/*
 * Copyright 2005-2010 the original author or authors.
 * 
 * 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.wamblee.wicket.jquery;

import java.util.Arrays;

import org.apache.wicket.Component;
import org.apache.wicket.Page;
import org.apache.wicket.behavior.IBehavior;
import org.apache.wicket.markup.html.IHeaderResponse;
import org.wamblee.wicket.behavior.CompositeBehavior;

import flexjson.JSONSerializer;

/**
 * Abstract JQuery hehavior class that makes it easy to write jQuery behaviors:
 * <ul>
 * <li>Creating a ready function which will be invoked for the component</li>
 * <li>Checking whether or not the behavior may be attached to a page using
 * {@link #isPageAllowed()}. By default, the behavior may be attached to
 * pages. Behaviors that should not be allowed to be attached to pages should
 * override this method.</li>
 * <li>Ensuring that the markup id of the component is output</li>
 * <li>Creating a call to an intialization function from the ready handler using
 * the component id</li>
 * </ul>
 * 
 * The ready function will be invoked as part of a ready handler and will invoke
 * a function with two arguments. The first is the selector of the component and
 * the second is a configuration object. In case the behavior is attached to a
 * component, a selector is used based on the unique markup id. When used on a
 * page, the selector matches with the "body" of the page.
 * <p>
 * The second parameter is obtained through a call to
 * {@link #getConfigurationJavascript()}.
 * 
 * 
 * @author Erik Brakkee
 * 
 *         <ConfigType>
 */
public class AbstractJQueryBehavior<ConfigType> extends CompositeBehavior {

    private static final String DEFAULT_NAMESPACE = "org.wamblee";
    private static JSONSerializer DEFAULT_JSON_SERIALIZER = new JSONSerializer();

    private Component component;
    private String function;

    /**
     * Constructs the behavior.
     * 
     * @param aFunction
     *            Function to be invoked from the ready handler. This function
     *            is invoked with a CSS selector that identifies the component.
     * @param aBehaviors
     *            Behaviors to add in addition to the basic JQuery stuff.
     */
    public AbstractJQueryBehavior(String aFunction, IBehavior... aBehaviors) {
        super(getBehaviors(aBehaviors));
        function = aFunction;
    }

    /**
     * Determines whether the behavior is allowed to be attached toa page.
     * 
     * @return True. 
     */
    protected boolean isPageAllowed() {
        return true;
    }

    private static IBehavior[] getBehaviors(IBehavior[] aBehaviors) {
        IBehavior[] behaviors = new IBehavior[aBehaviors.length + 1];
        behaviors[0] = new JQueryHeaderContributor();
        for (int i = 0; i < aBehaviors.length; i++) {
            behaviors[i + 1] = aBehaviors[i];
        }
        return behaviors;
    }

    @Override
    public void bind(Component aComponent) {
        if (component != null) {
            throw new IllegalStateException(
                "this kind of handler cannot be attached to " +
                    "multiple components; it is already attached to component " +
                    component + ", but component " + aComponent +
                    " wants to be attached too");
        }
        if (!isPageAllowed() && aComponent instanceof Page) {
            throw new IllegalStateException(
                "This behavior cannot be applied to a page: " + aComponent);
        }
        component = aComponent;
        super.bind(aComponent);
        if (!(aComponent instanceof Page)) {
            aComponent.setOutputMarkupId(true);
        }
    }

    @Override
    public void renderHead(IHeaderResponse aResponse) {
        super.renderHead(aResponse);
        String jsString = createReadyFunction();
        aResponse.renderJavascript(jsString, null);
    }

    /**
     * Creates a jQuery ready handler that invokes a given javascript function
     * with the id of a component and with a second parameter of parameters to
     * pass additional information to the function.
     * 
     * @param aFunction
     *            Javascript function to invoke, the name of this function must
     *            include the namespace as it is called from a global scope.
     * @param aComponent
     *            Component to invoke the id for.
     * @return
     */
    String createReadyFunction() {
        if (!(component instanceof Page) && !component.getOutputMarkupId()) {
            throw new IllegalStateException(
                "The component " +
                    component +
                    " does not have its markup id set so this ready handler will not have any effect");
        }
        StringBuffer js = new StringBuffer();
        js.append("jQuery(function(){");
        js.append(function + "(");
        String selector = "body";
        if (!(component instanceof Page)) {
            selector = "#" + component.getMarkupId();
        }
        js.append("\"" + selector + "\"");
        String config = getConfigurationJavascript();
        if (config != null) {
            js.append(",");
            js.append(config);
        }
        js.append(");");
        js.append("});");
        String jsString = js.toString();
        return jsString;
    }

    /**
     * Returns a javascript object that is passed as second argument to the
     * ready function. This method uses {@link #getConfigurationObject()} to
     * obtain the configuration object to use which is then serialized to
     * javascript using {@link JSONSerializer}. Subclasses can override the
     * default JSONSerializer by implementing {@link #getCustomSerializer()}.
     * <p>
     * Subclasses should override this method to perform custom serialization.
     * 
     * @return Configuration object in javascript.
     */
    protected String getConfigurationJavascript() {
        Object config = getConfigurationObject();
        return getActualSerializer().serialize(config);
    }

    /**
     * Gets the actual serializer to use. It uses {@link #getCustomSerializer()}
     * to check if there is a custom serializer available.
     * 
     * @return Serializer.
     */
    private JSONSerializer getActualSerializer() {
        JSONSerializer serializer = getCustomSerializer();
        if (serializer != null) {
            return serializer;
        }
        return DEFAULT_JSON_SERIALIZER;
    }

    /**
     * Returns the serializer to use. Implementations can override this method
     * to perform custom initialization of the serializer knowing the type of
     * configuration object to use.
     * 
     * @return Custom serializer to use.
     */
    protected JSONSerializer getCustomSerializer() {
        return null;
    }

    /**
     * Gets the configuration object to use. This is transformed to JSON using
     * the serializer.
     * 
     * @return Configuration object.
     */
    protected ConfigType getConfigurationObject() {
        return null;
    }
}