/*
    * 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;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.math.MathContext;
  import java.net.URL;
  import java.nio.charset.Charset;
  import java.nio.file.Files;
  import java.util.Objects;
  
  import org.apache.commons.jexl3.introspection.JexlUberspect;
  
  /**
   * Creates and evaluates JexlExpression and JexlScript objects.
   * Determines the behavior of expressions and scripts during their evaluation with respect to:
   * <ul>
   * <li>Introspection, see {@link JexlUberspect}</li>
   * <li>Arithmetic and comparison, see {@link JexlArithmetic}</li>
   * <li>Error reporting</li>
   * <li>Logging</li>
   * </ul>
   *
   * <p>Note that methods that evaluate expressions may throw <em>unchecked</em> exceptions;
   * The {@link JexlException} are thrown in "non-silent" mode but since these are
   * RuntimeException, user-code <em>should</em> catch them wherever most appropriate.</p>
   *
   * @since 2.0
   */
  public abstract class JexlEngine {
  
      /** Default constructor */
      public JexlEngine() {} // Keep Javadoc happy
  
      /**
       * The empty context class, public for instrospection.
       */
      public static final class EmptyContext implements JexlContext {
          /**
           * Default ctor.
           */
          EmptyContext() {}
  
          @Override
          public Object get(final String name) {
              return null;
          }
  
          @Override
          public boolean has(final String name) {
              return false;
          }
  
          @Override
          public void set(final String name, final Object value) {
              throw new UnsupportedOperationException("Not supported in void context.");
          }
      }
  
      /**
       * The  empty/static/non-mutable JexlNamespace class, public for instrospection.
       */
      public static final class EmptyNamespaceResolver implements JexlContext.NamespaceResolver {
          /**
           * Default ctor.
           */
          EmptyNamespaceResolver() {}
  
          @Override
          public Object resolveNamespace(final String name) {
              return null;
          }
      }
  
      /** The failure marker class. */
      private static final class FailObject {
          /**
           * Default ctor.
           */
          FailObject() {}
  
         @Override
         public String toString() {
             return "tryExecute failed";
         }
     }
 
     /**
      * Script evaluation options.
      * <p>The JexlContext used for evaluation can implement this interface to alter behavior.</p>
      * @deprecated 3.2
      */
     @Deprecated
     public interface Options {
 
         /**
          * The MathContext instance used for +,-,/,*,% operations on big decimals.
          *
          * @return the math context
          */
         MathContext getArithmeticMathContext();
         /**
          * The BigDecimal scale used for comparison and coercion operations.
          *
          * @return the scale
          */
         int getArithmeticMathScale();
 
         /**
          * The charset used for parsing.
          *
          * @return the charset
          */
         Charset getCharset();
 
         /**
          * Tests whether evaluation will throw JexlException.Cancel (true) or return null (false) when interrupted.
          * @return true when cancellable, false otherwise
          * @since 3.1
          */
         Boolean isCancellable();
 
         /**
          * Tests whether the engine will throw a {@link JexlException} when an error is encountered during evaluation.
          *
          * @return true if silent, false otherwise
          */
         Boolean isSilent();
 
         /**
          * Tests whether the engine considers unknown variables, methods, functions and constructors as errors or
          * evaluates them as null.
          *
          * @return true if strict, false otherwise
          */
         Boolean isStrict();
 
         /**
          * Tests whether the arithmetic triggers errors during evaluation when null is used as an operand.
          *
          * @return true if strict, false otherwise
          */
         Boolean isStrictArithmetic();
     }
 
     /** A marker singleton for invocation failures in tryInvoke. */
     public static final Object TRY_FAILED = new FailObject();
 
     /**
      * The thread local context.
      */
     protected static final java.lang.ThreadLocal<JexlContext.ThreadLocal> CONTEXT =
                        new java.lang.ThreadLocal<>();
 
     /**
      * The thread local engine.
      */
     protected static final java.lang.ThreadLocal<JexlEngine> ENGINE =
                        new java.lang.ThreadLocal<>();
 
     /** Default features. */
     public static final JexlFeatures DEFAULT_FEATURES = new JexlFeatures();
 
     /**
      * An empty/static/non-mutable JexlContext singleton used instead of null context.
      */
     public static final JexlContext EMPTY_CONTEXT = new EmptyContext();
 
     /**
      * An empty/static/non-mutable JexlNamespace singleton used instead of null namespace.
      */
     public static final JexlContext.NamespaceResolver EMPTY_NS = new EmptyNamespaceResolver();
 
     /** The default Jxlt cache size. */
     private static final int JXLT_CACHE_SIZE = 256;
 
     /**
      * Accesses the current thread local context.
      *
      * @return the context or null
      */
     public static JexlContext.ThreadLocal getThreadContext() {
         return CONTEXT.get();
     }
 
     /**
      * Accesses the current thread local engine.
      * <p>Advanced: you should only use this to retrieve the engine within a method/ctor called through the evaluation
      * of a script/expression.</p>
      * @return the engine or null
      */
     public static JexlEngine getThreadEngine() {
         return ENGINE.get();
     }
 
     /**
      * Sets the current thread local context.
      * <p>This should only be used carefully, for instance when re-evaluating a "stored" script that requires a
      * given Namespace resolver. Remember to synchronize access if context is shared between threads.
      *
      * @param tls the thread local context to set
      */
     public static void setThreadContext(final JexlContext.ThreadLocal tls) {
         CONTEXT.set(tls);
     }
 
     /**
      * Creates a string from a reader.
      *
      * @param reader to be read.
      * @return the contents of the reader as a String.
      * @throws IOException on any error reading the reader.
      */
     protected static String toString(final BufferedReader reader) throws IOException {
         final StringBuilder buffer = new StringBuilder();
         String line;
         while ((line = reader.readLine()) != null) {
             buffer.append(line).append('\n');
         }
         return buffer.toString();
     }
 
     /**
      * Clears the expression cache.
      */
     public abstract void clearCache();
 
     /**
      * Creates an JexlExpression from a String containing valid JEXL syntax.
      * This method parses the expression which must contain either a reference or an expression.
      *
      * @param info       An info structure to carry debugging information if needed
      * @param expression A String containing valid JEXL syntax
      * @return An {@link JexlExpression} which can be evaluated using a {@link JexlContext}
      * @throws JexlException if there is a problem parsing the script
      */
     public abstract JexlExpression createExpression(JexlInfo info, String expression);
 
     /**
      * Creates a JexlExpression from a String containing valid JEXL syntax.
      * This method parses the expression which must contain either a reference or an expression.
      *
      * @param expression A String containing valid JEXL syntax
      * @return An {@link JexlExpression} which can be evaluated using a {@link JexlContext}
      * @throws JexlException if there is a problem parsing the script
      */
     public final JexlExpression createExpression(final String expression) {
         return createExpression(null, expression);
     }
 
     /**
      * Create an information structure for dynamic set/get/invoke/new.
      * <p>This gathers the class, method and line number of the first calling method
      * outside of o.a.c.jexl3.</p>
      *
      * @return a JexlInfo instance
      */
     public JexlInfo createInfo() {
         return new JexlInfo();
     }
 
     /**
      * Creates a JexlInfo instance.
      *
      * @param fn url/file/template/script user given name
      * @param l  line number
      * @param c  column number
      * @return a JexlInfo instance
      */
     public JexlInfo createInfo(final String fn, final int l, final int c) {
         return new JexlInfo(fn, l, c);
     }
 
     /**
      * Creates a new {@link JxltEngine} instance using this engine.
      *
      * @return a JEXL Template engine
      */
     public JxltEngine createJxltEngine() {
         return createJxltEngine(true);
     }
 
     /**
      * Creates a new {@link JxltEngine} instance using this engine.
      *
      * @param noScript  whether the JxltEngine only allows Jexl expressions or scripts
      * @return a JEXL Template engine
      */
     public JxltEngine createJxltEngine(final boolean noScript) {
         return createJxltEngine(noScript, JXLT_CACHE_SIZE, '$', '#');
     }
 
     /**
      * Creates a new instance of {@link JxltEngine} using this engine.
      *
      * @param noScript  whether the JxltEngine only allows JEXL expressions or scripts
      * @param cacheSize the number of expressions in this cache, default is 256
      * @param immediate the immediate template expression character, default is '$'
      * @param deferred  the deferred template expression character, default is '#'
      * @return a JEXL Template engine
      */
     public abstract JxltEngine createJxltEngine(boolean noScript, int cacheSize, char immediate, char deferred);
 
     /**
      * Creates a Script from a {@link File} containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param scriptFile A {@link File} containing valid JEXL syntax. Must not be null. Must be a readable file.
      * @return A {@link JexlScript} which can be executed with a {@link JexlContext}.
      * @throws JexlException if there is a problem reading or parsing the script.
      */
     public final JexlScript createScript(final File scriptFile) {
         return createScript(null, null, readSource(scriptFile), (String[]) null);
     }
 
     /**
      * Creates a Script from a {@link File} containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param scriptFile A {@link File} containing valid JEXL syntax. Must not be null. Must be a readable file.
      * @param names      The script parameter names used during parsing; a corresponding array of arguments containing
      * values should be used during evaluation.
      * @return A {@link JexlScript} which can be executed with a {@link JexlContext}.
      * @throws JexlException if there is a problem reading or parsing the script.
      */
     public final JexlScript createScript(final File scriptFile, final String... names) {
         return createScript(null, null, readSource(scriptFile), names);
     }
 
     /**
      * Creates a JexlScript from a String containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param features A set of features that will be enforced during parsing
      * @param info   An info structure to carry debugging information if needed
      * @param source A string containing valid JEXL syntax
      * @param names  The script parameter names used during parsing; a corresponding array of arguments containing
      * values should be used during evaluation
      * @return A {@link JexlScript} which can be executed using a {@link JexlContext}
      * @throws JexlException if there is a problem parsing the script
      */
     public abstract JexlScript createScript(JexlFeatures features, JexlInfo info, String source, String... names);
 
     /**
      * Creates a Script from a {@link File} containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param info       An info structure to carry debugging information if needed
      * @param scriptFile A {@link File} containing valid JEXL syntax. Must not be null. Must be a readable file.
      * @param names      The script parameter names used during parsing; a corresponding array of arguments containing
      * values should be used during evaluation.
      * @return A {@link JexlScript} which can be executed with a {@link JexlContext}.
      * @throws JexlException if there is a problem reading or parsing the script.
      */
     public final JexlScript createScript(final JexlInfo info, final File scriptFile, final String... names) {
         return createScript(null, info, readSource(scriptFile), names);
     }
 
     /**
      * Creates a JexlScript from a String containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param info   An info structure to carry debugging information if needed
      * @param source A string containing valid JEXL syntax
      * @param names  The script parameter names used during parsing; a corresponding array of arguments containing
      * values should be used during evaluation
      * @return A {@link JexlScript} which can be executed using a {@link JexlContext}
      * @throws JexlException if there is a problem parsing the script
      */
     public final JexlScript createScript(final JexlInfo info, final String source, final String... names) {
         return createScript(null, info, source, names);
     }
     /**
      * Creates a Script from a {@link URL} containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param info      An info structure to carry debugging information if needed
      * @param scriptUrl A {@link URL} containing valid JEXL syntax. Must not be null.
      * @param names     The script parameter names used during parsing; a corresponding array of arguments containing
      * values should be used during evaluation.
      * @return A {@link JexlScript} which can be executed with a {@link JexlContext}.
      * @throws JexlException if there is a problem reading or parsing the script.
      */
     public final JexlScript createScript(final JexlInfo info, final URL scriptUrl, final String... names) {
         return createScript(null, info, readSource(scriptUrl), names);
     }
 
     /**
      * Creates a Script from a String containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param scriptText A String containing valid JEXL syntax
      * @return A {@link JexlScript} which can be executed using a {@link JexlContext}
      * @throws JexlException if there is a problem parsing the script.
      */
     public final JexlScript createScript(final String scriptText) {
         return createScript(null, null, scriptText, (String[]) null);
     }
 
     /**
      * Creates a Script from a String containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param source A String containing valid JEXL syntax
      * @param names      The script parameter names used during parsing; a corresponding array of arguments containing
      * values should be used during evaluation
      * @return A {@link JexlScript} which can be executed using a {@link JexlContext}
      * @throws JexlException if there is a problem parsing the script
      */
     public final JexlScript createScript(final String source, final String... names) {
         return createScript(null, null, source, names);
     }
 
     /**
      * Creates a Script from a {@link URL} containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param scriptUrl A {@link URL} containing valid JEXL syntax. Must not be null.
      * @return A {@link JexlScript} which can be executed with a {@link JexlContext}.
      * @throws JexlException if there is a problem reading or parsing the script.
      */
     public final JexlScript createScript(final URL scriptUrl) {
         return createScript(null, readSource(scriptUrl), (String[]) null);
     }
 
     /**
      * Creates a Script from a {@link URL} containing valid JEXL syntax.
      * This method parses the script and validates the syntax.
      *
      * @param scriptUrl A {@link URL} containing valid JEXL syntax. Must not be null.
      * @param names     The script parameter names used during parsing; a corresponding array of arguments containing
      * values should be used during evaluation.
      * @return A {@link JexlScript} which can be executed with a {@link JexlContext}.
      * @throws JexlException if there is a problem reading or parsing the script.
      */
     public final JexlScript createScript(final URL scriptUrl, final String... names) {
         return createScript(null, null, readSource(scriptUrl), names);
     }
 
     /**
      * Gets this engine underlying {@link JexlArithmetic}.
      *
      * @return the arithmetic
      */
     public abstract JexlArithmetic getArithmetic();
 
     /**
      * Gets the charset used for parsing.
      *
      * @return the charset
      */
     public abstract Charset getCharset();
 
     /**
      * Accesses properties of a bean using an expression.
      * <p>
      * If the JEXL engine is silent, errors will be logged through its logger as warning.
      * </p>
      *
      * @param context the evaluation context
      * @param bean    the bean to get properties from
      * @param expr    the property expression
      * @return the value of the property
      * @throws JexlException if there is an error parsing the expression or during evaluation
      */
     public abstract Object getProperty(JexlContext context, Object bean, String expr);
 
     /**
      * Accesses properties of a bean using an expression.
      * <p>
      * jexl.get(myobject, "foo.bar"); should equate to
      * myobject.getFoo().getBar(); (or myobject.getFoo().get("bar"))
      * </p>
      * <p>
      * If the JEXL engine is silent, errors will be logged through its logger as warning.
      * </p>
      *
      * @param bean the bean to get properties from
      * @param expr the property expression
      * @return the value of the property
      * @throws JexlException if there is an error parsing the expression or during evaluation
      */
     public abstract Object getProperty(Object bean, String expr);
 
     /**
      * Gets this engine underlying {@link JexlUberspect}.
      *
      * @return the uberspect
      */
     public abstract JexlUberspect getUberspect();
 
     /**
      * Invokes an object's method by name and arguments.
      *
      * @param obj  the method's invoker object
      * @param meth the method's name
      * @param args the method's arguments
      * @return the method returned value or null if it failed and engine is silent
      * @throws JexlException if method could not be found or failed and engine is not silent
      */
     public abstract Object invokeMethod(Object obj, String meth, Object... args);
 
     /**
      * Checks whether this engine will throw JexlException.Cancel (true) or return null (false) when interrupted
      * during an execution.
      *
      * @return true if cancellable, false otherwise
      */
     public abstract boolean isCancellable();
 
     /**
      * Checks whether this engine is in debug mode.
      *
      * @return true if debug is on, false otherwise
      */
     public abstract boolean isDebug();
 
     /**
      * Checks whether this engine throws JexlException during evaluation.
      *
      * @return true if silent, false (default) otherwise
      */
     public abstract boolean isSilent();
 
     /**
      * Checks whether this engine considers unknown variables, methods, functions and constructors as errors.
      *
      * @return true if strict, false otherwise
      */
     public abstract boolean isStrict();
 
     /**
      * Creates a new instance of an object using the most appropriate constructor based on the arguments.
      *
      * @param <T>   the type of object
      * @param clazz the class to instantiate
      * @param args  the constructor arguments
      * @return the created object instance or null on failure when silent
      */
     public abstract <T> T newInstance(Class<? extends T> clazz, Object... args);
 
     /**
      * Creates a new instance of an object using the most appropriate constructor based on the arguments.
      *
      * @param clazz the name of the class to instantiate resolved through this engine's class loader
      * @param args  the constructor arguments
      * @return the created object instance or null on failure when silent
      */
     public abstract Object newInstance(String clazz, Object... args);
 
     /**
      * Reads a JEXL source from a File.
      *
      * @param file the script file
      * @return the source
      */
     protected String readSource(final File file) {
         Objects.requireNonNull(file, "file");
         try (BufferedReader reader = Files.newBufferedReader(file.toPath(), getCharset())) {
             return toString(reader);
         } catch (final IOException xio) {
             throw new JexlException(createInfo(file.toString(), 1, 1), "could not read source File", xio);
         }
     }
 
     /**
      * Reads a JEXL source from an URL.
      *
      * @param url the script url
      * @return the source
      */
     protected String readSource(final URL url) {
         Objects.requireNonNull(url, "url");
         try (BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream(), getCharset()))) {
             return toString(reader);
         } catch (final IOException xio) {
             throw new JexlException(createInfo(url.toString(), 1, 1), "could not read source URL", xio);
         }
     }
 
     /**
      * Sets the class loader used to discover classes in 'new' expressions.
      * <p>This method is <em>not</em> thread safe; it may be called after JexlEngine
      * initialization and allow scripts to use new classes definitions.</p>
      *
      * @param loader the class loader to use
      */
     public abstract void setClassLoader(ClassLoader loader);
 
     /**
      * Assign properties of a bean using an expression.
      * <p>
      * If the JEXL engine is silent, errors will be logged through
      * its logger as warning.
      * </p>
      *
      * @param context the evaluation context
      * @param bean    the bean to set properties in
      * @param expr    the property expression
      * @param value   the value of the property
      * @throws JexlException if there is an error parsing the expression or during evaluation
      */
     public abstract void setProperty(JexlContext context, Object bean, String expr, Object value);
 
     /**
      * Assign properties of a bean using an expression.
      * <p>
      * jexl.set(myobject, "foo.bar", 10); should equate to
      * myobject.getFoo().setBar(10); (or myobject.getFoo().put("bar", 10) )
      * </p>
      * <p>
      * If the JEXL engine is silent, errors will be logged through its logger as warning.
      * </p>
      *
      * @param bean  the bean to set properties in
      * @param expr  the property expression
      * @param value the value of the property
      * @throws JexlException if there is an error parsing the expression or during evaluation
      */
     public abstract void setProperty(Object bean, String expr, Object value);
 }