import { raw } from "body-parser";
import * as http from "http";
import { JSONParseError, SignatureValidationFailed } from "./exceptions";
import * as Types from "./types";
import validateSignature from "./validate-signature";

export type Request = http.IncomingMessage & { body: any };
export type Response = http.ServerResponse;
export type NextCallback = (err?: Error) => void;

export type Middleware = (
  req: Request,
  res: Response,
  next: NextCallback,
) => void | Promise<void>;

function isValidBody(body?: any): body is string | Buffer {
  return (body && typeof body === "string") || Buffer.isBuffer(body);
}

export default function middleware(config: Types.MiddlewareConfig): Middleware {
  if (!config.channelSecret) {
    throw new Error("no channel secret");
  }

  const secret = config.channelSecret;

  const _middleware: Middleware = async (req, res, next) => {
    // header names are lower-cased
    // https://nodejs.org/api/http.html#http_message_headers
    const signature = req.headers["x-line-signature"] as string;

    if (!signature) {
      next(new SignatureValidationFailed("no signature"));
      return;
    }

    const body = await (async (): Promise<string | Buffer> => {
      if (isValidBody((req as any).rawBody)) {
        // rawBody is provided in Google Cloud Functions and others
        return (req as any).rawBody;
      } else if (isValidBody(req.body)) {
        return req.body;
      } else {
        // body may not be parsed yet, parse it to a buffer
        return new Promise<Buffer>((resolve, reject) =>
          raw({ type: "*/*" })(req as any, res as any, (error: Error) =>
            error ? reject(error) : resolve(req.body),
          ),
        );
      }
    })();

    if (!validateSignature(body, secret, signature)) {
      next(
        new SignatureValidationFailed("signature validation failed", signature),
      );
      return;
    }

    const strBody = Buffer.isBuffer(body) ? body.toString() : body;

    try {
      req.body = JSON.parse(strBody);
      next();
    } catch (err) {
      next(new JSONParseError(err.message, strBody));
    }
  };
  return (req, res, next): void => {
    (<Promise<void>>_middleware(req, res, next)).catch(next);
  };
}