added middleware exercise

exercice6.ts

@@ -0,0 +1,81 @@
+import { Application, Context, Next, Router } from "jsr:@oak/oak";
+
+export enum APIErrorCode {
+  NOT_IMPLEMENTED = "NOT_IMPLEMENTED",
+  SERVER_ERROR = "SERVER_ERROR",
+}
+
+export interface APIError {
+  code: APIErrorCode;
+  message: string;
+}
+
+export interface APISuccess<T> {
+  success: true;
+  data: T;
+  error?: never;
+}
+
+export interface APIFailure {
+  success: false;
+  data?: never;
+  error: APIError;
+}
+
+export type APIResponse<T> = APISuccess<T> | APIFailure;
+
+class APIException extends Error {
+  readonly code: APIErrorCode;
+  readonly status: number;
+
+  constructor(code: APIErrorCode, status: number, message: string) {
+    super(message);
+    this.code = code;
+    this.status = status;
+  }
+}
+
+async function errorMiddleware(ctx: Context, next: Next) {
+  try {
+    // On passe à la prochaine fonction de la chaîne
+    await next();
+  } catch (err) {
+    if (err instanceof APIException) {
+      const responseBody: APIFailure = {
+        success: false,
+        error: {
+          code: err.code,
+          message: err.message,
+        }
+      };
+
+      ctx.response.status = err.status;
+      ctx.response.body = responseBody;
+    } else {
+      console.error(err);
+
+      const responseBody: APIFailure = {
+        success: false,
+        error: {
+          code: APIErrorCode.SERVER_ERROR,
+          message: "Unexpected server error",
+        }
+      };
+
+      ctx.response.status = 500;
+      ctx.response.body = responseBody;
+    }
+  }
+}
+
+const router = new Router();
+
+router.get("/", errorMiddleware, (ctx) => {
+  throw new APIException(APIErrorCode.NOT_IMPLEMENTED, 501, "I need more time...");
+});
+
+const app = new Application();
+app.use(router.routes());
+app.use(router.allowedMethods());
+
+app.listen({ port: 8000 });