// This [jQuery](http://jquery.com/) plugin implements an `<iframe>`
// [transport](http://api.jquery.com/extending-ajax/#Transports) so that
// `$.ajax()` calls support the uploading of files using standard HTML file
// input fields. This is done by switching the exchange from `XMLHttpRequest`
// to a hidden `iframe` element containing a form that is submitted.

// The [source for the plugin](http://github.com/cmlenz/jquery-iframe-transport)
// is available on [Github](http://github.com/) and dual licensed under the MIT
// or GPL Version 2 licenses.

// ## Usage

// To use this plugin, you simply add an `iframe` option with the value `true`
// to the Ajax settings an `$.ajax()` call, and specify the file fields to
// include in the submssion using the `files` option, which can be a selector,
// jQuery object, or a list of DOM elements containing one or more
// `<input type="file">` elements:

//     $("#myform").submit(function() {
//         $.ajax(this.action, {
//             files: $(":file", this),
//             iframe: true
//         }).complete(function(data) {
//             console.log(data);
//         });
//     });

// The plugin will construct hidden `<iframe>` and `<form>` elements, add the
// file field(s) to that form, submit the form, and process the response.

// If you want to include other form fields in the form submission, include
// them in the `data` option, and set the `processData` option to `false`:

//     $("#myform").submit(function() {
//         $.ajax(this.action, {
//             data: $(":text", this).serializeArray(),
//             files: $(":file", this),
//             iframe: true,
//             processData: false
//         }).complete(function(data) {
//             console.log(data);
//         });
//     });

// ### Response Data Types

// As the transport does not have access to the HTTP headers of the server
// response, it is not as simple to make use of the automatic content type
// detection provided by jQuery as with regular XHR. If you can't set the
// expected response data type (for example because it may vary depending on
// the outcome of processing by the server), you will need to employ a
// workaround on the server side: Send back an HTML document containing just a
// `<textarea>` element with a `data-type` attribute that specifies the MIME
// type, and put the actual payload in the textarea:

//     <textarea data-type="application/json">
//       {"ok": true, "message": "Thanks so much"}
//     </textarea>

// The iframe transport plugin will detect this and pass the value of the
// `data-type` attribute on to jQuery as if it was the "Content-Type" response
// header, thereby enabling the same kind of conversions that jQuery applies
// to regular responses. For the example above you should get a Javascript
// object as the `data` parameter of the `complete` callback, with the
// properties `ok: true` and `message: "Thanks so much"`.

// ### Handling Server Errors

// Another problem with using an `iframe` for file uploads is that it is
// impossible for the javascript code to determine the HTTP status code of the
// servers response. Effectively, all of the calls you make will look like they
// are getting successful responses, and thus invoke the `done()` or
// `complete()` callbacks. You can only determine communicate problems using
// the content of the response payload. For example, consider using a JSON
// response such as the following to indicate a problem with an uploaded file:

//     <textarea data-type="application/json">
//       {"ok": false, "message": "Please only upload reasonably sized files."}
//     </textarea>

// ### Compatibility

// This plugin has primarily been tested on Safari 5 (or later), Firefox 4 (or
// later), and Internet Explorer (all the way back to version 6). While I
// haven't found any issues with it so far, I'm fairly sure it still doesn't
// work around all the quirks in all different browsers. But the code is still
// pretty simple overall, so you should be able to fix it and contribute a
// patch :)

// ## Annotated Source

(function($, undefined) {
  "use strict";

  // Register a prefilter that checks whether the `iframe` option is set, and
  // switches to the "iframe" data type if it is `true`.
  $.ajaxPrefilter(function(options, origOptions, jqXHR) {
    if (options.iframe) {
      return "iframe";
    }
  });

  // Register a transport for the "iframe" data type. It will only activate
  // when the "files" option has been set to a non-empty list of enabled file
  // inputs.
  $.ajaxTransport("iframe", function(options, origOptions, jqXHR) {
    var form = null,
        iframe = null,
        name = "iframe-" + $.now(),
        files = $(options.files).filter(":file:enabled"),
        markers = null;

    // This function gets called after a successful submission or an abortion
    // and should revert all changes made to the page to enable the
    // submission via this transport.
    function cleanUp() {
      markers.replaceWith(function(idx) {
        return files.get(idx);
      });
      form.remove();
      iframe.attr("src", "javascript:false;").remove();
    }

    // Remove "iframe" from the data types list so that further processing is
    // based on the content type returned by the server, without attempting an
    // (unsupported) conversion from "iframe" to the actual type.
    options.dataTypes.shift();

    if (files.length) {
      form = $("<form enctype='multipart/form-data' method='post'></form>").
        hide().attr({action: options.url, target: name});

      // If there is any additional data specified via the `data` option,
      // we add it as hidden fields to the form. This (currently) requires
      // the `processData` option to be set to false so that the data doesn't
      // get serialized to a string.
      if (typeof(options.data) === "string" && options.data.length > 0) {
        $.error("data must not be serialized");
      }
      $.each(options.data || {}, function(name, value) {
        if ($.isPlainObject(value)) {
          name = value.name;
          value = value.value;
        }
        $("<input type='hidden' />").attr({name:  name, value: value}).
          appendTo(form);
      });

      // Add a hidden `X-Requested-With` field with the value `IFrame` to the
      // field, to help server-side code to determine that the upload happened
      // through this transport.
      $("<input type='hidden' value='IFrame' name='X-Requested-With' />").
        appendTo(form);

      // Move the file fields into the hidden form, but first remember their
      // original locations in the document by replacing them with disabled
      // clones. This should also avoid introducing unwanted changes to the
      // page layout during submission.
      markers = files.after(function(idx) {
        return $(this).clone().prop("disabled", true);
      }).next();
      files.appendTo(form);

      return {

        // The `send` function is called by jQuery when the request should be
        // sent.
        send: function(headers, completeCallback) {
          iframe = $("<iframe src='javascript:false;' name='" + name +
            "' id='" + name + "' style='display:none'></iframe>");

          // The first load event gets fired after the iframe has been injected
          // into the DOM, and is used to prepare the actual submission.
          iframe.bind("load", function() {

            // The second load event gets fired when the response to the form
            // submission is received. The implementation detects whether the
            // actual payload is embedded in a `<textarea>` element, and
            // prepares the required conversions to be made in that case.
            iframe.unbind("load").bind("load", function() {
              var doc = this.contentWindow ? this.contentWindow.document :
                (this.contentDocument ? this.contentDocument : this.document),
                root = doc.documentElement ? doc.documentElement : doc.body,
                textarea = root.getElementsByTagName("textarea")[0],
                type = textarea ? textarea.getAttribute("data-type") : null,
                status = textarea ? textarea.getAttribute("data-status") : 200,
                statusText = textarea ? textarea.getAttribute("data-statusText") : "OK",
                content = {
                  html: root.innerHTML,
                  text: type ?
                    textarea.value :
                    root ? (root.textContent || root.innerText) : null
                };
              cleanUp();
              completeCallback(status, statusText, content, type ?
                ("Content-Type: " + type) :
                null);
            });

            // Now that the load handler has been set up, submit the form.
            form[0].submit();
          });

          // After everything has been set up correctly, the form and iframe
          // get injected into the DOM so that the submission can be
          // initiated.
          $("body").append(form, iframe);
        },

        // The `abort` function is called by jQuery when the request should be
        // aborted.
        abort: function() {
          if (iframe !== null) {
            iframe.unbind("load").attr("src", "javascript:false;");
            cleanUp();
          }
        }

      };
    }
  });

})(jQuery);
