/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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.apache.commons.jexl3.scripting;
  
  import java.io.BufferedReader;
  import java.io.IOException;
  import java.io.PrintWriter;
  import java.io.Reader;
  import java.io.Writer;
  import java.lang.ref.Reference;
  import java.lang.ref.SoftReference;
  import java.util.Objects;
  
  import javax.script.AbstractScriptEngine;
  import javax.script.Bindings;
  import javax.script.Compilable;
  import javax.script.CompiledScript;
  import javax.script.ScriptContext;
  import javax.script.ScriptEngine;
  import javax.script.ScriptEngineFactory;
  import javax.script.ScriptException;
  import javax.script.SimpleBindings;
  
  import org.apache.commons.jexl3.JexlBuilder;
  import org.apache.commons.jexl3.JexlContext;
  import org.apache.commons.jexl3.JexlEngine;
  import org.apache.commons.jexl3.JexlException;
  import org.apache.commons.jexl3.JexlScript;
  import org.apache.commons.jexl3.introspection.JexlPermissions;
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  /**
   * Implements the JEXL ScriptEngine for JSF-223.
   * <p>
   * This implementation gives access to both ENGINE_SCOPE and GLOBAL_SCOPE bindings.
   * When a JEXL script accesses a variable for read or write,
   * this implementation checks first ENGINE and then GLOBAL scope.
   * The first one found is used.
   * If no variable is found, and the JEXL script is writing to a variable,
   * it will be stored in the ENGINE scope.
   * </p>
   * <p>
   * The implementation also creates the "JEXL" script object as an instance of the
   * class {@link JexlScriptObject} for access to utility methods and variables.
   * </p>
   * See
   * <a href="https://java.sun.com/javase/6/docs/api/javax/script/package-summary.html">Java Scripting API</a>
   * Javadoc.
   *
   * @since 2.0
   */
  public class JexlScriptEngine extends AbstractScriptEngine implements Compilable {
      /**
       * Holds singleton JexlScriptEngineFactory (IODH).
       */
      private static final class FactorySingletonHolder {
          /** The engine factory singleton instance. */
          static final JexlScriptEngineFactory DEFAULT_FACTORY = new JexlScriptEngineFactory();
  
          /** Non instantiable. */
          private FactorySingletonHolder() {}
      }
  
      /**
       * Wrapper to help convert a JEXL JexlScript into a JSR-223 CompiledScript.
       */
      private final class JexlCompiledScript extends CompiledScript {
          /** The underlying JEXL expression instance. */
          private final JexlScript script;
  
          /**
           * Creates an instance.
           *
           * @param theScript to wrap
           */
          JexlCompiledScript(final JexlScript theScript) {
              script = theScript;
          }
  
          @Override
          public Object eval(final ScriptContext context) throws ScriptException {
              // This is mandated by JSR-223 (end of section SCR.4.3.4.1.2 - JexlScript Execution)
              context.setAttribute(CONTEXT_KEY, context, ScriptContext.ENGINE_SCOPE);
             try {
                 final JexlContext ctxt = new JexlContextWrapper(context);
                 return script.execute(ctxt);
             } catch (final Exception e) {
                 throw scriptException(e);
             }
         }
 
         @Override
         public ScriptEngine getEngine() {
             return JexlScriptEngine.this;
         }
 
         @Override
         public String toString() {
             return script.getSourceText();
         }
     }
     /**
      * Wrapper to help convert a JSR-223 ScriptContext into a JexlContext.
      *
      * Current implementation only gives access to ENGINE_SCOPE binding.
      */
     private final class JexlContextWrapper implements JexlContext {
         /** The wrapped script context. */
         final ScriptContext scriptContext;
 
         /**
          * Creates a context wrapper.
          *
          * @param theContext the engine context.
          */
         JexlContextWrapper (final ScriptContext theContext){
             scriptContext = theContext;
         }
 
         @Override
         public Object get(final String name) {
             final Object o = scriptContext.getAttribute(name);
             if (JEXL_OBJECT_KEY.equals(name)) {
                 if (o != null) {
                     LOG.warn("JEXL is a reserved variable name, user-defined value is ignored");
                 }
                 return jexlObject;
             }
             return o;
         }
 
         @Override
         public boolean has(final String name) {
             final Bindings bnd = scriptContext.getBindings(ScriptContext.ENGINE_SCOPE);
             return bnd.containsKey(name);
         }
 
         @Override
         public void set(final String name, final Object value) {
             int scope = scriptContext.getAttributesScope(name);
             if (scope == -1) { // not found, default to engine
                 scope = ScriptContext.ENGINE_SCOPE;
             }
             scriptContext.getBindings(scope).put(name , value);
         }
 
     }
 
     /**
      * Implements engine and engine context properties for use by JEXL scripts.
      * Those properties are always bound to the default engine scope context.
      *
      * <p>The following properties are defined:</p>
      *
      * <ul>
      *   <li>in - refers to the engine scope reader that defaults to reading System.err</li>
      *   <li>out - refers the engine scope writer that defaults to writing in System.out</li>
      *   <li>err - refers to the engine scope writer that defaults to writing in System.err</li>
      *   <li>logger - the JexlScriptEngine logger</li>
      *   <li>System - the System.class</li>
      * </ul>
      *
      * @since 2.0
      */
     public class JexlScriptObject {
 
         /** Default constructor */
         public JexlScriptObject() {} // Keep Javadoc happy
 
         /**
          * Gives access to the underlying JEXL engine shared between all ScriptEngine instances.
          * <p>Although this allows to manipulate various engine flags (lenient, debug, cache...)
          * for <strong>all</strong> JexlScriptEngine instances, you probably should only do so
          * if you are in strict control and sole user of the JEXL scripting feature.</p>
          *
          * @return the shared underlying JEXL engine
          */
         public JexlEngine getEngine() {
             return jexlEngine;
         }
 
         /**
          * Gives access to the engine scope error writer (defaults to System.err).
          *
          * @return the engine error writer
          */
         public PrintWriter getErr() {
             final Writer error = context.getErrorWriter();
             if (error instanceof PrintWriter) {
                 return (PrintWriter) error;
             }
             if (error != null) {
                 return new PrintWriter(error, true);
             }
             return null;
         }
 
         /**
          * Gives access to the engine scope input reader (defaults to System.in).
          *
          * @return the engine input reader
          */
         public Reader getIn() {
             return context.getReader();
         }
 
         /**
          * Gives access to the engine logger.
          *
          * @return the JexlScriptEngine logger
          */
         public Log getLogger() {
             return LOG;
         }
 
         /**
          * Gives access to the engine scope output writer (defaults to System.out).
          *
          * @return the engine output writer
          */
         public PrintWriter getOut() {
             final Writer out = context.getWriter();
             if (out instanceof PrintWriter) {
                 return (PrintWriter) out;
             }
             if (out != null) {
                 return new PrintWriter(out, true);
             }
             return null;
         }
 
         /**
          * Gives access to System class.
          *
          * @return System.class
          */
         public Class<System> getSystem() {
             return System.class;
         }
     }
 
     /**
      * The shared engine instance.
      * <p>A single soft-reference JEXL engine and JexlUberspect is shared by all instances of JexlScriptEngine.</p>
      */
     private static Reference<JexlEngine> ENGINE;
 
     /**
      * The permissions used to create the script engine.
      */
     private static JexlPermissions PERMISSIONS;
 
     /** The logger. */
     static final Log LOG = LogFactory.getLog(JexlScriptEngine.class);
 
     /** The shared expression cache size. */
     static final int CACHE_SIZE = 512;
 
     /** Reserved key for context (mandated by JSR-223). */
     public static final String CONTEXT_KEY = "context";
 
     /** Reserved key for JexlScriptObject. */
     public static final String JEXL_OBJECT_KEY = "JEXL";
 
     /**
      * @return the shared JexlEngine instance, create it if necessary
      */
     private static JexlEngine getEngine() {
         JexlEngine engine = ENGINE != null ? ENGINE.get() : null;
         if (engine == null) {
             synchronized (JexlScriptEngineFactory.class) {
                 engine = ENGINE != null ? ENGINE.get() : null;
                 if (engine == null) {
                     final JexlBuilder builder = new JexlBuilder()
                             .strict(true)
                             .safe(false)
                             .logger(JexlScriptEngine.LOG)
                             .cache(JexlScriptEngine.CACHE_SIZE);
                     if (PERMISSIONS != null) {
                         builder.permissions(PERMISSIONS);
                     }
                     engine = builder.create();
                     ENGINE = new SoftReference<>(engine);
                 }
             }
         }
         return engine;
     }
 
     /**
      * Read from a reader into a local buffer and return a String with
      * the contents of the reader.
      *
      * @param scriptReader to be read.
      * @return the contents of the reader as a String.
      * @throws ScriptException on any error reading the reader.
      */
     private static String readerToString(final Reader scriptReader) throws ScriptException {
         final StringBuilder buffer = new StringBuilder();
         BufferedReader reader;
         if (scriptReader instanceof BufferedReader) {
             reader = (BufferedReader) scriptReader;
         } else {
             reader = new BufferedReader(scriptReader);
         }
         try {
             String line;
             while ((line = reader.readLine()) != null) {
                 buffer.append(line).append('\n');
             }
             return buffer.toString();
         } catch (final IOException e) {
             throw new ScriptException(e);
         }
     }
 
     static ScriptException scriptException(final Exception e) {
         Exception xany = e;
         // unwrap a jexl exception
         if (xany instanceof JexlException) {
             final Throwable cause = xany.getCause();
             if (cause instanceof Exception) {
                 xany = (Exception) cause;
             }
         }
         return new ScriptException(xany);
     }
 
     /**
      * Sets the shared instance used for the script engine.
      * <p>This should be called early enough to have an effect, ie before any
      * {@link javax.script.ScriptEngineManager} features.</p>
      * <p>To restore 3.2 script behavior:</p>
      * {@code
      *         JexlScriptEngine.setInstance(new JexlBuilder()
      *                 .cache(512)
      *                 .logger(LogFactory.getLog(JexlScriptEngine.class))
      *                 .permissions(JexlPermissions.UNRESTRICTED)
      *                 .create());
      * }
      * @param engine the JexlEngine instance to use
      * @since 3.3
      */
     public static void setInstance(final JexlEngine engine) {
         ENGINE = new SoftReference<>(engine);
     }
 
     /**
      * Sets the permissions instance used to create the script engine.
      * <p>Calling this method will force engine instance re-creation.</p>
      * <p>To restore 3.2 script behavior:</p>
      * {@code
      *         JexlScriptEngine.setPermissions(JexlPermissions.UNRESTRICTED);
      * }
      * @param permissions the permissions instance to use or null to use the {@link JexlBuilder} default
      * @since 3.3
      */
     public static void setPermissions(final JexlPermissions permissions) {
         PERMISSIONS = permissions;
         ENGINE = null; // will force recreation
     }
 
     /** The JexlScriptObject instance. */
     final JexlScriptObject jexlObject;
 
     /** The factory which created this instance. */
     final ScriptEngineFactory parentFactory;
 
     /** The JEXL EL engine. */
     final JexlEngine jexlEngine;
 
     /**
      * Default constructor.
      *
      * <p>Only intended for use when not using a factory.
      * Sets the factory to {@link JexlScriptEngineFactory}.</p>
      */
     public JexlScriptEngine() {
         this(FactorySingletonHolder.DEFAULT_FACTORY);
     }
 
     /**
      * Create a scripting engine using the supplied factory.
      *
      * @param scriptEngineFactory the factory which created this instance.
      * @throws NullPointerException if factory is null
      */
     public JexlScriptEngine(final ScriptEngineFactory scriptEngineFactory) {
         Objects.requireNonNull(scriptEngineFactory, "scriptEngineFactory");
         parentFactory = scriptEngineFactory;
         jexlEngine = getEngine();
         jexlObject = new JexlScriptObject();
     }
 
     @Override
     public CompiledScript compile(final Reader script) throws ScriptException {
         // This is mandated by JSR-223
         Objects.requireNonNull(script, "script");
         return compile(readerToString(script));
     }
 
     @Override
     public CompiledScript compile(final String script) throws ScriptException {
         // This is mandated by JSR-223
         Objects.requireNonNull(script, "script");
         try {
             final JexlScript jexlScript = jexlEngine.createScript(script);
             return new JexlCompiledScript(jexlScript);
         } catch (final Exception e) {
             throw scriptException(e);
         }
     }
 
     @Override
     public Bindings createBindings() {
         return new SimpleBindings();
     }
 
     @Override
     public Object eval(final Reader reader, final ScriptContext context) throws ScriptException {
         // This is mandated by JSR-223 (see SCR.5.5.2   Methods)
         Objects.requireNonNull(reader, "reader");
         Objects.requireNonNull(context, "context");
         return eval(readerToString(reader), context);
     }
 
     @Override
     public Object eval(final String script, final ScriptContext context) throws ScriptException {
         // This is mandated by JSR-223 (see SCR.5.5.2   Methods)
         Objects.requireNonNull(script, "context");
         Objects.requireNonNull(context, "context");
         // This is mandated by JSR-223 (end of section SCR.4.3.4.1.2 - JexlScript Execution)
         context.setAttribute(CONTEXT_KEY, context, ScriptContext.ENGINE_SCOPE);
         try {
             final JexlScript jexlScript = jexlEngine.createScript(script);
             final JexlContext ctxt = new JexlContextWrapper(context);
             return jexlScript.execute(ctxt);
         } catch (final Exception e) {
             throw scriptException(e);
         }
     }
 
     @Override
     public ScriptEngineFactory getFactory() {
         return parentFactory;
     }
 }