/**

 * HTML via Java(tm) Language Bindings

 * Copyright (C) 2013 Jaroslav Tulach <jaroslav.tulach@apidesign.org>

 *

 * This program is free software: you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation, version 2 of the License.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details. apidesign.org

 * designates this particular file as subject to the

 * "Classpath" exception as provided by apidesign.org

 * in the License file that accompanied this code.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program. Look for COPYING file in the top folder.

 * If not, see http://wiki.apidesign.org/wiki/GPLwithClassPathException

 */

package org.apidesign.html.boot.spi;

import java.io.Closeable;

import java.io.Reader;

import java.net.URL;

import net.java.html.js.JavaScriptBody;

import org.apidesign.html.boot.impl.FnContext;

/** Represents single JavaScript function that can be invoked. 

 * Created via {@link Presenter#defineFn(java.lang.String, java.lang.String...)}.

 *

 * @author Jaroslav Tulach <jaroslav.tulach@apidesign.org>

 */

public abstract class Fn {

    private final Presenter presenter;

    /**

     * @deprecated Ineffective as of 0.6. 

     * Provide a presenter via {@link #Fn(org.apidesign.html.boot.spi.Fn.Presenter)}

     * constructor

     */

    @Deprecated

    protected Fn() {

        this(null);

    }

    /** Creates new function object and associates it with given presenter.

     * 

     * @param presenter the browser presenter associated with this function

     * @since 0.6 

     */

    protected Fn(Presenter presenter) {

        this.presenter = presenter;

    }

    /** True, if currently active presenter is the same as presenter this

     * function has been created for via {@link #Fn(org.apidesign.html.boot.spi.Fn.Presenter)}.

     * 

     * @return true, if proper presenter is used

     */

    public final boolean isValid() {

        return FnContext.currentPresenter() == presenter;

    }

    /** Helper method to check if the provided instance is valid function.

     * Checks if the parameter is non-null and if so, does {@link #isValid()}

     * check.

     * 

     * @param fnOrNull function or <code>null</code>

     * @return true if the parameter is non-null and valid

     * @since 0.7

     */

    public static boolean isValid(Fn fnOrNull) {

        return fnOrNull != null && fnOrNull.isValid();

    }

    /** Helper method to find current presenter and ask it to define new

     * function by calling {@link Presenter#defineFn(java.lang.String, java.lang.String...)}.

     * 

     * @param caller the class who wishes to define the function

     * @param code the body of the function (can reference <code>this</code> and <code>names</code> variables)

     * @param names names of individual parameters

     * @return the function object that can be {@link Fn#invoke(java.lang.Object, java.lang.Object...) invoked}

     * @since 0.7

     */

    public static Fn define(Class<?> caller, String code, String... names) {

        return FnContext.currentPresenter().defineFn(code, names);

    }

    /** The currently active presenter.

     * 

     * @return the currently active presenter or <code>null</code>

     * @since 0.7

     */

    public static Presenter activePresenter() {

        return FnContext.currentPresenter();

    }

    /** Activates given presenter. Used by the code generated by 

     * {@link JavaScriptBody} annotation: 

     * <pre>

     * try ({@link Closeable} c = Fn.activate(presenter)) {

     *   doCallsInPresenterContext();

     * }

     * </pre>

     * 

     * @param p the presenter that should be active until closable is closed

     * @return the closable to close

     * @since 0.7

     */

    public static Closeable activate(Presenter p) {

        return FnContext.activate(p);

    }

    /** Invokes the defined function with specified <code>this</code> and

     * appropriate arguments.

     * 

     * @param thiz the meaning of <code>this</code> inside of the JavaScript

     *   function - can be <code>null</code>

     * @param args arguments for the function

     * @return return value from the function

     * @throws Exception if something goes wrong, as exception may be thrown

     */

    public abstract Object invoke(Object thiz, Object... args) throws Exception;

    /** The representation of a <em>presenter</em> - usually a browser window.

     * Should be provided by a library included in the application and registered

     * in <code>META-INF/services</code>, for example with

     * <code>@ServiceProvider(service = Fn.Presenter.class)</code> annotation.

     */

    public interface Presenter {

        /** Creates new function with given parameter names and provided body.

         * 

         * @param code the body of the function. Can refer to variables named

         *   as <code>names</code>

         * @param names names of parameters of the function - these will be 

         *   available when the <code>code</code> body executes

         * 

         * @return function that can be later invoked

         */

        public Fn defineFn(String code, String... names);

        /** Opens the browser, loads provided page and when the

         * page is ready, it calls back to the provider runnable.

         * 

         * @param page the URL for the page to display

         * @param onPageLoad callback when the page is ready

         */

        public void displayPage(URL page, Runnable onPageLoad);

        /** Loads a script into the browser JavaScript interpreter and 

         * executes it.

         * @param code the script to execute

         * @throws Exception if something goes wrong, throw an exception

         */

        public void loadScript(Reader code) throws Exception;

    }

}