feat: add API router

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/src/lib/router.ts

@@ -0,0 +1,81 @@
+import { NextResponse } from 'next/server';
+
+export type HandlerFn = (ctx: HandlerContext) => unknown | Promise<unknown>;
+
+export type HandlerContext = {
+  params: Record<string, string>;
+  method: string;
+  body: unknown;
+  searchParams: URLSearchParams;
+};
+
+type RouteEntry = {
+  pattern: string[];
+  methods: string[];
+  handler: HandlerFn;
+};
+
+const routes: RouteEntry[] = [];
+
+export function route(pattern: string, methods: string[], handler: HandlerFn) {
+  const parts = pattern.split('/').filter(Boolean);
+  routes.push({ pattern: parts, methods: methods.map(m => m.toUpperCase()), handler });
+}
+
+export async function dispatch(
+  request: Request,
+  pathSegments: string[],
+  method: string
+): Promise<NextResponse> {
+  for (const entry of routes) {
+    if (!entry.methods.includes(method)) continue;
+    const params: Record<string, string> = {};
+    let match = true;
+
+    if (entry.pattern.length !== pathSegments.length) continue;
+
+    for (let i = 0; i < entry.pattern.length; i++) {
+      const ep = entry.pattern[i];
+      const sp = pathSegments[i];
+      if (ep.startsWith(':')) {
+        params[ep.slice(1)] = sp;
+      } else if (ep !== sp) {
+        match = false;
+        break;
+      }
+    }
+
+    if (!match) continue;
+
+    let body: unknown = undefined;
+    const ct = request.headers.get('content-type') || '';
+    if (ct.includes('application/json')) {
+      try { body = await request.json(); } catch { body = undefined; }
+    }
+
+    const ctx: HandlerContext = {
+      params,
+      method,
+      body,
+      searchParams: new URL(request.url).searchParams,
+    };
+
+    try {
+      const result = await entry.handler(ctx);
+      return NextResponse.json(result, { status: 200 });
+    } catch (err: any) {
+      const status = err.status || 500;
+      return NextResponse.json({ error: err.message || 'Internal error' }, { status });
+    }
+  }
+
+  return NextResponse.json({ error: 'Not found' }, { status: 404 });
+}
+
+export class HttpError extends Error {
+  status: number;
+  constructor(status: number, message: string) {
+    super(message);
+    this.status = status;
+  }
+}