/*
 * Copyright (C) 2015 Red Hat, Inc. and/or its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.jboss.errai.ui.client.widget;

import javax.annotation.PostConstruct;

import com.google.gwt.dom.client.Document;
import com.google.gwt.dom.client.FormElement;
import com.google.gwt.dom.client.IFrameElement;
import com.google.gwt.dom.client.Style.Display;
import com.google.gwt.event.dom.client.ClickHandler;
import com.google.gwt.safehtml.client.SafeHtmlTemplates.Template;
import com.google.gwt.user.client.ui.Composite;

/**
 * Base class for {@link Template Templated} widgets that require native form
 * support for asynchronous {@code GET} or {@code POST} requests.
 * 
 * <p>
 * Calls to {@link AbstractForm#submit()} trigger a form submission that is
 * null-routed and targets a hidden iframe.
 * 
 * <p>
 * The typical usage will be for login forms, where calling
 * {@link AbstractForm#submit()} after a successful login will prompt the
 * browser to remember a user's credentials.
 * 
 * <p>
 * If you use an {@link AbstractForm} and still encounter issues getting proper
 * browser form support:
 * 
 * <ul>
 * <li>make sure that your text-fields are actual form inputs
 * 
 * <li>make sure the UI "submit" button triggers a {@link ClickHandler} that
 * calls {@link AbstractForm}{@link #submit()}
 * 
 * <li>make sure the UI "submit" button does not directly trigger submission
 * (i.e. it should <b>not</b> have {@code type="submit"}
 * 
 * 
 * @author Max Barkley <mbarkley@redhat.com>
 */
public abstract class AbstractForm extends Composite {

  public static final String DEFAULT_FORM_ACTION = "0.0.0.0";
  public static final String ERRAI_FORM_FRAME_ID = "ERRAI-FORM-FRAME";

  private IFrameElement iFrame;

  @PostConstruct
  private void setupIFrame() {
    iFrame = getOrMakeIFrame();

    iFrame.getStyle().setDisplay(Display.NONE);
    final String uniqueId = ERRAI_FORM_FRAME_ID;
    iFrame.setId(uniqueId);
    iFrame.setName(uniqueId);

    Document.get().getBody().appendChild(iFrame);
  }

  private void prepareFormForSubmission(final FormElement form) {
    form.setMethod("post");
    form.setTarget(iFrame.getName());
    form.setAction(getFormAction());
  }

  /**
   * Subclasses may override this method if they want the form to submit to a
   * different url than {@link AbstractForm#DEFAULT_FORM_ACTION}.
   * 
   * @return The value that will be set to the
   *         {@link AbstractForm#getFormElement()} {@code action} attribute
   *         before submission.
   */
  protected String getFormAction() {
    return DEFAULT_FORM_ACTION;
  }

  private IFrameElement getOrMakeIFrame() {
    IFrameElement iFrame = null;
    try {
      iFrame = (IFrameElement) Document.get().getElementById(ERRAI_FORM_FRAME_ID);
    }
    catch (Exception e) {
    }

    if (iFrame == null)
      iFrame = Document.get().createIFrameElement();

    return iFrame;
  }

  /**
   * Submit the form returned from {@link AbstractForm#getFormElement()}. Before
   * the form is submitted, it will be modifed so that it targets a hidden
   * iframe with the id {@link AbstractForm#ERRAI_FORM_FRAME_ID} with the
   * {@code action} set to the return value of
   * {@link AbstractForm#getFormAction()}.
   */
  public void submit() {
    final FormElement form = getFormElement();
    prepareFormForSubmission(form);
    form.submit();
  }

  /**
   * @return The form element that will be submitted when
   *         {@link AbstractForm#submit()} is called.
   */
  protected abstract FormElement getFormElement();

}