Error middleware en Result-typen

// Result pattern for services and controllers
export type Ok<T> = { ok: true; value: T }
export type Err<E> = { ok: false; error: E }
export type Result<T, E = string> = Ok<T> | Err<E>

export const ok = <T>(value: T): Ok<T> => ({ ok: true, value })
export const err = <E>(error: E): Err<E> => ({ ok: false, error })

// Example usage
async function getUserName(id: string): Promise<Result<string, "NOT_FOUND" | "DB">> {
  if (id === "missing") return err("NOT_FOUND")
  try { return ok("Ada") } catch { return err("DB") }
}

// Canonical error envelope
export type ErrorEnvelope = {
  error: string
  code?: string
  details?: unknown
}

export function mapError(u: unknown): ErrorEnvelope {
  if (u instanceof Error) return { error: u.message }
  if (typeof u === "string") return { error: u }
  try { return { error: JSON.stringify(u) } } catch { return { error: "Unknown error" } }
}

import express, { Request, Response, NextFunction } from "express"

export const asyncHandler = <P, ResBody, ReqBody, Query>(fn: (req: Request<P, ResBody, ReqBody, Query>, res: Response<ResBody>, next: NextFunction) => Promise<unknown>) => {
  return (req: Request<P, ResBody, ReqBody, Query>, res: Response<ResBody>, next: NextFunction) => {
    Promise.resolve(fn(req, res, next)).catch(next)
  }
}

export function errorMiddleware(err: unknown, _req: Request, res: Response, _next: NextFunction) {
  const env = mapError(err)
  const status = env.code === "NOT_FOUND" ? 404 : 500
  res.status(status).json(env)
}

// Usage
// app.get("/", asyncHandler(async (req, res) => { throw new Error("boom") }))
// app.use(errorMiddleware)

import express from "express"
import { z } from "zod"
import { asyncHandler, errorMiddleware } from "./errors"

const createUserSchema = z.object({ name: z.string().min(1) })

const app = express()
app.use(express.json())

app.post("/users", asyncHandler(async (req, res) => {
  const parsed = createUserSchema.safeParse(req.body)
  if (!parsed.success) {
    res.status(400).json({ error: "Invalid body", details: parsed.error.format() })
    return
  }
  res.status(201).json({ id: "u_1", name: parsed.data.name })
}))

app.use(errorMiddleware)

app.listen(3000, () => console.log("http://localhost:3000"))