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/*
 * Based on JUEL 2.2.1 code, 2006-2009 Odysseus Software GmbH
 *
 * 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
 *
 *     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.activiti.engine.impl.juel;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.PrintWriter;
import java.util.Arrays;

import org.activiti.engine.impl.javax.el.ELContext;
import org.activiti.engine.impl.javax.el.ELException;
import org.activiti.engine.impl.javax.el.FunctionMapper;
import org.activiti.engine.impl.javax.el.MethodInfo;
import org.activiti.engine.impl.javax.el.VariableMapper;

/**
 * A method expression is ready to be evaluated (by calling either {@link #invoke(ELContext, Object[])} or {@link #getMethodInfo(ELContext)}).
 * 
 * Instances of this class are usually created using an {@link ExpressionFactoryImpl}.
 * 
 * @author Christoph Beck
 */
public final class TreeMethodExpression extends org.activiti.engine.impl.javax.el.MethodExpression {
  private static final long serialVersionUID = 1L;

  private final TreeBuilder builder;
  private final Bindings bindings;
  private final String expr;
  private final Class type;
  private final Class[] types;
  private final boolean deferred;

  private transient ExpressionNode node;

  private String structure;

  /**
   * Create a new method expression. The expression must be an lvalue expression or literal text. The expected return type may be null, meaning "don't care". If it is an lvalue
   * expression, the parameter types must not be null. If it is literal text, the expected return type must not be void.
   * 
   * @param store
   *          used to get the parse tree from.
   * @param functions
   *          the function mapper used to bind functions
   * @param variables
   *          the variable mapper used to bind variables
   * @param expr
   *          the expression string
   * @param returnType
   *          the expected return type (may be null)
   * @param paramTypes
   *          the expected parameter types (must not be null for lvalues)
   */
  public TreeMethodExpression(TreeStore store, FunctionMapper functions, VariableMapper variables, TypeConverter converter, String expr, Class returnType, Class[] paramTypes) {
    super();

    Tree tree = store.get(expr);

    this.builder = store.getBuilder();
    this.bindings = tree.bind(functions, variables, converter);
    this.expr = expr;
    this.type = returnType;
    this.types = paramTypes;
    this.node = tree.getRoot();
    this.deferred = tree.isDeferred();

    if (node.isLiteralText()) {
      if (returnType == void.class) {
        throw new ELException(LocalMessages.get("error.method.literal.void", expr));
      }
    } else if (!node.isMethodInvocation()) {
      if (!node.isLeftValue()) {
        throw new ELException(LocalMessages.get("error.method.invalid", expr));
      }
      if (paramTypes == null) {
        throw new ELException(LocalMessages.get("error.method.notypes"));
      }
    }
  }

  private String getStructuralId() {
    if (structure == null) {
      structure = node.getStructuralId(bindings);
    }
    return structure;
  }

  /**
   * Evaluates the expression and answers information about the method
   * 
   * @param context
   *          used to resolve properties (base.property and base[property])
   * @return method information or null for literal expressions
   * @throws ELException
   *           if evaluation fails (e.g. suitable method not found)
   */
  @Override
  public MethodInfo getMethodInfo(ELContext context) throws ELException {
    return node.getMethodInfo(bindings, context, type, types);
  }

  @Override
  public String getExpressionString() {
    return expr;
  }

  /**
   * Evaluates the expression and invokes the method.
   * 
   * @param context
   *          used to resolve properties (base.property and base[property])
   * @param paramValues
   * @return method result or null if this is a literal text expression
   * @throws ELException
   *           if evaluation fails (e.g. suitable method not found)
   */
  @Override
  public Object invoke(ELContext context, Object[] paramValues) throws ELException {
    return node.invoke(bindings, context, type, types, paramValues);
  }

  /**
   * @return true if this is a literal text expression
   */
  @Override
  public boolean isLiteralText() {
    return node.isLiteralText();
  }

  /**
   * @return true if this is a method invocation expression
   */
  @Override
  public boolean isParmetersProvided() {
    return node.isMethodInvocation();
  }

  /**
   * Answer true if this is a deferred expression (starting with #{)
   */
  public boolean isDeferred() {
    return deferred;
  }

  /**
   * Expressions are compared using the concept of a structural id: variable and function names are anonymized such that two expressions with same tree structure will also have the same
   * structural id and vice versa. Two method expressions are equal if
   * 
   * their builders are equal
   * their structural id's are equal
   * their bindings are equal
   * their expected types match
   * their parameter types are equal
   * 
   */
  @Override
  public boolean equals(Object obj) {
    if (obj != null && obj.getClass() == getClass()) {
      TreeMethodExpression other = (TreeMethodExpression) obj;
      if (!builder.equals(other.builder)) {
        return false;
      }
      if (type != other.type) {
        return false;
      }
      if (!Arrays.equals(types, other.types)) {
        return false;
      }
      return getStructuralId().equals(other.getStructuralId()) && bindings.equals(other.bindings);
    }
    return false;
  }

  @Override
  public int hashCode() {
    return getStructuralId().hashCode();
  }

  @Override
  public String toString() {
    return "TreeMethodExpression(" + expr + ")";
  }

  /**
   * Print the parse tree.
   * 
   * @param writer
   */
  public void dump(PrintWriter writer) {
    NodePrinter.dump(writer, node);
  }

  private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
    in.defaultReadObject();
    try {
      node = builder.build(expr).getRoot();
    } catch (ELException e) {
      throw new IOException(e.getMessage());
    }
  }
}