/**
 * Sandbox for executing javascript, parsing css styles and doing dom operations in a secure way
 *
 * Browser Compatibility:
 *  - Secure in MSIE 6+, but only when the user hasn't made changes to his security level "restricted"
 *  - Partially secure in other browsers (Firefox, Opera, Safari, Chrome, ...)
 *
 * Please note that this class can't benefit from the HTML5 sandbox attribute for the following reasons:
 *    - sandboxing doesn't work correctly with inlined content (src="javascript:'<html>...</html>'")
 *    - sandboxing of physical documents causes that the dom isn't accessible anymore from the outside (iframe.contentWindow, ...)
 *    - setting the "allow-same-origin" flag would fix that, but then still javascript and dom events refuse to fire
 *    - therefore the "allow-scripts" flag is needed, which then would deactivate any security, as the js executed inside the iframe
 *      can do anything as if the sandbox attribute wasn't set
 *
 * @param {Function} [readyCallback] Method that gets invoked when the sandbox is ready
 * @param {Object} [config] Optional parameters
 *
 * @example
 *    new wysihtml5.dom.Sandbox(function(sandbox) {
 *      sandbox.getWindow().document.body.innerHTML = '<img src=foo.gif onerror="alert(document.cookie)">';
 *    });
 */
(function(wysihtml5) {
  var /**
       * Default configuration
       */
      doc                 = document,
      /**
       * Properties to unset/protect on the window object
       */
      windowProperties    = [
        "parent", "top", "opener", "frameElement", "frames",
        "localStorage", "globalStorage", "sessionStorage", "indexedDB"
      ],
      /**
       * Properties on the window object which are set to an empty function
       */
      windowProperties2   = [
        "open", "close", "openDialog", "showModalDialog",
        "alert", "confirm", "prompt",
        "openDatabase", "postMessage",
        "XMLHttpRequest", "XDomainRequest"
      ],
      /**
       * Properties to unset/protect on the document object
       */
      documentProperties  = [
        "referrer",
        "write", "open", "close"
      ];
  
  wysihtml5.dom.Sandbox = Base.extend(
    /** @scope wysihtml5.dom.Sandbox.prototype */ {

    constructor: function(readyCallback, config) {
      this.callback = readyCallback || wysihtml5.EMPTY_FUNCTION;
      this.config   = wysihtml5.lang.object({}).merge(config).get();
      this.iframe   = this._createIframe();
    },
    
    insertInto: function(element) {
      if (typeof(element) === "string") {
        element = doc.getElementById(element);
      }
      
      element.appendChild(this.iframe);
    },

    getIframe: function() {
      return this.iframe;
    },

    getWindow: function() {
      this._readyError();
    },

    getDocument: function() {
      this._readyError();
    },

    destroy: function() {
      var iframe = this.getIframe();
      iframe.parentNode.removeChild(iframe);
    },

    _readyError: function() {
      throw new Error("wysihtml5.Sandbox: Sandbox iframe isn't loaded yet");
    },

    /**
     * Creates the sandbox iframe
     *
     * Some important notes:
     *  - We can't use HTML5 sandbox for now:
     *    setting it causes that the iframe's dom can't be accessed from the outside
     *    Therefore we need to set the "allow-same-origin" flag which enables accessing the iframe's dom
     *    But then there's another problem, DOM events (focus, blur, change, keypress, ...) aren't fired.
     *    In order to make this happen we need to set the "allow-scripts" flag.
     *    A combination of allow-scripts and allow-same-origin is almost the same as setting no sandbox attribute at all.
     *  - Chrome & Safari, doesn't seem to support sandboxing correctly when the iframe's html is inlined (no physical document)
     *  - IE needs to have the security="restricted" attribute set before the iframe is 
     *    inserted into the dom tree
     *  - Believe it or not but in IE "security" in document.createElement("iframe") is false, even
     *    though it supports it
     *  - When an iframe has security="restricted", in IE eval() & execScript() don't work anymore
     *  - IE doesn't fire the onload event when the content is inlined in the src attribute, therefore we rely
     *    on the onreadystatechange event
     */
    _createIframe: function() {
      var that   = this,
          iframe = doc.createElement("iframe");
      iframe.className = "wysihtml5-sandbox";
      wysihtml5.dom.setAttributes({
        "security":           "restricted",
        "allowtransparency":  "true",
        "frameborder":        0,
        "width":              0,
        "height":             0,
        "marginwidth":        0,
        "marginheight":       0
      }).on(iframe);

      // Setting the src like this prevents ssl warnings in IE6
      if (wysihtml5.browser.throwsMixedContentWarningWhenIframeSrcIsEmpty()) {
        iframe.src = "javascript:'<html></html>'";
      }

      iframe.onload = function() {
        iframe.onreadystatechange = iframe.onload = null;
        that._onLoadIframe(iframe);
      };

      iframe.onreadystatechange = function() {
        if (/loaded|complete/.test(iframe.readyState)) {
          iframe.onreadystatechange = iframe.onload = null;
          that._onLoadIframe(iframe);
        }
      };

      return iframe;
    },

    /**
     * Callback for when the iframe has finished loading
     */
    _onLoadIframe: function(iframe) {
      // don't resume when the iframe got unloaded (eg. by removing it from the dom)
      if (!wysihtml5.dom.contains(doc.documentElement, iframe)) {
        return;
      }

      var that           = this,
          iframeWindow   = iframe.contentWindow,
          iframeDocument = iframe.contentWindow.document,
          charset        = doc.characterSet || doc.charset || "utf-8",
          sandboxHtml    = this._getHtml({
            charset:      charset,
            stylesheets:  this.config.stylesheets
          });

      // Create the basic dom tree including proper DOCTYPE and charset
      iframeDocument.open("text/html", "replace");
      iframeDocument.write(sandboxHtml);
      iframeDocument.close();

      this.getWindow = function() { return iframe.contentWindow; };
      this.getDocument = function() { return iframe.contentWindow.document; };

      // Catch js errors and pass them to the parent's onerror event
      // addEventListener("error") doesn't work properly in some browsers
      // TODO: apparently this doesn't work in IE9!
      iframeWindow.onerror = function(errorMessage, fileName, lineNumber) {
        throw new Error("wysihtml5.Sandbox: " + errorMessage, fileName, lineNumber);
      };

      if (!wysihtml5.browser.supportsSandboxedIframes()) {
        // Unset a bunch of sensitive variables
        // Please note: This isn't hack safe!  
        // It more or less just takes care of basic attacks and prevents accidental theft of sensitive information
        // IE is secure though, which is the most important thing, since IE is the only browser, who
        // takes over scripts & styles into contentEditable elements when copied from external websites
        // or applications (Microsoft Word, ...)
        var i, length;
        for (i=0, length=windowProperties.length; i<length; i++) {
          this._unset(iframeWindow, windowProperties[i]);
        }
        for (i=0, length=windowProperties2.length; i<length; i++) {
          this._unset(iframeWindow, windowProperties2[i], wysihtml5.EMPTY_FUNCTION);
        }
        for (i=0, length=documentProperties.length; i<length; i++) {
          this._unset(iframeDocument, documentProperties[i]);
        }
        // This doesn't work in Safari 5 
        // See http://stackoverflow.com/questions/992461/is-it-possible-to-override-document-cookie-in-webkit
        this._unset(iframeDocument, "cookie", "", true);
      }

      this.loaded = true;

      // Trigger the callback
      setTimeout(function() { that.callback(that); }, 0);
    },

    _getHtml: function(templateVars) {
      var stylesheets = templateVars.stylesheets,
          html        = "",
          i           = 0,
          length;
      stylesheets = typeof(stylesheets) === "string" ? [stylesheets] : stylesheets;
      if (stylesheets) {
        length = stylesheets.length;
        for (; i<length; i++) {
          html += '<link rel="stylesheet" href="' + stylesheets[i] + '">';
        }
      }
      templateVars.stylesheets = html;

      return wysihtml5.lang.string(
        '<!DOCTYPE html><html><head>'
        + '<meta charset="#{charset}">#{stylesheets}</head>'
        + '<body></body></html>'
      ).interpolate(templateVars);
    },

    /**
     * Method to unset/override existing variables
     * @example
     *    // Make cookie unreadable and unwritable
     *    this._unset(document, "cookie", "", true);
     */
    _unset: function(object, property, value, setter) {
      try { object[property] = value; } catch(e) {}

      try { object.__defineGetter__(property, function() { return value; }); } catch(e) {}
      if (setter) {
        try { object.__defineSetter__(property, function() {}); } catch(e) {}
      }

      if (!wysihtml5.browser.crashesWhenDefineProperty(property)) {
        try {
          var config = {
            get: function() { return value; }
          };
          if (setter) {
            config.set = function() {};
          }
          Object.defineProperty(object, property, config);
        } catch(e) {}
      }
    }
  });
})(wysihtml5);
