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

export function customDomainAdaptorMiddleware(req: Request, res: Response, next: NextFunction) {
    const apigatewayHeader = req.headers["x-apigateway-event"] as string|undefined;

    if (apigatewayHeader === undefined) {
        next();
        return;
    }

    const event = JSON.parse(decodeURIComponent(apigatewayHeader));
    const params = event.pathParameters || {};
    const interprolatedResource = Object.keys(params)
        .reduce((acc, k) => acc.replace("{" + k + "}", params[k]), event.resource);

    if (shouldInterprolateUrl(apigatewayHeader)) {
        req.url = req.originalUrl = interprolatedResource;
    }

    next();
}

function shouldInterprolateUrl(apigatewayHeader: string): boolean {
    const event = JSON.parse(decodeURIComponent(apigatewayHeader));
    const params = event.pathParameters || {};
    const interprolatedResource = Object.keys(params)
        .reduce((acc, k) => acc.replace("{" + k + "}", params[k]), event.resource);

    if (!event.path) {
        return false;
    }
    if (!interprolatedResource) {
        return false;
    }
    if (event.path === interprolatedResource) {
        return false;
    }
    return true;
}