import * as API from '../api/types';
import {getAuth} from '../auth/auth';
import fetch from 'node-fetch';
import URL from 'url';

export type Match<T, S extends API.APIKey> =
  T extends API.API<
    infer U,
    infer UP,
    infer M,
    infer P,
    infer R> ?
  S extends "uri" ? U :
  S extends "uriParams" ? UP :
  S extends "method" ? M :
  S extends "param" ? P :
  S extends "response" ? R : never : never;

export function mkHeader(extra: any = {}) { // throw
  return {
    "Authorization": `Bearer ${getAuth().token}`,
    ...extra
  }
}

export async function canvas<T>(props: {
  uri: Match<T, "uri">,
  method: Match<T, "method">,
  uriParams?: Match<T, "uriParams">,
  param: Match<T, "param">,
  extraHeaders?: any,
}): Promise<Match<T, "response">> {
  const {method, uriParams, param, extraHeaders} = props;

  const uri = uriParamsReplace(props.uri, uriParams ?? {});
  const headers = mkHeader(extraHeaders);

  // build parameter used by `fetch`.
  const [url, config] = ((): [string, any] => {
    const base = getAuth().url;
    const url = URL.resolve(base, uri);

    switch (method) {
      // build get url. not .env requires a full url with protocol,
      // here we need to remove it to use url.,format.
      case "GET": {
        const hostname = base.split("https://").pop();
        const url = URL.format({
          protocol: "https",
          hostname,
          pathname: uri,
          query: param as any,
        });

        return [url, {headers}];
      }

      case "POST": {
        return [url, {method: "post", body: JSON.stringify(param), headers, }];
      }

      case "DELETE": {
        return [url, {method: "delete", headers, }];
      }

      case "PUT":
        return [url, {method: "put", body: JSON.stringify(param), headers, }];

      default:
        throw new Error(`Wrong HTTP method ${method}`);
    }
  })();

  return (await fetch(url, config)).json();
}


// replace api endpoint params with uriParams.
// throw an exceptoin when uriParams.length and number of endpoint params doesn't match up.
function uriParamsReplace(uri: string, uriParams: {[key: string]: string | number}) {
  return uri.split("/").map(e => {
    if (e.startsWith(":")) {

      const key = e.slice(1).trim();
      const val = uriParams[key]?.toString();

      if (val !== undefined) {
        return val;
      }

      throw new Error(""
        + `Uri parameter is not matched with the api endpoint. ${uri}, `
        + `no parameter corresponds to ${e}.`);

    } else if (e.startsWith("*")) { // combine full path.
      const cdr = e.slice(1).trim();
      return  cdr.startsWith("/") ? cdr.slice(1) : cdr;
    }
    return e;
  }).join("/");
}