/*
 * Copyright 2002-2016 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
 *
 *      https://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.springframework.scripting.bsh;

import java.io.IOException;

import bsh.EvalError;

import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.scripting.ScriptCompilationException;
import org.springframework.scripting.ScriptFactory;
import org.springframework.scripting.ScriptSource;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;

/**
 * {@link org.springframework.scripting.ScriptFactory} implementation
 * for a BeanShell script.
 *
 * <p>Typically used in combination with a
 * {@link org.springframework.scripting.support.ScriptFactoryPostProcessor};
 * see the latter's javadoc for a configuration example.
 *
 * @author Juergen Hoeller
 * @author Rob Harrop
 * @since 2.0
 * @see BshScriptUtils
 * @see org.springframework.scripting.support.ScriptFactoryPostProcessor
 */
public class BshScriptFactory implements ScriptFactory, BeanClassLoaderAware {

        private final String scriptSourceLocator;

        private final Class<?>[] scriptInterfaces;

        private ClassLoader beanClassLoader = ClassUtils.getDefaultClassLoader();

        private Class<?> scriptClass;

        private final Object scriptClassMonitor = new Object();

        private boolean wasModifiedForTypeCheck = false;


        /**
         * Create a new BshScriptFactory for the given script source.
         * <p>With this {@code BshScriptFactory} variant, the script needs to
         * declare a full class or return an actual instance of the scripted object.
         * @param scriptSourceLocator a locator that points to the source of the script.
         * Interpreted by the post-processor that actually creates the script.
         */
        public BshScriptFactory(String scriptSourceLocator) {
                Assert.hasText(scriptSourceLocator, "'scriptSourceLocator' must not be empty");
                this.scriptSourceLocator = scriptSourceLocator;
                this.scriptInterfaces = null;
        }

        /**
         * Create a new BshScriptFactory for the given script source.
         * <p>The script may either be a simple script that needs a corresponding proxy
         * generated (implementing the specified interfaces), or declare a full class
         * or return an actual instance of the scripted object (in which case the
         * specified interfaces, if any, need to be implemented by that class/instance).
         * @param scriptSourceLocator a locator that points to the source of the script.
         * Interpreted by the post-processor that actually creates the script.
         * @param scriptInterfaces the Java interfaces that the scripted object
         * is supposed to implement (may be {@code null})
         */
        public BshScriptFactory(String scriptSourceLocator, Class<?>... scriptInterfaces) {
                Assert.hasText(scriptSourceLocator, "'scriptSourceLocator' must not be empty");
                this.scriptSourceLocator = scriptSourceLocator;
                this.scriptInterfaces = scriptInterfaces;
        }


        @Override
        public void setBeanClassLoader(ClassLoader classLoader) {
                this.beanClassLoader = classLoader;
        }


        @Override
        public String getScriptSourceLocator() {
                return this.scriptSourceLocator;
        }

        @Override
        public Class<?>[] getScriptInterfaces() {
                return this.scriptInterfaces;
        }

        /**
         * BeanShell scripts do require a config interface.
         */
        @Override
        public boolean requiresConfigInterface() {
                return true;
        }

        /**
         * Load and parse the BeanShell script via {@link BshScriptUtils}.
         * @see BshScriptUtils#createBshObject(String, Class[], ClassLoader)
         */
        @Override
        public Object getScriptedObject(ScriptSource scriptSource, Class<?>... actualInterfaces)
                        throws IOException, ScriptCompilationException {

                Class<?> clazz;

                try {
                        synchronized (this.scriptClassMonitor) {
                                boolean requiresScriptEvaluation = (this.wasModifiedForTypeCheck && this.scriptClass == null);
                                this.wasModifiedForTypeCheck = false;

                                if (scriptSource.isModified() || requiresScriptEvaluation) {
                                        // New script content: Let's check whether it evaluates to a Class.
                                        Object result = BshScriptUtils.evaluateBshScript(
                                                        scriptSource.getScriptAsString(), actualInterfaces, this.beanClassLoader);
                                        if (result instanceof Class) {
                                                // A Class: We'll cache the Class here and create an instance
                                                // outside of the synchronized block.
                                                this.scriptClass = (Class<?>) result;
                                        }
                                        else {
                                                // Not a Class: OK, we'll simply create BeanShell objects
                                                // through evaluating the script for every call later on.
                                                // For this first-time check, let's simply return the
                                                // already evaluated object.
                                                return result;
                                        }
                                }
                                clazz = this.scriptClass;
                        }
                }
                catch (EvalError ex) {
                        this.scriptClass = null;
                        throw new ScriptCompilationException(scriptSource, ex);
                }

                if (clazz != null) {
                        // A Class: We need to create an instance for every call.
                        try {
                                return clazz.newInstance();
                        }
                        catch (Throwable ex) {
                                throw new ScriptCompilationException(
                                                scriptSource, "Could not instantiate script class: " + clazz.getName(), ex);
                        }
                }
                else {
                        // Not a Class: We need to evaluate the script for every call.
                        try {
                                return BshScriptUtils.createBshObject(
                                                scriptSource.getScriptAsString(), actualInterfaces, this.beanClassLoader);
                        }
                        catch (EvalError ex) {
                                throw new ScriptCompilationException(scriptSource, ex);
                        }
                }
        }

        @Override
        public Class<?> getScriptedObjectType(ScriptSource scriptSource)
                        throws IOException, ScriptCompilationException {

                synchronized (this.scriptClassMonitor) {
                        try {
                                if (scriptSource.isModified()) {
                                        // New script content: Let's check whether it evaluates to a Class.
                                        this.wasModifiedForTypeCheck = true;
                                        this.scriptClass = BshScriptUtils.determineBshObjectType(
                                                        scriptSource.getScriptAsString(), this.beanClassLoader);
                                }
                                return this.scriptClass;
                        }
                        catch (EvalError ex) {
                                this.scriptClass = null;
                                throw new ScriptCompilationException(scriptSource, ex);
                        }
                }
        }

        @Override
        public boolean requiresScriptedObjectRefresh(ScriptSource scriptSource) {
                synchronized (this.scriptClassMonitor) {
                        return (scriptSource.isModified() || this.wasModifiedForTypeCheck);
                }
        }


        @Override
        public String toString() {
                return "BshScriptFactory: script source locator [" + this.scriptSourceLocator + "]";
        }

}