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;

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;

  return (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;
    }

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

    getBody.then(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));
      }
    });
  };
}