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Library providing immutable/persistent collection classes for Java. While collections are immutable they provide methods for adding and removing values by creating new modified copies of themselves. Each copy shares almost all of its structure with other copies to minimize memory consumption.
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///###////////////////////////////////////////////////////////////////////////
//
// Burton Computer Corporation
// http://www.burton-computer.com
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// Copyright (c) 2014, Burton Computer Corporation
// All rights reserved.
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package org.javimmutable.collections.common;

import org.javimmutable.collections.Cursor;
import org.javimmutable.collections.Cursorable;
import org.javimmutable.collections.JImmutableMap;
import org.javimmutable.collections.JImmutableSet;
import org.javimmutable.collections.cursors.Cursors;
import org.javimmutable.collections.cursors.TransformCursor;

import java.util.Iterator;
import java.util.Set;

public abstract class AbstractJImmutableSet
        implements JImmutableSet
{
    private final JImmutableMap map;

    protected AbstractJImmutableSet(JImmutableMap map)
    {
        this.map = map;
    }

    @Override
    public JImmutableSet insert(T value)
    {
        JImmutableMap newMap = map.assign(value, Boolean.TRUE);
        return (newMap != map) ? create(newMap) : this;
    }

    @Override
    public JImmutableSet union(Cursorable other)
    {
        JImmutableMap newMap = map;
        for (Cursor cursor = other.cursor().start(); cursor.hasValue(); cursor = cursor.next()) {
            T value = cursor.getValue();
            newMap = newMap.assign(value, Boolean.TRUE);
        }
        return (newMap != map) ? create(newMap) : this;
    }

    @Override
    public JImmutableSet delete(T value)
    {
        JImmutableMap newMap = map.delete(value);
        return (newMap != map) ? create(newMap) : this;
    }

    @Override
    public JImmutableSet deleteAll(Cursorable other)
    {
        JImmutableMap newMap = map;
        for (Cursor cursor = other.cursor().start(); cursor.hasValue(); cursor = cursor.next()) {
            T value = cursor.getValue();
            newMap = newMap.delete(value);
        }
        return (newMap != map) ? create(newMap) : this;
    }

    @Override
    public JImmutableSet intersection(JImmutableSet other)
    {
        JImmutableSet smaller, larger;
        if (other.getClass() == getClass() && other.size() < size()) {
            smaller = other;
            larger = this;
        } else {
            smaller = this;
            larger = other;
        }
        for (T value : smaller) {
            if (!larger.contains(value)) {
                smaller = smaller.delete(value);
            }
        }
        return smaller;
    }

    @Override
    public JImmutableSet intersection(Cursorable other)
    {
        JImmutableMap newMap = emptyMap();
        for (Cursor cursor = other.cursor().start(); cursor.hasValue(); cursor = cursor.next()) {
            T value = cursor.getValue();
            if (map.getValueOr(value, Boolean.FALSE)) {
                newMap = newMap.assign(value, Boolean.TRUE);
            }
        }
        return (newMap != map) ? create(newMap) : this;
    }

    @Override
    public boolean contains(T value)
    {
        return value != null && map.getValueOr(value, Boolean.FALSE);
    }

    @Override
    public boolean containsAll(Cursorable value)
    {
        for (Cursor cursor = value.cursor().start(); cursor.hasValue(); cursor = cursor.next()) {
            if (!contains(cursor.getValue())) {
                return false;
            }
        }
        return true;
    }

    @Override
    public boolean containsAny(Cursorable value)
    {
        for (Cursor cursor = value.cursor().start(); cursor.hasValue(); cursor = cursor.next()) {
            if (contains(cursor.getValue())) {
                return true;
            }
        }
        return false;
    }

    @Override
    public int size()
    {
        return map.size();
    }

    @Override
    public boolean isEmpty()
    {
        return map.size() == 0;
    }

    @Override
    public Set getSet()
    {
        return SetAdaptor.of(this);
    }

    @Override
    public Cursor cursor()
    {
        return TransformCursor.ofKeys(map.cursor());
    }

    @Override
    public Iterator iterator()
    {
        return IteratorAdaptor.of(cursor());
    }

    @Override
    public int hashCode()
    {
        return Cursors.computeHashCode(cursor());
    }

    @Override
    public boolean equals(Object o)
    {
        if (o == this) {
            return true;
        } else if (o == null) {
            return false;
        } else if (o instanceof JImmutableSet) {
            return getSet().equals(((JImmutableSet)o).getSet());
        } else {
            return (o instanceof Set) && getSet().equals(o);
        }
    }

    @Override
    public String toString()
    {
        return Cursors.makeString(cursor());
    }

    /**
     * Implemented by derived classes to create a new instance of the appropriate class.
     *
     * @param map
     * @return
     */
    protected abstract JImmutableSet create(JImmutableMap map);

    /**
     * Implemented by derived classes to create a new empty PersistentMap for use by retainAll()
     *
     * @return
     */
    protected abstract JImmutableMap emptyMap();
}