import { KeyValueStorage } from "./basic";

function protectKey(key: string): string {
  return encodeURIComponent(key);
}

type RestClient = (method: "GET" | "POST" | "PUT" | "DELETE", uri: string, body?: string) => Promise<string | null>
export const HEADER_REQUESTER = "X-TK-Storage-App"
export const HEADER_REPLYIER = "X-TK-Storage-Control"

/**
 * Storage on a remote server, directly usable using HTTP REST verbs
 */
export class RestRemoteStorage implements KeyValueStorage {
  readonly appname: string
  readonly base_url: string
  readonly client: RestClient

  constructor(appname: string, url: string) {
    this.appname = appname;
    this.base_url = (url[url.length - 1] != "/") ? url + "/" : url;
    this.client = this.createClient();
  }

  async get(key: string): Promise<string | null> {
    key = protectKey(key);
    return await this.client("GET", key);
  }

  async set(key: string, value: string | null): Promise<void> {
    key = protectKey(key);
    if (value === null) {
      await this.client("DELETE", key);
    } else {
      await this.client("PUT", key, value);
    }
  }

  private createClient(): RestClient {
    const Request: typeof XMLHttpRequest = (typeof XMLHttpRequest === "undefined") ? require("xmlhttprequest").XMLHttpRequest : XMLHttpRequest;
    const client: RestClient = (method, path, body?) => new Promise((resolve, reject) => {
      const xhr = new Request();
      xhr.open(method, `${this.base_url}${path}`);
      xhr.responseType = 'text';
      xhr.setRequestHeader(HEADER_REQUESTER, this.appname);
      xhr.onload = function () {
        if (xhr.getResponseHeader(HEADER_REPLYIER) != "ok") {
          reject("storage not compatible with tk-storage");
        } else if (xhr.status == 200) {
          resolve(xhr.responseText);
        } else if (xhr.status == 404) {
          resolve(null);
        } else {
          reject(`http error ${xhr.status}: ${xhr.statusText}`);
        }
      };
      xhr.onerror = function () {
        reject("unknown error");
      };
      xhr.send(body);
    });
    return client;
  }
}