/*
 * Copyright 2002-2009 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.util.ArrayList;
import java.util.List;

import org.springframework.core.convert.TypeDescriptor;
import org.springframework.expression.AccessException;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.PropertyAccessor;
import org.springframework.expression.TypedValue;
import org.springframework.expression.spel.ExpressionState;
import org.springframework.expression.spel.SpelEvaluationException;
import org.springframework.expression.spel.SpelMessage;

/**
 * Represents a simple property or field reference.
 * 
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public class PropertyOrFieldReference extends SpelNodeImpl {

	private final String name;

	private volatile PropertyAccessor cachedReadAccessor;

	private volatile PropertyAccessor cachedWriteAccessor;
	
	private final boolean nullSafe;

	public PropertyOrFieldReference(boolean nullSafe, String propertyOrFieldName, int pos) {
		super(pos);
		name = propertyOrFieldName;
		this.nullSafe = nullSafe;
	}

	@Override
	public TypedValue getValueInternal(ExpressionState state) throws SpelEvaluationException {
		TypedValue result = readProperty(state, this.name);
		if (result.getValue()==null && state.configuredToCreateCollection() && result.getTypeDescriptor().getType().equals(List.class) && nextChildIs(Indexer.class)) {
			// Create a new list ready for the indexer
			try {
				if (isWritable(state)) {
					List newList = ArrayList.class.newInstance();
					writeProperty(state, name, newList);
					result = readProperty(state, this.name);
				}
			} catch (InstantiationException e) {
				throw new SpelEvaluationException(getStartPosition(), e, SpelMessage.UNABLE_TO_CREATE_LIST_FOR_INDEXING);
			} catch (IllegalAccessException e) {
				throw new SpelEvaluationException(getStartPosition(), e, SpelMessage.UNABLE_TO_CREATE_LIST_FOR_INDEXING);
			}
		}
		return result;
	}

	@Override
	public void setValue(ExpressionState state, Object newValue) throws SpelEvaluationException {
		writeProperty(state, this.name, newValue);
	}

	@Override
	public boolean isWritable(ExpressionState state) throws SpelEvaluationException {
		return isWritableProperty(this.name, state);
	}

	@Override
	public String toStringAST() {
		return this.name;
	}

	/**
	 * Attempt to read the named property from the current context object.
	 * @param state the evaluation state
	 * @param name the name of the property
	 * @return the value of the property
	 * @throws SpelEvaluationException if any problem accessing the property or it cannot be found
	 */
	private TypedValue readProperty(ExpressionState state, String name) throws SpelEvaluationException {
		TypedValue contextObject = state.getActiveContextObject();
		EvaluationContext eContext = state.getEvaluationContext();

		if (contextObject.getValue() == null && nullSafe) {
			return TypedValue.NULL_TYPED_VALUE;
		}

		PropertyAccessor accessorToUse = this.cachedReadAccessor;
		if (accessorToUse != null) {
			try {
				return accessorToUse.read(state.getEvaluationContext(), contextObject.getValue(), name);
			}
			catch (AccessException ae) {
				// this is OK - it may have gone stale due to a class change,
				// let's try to get a new one and call it before giving up
				this.cachedReadAccessor = null;
			}
		}

		Class<?> contextObjectClass = getObjectClass(contextObject.getValue());
		List<PropertyAccessor> accessorsToTry = getPropertyAccessorsToTry(contextObjectClass, state);

		// Go through the accessors that may be able to resolve it. If they are a cacheable accessor then
		// get the accessor and use it. If they are not cacheable but report they can read the property
		// then ask them to read it
		if (accessorsToTry != null) {
			try {
				for (PropertyAccessor accessor : accessorsToTry) {
					if (accessor.canRead(eContext, contextObject.getValue(), name)) {
						this.cachedReadAccessor = accessor;
						return accessor.read(eContext, contextObject.getValue(), name);
					}
				}
			}
			catch (AccessException ae) {
				throw new SpelEvaluationException(ae, SpelMessage.EXCEPTION_DURING_PROPERTY_READ, name, ae.getMessage());
			}
		}
		if (contextObject.getValue() == null) {
			throw new SpelEvaluationException(SpelMessage.PROPERTY_OR_FIELD_NOT_READABLE_ON_NULL, name);
		} else {
			throw new SpelEvaluationException(getStartPosition(),SpelMessage.PROPERTY_OR_FIELD_NOT_READABLE, name,
					FormatHelper.formatClassNameForMessage(contextObjectClass));
		}
	}

	private void writeProperty(ExpressionState state, String name, Object newValue) throws SpelEvaluationException {
		TypedValue contextObject = state.getActiveContextObject();
		EvaluationContext eContext = state.getEvaluationContext();
		
		if (contextObject.getValue() == null && nullSafe) {
			return;
		}

		PropertyAccessor accessorToUse = this.cachedWriteAccessor;
		if (accessorToUse != null) {
			try {				
				accessorToUse.write(state.getEvaluationContext(), contextObject.getValue(), name, newValue);
				return;
			}
			catch (AccessException ae) {
				// this is OK - it may have gone stale due to a class change,
				// let's try to get a new one and call it before giving up
				this.cachedWriteAccessor = null;
			}
		}

		Class<?> contextObjectClass = getObjectClass(contextObject.getValue());

		List<PropertyAccessor> accessorsToTry = getPropertyAccessorsToTry(contextObjectClass, state);
		if (accessorsToTry != null) {
			try {
				for (PropertyAccessor accessor : accessorsToTry) {
					if (accessor.canWrite(eContext, contextObject.getValue(), name)) {
						this.cachedWriteAccessor = accessor;
						accessor.write(eContext, contextObject.getValue(), name, newValue);
						return;
					}
				}
			} catch (AccessException ae) {
				throw new SpelEvaluationException(getStartPosition(), ae, SpelMessage.EXCEPTION_DURING_PROPERTY_WRITE,
						name, ae.getMessage());
			}
		}
		if (contextObject.getValue()==null) {
			throw new SpelEvaluationException(getStartPosition(),SpelMessage.PROPERTY_OR_FIELD_NOT_WRITABLE_ON_NULL, name);
		} else {
			throw new SpelEvaluationException(getStartPosition(),SpelMessage.PROPERTY_OR_FIELD_NOT_WRITABLE, name, FormatHelper
					.formatClassNameForMessage(contextObjectClass));
		}
	}

	public boolean isWritableProperty(String name, ExpressionState state) throws SpelEvaluationException {
		Object contextObject = state.getActiveContextObject().getValue();
		TypeDescriptor td = state.getActiveContextObject().getTypeDescriptor();
		EvaluationContext eContext = state.getEvaluationContext();

		List<PropertyAccessor> resolversToTry = getPropertyAccessorsToTry(getObjectClass(contextObject),state);

		if (resolversToTry != null) {
			for (PropertyAccessor pfResolver : resolversToTry) {
				try {
					if (pfResolver.canWrite(eContext, contextObject, name)) {
						return true;
					}
				} catch (AccessException ae) {
					// let others try
				}
			}
		}
		return false;
	}

	/**
	 * Determines the set of property resolvers that should be used to try and access a property on the specified target
	 * type. The resolvers are considered to be in an ordered list, however in the returned list any that are exact
	 * matches for the input target type (as opposed to 'general' resolvers that could work for any type) are placed at
	 * the start of the list. In addition, there are specific resolvers that exactly name the class in question and
	 * resolvers that name a specific class but it is a supertype of the class we have. These are put at the end of the
	 * specific resolvers set and will be tried after exactly matching accessors but before generic accessors.
	 * @param targetType the type upon which property access is being attempted
	 * @return a list of resolvers that should be tried in order to access the property
	 */
	private List<PropertyAccessor> getPropertyAccessorsToTry(Class<?> targetType, ExpressionState state) {
		List<PropertyAccessor> specificAccessors = new ArrayList<PropertyAccessor>();
		List<PropertyAccessor> generalAccessors = new ArrayList<PropertyAccessor>();
		for (PropertyAccessor resolver : state.getPropertyAccessors()) {
			Class<?>[] targets = resolver.getSpecificTargetClasses();
			if (targets == null) { // generic resolver that says it can be used for any type
				generalAccessors.add(resolver);
			}
			else {
				if (targetType != null) {
					int pos = 0;
					for (Class<?> clazz : targets) {
						if (clazz == targetType) { // put exact matches on the front to be tried first?
							specificAccessors.add(pos++, resolver);
						}
						else if (clazz.isAssignableFrom(targetType)) { // put supertype matches at the end of the
							// specificAccessor list
							generalAccessors.add(resolver);
						}
					}
				}
			}
		}
		List<PropertyAccessor> resolvers = new ArrayList<PropertyAccessor>();
		resolvers.addAll(specificAccessors);
		resolvers.addAll(generalAccessors);
		return resolvers;
	}

}