/*
    * This file is a part of CAST project.
    * (c) Copyright 2007, AGH University of Science & Technology
    * https://caribou.iisg.agh.edu.pl/trac/cast
    *
    * Licensed under the Eclipse Public License, Version 1.0 (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.eclipse.org/legal/epl-v10.html
   */
  /*
   * File: AttributeMergePolicy.java
   * Created: 2008-11-24
   * Author: tmilos
   * $Id: AttributeMergePolicy.java 3047 2009-07-23 20:39:18Z fibinger $
   */
  
  package pl.edu.agh.cast.model.attributes;
  
  import java.io.Serializable;
  import java.util.HashMap;
  import java.util.Map;
  
  import com.thoughtworks.xstream.annotations.XStreamAlias;
  
  /**
   * This class represents a policy of merging two values of an {@link VisualAttribute} into one. It defines a few basic
   * policies, however custom ones may be defined by extending this class.
   *
   * @author AGH CAST Team
   */
  public abstract class AttributeMergePolicy implements Serializable {
  
  	private static final long serialVersionUID = 6800412459178310697L;
  
  	/**
  	 * A merge policy that always returns the logical alternative (OR) of given values. It is valid only for two values
  	 * of type {@link Boolean}
  	 *
  	 * @author AGH CAST Team
  	 */
  	@XStreamAlias("MERGE_POLICY_LOGICAL_OR")
  	public static final class MergePolicyLogicalOr extends AttributeMergePolicy {
  		private static final long serialVersionUID = -6698802554723374885L;
  
  		private MergePolicyLogicalOr() {
  			super();
  		}
  
  		/**
  		 * {@inheritDoc}
  		 *
  		 * @see pl.edu.agh.cast.model.attributes.AttributeMergePolicy
  		 *      #mergeValues(pl.edu.agh.cast.model.attributes.VisualAttribute, java.lang.Object, java.lang.Object)
  		 */
  		@Override
  		public Object mergeValues(Attribute attribute, Object firstValue, Object secondValue) {
  			checkIfBoolean(firstValue, secondValue);
  			return ((Boolean)firstValue) || ((Boolean)secondValue);
  		}
  
  		/**
  		 * {@inheritDoc}
  		 *
  		 * @see pl.edu.agh.cast.model.attributes.AttributeMergePolicy#getId()
  		 */
  		@Override
  		public String getId() {
  			return "MERGE_POLICY_LOGICAL_OR"; //$NON-NLS-1$
  		}
  	}
  
  	/**
  	 * A merge policy that always returns the logical conjunction (AND) of given values. It is valid only for two values
  	 * of type {@link Boolean}
  	 *
  	 * @author AGH CAST Team
  	 */
  	@XStreamAlias("MERGE_POLICY_LOGICAL_AND")
  	public static final class MergePolicyLogicalAnd extends AttributeMergePolicy {
  		private static final long serialVersionUID = 2306183502914013676L;
  
  		private MergePolicyLogicalAnd() {
  			super();
  		}
  
  		/**
  		 * {@inheritDoc}
  		 *
  		 * @see pl.edu.agh.cast.model.attributes.AttributeMergePolicy
  		 *      #mergeValues(pl.edu.agh.cast.model.attributes.VisualAttribute, java.lang.Object, java.lang.Object)
  		 */
  		@Override
  		public Object mergeValues(Attribute attribute, Object firstValue, Object secondValue) {
  			checkIfBoolean(firstValue, secondValue);
  			return ((Boolean)firstValue) && ((Boolean)secondValue);
  		}
  
  		/**
 		 * {@inheritDoc}
 		 *
 		 * @see pl.edu.agh.cast.model.attributes.AttributeMergePolicy#getId()
 		 */
 		@Override
 		public String getId() {
 			return "MERGE_POLICY_LOGICAL_AND"; //$NON-NLS-1$
 		}
 	}
 
 	/**
 	 * A merge policy that always returns the second value.
 	 *
 	 * @author AGH CAST Team
 	 */
 	@XStreamAlias("MERGE_POLICY_ALWAYS_SECOND")
 	public static final class MergePolicyAlwaysSecond extends AttributeMergePolicy {
 		private static final long serialVersionUID = -6798718594185971003L;
 
 		private MergePolicyAlwaysSecond() {
 			super();
 		}
 
 		/**
 		 * {@inheritDoc}
 		 *
 		 * @see pl.edu.agh.cast.model.attributes.AttributeMergePolicy
 		 *      #mergeValues(pl.edu.agh.cast.model.attributes.VisualAttribute, java.lang.Object, java.lang.Object)
 		 */
 		@Override
 		public Object mergeValues(Attribute attribute, Object firstValue, Object secondValue) {
 			return secondValue;
 		}
 
 		/**
 		 * {@inheritDoc}
 		 *
 		 * @see pl.edu.agh.cast.model.attributes.AttributeMergePolicy#getId()
 		 */
 		@Override
 		public String getId() {
 			return "MERGE_POLICY_ALWAYS_SECOND"; //$NON-NLS-1$
 		}
 	}
 
 	/**
 	 * A merge policy that always returns the first value.
 	 *
 	 * @author AGH CAST Team
 	 */
 	@XStreamAlias("MERGE_POLICY_ALWAYS_FIRST")
 	public static final class MergePolicyAlwaysFirst extends AttributeMergePolicy {
 		private static final long serialVersionUID = 3645856921319121245L;
 
 		private MergePolicyAlwaysFirst() {
 			super();
 		}
 
 		/**
 		 * {@inheritDoc}
 		 *
 		 * @see pl.edu.agh.cast.model.attributes.AttributeMergePolicy
 		 *      #mergeValues(pl.edu.agh.cast.model.attributes.VisualAttribute, java.lang.Object, java.lang.Object)
 		 */
 		@Override
 		public Object mergeValues(Attribute attribute, Object firstValue, Object secondValue) {
 			return firstValue;
 		}
 
 		/**
 		 * {@inheritDoc}
 		 *
 		 * @see pl.edu.agh.cast.model.attributes.AttributeMergePolicy#getId()
 		 */
 		@Override
 		public String getId() {
 			return "MERGE_POLICY_ALWAYS_FIRST"; //$NON-NLS-1$
 		}
 
 	};
 
 	/**
 	 * Merge policy registry.
 	 */
 	private static Map<String, AttributeMergePolicy> policyRegistry = new HashMap<String, AttributeMergePolicy>();
 
 	/**
 	 * A merge policy that always returns the first value.
 	 */
 	public static final AttributeMergePolicy MERGE_POLICY_ALWAYS_FIRST = new MergePolicyAlwaysFirst();
 
 	/**
 	 * A merge policy that always returns the second value.
 	 */
 	public static final AttributeMergePolicy MERGE_POLICY_ALWAYS_SECOND = new MergePolicyAlwaysSecond();
 
 	/**
 	 * A merge policy that always returns the logical conjunction (AND) of given values. It is valid only for two values
 	 * of type {@link Boolean}
 	 */
 	public static final AttributeMergePolicy MERGE_POLICY_LOGICAL_AND = new MergePolicyLogicalAnd();
 
 	/**
 	 * A merge policy that always returns the logical alternative (OR) of given values. It is valid only for two values
 	 * of type {@link Boolean}
 	 */
 	public static final AttributeMergePolicy MERGE_POLICY_LOGICAL_OR = new MergePolicyLogicalOr();
 
 	protected AttributeMergePolicy() {
 		if (!policyRegistry.containsKey(getId())) {
 			policyRegistry.put(toString(), this);
 		} else if (!policyRegistry.get(getId()).getClass().equals(this.getClass())) {
 			throw new AttributeMergePolicyNotUniqueException(
 			        "An instance of AttributeMergePolicy with given ID is already registered: " //$NON-NLS-1$
 			                + getId());
 		}
 	}
 
 	/**
 	 * Verifies if two values are of type {@link Boolean}. Helper method.
 	 *
 	 * @param first
 	 * @param second
 	 * @return <code>true</code> if types of both values are of type {@link Boolean}
 	 */
 	protected boolean checkIfBoolean(Object firstValue, Object secondValue) {
 		if (!(firstValue instanceof Boolean)) {
 			throw new IllegalArgumentException("First value is not of type Boolean"); //$NON-NLS-1$
 		}
 		if (!(secondValue instanceof Boolean)) {
 			throw new IllegalArgumentException("Second value is not of type Boolean"); //$NON-NLS-1$
 		}
 		return true;
 	}
 
 	/**
 	 * Returns the unique id of this policy.
 	 *
 	 * @return policy id
 	 */
 	public abstract String getId();
 
 	/**
 	 * Merges two {@link Attribute} values into one. It is possible that the returned value will be one of the
 	 * parameters, or a completely new object.
 	 *
 	 * @param attribute
 	 *            {@link Attribute} to merge
 	 * @param firstValue
 	 *            first value
 	 * @param secondValue
 	 *            second value
 	 * @return an {@link AttributeValue} that is the result of merging given values according to the policy
 	 */
 	public abstract Object mergeValues(Attribute attribute, Object firstValue, Object secondValue);
 
 	/**
 	 * Returns policy based on its id.
 	 *
 	 * @param id
 	 *            policy id
 	 * @return the policy
 	 */
 	public static final AttributeMergePolicy resolve(String id) {
 		return policyRegistry.get(id);
 	}
 
 	/**
 	 * {@inheritDoc}
 	 *
 	 * @see java.lang.Object#equals(java.lang.Object)
 	 */
 	@Override
 	public boolean equals(Object obj) {
 		if (obj == this) {
 			return true;
 		}
 		if (!(obj instanceof AttributeMergePolicy)) {
 			return false;
 		}
 		AttributeMergePolicy that = (AttributeMergePolicy)obj;
 		if (!this.getId().equals(that.getId())) {
 			return false;
 		}
 		return true;
 	}
 
 	/**
 	 * {@inheritDoc}
 	 *
 	 * @see java.lang.Object#toString()
 	 */
 	@Override
 	public String toString() {
 		return getId();
 	}
 
 	/**
 	 * {@inheritDoc}
 	 *
 	 * @see java.lang.Object#hashCode()
 	 */
 	@Override
 	public int hashCode() {
 		return getId().hashCode();
 	}
 
 }