SquirrelJME/SquirrelJME

// -*- Mode: Java; indent-tabs-mode: t; tab-width: 4 -*-
// ---------------------------------------------------------------------------
// SquirrelJME
//     Copyright (C) Stephanie Gawroriski <xer@multiphasicapps.net>
// ---------------------------------------------------------------------------
// SquirrelJME is under the Mozilla Public License Version 2.0.
// See license.mkd for licensing and copyright information.
// ---------------------------------------------------------------------------

package net.multiphasicapps.collections;

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.util.AbstractMap;
import java.util.AbstractSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import org.jetbrains.annotations.UnmodifiableView;

/**
 * This is a map which cannot be modified.
 *
 * @param <K> Key type to use.
 * @param <V> Value type to store.
 * @since 2016/02/29
 */
@UnmodifiableView
public final class UnmodifiableMap<K, V>
    extends AbstractMap<K, V>
{
    /** The existing map to wrap. */
    protected final Map<K, V> wrapped;
    
    /** Entry set cache, since it is not always needed. */
    private Reference<Set<Map.Entry<K, V>>> _escache;
    
    /**
     * Initializes the unmodifiable wrapped map.
     *
     * @param __w The map to wrap.
     * @throws NullPointerException On null arguments.
     * @since 2016/02/29
     */
    private UnmodifiableMap(Map<K, V> __w)
        throws NullPointerException
    {
        // Check
        if (__w == null)
            throw new NullPointerException("NARG");
        
        // Set
        this.wrapped = __w;
    }
    
    /**
     * {@inheritDoc}
     * @since 2016/02/29
     */
    @Override
    public boolean containsKey(Object __o)
    {
        return this.wrapped.containsKey(__o);
    }
    
    /**
     * {@inheritDoc}
     * @since 2016/05/12
     */
    @Override
    public boolean containsValue(Object __o)
    {
        return this.wrapped.containsValue(__o);
    }
    
    /**
     * {@inheritDoc}
     * @since 2016/02/29
     */
    @Override
    public Set<Map.Entry<K, V>> entrySet()
    {
        // Get reference to the map
        Reference<Set<Map.Entry<K, V>>> ref = this._escache;
        Set<Map.Entry<K, V>> rv = null;
        
        // In reference?
        if (ref != null)
            rv = ref.get();
        
        // Needs initialization?
        if (rv == null)
            this._escache = new WeakReference<>((rv = new __SetView__()));
        
        // Return it
        return rv;
    }
    
    /**
     * {@inheritDoc}
     * @since 2016/02/29
     * @param __k
     */
    @Override
    public V get(Object __k)
    {
        return this.wrapped.get(__k);
    }
    
    /**
     * {@inheritDoc}
     * @since 2016/05/12
     */
    @Override
    public boolean isEmpty()
    {
        return this.wrapped.isEmpty();
    }
    
    /**
     * {@inheritDoc}
     * @since 2016/02/29
     */
    @Override
    public int size()
    {
        return this.wrapped.size();
    }
    
    /**
     * This creates a view of the specified map which cannot be modified.
     *
     * @param <K> The map key.
     * @param <V> The map value.
     * @param __m The map to wrap.
     * @return An unmodifiable view of the map.
     * @since 2016/02/28
     */
    public static <K, V> Map<K, V> of(Map<K, V> __m)
    {
        // If already one, return it
        if (__m instanceof UnmodifiableMap)
            return __m;
        
        // Wrap
        return new UnmodifiableMap<K, V>(__m);
    }
    
    /**
     * This is the iterator over the entry set of the map.
     *
     * @since 2016/02/29
     */
    private final class __SetIterator__
        implements Iterator<Map.Entry<K, V>>
    {
        /** The base iterator. */
        protected final Iterator<Map.Entry<K, V>> from =
            UnmodifiableMap.this.wrapped.entrySet().iterator();
        
        /**
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public boolean hasNext()
        {
            return this.from.hasNext();
        }
    
        /**    
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public Map.Entry<K, V> next()
        {
            // Get the next entry
            Map.Entry<K, V> ent = this.from.next();
            
            // If null, this is a bad map but possibly might be valid
            if (ent == null)
                return null;
            
            // Wrap it
            return new __SetEntry__<K, V>(ent);
        }
        
        /**    
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public void remove()
        {
            throw new UnsupportedOperationException("RORO");
        }
    }
    
    /**
     * This implements the unmodifiable set view.
     *
     * @since 2016/02/29
     */
    private final class __SetView__
        extends AbstractSet<Map.Entry<K, V>>
    {
        
        /**    
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public Iterator<Map.Entry<K, V>> iterator()
        {
            return new __SetIterator__();
        }
    
        /**
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public int size()
        {
            return UnmodifiableMap.this.wrapped.size();
        }
    }
    
    /**
     * This is a single entry in the set.
     *
     * @param <K> The key type.
     * @param <V> The value type.
     * @since 2016/02/29
     */
    private static final class __SetEntry__<K, V>
        implements Map.Entry<K, V>
    {
        /** The base entry. */
        protected final Map.Entry<K, V> base;
        
        /**
         * Initializes the set entry.
         *
         * @param __e The entry to wrap.
         * @throws NullPointerException On null arguments.
         * @since 2016/02/29
         */
        private __SetEntry__(Map.Entry<K, V> __e)
            throws NullPointerException
        {
            // Check
            if (__e == null)
                throw new NullPointerException("NARG");
            
            // Set
            this.base = __e;
        }
        
        /**
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public boolean equals(Object __a)
        {
            return this.base.equals(__a);
        }
        
        /**
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public K getKey()
        {
            return this.base.getKey();
        }
        
        /**
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public V getValue()
        {
            return this.base.getValue();
        }
        
        /**
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public int hashCode()
        {
            return this.base.hashCode();
        }
        
        /**
         * {@inheritDoc}
         * @since 2016/02/29
         */
        @Override
        public V setValue(V __v)
        {
            throw new UnsupportedOperationException("RORO");
        }
    }
}