

### For Game Logic
- `Game::run()` - Main game loop
- `Room` class - Collision and level logic
- `Player::update()` - Physics and movement

### For Asset Management
- `Asset::add()` - Asset registration
- `Resource::load()` - Asset loading
- `Director::setFileList()` - Complete asset registry

---

## 13. Future Enhancement Points

### Identified Areas for Expansion

1. **Network Play:** Stats upload to online service
2. **More Scenes:** Additional game modes
3. **Custom Rooms:** Level editor integration
4. **Audio Streaming:** Background music without loading entire file
5. **Particle System:** Visual effects for pickups/collisions
6. **Controller Feedback:** Haptic feedback for game events
7. **Accessibility:** Font scaling, color-blind modes, key remapping UI

---

## Development Notes

- **Language:** All code comments and some variable names are in Spanish (maintaining original author style)
- **Compilation:** Use CMake - automatically handles platform differences
- **Performance Profiling:** Use debug overlay (F12) for basic metrics; consider external profilers for deeper analysis
- **Common Warnings:** The codebase has been cleaned of the `struct`/`class` forward declaration inconsistency warnings that previously appeared

### Important Code Consistency Rules

1. **Forward Declarations:** Always use `class` for forward declarations of classes defined with `class` (not `struct`). The `Surface` class is defined as `class Surface` in `surface.hpp:57`, so all forward declarations must use `class Surface;`

2. **Singleton Pattern:** When creating new singletons, follow the existing pattern:
   - Private static instance pointer
   - Private constructor/destructor
   - Public `init()`, `destroy()`, and `get()` methods

3. **Delta Time:** Always use `DeltaTimer` for frame-rate independent physics calculations

4. **Memory Management:** Prefer `std::shared_ptr` for shared resources (Surfaces, Sprites) and `std::unique_ptr` for sole ownership

---

**Last Updated:** November 2022 (per README)
**Original Author:** JailDesigner
**Repository:** Gitea (internal)