root/trunk/ProjectFortress/src/com/sun/fortress/useful/UsefulPLT.java @ 3134

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    Copyright 2008 Sun Microsystems, Inc.,
    4150 Network Circle, Santa Clara, California 95054, U.S.A.
    All rights reserved.

    U.S. Government Rights - Commercial software.
    Government users are subject to the Sun Microsystems, Inc. standard
    license agreement and applicable provisions of the FAR and its supplements.

    Use is subject to license terms.

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    Sun, Sun Microsystems, the Sun logo and Java are trademarks or registered
    trademarks of Sun Microsystems, Inc. in the U.S. and other countries.
 ******************************************************************************/

package com.sun.fortress.useful;

import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.Map.Entry;

import edu.rice.cs.plt.collect.ConsList;
import edu.rice.cs.plt.collect.ImmutableRelation;
import edu.rice.cs.plt.collect.IndexedRelation;
import edu.rice.cs.plt.collect.Relation;
import edu.rice.cs.plt.iter.IterUtil;

/**
 * It is helpful for Useful to not depend on external libraries.
 * Those useful methods that do, were moved here.
 * @author dr2chase
 */

public class UsefulPLT {
    /**
     * Returns an immutable {@code Relation} with the same contents as the given
     * {@code Map}.
     */
    public static <K,V> Relation<K,V> relation(Map<? extends K, ? extends V> map) {
        IndexedRelation<K,V> result = new IndexedRelation<K,V>();
        for( Map.Entry<? extends K, ? extends V> entry : map.entrySet() ) {
                result.add(entry.getKey(), entry.getValue());
        }
        return new ImmutableRelation<K,V>(result);
    }
    
    /**
     * Does the given ConsList contain the given element?
     */
        public static <T> boolean consListContains(T item, ConsList<? extends T> list) {
                Iterator<? extends T> iter = list.iterator();
                while( iter.hasNext() ) {
                        T t = iter.next();
                        if( t.equals(item) )
                                return true;
                }
                return false;
        }
        
        public static <K,V> IMultiMap<K,V> shrinkMultiMap(IMultiMap<K,V> map) {
            if( map.isEmpty() )
                return emptyMultiMap();
            else if( map.size() == 1 ) {
                Map.Entry<K,Set<V>> r = IterUtil.first(map.entrySet());
                if( r.getValue().isEmpty() ) {
                    return singletonMultiMap(r.getKey(), Collections.<V>emptySet());
                }
                else if( r.getValue().size() == 1 ) {
                    return singletonMultiMap(r.getKey(), IterUtil.first(r.getValue()));
                }
                else {
                    return singletonMultiMap(r.getKey(), r.getValue());
                }
            }
            else
                return map;
        }
        public static <K,V> IMultiMap<K,V> emptyMultiMap() {
            return (IMultiMap<K,V>)IMultiMap.EMPTY_MULTIMAP;
        }
        
        public static <K,V> IMultiMap<K,V> singletonMultiMap(final K key, final V value) {
            return singletonMultiMap(key, Collections.singleton(value));
        }
        
        public static <K,V> IMultiMap<K,V> singletonMultiMap(final K key, final Set<V> value) {
            return new IMultiMap<K,V>() {
                private final Map<K,Set<V>> singleton = Collections.singletonMap(key, value);
                private <T> T error() { throw new IllegalStateException("Singleton IMultiMap is immutable."); }
                public void clear() { singleton.clear(); }
                public boolean containsKey(Object key) { return singleton.containsKey(key); }
                public boolean containsValue(Object value) { return singleton.containsValue(value); }
                public Set<Entry<K, Set<V>>> entrySet() { return singleton.entrySet(); }
                public boolean equals(Object o) { return singleton.equals(o); }
                public Set<V> get(Object key) { return singleton.get(key); }
                public int hashCode() { return singleton.hashCode(); }
                public boolean isEmpty() { return false; }
                public Set<K> keySet() { return singleton.keySet(); }
                public Set<V> put(K key, Set<V> value) { return singleton.put(key, value); }
                public void putAll(Map<? extends K, ? extends Set<V>> t) { singleton.putAll(t); }
                public Set<V> remove(Object key) { return singleton.remove(key); }
                public int size() { return 1; }
                public Collection<Set<V>> values() { return singleton.values(); }
                public void addInverse(Map<V, K> m) { error(); }
                public Set<V> putItem(K k, V v) { return error(); }
                public Set<V> putItems(K k, Set<V> vs) { return error(); }
                public Set<V> removeItem(K k, V v) { return error(); }
                };
        }
        


}