/*
 * Copyright 2000-2016 Vaadin Ltd.
 *
 * 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 com.vaadin.annotations;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import com.vaadin.server.ClientConnector;

/**
 * If this annotation is present on a {@link ClientConnector} class, the
 * framework ensures the referenced style sheets are loaded before the init
 * method for the corresponding client-side connector is invoked.
 * <p>
 * Absolute URLs including protocol and host are used as is on the client-side.
 * Relative URLs are mapped to APP/PUBLISHED/[url] which are by default served
 * from the classpath relative to the class where the annotation is defined.
 * <p>
 * The file is only loaded if it has not already been loaded, determined as
 * follows:
 * <ul>
 * <li>For absolute URLs, the URL is considered loaded if the same URL has
 * previously been loaded using {@code StyleSheet} or if a
 * {@code <link rel="stylesheet">} tag using the same URL was present in the DOM
 * when the Vaadin client-side was initialized.
 * <li>For relative URLs, the URL is considered loaded if another file with the
 * same name has already been loaded using {@code StyleSheet}, even if that file
 * was loaded from a different folder.
 * </ul>
 * <p>
 * Special Vaadin urls are also supported. The most useful is vaadin:// which
 * maps to the location of the automatically published VAADIN folder. Using the
 * VAADIN folder and vaadin:// you can publish stylesheets which use images or
 * other files with relative paths.
 * <p>
 * Example: <code>@StyleSheet({"http://host.com/file1.css", "file2.css"})</code>
 * on the class com.example.MyConnector would load the file
 * http://host.com/file1.css as is and file2.css from /com/example/file2.css on
 * the server's classpath using the ClassLoader that was used to load
 * com.example.MyConnector.
 * <p>
 * For adding multiple style sheets for a single component, you can use this
 * annotation multiple times.
 *
 * @author Vaadin Ltd
 * @since 7.0.0
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Repeatable(InternalContainerAnnotationForSS.class)
public @interface StyleSheet {
    /**
     * Style sheets to load before initializing the client-side connector.
     *
     * @return an array of style sheet urls
     */
    public String[] value();
}