discogs_show_thumbnail.user.js

// ==UserScript==
// @name           Discogs.com: show thumbnail
// @namespace      http://d.hatena.ne.jp/youpy/
// @include        http://www.discogs.com/*
// @require        http://gist.github.com/3242.txt
// @require        http://github.com/cho45/jsdeferred/raw/master/jsdeferred.userscript.js
// ==/UserScript==

// API usage is limited to 5,000 requests per 24-hour period, per IP address.

with(D()) {
  (function() {
    var Storage = function() {
      this.apiRoot = 'http://globalstorage.jgate.de/';
    }
    Storage.prototype.get = function(key) {
      var url = this.apiRoot + 'get?key=' + encodeURIComponent(key);
      return xhttp.get(url).
        next(function(res) {
          var json = eval('(' + res.responseText + ')');
          return json.value;
        });
    };
    Storage.prototype.set = function(key, value) {
      var url = this.apiRoot + 'set?key=' + encodeURIComponent(key) + '&value=' + encodeURIComponent(value);
      return xhttp.get(url).
        next(function() {
          return value;
        });
    };

    var API_KEY = 'be37d50363';
    var NOT_AVAILABLE_IMAGE_URL = 'http://buycheapviagraonlinenow.com/images/image_not_available.jpg';
    var LOADING_IMAGE_URL = 'http://buycheapviagraonlinenow.com/images/loading.gif';
    var KEY_PREFIX = 'discogs_com_thumbnail_url_';
    var storage = new Storage();

    $X('//tr[starts-with(@class, "r_tr")]').forEach(function(tr) {
      var matches, releaseId;

      if(!(matches = tr.className.match(/r(\d+)/)))
        return;

      releaseId = matches[1];

      var image = new Image();
      image.src = LOADING_IMAGE_URL;
      image.style.marginRight = '5px';
      tr.childNodes[3].insertBefore(image, tr.childNodes[3].childNodes[0]);

      getThumbnail(releaseId).
        next(function(imageUrl) {
          if(imageUrl) {
            image.src = imageUrl;
          } else {
            image.src = NOT_AVAILABLE_IMAGE_URL;
            image.style.padding = '49px';
            image.style.border = '1px solid #ccc';
          }
        });
    });

    function getThumbnail(releaseId) {
      var url = 'http://www.discogs.com/release/' + releaseId + '?f=xml&api_key=' + API_KEY;

      return storage.
        get(KEY_PREFIX + releaseId).
        next(function(value) {
          if(value) {
            return next(function() {
              return value;
            });
          } else {
            return xhttp.get(url).
              next(function(res) {
                var xml = new XML(res.responseText);

                if(xml..image.length() != 0) {
                  return storage.set(KEY_PREFIX + releaseId, xml..image[0].@uri150);
                } else {
                  return next(function() { return null; });
                }
              });
          }
        });
    };
  })();
}