/**
 * 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.apex.malhar.lib.util;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

import org.codehaus.commons.compiler.CompileException;
import org.codehaus.commons.compiler.CompilerFactoryFactory;
import org.codehaus.commons.compiler.IScriptEvaluator;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.apex.malhar.lib.expression.Expression;
import org.apache.apex.malhar.lib.expression.JavaExpressionParser;
import org.apache.commons.lang3.ClassUtils;
import org.apache.commons.lang3.StringUtils;

import com.google.common.base.Preconditions;
import com.google.common.collect.Maps;

/**
 * @since 2.1.0
 */
public class PojoUtils
{
  private static final Logger logger = LoggerFactory.getLogger(PojoUtils.class);

  public static final String DEFAULT_EXP_OBJECT_PLACEHOLDER = "{$}";
  public static final String DEFAULT_EXP_VAL_PLACEHOLDER = "{#}";
  public static final String DEFAULT_EXPRESSION_OBJ_PLACEHOLDER = "$";

  private static final String OBJECT = "object";
  private static final String VAL = "val";

  private static final String GET = "get";
  private static final String IS = "is";
  private static final String SET = "set";

  private static final Map<Class<?>, Class<?>> primitiveClassToGetterInterface = Maps.newHashMap();
  private static final Map<Class<?>, Class<?>> primitiveClassToSetterInterface = Maps.newHashMap();

  static {
    primitiveClassToGetterInterface.put(boolean.class, GetterBoolean.class);
    primitiveClassToGetterInterface.put(byte.class, GetterByte.class);
    primitiveClassToGetterInterface.put(char.class, GetterChar.class);
    primitiveClassToGetterInterface.put(short.class, GetterShort.class);
    primitiveClassToGetterInterface.put(int.class, GetterInt.class);
    primitiveClassToGetterInterface.put(long.class, GetterLong.class);
    primitiveClassToGetterInterface.put(float.class, GetterFloat.class);
    primitiveClassToGetterInterface.put(double.class, GetterDouble.class);

    primitiveClassToSetterInterface.put(boolean.class, SetterBoolean.class);
    primitiveClassToSetterInterface.put(byte.class, SetterByte.class);
    primitiveClassToSetterInterface.put(char.class, SetterChar.class);
    primitiveClassToSetterInterface.put(short.class, SetterShort.class);
    primitiveClassToSetterInterface.put(int.class, SetterInt.class);
    primitiveClassToSetterInterface.put(long.class, SetterLong.class);
    primitiveClassToSetterInterface.put(float.class, SetterFloat.class);
    primitiveClassToSetterInterface.put(double.class, SetterDouble.class);
  }

  private PojoUtils()
  {
  }

  public interface GetterBoolean<T>
  {
    boolean get(T obj);
  }

  public interface GetterByte<T>
  {
    byte get(T obj);
  }

  public interface GetterChar<T>
  {
    char get(T obj);
  }

  public interface GetterShort<T>
  {
    short get(T obj);
  }

  public interface GetterInt<T>
  {
    int get(T obj);
  }

  public interface GetterLong<T>
  {
    long get(T obj);
  }

  public interface GetterFloat<T>
  {
    float get(T obj);
  }

  public interface GetterDouble<T>
  {
    double get(T obj);
  }

  public interface Getter<T, V>
  {
    V get(T obj);
  }

  public static <T> GetterBoolean<T> createGetterBoolean(Class<? extends T> pojoClass, String getterExpr)
  {
    return createGetterBoolean(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> GetterBoolean<T> createGetterBoolean(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder)
  {
    return (GetterBoolean<T>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, boolean.class,
        GetterBoolean.class);
  }

  public static <T> GetterByte<T> createGetterByte(Class<? extends T> pojoClass, String getterExpr)
  {
    return createGetterByte(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> GetterByte<T> createGetterByte(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder)
  {
    return (GetterByte<T>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, byte.class, GetterByte.class);
  }

  public static <T> GetterChar<T> createGetterChar(Class<? extends T> pojoClass, String getterExpr)
  {
    return createGetterChar(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER);
  }

  @SuppressWarnings({ "unchecked"})
  public static <T> GetterChar<T> createGetterChar(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder)
  {
    return (GetterChar<T>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, char.class, GetterChar.class);
  }

  public static <T> GetterShort<T> createGetterShort(Class<? extends T> pojoClass, String getterExpr)
  {
    return createGetterShort(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> GetterShort<T> createGetterShort(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder)
  {
    return (GetterShort<T>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, short.class, GetterShort.class);
  }

  public static <T> GetterInt<T> createGetterInt(Class<? extends T> pojoClass, String getterExpr)
  {
    return createGetterInt(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> GetterInt<T> createGetterInt(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder)
  {
    return (GetterInt<T>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, int.class, GetterInt.class);
  }

  public static <T> GetterLong<T> createGetterLong(Class<? extends T> pojoClass, String getterExpr)
  {
    return createGetterLong(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> GetterLong<T> createGetterLong(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder)
  {
    return (GetterLong<T>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, long.class, GetterLong.class);
  }

  public static <T> GetterFloat<T> createGetterFloat(Class<? extends T> pojoClass, String getterExpr)
  {
    return createGetterFloat(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> GetterFloat<T> createGetterFloat(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder)
  {
    return (GetterFloat<T>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, float.class, GetterFloat.class);
  }

  public static <T> GetterDouble<T> createGetterDouble(Class<? extends T> pojoClass, String getterExpr)
  {
    return createGetterDouble(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> GetterDouble<T> createGetterDouble(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder)
  {
    return (GetterDouble<T>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, double.class,
        GetterDouble.class);
  }

  public static <T, V> Getter<T, V> createGetter(Class<? extends T> pojoClass, String getterExpr, Class<? extends V> exprClass)
  {
    return createGetter(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, exprClass);
  }

  @SuppressWarnings("unchecked")
  public static <T, V> Getter<T, V> createGetter(Class<? extends T> pojoClass, String getterExpr, String exprObjectPlaceholder, Class<? extends V> exprClass)
  {
    if (primitiveClassToGetterInterface.get(exprClass) != null) {
      throw new IllegalArgumentException("createGetter does not allow primitive class \"" + exprClass.getName() +
              "\" for exprClass argument. Use createGetter" + upperCaseWord(exprClass.getName()) + " or constructGetter().");
    }
    return (Getter<T, V>)createGetter(pojoClass, getterExpr, exprObjectPlaceholder, exprClass, Getter.class);
  }

  public static Object constructGetter(Class<?> pojoClass, String getterExpr, Class<?> exprClass)
  {
    return constructGetter(pojoClass, getterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, exprClass);
  }

  public static Object constructGetter(Class<?> pojoClass, String getterExpr, String exprObjectPlaceholder, Class<?> exprClass)
  {
    Class<?> interfaceToImplement = primitiveClassToGetterInterface.get(exprClass);
    if (interfaceToImplement == null) {
      interfaceToImplement = Getter.class;
    }
    return createGetter(pojoClass, getterExpr, exprObjectPlaceholder, exprClass, interfaceToImplement);
  }

  /**
   * Setter interface for <tt>boolean</tt> primitives
   * @param <T> class of objects that the setter applies to
   */
  public interface SetterBoolean<T>
  {
    void set(T obj, boolean booleanVal);
  }

  /**
   * Setter interface for <tt>byte</tt> primitives
   * @param <T> class of objects that the setter applies to
   */
  public interface SetterByte<T>
  {
    void set(T obj, byte byteVal);
  }

  /**
   * Setter interface for <tt>char</tt> primitives
   * @param <T> class of objects that the setter applies to
   */
  public interface SetterChar<T>
  {
    void set(T obj, char charVal);
  }

  /**
   * Setter interface for <tt>short</tt> primitives
   * @param <T> class of objects that the setter applies to
   */
  public interface SetterShort<T>
  {
    void set(T obj, short shortVal);
  }

  /**
   * Setter interface for <tt>int</tt> primitives
   * @param <T> class of objects that the setter applies to
   */
  public interface SetterInt<T>
  {
    void set(T obj, int intVal);
  }

  /**
   * Setter interface for <tt>long</tt> primitives
   * @param <T> class of objects that the setter applies to
   */
  public interface SetterLong<T>
  {
    void set(T obj, long longVal);
  }

  /**
   * Setter interface for <tt>float</tt> primitives
   * @param <T> class of objects that the setter applies to
   */
  public interface SetterFloat<T>
  {
    void set(T obj, float floatVal);
  }

  /**
   * Setter interface for <tt>double</tt> primitives
   * @param <T> class of objects that the setter applies to
   */
  public interface SetterDouble<T>
  {
    void set(T obj, double doubleVal);
  }

  /**
   * Setter interface for arbitrary object
   * @param <T> class of objects that the setter applies to
   * @param <V> class of the rhs expression
   */
  public interface Setter<T, V>
  {
    void set(T obj, V value);
  }

  public static <T> SetterBoolean<T> createSetterBoolean(Class<? extends T> pojoClass, String setterExpr)
  {
    return createSetterBoolean(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> SetterBoolean<T> createSetterBoolean(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder)
  {
    return (SetterBoolean<T>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder,
        boolean.class, SetterBoolean.class);
  }

  public static <T> SetterByte<T> createSetterByte(Class<? extends T> pojoClass, String setterExpr)
  {
    return createSetterByte(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> SetterByte<T> createSetterByte(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder)
  {
    return (SetterByte<T>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder, byte.class,
        SetterByte.class);
  }

  public static <T> SetterChar<T> createSetterChar(Class<? extends T> pojoClass, String setterExpr)
  {
    return createSetterChar(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> SetterChar<T> createSetterChar(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder)
  {
    return (SetterChar<T>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder, char.class,
        SetterChar.class);
  }

  public static <T> SetterShort<T> createSetterShort(Class<? extends T> pojoClass, String setterExpr)
  {
    return createSetterShort(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> SetterShort<T> createSetterShort(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder)
  {
    return (SetterShort<T>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder, short.class,
        SetterShort.class);
  }

  public static <T> SetterInt<T> createSetterInt(Class<? extends T> pojoClass, String setterExpr)
  {
    return createSetterInt(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> SetterInt<T> createSetterInt(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder)
  {
    return (SetterInt<T>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder, int.class,
        SetterInt.class);
  }

  public static <T> SetterLong<T> createSetterLong(Class<? extends T> pojoClass, String setterExpr)
  {
    return createSetterLong(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> SetterLong<T> createSetterLong(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder)
  {
    return (SetterLong<T>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder, long.class,
        SetterLong.class);
  }

  public static <T> SetterFloat<T> createSetterFloat(Class<? extends T> pojoClass, String setterExpr)
  {
    return createSetterFloat(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> SetterFloat<T> createSetterFloat(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder)
  {
    return (SetterFloat<T>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder, float.class,
        SetterFloat.class);
  }

  public static <T> SetterDouble<T> createSetterDouble(Class<? extends T> pojoClass, String setterExpr)
  {
    return createSetterDouble(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER);
  }

  @SuppressWarnings("unchecked")
  public static <T> SetterDouble<T> createSetterDouble(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder)
  {
    return (SetterDouble<T>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder,
        double.class, SetterDouble.class);
  }

  public static <T, V> Setter<T, V> createSetter(Class<? extends T> pojoClass, String setterExpr, Class<? extends V> exprClass)
  {
    return createSetter(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER, exprClass);
  }

  @SuppressWarnings("unchecked")
  public static <T, V> Setter<T, V> createSetter(Class<? extends T> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValuePlaceholder, Class<? extends V> exprClass)
  {
    if (primitiveClassToSetterInterface.get(exprClass) != null) {
      throw new IllegalArgumentException("createSetter does not allow primitive class \"" + exprClass.getName() +
              "\" for exprClass argument. Use createSetter" + upperCaseWord(exprClass.getName()) + " or constructSetter().");
    }
    return (Setter<T, V>)createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValuePlaceholder, exprClass,
        Setter.class);
  }

  public static Object constructSetter(Class<?> pojoClass, String setterExpr, Class<?> exprClass)
  {
    return constructSetter(pojoClass, setterExpr, DEFAULT_EXP_OBJECT_PLACEHOLDER, DEFAULT_EXP_VAL_PLACEHOLDER, exprClass);
  }

  /**
   *
   * @param pojoClass Class object that the setter applies to
   * @param setterExpr expression to use for setter
   * @param exprClass Class that setter will accept as parameter
   * @return instance of a class that implements requested Setter interface
   */
  public static Object constructSetter(Class<?> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValPlaceholder, Class<?> exprClass)
  {
    Class<?> interfaceToImplement = primitiveClassToSetterInterface.get(exprClass);
    if (interfaceToImplement == null) {
      interfaceToImplement = Setter.class;
    }
    return createSetter(pojoClass, setterExpr, exprObjectPlaceholder, exprValPlaceholder, exprClass, interfaceToImplement);
  }

  private static class JavaStatement
  {
    private final StringBuilder javaStatement;
    private final int capacity;

    private JavaStatement()
    {
      javaStatement = new StringBuilder();
      capacity = javaStatement.capacity();
    }

    private JavaStatement(int length)
    {
      javaStatement = new StringBuilder(length);
      capacity = javaStatement.capacity();
    }

    @Override
    public String toString()
    {
      return javaStatement.toString();
    }

    protected JavaStatement append(String string)
    {
      javaStatement.append(string);
      return this;
    }

    private JavaStatement appendCastToTypeExpr(Class<?> type, String expr)
    {
      return append("((").append(type.getName()).append(")(").append(expr).append("))");
    }

    protected String getStatement()
    {
      if (capacity < javaStatement.length() + 1) {
        logger.debug("Java statement capacity {} was not sufficient for the statement length {}. Actual statement {}", capacity, javaStatement.length(), javaStatement);
      }
      return javaStatement.append(";").toString();
    }
  }

  private static class JavaReturnStatement extends JavaStatement
  {
    private JavaReturnStatement(Class<?> returnType)
    {
      super();
      append("return (").append(returnType.getName()).append(")");
    }

    private JavaReturnStatement(int length, Class<?> returnType)
    {
      super(length);
      append("return ((").append(returnType.getName()).append(")");
    }

    @Override
    protected String getStatement()
    {
      append(")");
      return super.getStatement();
    }
  }

  private static String upperCaseWord(String field)
  {
    Preconditions.checkArgument(!field.isEmpty(), field);
    return field.substring(0, 1).toUpperCase() + field.substring(1);
  }

  /**
   * Return the getter expression for the given field.
   * <p>
   * If the field is a public member, the field name is used else the getter function. If no matching field or getter
   * method is found, the expression is returned unmodified.
   *
   * @param pojoClass class to check for the field
   * @param fieldExpression field name expression
   * @param exprClass expected field type
   * @return java code fragment
   */
  private static String getSingleFieldGetterExpression(final Class<?> pojoClass, final String fieldExpression, final Class<?> exprClass)
  {
    JavaStatement code = new JavaReturnStatement(pojoClass.getName().length() + fieldExpression.length() + exprClass.getName().length() + 32, exprClass);
    code.appendCastToTypeExpr(pojoClass, OBJECT).append(".");
    try {
      final Field field = pojoClass.getField(fieldExpression);
      if (ClassUtils.isAssignable(field.getType(), exprClass)) {
        return code.append(field.getName()).getStatement();
      }
      logger.debug("Field {} can not be assigned to {}. Proceeding to locate a getter method.", field, exprClass);
    } catch (NoSuchFieldException ex) {
      logger.debug("{} does not have field {}. Proceeding to locate a getter method.", pojoClass, fieldExpression);
    } catch (SecurityException ex) {
      logger.debug("{} does not have field {}. Proceeding to locate a getter method.", pojoClass, fieldExpression);
    }

    String methodName = GET + upperCaseWord(fieldExpression);
    try {
      Method method = pojoClass.getMethod(methodName);
      if (ClassUtils.isAssignable(method.getReturnType(), exprClass)) {
        return code.append(methodName).append("()").getStatement();
      }
      logger.debug("method {} of the {} returns {} that can not be assigned to {}. Proceeding to locate another getter method.",
          pojoClass, methodName, method.getReturnType(), exprClass);
    } catch (NoSuchMethodException | SecurityException ex) {
      logger.debug("{} does not have method {}. Proceeding to locate another getter method.",
          pojoClass, methodName);
    }

    methodName = IS + upperCaseWord(fieldExpression);
    try {
      Method method = pojoClass.getMethod(methodName);
      if (ClassUtils.isAssignable(method.getReturnType(), exprClass)) {
        return code.append(methodName).append("()").getStatement();
      }
      logger.debug("method {} of the {} returns {} that can not be assigned to {}. Proceeding with the original expression {}.",
          pojoClass, methodName, method.getReturnType(), exprClass, fieldExpression);
    } catch (NoSuchMethodException | SecurityException ex) {
      logger.debug("{} does not have method {}. Proceeding with the original expression {}.",
          pojoClass, methodName, fieldExpression);
    }

    return code.append(fieldExpression).getStatement();
  }

  @SuppressWarnings("StringEquality")
  private static Object createGetter(Class<?> pojoClass, String getterExpr, String exprObjectPlaceholder, Class<?> exprClass, Class<?> getterClass)
  {
    logger.debug("{} {} {} {}", pojoClass, getterExpr, exprClass, getterClass);

    JavaExpressionParser javaExpressionParser = new JavaExpressionParser();
    javaExpressionParser.setInputObjectPlaceholder(PojoUtils.DEFAULT_EXPRESSION_OBJ_PLACEHOLDER, PojoUtils.OBJECT);
    String code = javaExpressionParser.convertToCompilableExpression(getterExpr, pojoClass, exprClass);

    return compileExpression(code, getterClass, new String[] {PojoUtils.OBJECT});
  }

  private static String getSingleFieldSetterExpression(final Class<?> pojoClass, final String fieldExpression, final Class<?> exprClass)
  {
    JavaStatement code = new JavaStatement(pojoClass.getName().length() + fieldExpression.length() + exprClass.getName().length() + 32);
    /* Construct ((<pojo class name>)pojo). */
    code.appendCastToTypeExpr(pojoClass, OBJECT).append(".");
    try {
      final Field field = pojoClass.getField(fieldExpression);
      if (ClassUtils.isAssignable(exprClass, field.getType())) {
        /* there is public field on the class, use direct assignment. */
        /* append <field name> = (<field type>)val; */
        return code.append(field.getName()).append(" = ").appendCastToTypeExpr(exprClass, VAL).getStatement();
      }
      logger.debug("{} can not be assigned to {}. Proceeding to locate a setter method.", exprClass, field);
    } catch (NoSuchFieldException ex) {
      logger.debug("{} does not have field {}. Proceeding to locate a setter method.", pojoClass, fieldExpression);
    } catch (SecurityException ex) {
      logger.debug("{} does not have field {}. Proceeding to locate a setter method.", pojoClass, fieldExpression);
    }

    final String setMethodName = SET + upperCaseWord(fieldExpression);
    Method bestMatchMethod = null;
    List<Method> candidates = new ArrayList<Method>();
    for (Method method : pojoClass.getMethods()) {
      if (setMethodName.equals(method.getName())) {
        Class<?>[] parameterTypes = method.getParameterTypes();
        if (parameterTypes.length == 1) {
          if (exprClass == parameterTypes[0]) {
            bestMatchMethod = method;
            break;
          } else if (ClassUtils.isAssignable(exprClass, parameterTypes[0])) {
            candidates.add(method);
          }
        }
      }
    }

    if (bestMatchMethod == null) { // We did not find the exact match, use candidates to find the match
      if (candidates.size() == 0) {
        logger.debug("{} does not have suitable setter method {}. Returning original expression {}.",
            pojoClass, setMethodName, fieldExpression);
        /* We did not find any match at all, use original expression */
        /* append = (<expr type>)val;*/
        return code.append(fieldExpression).append(" = ").appendCastToTypeExpr(exprClass, VAL).getStatement();
      } else {
        // TODO: see if we can find a better match
        bestMatchMethod = candidates.get(0);
      }
    }

    /* We found a method that we may use for setter */
    /* append <method name>((<expr class)val); */
    return code.append(bestMatchMethod.getName()).append("(").appendCastToTypeExpr(exprClass, VAL).append(")").getStatement();
  }

  @SuppressWarnings("StringEquality")
  private static Object createSetter(Class<?> pojoClass, String setterExpr, String exprObjectPlaceholder, String exprValPlaceholder, Class<?> exprClass, Class<?> setterClass)
  {
    if (setterExpr.startsWith(".")) {
      setterExpr = setterExpr.substring(1);
    }

    if (setterExpr.isEmpty()) {
      throw new IllegalArgumentException("The setter expression: \"" + setterExpr + "\" is invalid.");
    }

    logger.debug("{} {} {} {}", pojoClass, setterExpr, exprClass, setterClass);


    String code = StringUtils.replaceEach(setterExpr, new String[]{exprObjectPlaceholder, exprValPlaceholder},
        new String[]{new JavaStatement().appendCastToTypeExpr(pojoClass, OBJECT).toString(), new JavaStatement().appendCastToTypeExpr(exprClass, VAL).toString()});
    if (code != setterExpr) {
      code = new JavaStatement(code.length() + 1).append(code).getStatement();
      logger.debug("Original expression {} is a complex expression. Replacing it with {}.", setterExpr, code);
    } else {
      code = getSingleFieldSetterExpression(pojoClass, setterExpr, exprClass);
    }

    return compileExpression(code, setterClass, new String[] {PojoUtils.OBJECT, PojoUtils.VAL});
  }

  /**
   * This method takes in expression, compiles the expression to provide a executable form of expression.
   * This method uses {@link org.apache.apex.malhar.lib.expression.JavaExpressionParser} as expression parser.
   *
   * @param inputType  Type of input object
   * @param expr       expression to be compiled.
   * @param returnType Return type of the expression.
   * @return Object of type {@link Expression} which can be directly executed.
   */
  public static Expression createExpression(Class<?> inputType, String expr, Class<?> returnType)
  {
    return createExpression(inputType, expr, returnType, null);
  }

  /**
   * This method takes in expression, compiles the expression to provide a executable form of expression.
   * This methods also takes in list of classes and method which can be imported statically in expression.
   * <p/>
   * This method uses {@link JavaExpressionParser} as expression parser.
   *
   * @param inputType      Type of input object
   * @param expr           expression to be compiled.
   * @param returnType     Return type of the expression.
   * @param defaultImports List of classes/method which will be statically imported to expression compilation.
   * @return Object of type {@link Expression} which can be directly executed.
   */
  public static Expression createExpression(Class<?> inputType, String expr, Class<?> returnType,
      String[] defaultImports)
  {
    JavaExpressionParser javaExpressionParser = new JavaExpressionParser();
    javaExpressionParser.setInputObjectPlaceholder("$", PojoUtils.OBJECT);

    return createExpression(inputType, expr, returnType, defaultImports, javaExpressionParser);
  }

  /**
   * This method takes in expression, compiles the expression to provide a executable form of expression.
   * This methods also takes in list of classes and method which can be imported statically in expression.
   * <p/>
   * Using this method one can override expression parser implementation.
   *
   * @param inputType      Type of input object
   * @param expr           expression to be compiled.
   * @param returnType     Return type of the expression.
   * @param defaultImports List of classes/method which will be statically imported to expression compilation.
   * @param parser         Expression parser that should be used to parse expression.
   * @return Object of type {@link Expression} which can be directly executed.
   * @see {@link JavaExpressionParser} as a example.
   */
  public static Expression createExpression(Class<?> inputType, String expr, Class<?> returnType,
      String[] defaultImports, Expression.ExpressionParser parser)
  {
    String code = parser.convertToCompilableExpression(expr, inputType, returnType);

    return (Expression)compileExpression(code, Expression.class, new String[] {PojoUtils.OBJECT}, defaultImports);
  }

  private static Object compileExpression(String code, Class<?> implClass, String[] params)
  {
    return compileExpression(code, implClass, params, null);
  }

  private static Object compileExpression(String code, Class<?> implClass, String[] params, String[] defaultImports)
  {
    List<String> imports = new LinkedList<>();
    if (defaultImports != null && defaultImports.length != 0) {
      for (String defaultImport : defaultImports) {
        if (defaultImport != null) {
          if (!defaultImport.startsWith("static")) {
            imports.add("static " + defaultImport);
          } else {
            imports.add(defaultImport);
          }
        }
      }
    }

    IScriptEvaluator se;

    try {
      se = CompilerFactoryFactory.getDefaultCompilerFactory().newScriptEvaluator();
      se.setDefaultImports(imports.toArray(new String[imports.size()]));
    } catch (Exception ex) {
      throw new RuntimeException(ex);
    }

    try {
      logger.debug("code: {}", code);

      return se.createFastEvaluator(code, implClass, params);
    } catch (CompileException ex) {
      throw new RuntimeException(ex);
    }
  }

}