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  * Development and Distribution License("CDDL") (collectively, the

  * "License"). You may not use this file except in compliance with the

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  * or nbbuild/licenses/CDDL-GPL-2-CP. See the License for the

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  * The Original Software is NetBeans. The Initial Developer of the Original

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 package org.apidesign.html.boot.spi;

 import java.io.Closeable;

 import java.io.InputStream;

 import java.io.InputStreamReader;

 import java.io.Reader;

 import java.net.URL;

 import java.util.HashMap;

 import java.util.HashSet;

 import java.util.Map;

 import java.util.Set;

 import java.util.concurrent.Executor;

 import net.java.html.js.JavaScriptBody;

 import org.netbeans.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 presenter != null && FnContext.currentPresenter(false) == 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}

      *    - can return <code>null</code> if there is {@link #activePresenter() no presenter}

      * @since 0.7

      */

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

         final Presenter p = FnContext.currentPresenter(false);

         return p == null ? null : p.defineFn(code, names);

     }

     private static final Map<String,Set<Presenter>> LOADED = new HashMap<String, Set<Presenter>>();

     /** Wraps function to ensure that the script represented by <code>resource</code>

      * gets loaded into the browser environment before the function <code>fn</code>

      * is executed.

      * 

      * @param fn original function to call

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

      * @param resource resources (accessible via {@link ClassLoader#getResource(java.lang.String)}) 

      *   with a <em>JavaScript</em> that is supposed to loaded into the browser

      *   environment

      * @return function that ensures the script is loaded and then delegates

      *   to <code>fn</code>

      * @since 0.7

      */

     public static Fn preload(final Fn fn, final Class<?> caller, final String resource) {

         return new Fn() {

             @Override

             public Object invoke(Object thiz, Object... args) throws Exception {

                 final Presenter p = FnContext.currentPresenter(false);

                 Set<Presenter> there = LOADED.get(resource);

                 if (there == null) {

                     there = new HashSet<Presenter>();

                     LOADED.put(resource, there);

                 }

                 if (there.add(p)) {

                     InputStream is = caller.getClassLoader().getResourceAsStream(resource);

                     try {

                         InputStreamReader r = new InputStreamReader(is, "UTF-8");

                         p.loadScript(r);

                     } finally {

                         is.close();

                     }

                 }

                 return fn.invoke(thiz, args);

             }

         };

     }

     /** The currently active presenter.

      * 

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

      * @since 0.7

      */

     public static Presenter activePresenter() {

         return FnContext.currentPresenter(false);

     }

     /** 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;

     /** Provides the function implementation access to the presenter provided

      * in {@link #Fn(org.apidesign.html.boot.spi.Fn.Presenter) the constructor}.

      * 

      * @return presenter passed in the constructor (may be, but should not be <code>null</code>)

      * @since 0.7

      */

     protected final Presenter presenter() {

         return presenter;

     }

     /** 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.

      * <p>

      * Since 0.7 a presenter may implement {@link Executor} interface, in case

      * it supports single threaded execution environment. The executor's

      * {@link Executor#execute(java.lang.Runnable)} method is then supposed

      * to invoke the runnable immediately (in case we are on the right thread

      * already) or return and asynchronously invoke the runnable later on the

      * right thread (if we are on wrong thread).

      */

     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;

     }

     /** Additional interface to be implemented by {@link Presenter}s that

      * wish to control what objects are passed into the JavaScript virtual 

      * machine.

      * <p>

      * If a JavaScript engine makes callback to Java method that returns 

      * a value, the {@link #toJavaScript(java.lang.Object)} method is

      * consulted to convert the Java value to something reasonable inside

      * JavaScript VM.

      * <p>

      * <em>Note:</em> The implementation based on <em>JavaFX</em> <code>WebView</code>

      * uses this interface to convert Java arrays to JavaScript ones.

      * 

      * @see Presenter

      * @since 0.7

      */

     public interface ToJavaScript {

         /** Convert a Java return value into some object suitable for

          * JavaScript virtual machine.

          * 

          * @param toReturn the Java object to be returned

          * @return the replacement value to return instead

          */

         public Object toJavaScript(Object toReturn);

     }

     /** Additional interface to be implemented by {@link Presenter}s that

      * need to convert JavaScript object (usually array) to Java object 

      * when calling back from JavaScript to Java.

      * <p>

      * <em>Note:</em> The implementation based on <em>JavaFX</em>

      * <code>WebView</code> uses this interface to convert JavaScript arrays to

      * Java ones.

       * 

      * @since 0.7

      */

     public interface FromJavaScript {

         /** Convert a JavaScript object into suitable Java representation

          * before a Java method is called with this object as an argument.

          * 

          * @param js the JavaScript object

          * @return replacement object for 

          */

         public Object toJava(Object js);

     }

 }