/**
 * Copyright 2004-present Facebook. All Rights Reserved.
 *
 * @flow
 * @providesModule XMLHttpRequestBase
 */
'use strict';

/**
 * Shared base for platform-specific XMLHttpRequest implementations.
 */
class XMLHttpRequestBase {

  UNSENT: number;
  OPENED: number;
  HEADERS_RECEIVED: number;
  LOADING: number;
  DONE: number;

  onreadystatechange: ?Function;
  onload: ?Function;
  upload: any;
  readyState: number;
  responseHeaders: ?Object;
  responseText: ?string;
  status: ?string;

  _method: ?string;
  _url: ?string;
  _headers: Object;
  _sent: boolean;
  _aborted: boolean;

  constructor() {
    this.UNSENT = 0;
    this.OPENED = 1;
    this.HEADERS_RECEIVED = 2;
    this.LOADING = 3;
    this.DONE = 4;

    this.onreadystatechange = undefined;
    this.upload = undefined; /* Upload not supported */
    this.readyState = this.UNSENT;
    this.responseHeaders = undefined;
    this.responseText = undefined;
    this.status = undefined;

    this._method = null;
    this._url = null;
    this._headers = {};
    this._sent = false;
    this._aborted = false;
  }

  getAllResponseHeaders(): ?string {
    if (this.responseHeaders) {
      var headers = [];
      for (var headerName in this.responseHeaders) {
        headers.push(headerName + ': ' + this.responseHeaders[headerName]);
      }
      return headers.join('\n');
    }
    // according to the spec, return null <==> no response has been received
    return null;
  }

  getResponseHeader(header: string): ?string {
    if (this.responseHeaders) {
      var value = this.responseHeaders[header.toLowerCase()];
      return value !== undefined ? value : null;
    }
    return null;
  }

  setRequestHeader(header: string, value: any): void {
    this._headers[header] = value;
  }

  open(method: string, url: string, async: ?boolean): void {
    /* Other optional arguments are not supported */
    if (this.readyState !== this.UNSENT) {
      throw new Error('Cannot open, already sending');
    }
    if (async !== undefined && !async) {
      // async is default
      throw new Error('Synchronous http requests are not supported');
    }
    this._method = method;
    this._url = url;
    this._aborted = false;
    this._setReadyState(this.OPENED);
  }

  sendImpl(method: ?string, url: ?string, headers: Object, data: any): void {
    throw new Error('Subclass must define sendImpl method');
  }

  abortImpl(): void {
    throw new Error('Subclass must define abortImpl method');
  }

  send(data: any): void {
    if (this.readyState !== this.OPENED) {
      throw new Error('Request has not been opened');
    }
    if (this._sent) {
      throw new Error('Request has already been sent');
    }
    this._sent = true;
    this.sendImpl(this._method, this._url, this._headers, data);
  }

  abort(): void {
    this.abortImpl();
    // only call onreadystatechange if there is something to abort,
    // below logic is per spec
    if (!(this.readyState === this.UNSENT ||
        (this.readyState === this.OPENED && !this._sent) ||
        this.readyState === this.DONE)) {
      this._sent = false;
      this._setReadyState(this.DONE);
    }
    if (this.readyState === this.DONE) {
      this._sendLoad();
    }
    this.readyState = this.UNSENT;
    this._aborted = true;
  }

  callback(status: string, responseHeaders: ?Object, responseText: string): void {
    if (this._aborted) {
      return;
    }
    this.status = status;
    // Headers should be case-insensitive
    var lcResponseHeaders = {};
    for (var header in responseHeaders) {
      lcResponseHeaders[header.toLowerCase()] = responseHeaders[header];
    }
    this.responseHeaders = lcResponseHeaders;
    this.responseText = responseText;
    this._setReadyState(this.DONE);
    this._sendLoad();
  }

  _setReadyState(newState: number): void {
    this.readyState = newState;
    // TODO: workaround flow bug with nullable function checks
    var onreadystatechange = this.onreadystatechange;
    if (onreadystatechange) {
      // We should send an event to handler, but since we don't process that
      // event anywhere, let's leave it empty
      onreadystatechange(null);
    }
  }

  _sendLoad(): void {
    // TODO: workaround flow bug with nullable function checks
    var onload = this.onload;
    if (onload) {
      // We should send an event to handler, but since we don't process that
      // event anywhere, let's leave it empty
      onload(null);
    }
  }
}

module.exports = XMLHttpRequestBase;
