/*
    * Copyright 2002-2014 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
    *
    *      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.springframework.expression.spel.ast;
  
  import java.lang.reflect.Array;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collection;
  import java.util.List;
  import java.util.Map;
  
  import org.springframework.expression.EvaluationException;
  import org.springframework.expression.TypedValue;
  import org.springframework.expression.spel.ExpressionState;
  import org.springframework.expression.spel.SpelEvaluationException;
  import org.springframework.expression.spel.SpelMessage;
  import org.springframework.util.ClassUtils;
  import org.springframework.util.ObjectUtils;
  
  /**
   * Represents projection, where a given operation is performed on all elements in some
   * input sequence, returning a new sequence of the same size. For example:
   * "{1,2,3,4,5,6,7,8,9,10}.!{#isEven(#this)}" returns "[n, y, n, y, n, y, n, y, n, y]"
   *
   * @author Andy Clement
   * @author Mark Fisher
   * @since 3.0
   */
  public class Projection extends SpelNodeImpl {
  
  	private final boolean nullSafe;
  
  
  	public Projection(boolean nullSafe, int pos, SpelNodeImpl expression) {
  		super(pos, expression);
  		this.nullSafe = nullSafe;
  	}
  
  
  	@Override
  	public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
  		return getValueRef(state).getValue();
  	}
  
  	@Override
  	protected ValueRef getValueRef(ExpressionState state) throws EvaluationException {
  		TypedValue op = state.getActiveContextObject();
  
  		Object operand = op.getValue();
  		boolean operandIsArray = ObjectUtils.isArray(operand);
  		// TypeDescriptor operandTypeDescriptor = op.getTypeDescriptor();
  
  		// When the input is a map, we push a special context object on the stack
  		// before calling the specified operation. This special context object
  		// has two fields 'key' and 'value' that refer to the map entries key
  		// and value, and they can be referenced in the operation
  		// eg. {'a':'y','b':'n'}.!{value=='y'?key:null}" == ['a', null]
  		if (operand instanceof Map) {
  			Map<?, ?> mapData = (Map<?, ?>) operand;
  			List<Object> result = new ArrayList<Object>();
  			for (Map.Entry<?, ?> entry : mapData.entrySet()) {
  				try {
  					state.pushActiveContextObject(new TypedValue(entry));
  					result.add(this.children[0].getValueInternal(state).getValue());
  				}
  				finally {
  					state.popActiveContextObject();
  				}
  			}
  			return new ValueRef.TypedValueHolderValueRef(new TypedValue(result), this);  // TODO unable to build correct type descriptor
  		}
  
  		if (operand instanceof Collection || operandIsArray) {
  			Collection<?> data = (operand instanceof Collection ? (Collection<?>) operand :
  					Arrays.asList(ObjectUtils.toObjectArray(operand)));
  			List<Object> result = new ArrayList<Object>();
  			int idx = 0;
  			Class<?> arrayElementType = null;
  			for (Object element : data) {
  				try {
  					state.pushActiveContextObject(new TypedValue(element));
  					state.enterScope("index", idx);
  					Object value = this.children[0].getValueInternal(state).getValue();
  					if (value != null && operandIsArray) {
  						arrayElementType = determineCommonType(arrayElementType, value.getClass());
 					}
 					result.add(value);
 				}
 				finally {
 					state.exitScope();
 					state.popActiveContextObject();
 				}
 				idx++;
 			}
 			if (operandIsArray) {
 				if (arrayElementType == null) {
 					arrayElementType = Object.class;
 				}
 				Object resultArray = Array.newInstance(arrayElementType, result.size());
 				System.arraycopy(result.toArray(), 0, resultArray, 0, result.size());
 				return new ValueRef.TypedValueHolderValueRef(new TypedValue(resultArray),this);
 			}
 			return new ValueRef.TypedValueHolderValueRef(new TypedValue(result),this);
 		}
 
 		if (operand==null) {
 			if (this.nullSafe) {
 				return ValueRef.NullValueRef.INSTANCE;
 			}
 			throw new SpelEvaluationException(getStartPosition(), SpelMessage.PROJECTION_NOT_SUPPORTED_ON_TYPE, "null");
 		}
 
 		throw new SpelEvaluationException(getStartPosition(), SpelMessage.PROJECTION_NOT_SUPPORTED_ON_TYPE,
 				operand.getClass().getName());
 	}
 
 	@Override
 	public String toStringAST() {
 		return "![" + getChild(0).toStringAST() + "]";
 	}
 
 	private Class<?> determineCommonType(Class<?> oldType, Class<?> newType) {
 		if (oldType == null) {
 			return newType;
 		}
 		if (oldType.isAssignableFrom(newType)) {
 			return oldType;
 		}
 		Class<?> nextType = newType;
 		while (nextType != Object.class) {
 			if (nextType.isAssignableFrom(oldType)) {
 				return nextType;
 			}
 			nextType = nextType.getSuperclass();
 		}
 		Class<?>[] interfaces = ClassUtils.getAllInterfacesForClass(newType);
 		for (Class<?> nextInterface : interfaces) {
 			if (nextInterface.isAssignableFrom(oldType)) {
 				return nextInterface;
 			}
 		}
 		return Object.class;
 	}
 
 }