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

type StandardResponse = {
  code: number | string;
  msg: string;
  data: unknown;
};

function isStandardResponse(value: unknown): value is StandardResponse {
  if (value === null || typeof value !== "object") return false;
  return "code" in value && "msg" in value && "data" in value;
}

function extractSuccessData(body: unknown): unknown {
  if (body === null || typeof body !== "object") return body;
  const record = body as Record<string, unknown>;
  const keys = Object.keys(record);
  if (keys.length === 1 && keys[0] === "data") return record.data;
  return body;
}

function buildErrorResponse(statusCode: number, body: unknown): StandardResponse {
  let code: number | string = statusCode;
  let msg = "Request failed";
  let data: unknown = null;

  if (body && typeof body === "object") {
    const record = body as Record<string, unknown>;
    const error = record.error && typeof record.error === "object" ? (record.error as Record<string, unknown>) : null;

    const rawCode = record.code ?? error?.code;
    if (typeof rawCode === "string" || typeof rawCode === "number") code = rawCode;

    const rawMsg = record.msg ?? record.message ?? error?.message;
    if (typeof rawMsg === "string" && rawMsg.trim().length > 0) msg = rawMsg;

    if ("data" in record) data = record.data;
    else if ("details" in record) data = record.details;
    else if (error && "details" in error) data = error.details;
  }

  return { code, msg, data };
}

export function responseMiddleware(_req: Request, res: Response, next: NextFunction): void {
  const originalJson = res.json.bind(res);
  const originalSend = res.send.bind(res);

  res.json = ((body: unknown) => {
    if (isStandardResponse(body)) return originalJson(body);

    if (res.statusCode >= 400) {
      return originalJson(buildErrorResponse(res.statusCode, body));
    }

    const wrapped: StandardResponse = {
      code: 0,
      msg: "success",
      data: extractSuccessData(body)
    };
    return originalJson(wrapped);
  }) as Response["json"];

  res.send = ((body?: unknown) => {
    if (body && typeof body === "object") return res.json(body);
    return originalSend(body as never);
  }) as Response["send"];

  next();
}