/*
 * Copyright 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.flowable.common.engine.impl.javax.el;

import java.beans.FeatureDescriptor;
import java.util.Iterator;
import java.util.Map;

/**
 * Defines property resolution behavior on instances of java.util.Map. This resolver handles base
 * objects of type java.util.Map. It accepts any object as a property and uses that object as a key
 * in the map. The resulting value is the value in the map that is associated with that key. This
 * resolver can be constructed in read-only mode, which means that isReadOnly will always return
 * true and {@link #setValue(ELContext, Object, Object, Object)} will always throw
 * PropertyNotWritableException. ELResolvers are combined together using {@link CompositeELResolver}
 * s, to define rich semantics for evaluating an expression. See the javadocs for {@link ELResolver}
 * for details.
 */
public class MapELResolver extends ELResolver {
	private final boolean readOnly;

	/**
	 * Creates a new read/write MapELResolver.
	 */
	public MapELResolver() {
		this(false);
	}

	/**
	 * Creates a new MapELResolver whose read-only status is determined by the given parameter.
	 */
	public MapELResolver(boolean readOnly) {
		this.readOnly = readOnly;
	}

	/**
	 * If the base object is a map, returns the most general type that this resolver accepts for the
	 * property argument. Otherwise, returns null. Assuming the base is a Map, this method will
	 * always return Object.class. This is because Maps accept any object as a key.
	 * 
	 * @param context
	 *            The context of this evaluation.
	 * @param base
	 *            The map to analyze. Only bases of type Map are handled by this resolver.
	 * @return null if base is not a Map; otherwise Object.class.
	 */
	@Override
	public Class<?> getCommonPropertyType(ELContext context, Object base) {
		return isResolvable(base) ? Object.class : null;
	}

	/**
	 * If the base object is a map, returns an Iterator containing the set of keys available in the
	 * Map. Otherwise, returns null. The Iterator returned must contain zero or more instances of
	 * java.beans.FeatureDescriptor. Each info object contains information about a key in the Map,
	 * and is initialized as follows:
	 * <ul>
	 * <li>displayName - The return value of calling the toString method on this key, or "null" if
	 * the key is null</li>
	 * <li>name - Same as displayName property</li>
	 * <li>shortDescription - Empty string</li>
	 * <li>expert - false</li>
	 * <li>hidden - false</li>
	 * <li>preferred - true</li>
	 * </ul>
	 * In addition, the following named attributes must be set in the returned FeatureDescriptors:
	 * <ul>
	 * <li>{@link ELResolver#TYPE} - The return value of calling the getClass() method on this key,
	 * or null if the key is null.</li>
	 * <li>{@link ELResolver#RESOLVABLE_AT_DESIGN_TIME} - true</li>
	 * </ul>
	 * 
	 * @param context
	 *            The context of this evaluation.
	 * @param base
	 *            The map to analyze. Only bases of type Map are handled by this resolver.
	 * @return An Iterator containing zero or more (possibly infinitely more) FeatureDescriptor
	 *         objects, each representing a key in this map, or null if the base object is not a
	 *         map.
	 */
	@Override
	public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context, Object base) {
		if (isResolvable(base)) {
			Map<?, ?> map = (Map<?, ?>) base;
			final Iterator<?> keys = map.keySet().iterator();
			return new Iterator<FeatureDescriptor>() {
                @Override
				public boolean hasNext() {
					return keys.hasNext();
				}
                @Override
				public FeatureDescriptor next() {
					Object key = keys.next();
					FeatureDescriptor feature = new FeatureDescriptor();
					feature.setDisplayName(key == null ? "null" : key.toString());
					feature.setName(feature.getDisplayName());
					feature.setShortDescription("");
					feature.setExpert(true);
					feature.setHidden(false);
					feature.setPreferred(true);
					feature.setValue(TYPE, key == null ? null : key.getClass());
					feature.setValue(RESOLVABLE_AT_DESIGN_TIME, true);
					return feature;
					
				}
                @Override
				public void remove() {
					throw new UnsupportedOperationException("cannot remove");
				}
			};
		}
		return null;
	}

	/**
	 * If the base object is a map, returns the most general acceptable type for a value in this
	 * map. If the base is a Map, the propertyResolved property of the ELContext object must be set
	 * to true by this resolver, before returning. If this property is not true after this method is
	 * called, the caller should ignore the return value. Assuming the base is a Map, this method
	 * will always return Object.class. This is because Maps accept any object as the value for a
	 * given key.
	 * 
	 * @param context
	 *            The context of this evaluation.
	 * @param base
	 *            The map to analyze. Only bases of type Map are handled by this resolver.
	 * @param property
	 *            The key to return the acceptable type for. Ignored by this resolver.
	 * @return If the propertyResolved property of ELContext was set to true, then the most general
	 *         acceptable type; otherwise undefined.
	 * @throws NullPointerException
	 *             if context is null
	 * @throws ELException
	 *             if an exception was thrown while performing the property or variable resolution.
	 *             The thrown exception must be included as the cause property of this exception, if
	 *             available.
	 */
	@Override
	public Class<?> getType(ELContext context, Object base, Object property) {
		if (context == null) {
			throw new NullPointerException("context is null");
		}
		Class<?> result = null;
		if (isResolvable(base)) {
			result = Object.class;
			context.setPropertyResolved(true);
		}
		return result;
	}

	/**
	 * If the base object is a map, returns the value associated with the given key, as specified by
	 * the property argument. If the key was not found, null is returned. If the base is a Map, the
	 * propertyResolved property of the ELContext object must be set to true by this resolver,
	 * before returning. If this property is not true after this method is called, the caller should
	 * ignore the return value. Just as in java.util.Map.get(Object), just because null is returned
	 * doesn't mean there is no mapping for the key; it's also possible that the Map explicitly maps
	 * the key to null.
	 * 
	 * @param context
	 *            The context of this evaluation.
	 * @param base
	 *            The map to analyze. Only bases of type Map are handled by this resolver.
	 * @param property
	 *            The key to return the acceptable type for. Ignored by this resolver.
	 * @return If the propertyResolved property of ELContext was set to true, then the value
	 *         associated with the given key or null if the key was not found. Otherwise, undefined.
	 * @throws ClassCastException
	 *             if the key is of an inappropriate type for this map (optionally thrown by the
	 *             underlying Map).
	 * @throws NullPointerException
	 *             if context is null, or if the key is null and this map does not permit null keys
	 *             (the latter is optionally thrown by the underlying Map).
	 * @throws ELException
	 *             if an exception was thrown while performing the property or variable resolution.
	 *             The thrown exception must be included as the cause property of this exception, if
	 *             available.
	 */
	@Override
	public Object getValue(ELContext context, Object base, Object property) {
		if (context == null) {
			throw new NullPointerException("context is null");
		}
		Object result = null;
		if (isResolvable(base)) {
			result = ((Map<?, ?>) base).get(property);
			context.setPropertyResolved(true);
		}
		return result;
	}

	/**
	 * If the base object is a map, returns whether a call to
	 * {@link #setValue(ELContext, Object, Object, Object)} will always fail. If the base is a Map,
	 * the propertyResolved property of the ELContext object must be set to true by this resolver,
	 * before returning. If this property is not true after this method is called, the caller should
	 * ignore the return value. If this resolver was constructed in read-only mode, this method will
	 * always return true. If a Map was created using java.util.Collections.unmodifiableMap(Map),
	 * this method must return true. Unfortunately, there is no Collections API method to detect
	 * this. However, an implementation can create a prototype unmodifiable Map and query its
	 * runtime type to see if it matches the runtime type of the base object as a workaround.
	 * 
	 * @param context
	 *            The context of this evaluation.
	 * @param base
	 *            The map to analyze. Only bases of type Map are handled by this resolver.
	 * @param property
	 *            The key to return the acceptable type for. Ignored by this resolver.
	 * @return If the propertyResolved property of ELContext was set to true, then true if calling
	 *         the setValue method will always fail or false if it is possible that such a call may
	 *         succeed; otherwise undefined.
	 * @throws NullPointerException
	 *             if context is null.
	 * @throws ELException
	 *             if an exception was thrown while performing the property or variable resolution.
	 *             The thrown exception must be included as the cause property of this exception, if
	 *             available.
	 */
	@Override
	public boolean isReadOnly(ELContext context, Object base, Object property) {
		if (context == null) {
			throw new NullPointerException("context is null");
		}
		if (isResolvable(base)) {
			context.setPropertyResolved(true);
		}
		return readOnly;
	}

	/**
	 * If the base object is a map, attempts to set the value associated with the given key, as
	 * specified by the property argument. If the base is a Map, the propertyResolved property of
	 * the ELContext object must be set to true by this resolver, before returning. If this property
	 * is not true after this method is called, the caller can safely assume no value was set. If
	 * this resolver was constructed in read-only mode, this method will always throw
	 * PropertyNotWritableException. If a Map was created using
	 * java.util.Collections.unmodifiableMap(Map), this method must throw
	 * PropertyNotWritableException. Unfortunately, there is no Collections API method to detect
	 * this. However, an implementation can create a prototype unmodifiable Map and query its
	 * runtime type to see if it matches the runtime type of the base object as a workaround.
	 * 
	 * @param context
	 *            The context of this evaluation.
	 * @param base
	 *            The map to analyze. Only bases of type Map are handled by this resolver.
	 * @param property
	 *            The key to return the acceptable type for. Ignored by this resolver.
	 * @param value
	 *            The value to be associated with the specified key.
	 * @throws ClassCastException
	 *             if the class of the specified key or value prevents it from being stored in this
	 *             map.
	 * @throws NullPointerException
	 *             if context is null, or if this map does not permit null keys or values, and the
	 *             specified key or value is null.
	 * @throws IllegalArgumentException
	 *             if some aspect of this key or value prevents it from being stored in this map.
	 * @throws PropertyNotWritableException
	 *             if this resolver was constructed in read-only mode, or if the put operation is
	 *             not supported by the underlying map.
	 * @throws ELException
	 *             if an exception was thrown while performing the property or variable resolution.
	 *             The thrown exception must be included as the cause property of this exception, if
	 *             available.
	 */
	@Override
	@SuppressWarnings("unchecked")
	public void setValue(ELContext context, Object base, Object property, Object value) {
		if (context == null) {
			throw new NullPointerException("context is null");
		}
		if (isResolvable(base)) {
			if (readOnly) {
				throw new PropertyNotWritableException("resolver is read-only");
			}
			((Map) base).put(property, value);
			context.setPropertyResolved(true);
		}
	}

	/**
	 * Test whether the given base should be resolved by this ELResolver.
	 * 
	 * @param base
	 *            The bean to analyze.
	 * @return base instanceof Map
	 */
	private final boolean isResolvable(Object base) {
		return base instanceof Map<?,?>;
	}
}
