TypeScripttyped-router.ts
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// Extract params from route string
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type ExtractRouteParams<T extends string> =
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  string extends T ? Record<string, string> :
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  T extends `${infer _Start}:${infer Param}/${infer Rest}` ?
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    { [k in Param | keyof ExtractRouteParams<`/${Rest}`>]: string } :
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  T extends `${infer _Start}:${infer Param}` ?
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    { [k in Param]: string } :
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  Record<string, never>;
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// HTTP method map with capitalized type names
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type HttpMethod = 'get' | 'post' | 'put' | 'delete' | 'patch';
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type RouteHandler<Path extends string> = (
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  params: ExtractRouteParams<Path>,
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  query: Record<string, string>
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) => Promise<unknown>;
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// Type-safe router
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class Router {
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  private routes = new Map<string, RouteHandler<string>>();
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  on<Path extends string>(method: HttpMethod, path: Path, handler: RouteHandler<Path>) {
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    this.routes.set(`${method}:${path}`, handler as RouteHandler<string>);
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    return this;
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  }
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}
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// CSS-in-JS value type
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type CSSUnit = 'px' | 'em' | 'rem' | '%' | 'vw' | 'vh';
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type CSSSize = `${number}${CSSUnit}`;
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// Getter method names
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type Getters<T> = {
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  [K in keyof T as `get${Capitalize<string & K>}`]: () => T[K]
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};
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interface Config { host: string; port: number; debug: boolean; }
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type ConfigGetters = Getters<Config>;
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// { getHost: () => string; getPort: () => number; getDebug: () => boolean }
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// Event system
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type EventMap = {
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  'user:login': { userId: string; timestamp: Date };
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  'user:logout': { userId: string };
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  'order:placed': { orderId: string; total: number };
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};
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class TypedEventBus {
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  private handlers = new Map<string, Function[]>();
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  on<K extends keyof EventMap>(event: K, handler: (data: EventMap[K]) => void) {
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    if (!this.handlers.has(event)) this.handlers.set(event, []);
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    this.handlers.get(event)!.push(handler);
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  }
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  emit<K extends keyof EventMap>(event: K, data: EventMap[K]) {
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    this.handlers.get(event)?.forEach(h => h(data));
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  }
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}
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const bus = new TypedEventBus();
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bus.on('user:login', ({ userId, timestamp }) => {
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  console.log(`User ${userId} logged in at ${timestamp}`);
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});
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bus.emit('user:login', { userId: 'u-1', timestamp: new Date() });