Architecture Overview

Time Capsule is a Progressive Web App that recreates the 1990s Unix CDE (Common Desktop Environment) desktop experience. The architecture follows a modular, event-driven design pattern built on modern web technologies.

System Design

The application follows a layered architecture with clear separation of concerns:

Core Principles

1. Modular Architecture

Each core system is implemented as an independent module with a well-defined interface. This promotes code reusability and maintainability.

// src/scripts/core/config.ts
export interface Config {
  WINDOW: WindowConfig;
  AUDIO: AudioConfig;
  FS: FSConfig;
  TERMINAL: TerminalConfig;
  // ... more configuration sections
}

export const CONFIG: Config = {
  WINDOW: {
    MIN_VISIBLE: 20,
    BASE_Z_INDEX: 10000,
    TOP_BAR_HEIGHT: 30,
  },
  AUDIO: {
    BEEP_FREQUENCY: 880,
    BEEP_GAIN: 0.9,
    BEEP_DURATION: 0.1,
  },
  // ... configuration values
};

2. Event-Driven Communication

Components communicate through custom events dispatched on the window object, promoting loose coupling:

// Notify system of filesystem changes
function dispatchChange(path: string): void {
  window.dispatchEvent(
    new CustomEvent('cde-fs-change', {
      detail: { path },
    })
  );
}

3. Singleton Pattern for Core Systems

Core systems use the singleton pattern to ensure single instances throughout the application lifecycle:

class SettingsManager {
  private static instance: SettingsManager;
  private settings: SystemSettings;

  private constructor() {
    this.settings = this.getDefaultSettings();
    this.load();
  }

  public static getInstance(): SettingsManager {
    if (!SettingsManager.instance) {
      SettingsManager.instance = new SettingsManager();
    }
    return SettingsManager.instance;
  }
}

export const settingsManager = SettingsManager.getInstance();

4. Progressive Enhancement

The application provides a functional experience even with limited JavaScript, with enhanced features loading progressively.

Core Components

WindowManager

Handles all window lifecycle operations including creation, positioning, focus management, and z-index ordering. Key Responsibilities:

Window registration and lifecycle management
Drag and drop functionality
Z-index management (base: 10000 for windows, 90000 for modals)
Focus management with click and point-to-focus modes
Window state persistence (position, maximized state)
Workspace management (4 virtual desktops)
Mobile-specific centering and constraints

See Window Manager for detailed documentation.

Virtual Filesystem (VFS)

Provides a POSIX-like filesystem abstraction in browser memory with O(1) path lookups. Key Features:

Hierarchical folder structure
File metadata (size, mtime, owner, permissions)
CRUD operations (touch, mkdir, rm, rename, move, copy)
Trash functionality
Search with recursive option
Event notifications on changes

See Virtual Filesystem for detailed documentation.

SettingsManager

Centralized configuration management with persistent storage. Features:

Unified settings storage
Version-aware cache management
Migration from legacy localStorage keys
Section-based organization (theme, mouse, keyboard, beep, session, desktop)
Window session persistence

See Storage Management for detailed documentation.

AudioManager

Retro audio system using Web Audio API for classic CDE system sounds. Capabilities:

Lazy AudioContext initialization (on first user gesture)
System beeps with configurable frequency/duration
UI feedback sounds (click, error, success)
Window operation sounds (open, close, minimize, maximize, shade)
Melody playback for startup chimes
Volume control

export interface IAudioManager {
  beep(frequency?: number, duration?: number): void;
  click(): void;
  error(): void;
  success(): void;
  windowOpen(): void;
  windowClose(): void;
  windowMinimize(): void;
  windowMaximize(): void;
  windowShade(): void;
  menuOpen(): void;
  menuClose(): void;
  notification(): void;
  setVolume(volume: number): void;
  playMelody(notes: Array<{
    freq: number;
    duration: number;
    type?: OscillatorType;
    delay?: number
  }>): Promise<void>;
  playStartupChime(): void;
}

StyleManager

Orchestrates multiple style modules for system customization. Modules:

ThemeModule: Color palette management (CDE palettes)
FontModule: Font family and sizing controls
MouseModule: Cursor settings and acceleration
KeyboardModule: Keyboard repeat and shortcuts
BeepModule: Audio feedback settings
BackdropModule: Wallpaper/backdrop management with XPM parsing
WindowModule: Window behavior (focus mode, opaque dragging)
ScreenModule: Screen settings
StartupModule: Boot sequence customization

export class StyleManager {
  public theme: ThemeModule;
  public font: FontModule;
  public mouse: MouseModule;
  public keyboard: KeyboardModule;
  public beep: BeepModule;
  public backdrop: BackdropModule;
  public windowBehavior: WindowModule;
  public screen: ScreenModule;
  public startup: StartupModule;

  public init(): void {
    const themeSettings = settingsManager.getSection('theme');
    
    // Apply default palette if none saved
    if (!themeSettings.colors || 
        Object.keys(themeSettings.colors).length === 0) {
      this.theme.applyCdePalette('latesummer');
    } else {
      this.theme.loadSavedColors(themeSettings.colors);
    }
    
    // Initialize all modules
    this.mouse.load();
    this.keyboard.load();
    this.beep.load();
    this.backdrop.load();
    // ...
  }
}

Configuration System

Centralized configuration in config.ts provides type-safe access to all system constants:

export interface WindowConfig {
  MIN_VISIBLE: number;
  BASE_Z_INDEX: number;
  TOP_BAR_HEIGHT: number;
}

export interface FSConfig {
  HOME: string;
  DESKTOP: string;
  TRASH: string;
  NETWORK: string;
}

export interface TerminalConfig {
  HOME_PATH: string;
  MIN_TYPING_DELAY: number;
  MAX_TYPING_DELAY: number;
  POST_COMMAND_DELAY: number;
  POST_SEQUENCE_DELAY: number;
  MAX_LINES: number;
  CLEANUP_INTERVAL: number;
}

Data Flow Patterns

Window Creation Flow

Settings Persistence Flow

VFS Operation Flow

Performance Considerations

Z-Index Management

Z-index allocation uses separate counters for different layers:

let highestWindowZIndex = CONFIG.WINDOW.BASE_Z_INDEX; // 10000
let highestModalZIndex = 90000;

function getNextZIndex(isModal: boolean = false): number {
  if (isModal) {
    return ++highestModalZIndex;
  }
  return ++highestWindowZIndex;
}

This ensures modals always appear above regular windows, preventing z-index conflicts.

Memory-Optimized VFS

The VFS uses a flattened Map for O(1) path resolution instead of traversing a tree structure:

const fsMap: Record<string, VFSNode> = {};

function flatten(basePath: string, node: VFSNode): void {
  fsMap[basePath] = node;
  if (node.type === 'folder') {
    for (const [name, child] of Object.entries(node.children)) {
      const fullPath = basePath + name + 
        (child.type === 'folder' ? '/' : '');
      flatten(fullPath, child);
    }
  }
}

// O(1) lookup instead of tree traversal
getNode(path: string): VFSNode | null {
  return fsMap[path] || null;
}

Window Position Normalization

Window positions are normalized on viewport resize to ensure they remain accessible:

function normalizeWindowPosition(win: HTMLElement): void {
  const rect = win.getBoundingClientRect();
  const TOP_BAR_HEIGHT = CONFIG.WINDOW.TOP_BAR_HEIGHT;
  const viewportWidth = window.innerWidth;
  const viewportHeight = window.innerHeight;

  // Clamp within viewport bounds
  const minY = TOP_BAR_HEIGHT;
  const minX = 0;
  const maxX = Math.max(0, viewportWidth - rect.width);
  const maxY = Math.max(minY, viewportHeight - rect.height);

  let newTop = Math.max(rect.top, minY);
  newTop = Math.min(newTop, maxY);

  let newLeft = Math.max(rect.left, minX);
  newLeft = Math.min(newLeft, maxX);

  win.style.top = newTop + 'px';
  win.style.left = newLeft + 'px';
}

Error Handling

Graceful degradation is implemented throughout:

try {
  await storageAdapter.setItemSync(key, value);
} catch (e) {
  console.error('[SettingsManager] Failed to save:', e);
  // Continue operation, data will be lost on refresh
}

Type Safety

Strong TypeScript typing throughout the codebase:

export interface VFSMetadata {
  size: number;
  mtime: string; // ISO string
  owner: string;
  permissions: string;
}

export interface VFSFile {
  type: 'file';
  content: string;
  metadata?: VFSMetadata;
}

export interface VFSFolder {
  type: 'folder';
  children: Record<string, VFSNode>;
  metadata?: VFSMetadata;
}

export type VFSNode = VFSFile | VFSFolder;

Global Exposure

Core systems are exposed globally for debugging and feature access:

declare global {
  interface Window {
    WindowManager: typeof WindowManager;
    VirtualFS: IVFS;
    AudioManager: IAudioManager;
    styleManager: StyleManager;
    CONFIG: Config;
  }
}

if (typeof window !== 'undefined') {
  window.WindowManager = WindowManager;
  window.VirtualFS = VFS;
  window.AudioManager = AudioManager;
  window.CONFIG = CONFIG;
}

Next Steps

Window Manager

Deep dive into window management implementation

Virtual Filesystem

Learn about the VFS architecture and operations

Storage

Understand persistent data storage with IndexedDB

Development

Start building features for Time Capsule

Architecture

Development

​Architecture Overview

​System Design

​Core Principles

​1. Modular Architecture

​2. Event-Driven Communication

​3. Singleton Pattern for Core Systems

​4. Progressive Enhancement

​Core Components

​WindowManager

​Virtual Filesystem (VFS)

​SettingsManager

​AudioManager

​StyleManager

​Configuration System

​Data Flow Patterns

​Window Creation Flow

​Settings Persistence Flow

​VFS Operation Flow

​Performance Considerations

​Z-Index Management

​Memory-Optimized VFS

​Window Position Normalization

​Error Handling

​Type Safety

​Global Exposure

​Next Steps

Window Manager

Virtual Filesystem

Storage

Development

Architecture Overview

System Design

Core Principles

1. Modular Architecture

2. Event-Driven Communication

3. Singleton Pattern for Core Systems

4. Progressive Enhancement

Core Components

WindowManager

Virtual Filesystem (VFS)

SettingsManager

AudioManager

StyleManager

Configuration System

Data Flow Patterns

Window Creation Flow

Settings Persistence Flow

VFS Operation Flow

Performance Considerations

Z-Index Management

Memory-Optimized VFS

Window Position Normalization

Error Handling

Type Safety

Global Exposure

Next Steps