// Released under the MIT/X11 license
// http://www.opensource.org/licenses/mit-license.php

"use strict";
var Request = require("request").Request;
var xhrMod = require("xhr");

// Initialize myStorage if we don't have it.
var myStorage = require("simple-storage").storage;
if (!myStorage.cachedRequest) {
  myStorage.cachedRequest = {};
}

// https://bugzilla.mozilla.org/582760 is still alive
var debugOption = true;
function debug(str) {
  if (debugOption) {
    console.log(str);
  }
}

/**
 * Decorating cached response object with a bit of additional
 * functionality.
 */
function CachedResponse (url) {
  if (!myStorage.cachedRequest[url]) {
    myStorage.cachedRequest[url] = {};
    this.url = url;
    this.text = null;
    this.status = "";
    this.statusText = "";
    this.headers = {};
  }
  else {
    var storedResponse = myStorage.cachedRequest[url];
    this.url = url;
    this.text = storedResponse.text;
    this.status = storedResponse.status;
    this.statusText = storedResponse.statusText;
    this.headers = storedResponse.headers;
  }
}

/**
 * getter returning object from this.text
 * (so we don't save essentially the same object same)
 *
 * @return Object from this.text, if this.text isn't JSONable,
 *   return null
 */
CachedResponse.prototype.__defineGetter__("json", function() {
  try {
    return JSON.parse(this.text);
  }
  catch (ex) {
    if (ex instanceof SyntaxError) {
      return null;
    } else {
      throw ex;
    }
  }
});

/**
 * save the current object's values to myStorage.
 */
CachedResponse.prototype.saveCached = function() {
  var storedResponse = myStorage.cachedRequest[this.url];
  storedResponse.text = this.text;
  storedResponse.status = this.status;
  storedResponse.statusText = this.statusText;
  storedResponse.headers = this.headers;
};

/**
 * getter returning Last-Modified header as a Date object.
 *
 * @return Date when this has Last-Modified header, or null otherwise
 */
CachedResponse.prototype.__defineGetter__("lastModified", function() {
  if (this.headers && (this.headers.hasOwnProperty("Last-Modified"))) {
    return new Date(this.headers["Last-Modified"]);
  }
  return null;
});

/**
 * Emulates Request object, but caches the result for speedier access,
 * and protection when the remote site is down.
 *
 * @opts Object with properties same as Request
 *
 * Limitations: does only GET requests, so it doesn't even have
 *   .post(), .get() or any other methods.
 * Contrary to Request() opts can have onError callback, and
 * getExpiredAnyway property to allow using expired cached value,
 * if the remote connection returns error.
 */
exports.CachedRequest = function CachedRequest(opts) {
  var crStorage = new CachedResponse(opts.url);

  var req = new xhrMod.XMLHttpRequest();
  req.open("HEAD", opts.url, true);
  req.onreadystatechange = function () {
    if (req.readyState == 4) {
      if(req.status == 200) {
        var curETag = req.getResponseHeader("ETag");
        var curLastModified = new Date(req.getResponseHeader("Last-Modified"));
        if (crStorage && crStorage.headers &&
             ((curETag == crStorage.headers.eTag) ||
             (curLastModified <= crStorage.lastModified))) {
          debug("Loading from cache!");
          // use cached values
        }
        else { // cache is not up-to-date
          new Request({
            url: opts.url,
            onComplete: function(resp) {
              if (resp.status == 200) {
                debug("Too old cache! Reloaded");
                crStorage.headers = resp.headers;
                crStorage.text = resp.text;
                crStorage.status = resp.status;
                crStorage.statusText = resp.statusText;
                crStorage.saveCached();
              }
              else {
                // If we cannot get response from the real URL,
                // we may be happy with getting our fix from
                // anywhere, including (possibly) expired cache
                if (opts.getExpiredAnyway && crStorage && crStorage.text) {
                  debug("Nothing better to do! Returning expired cache.");
                }
                else {
                  // We definitively lost, just call .onComplete
                  // with what we have.
                  opts.onComplete({
                    text: resp.text,
                    json: null,
                    status: resp.status,
                    statusText: resp.statusText,
                    headers: resp.headers
                  });
                  // to avoid call opts.onComplete below
                  return ;
                }
              }
            }
          }).get();
        }
        opts.onComplete(crStorage);
      }
    }
  };
  req.send();
};

//vim: set ts=2 et sw=2 textwidth=80: