/*   Copyright 2004 The Apache Software Foundation
 *
 *   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.
 */
/**
 * Author: Cezar Andrei ( cezar.andrei at bea.com )
 * Date: Apr 25, 2004
 */
package org.apache.xmlbeans.impl.config;

import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

/**
 * Represents a non finite set of names.
 *
 * @see NameSetBuilder
 */
public class NameSet {
    /**
     * An empty NameSet, it doesn't contain any name
     */
    public static final NameSet EMPTY = new NameSet(true, Collections.emptySet());
    /**
     * The NameSet that contains any name
     */
    public static final NameSet EVERYTHING = new NameSet(false, Collections.emptySet());

    /*
    There are two big cases:
    1) - it represents "*", ie all except a finite set of names: _isFinite==false
    2) - if represents only a finite set of names: _isFinite==true
    */
    private final boolean _isFinite;
    private final Set<String> _finiteSet;

    private NameSet(boolean isFinite, Set<String> finiteSet) {
        _isFinite = isFinite;
        _finiteSet = finiteSet;
    }

    static NameSet newInstance(boolean isFinite, Set<String> finiteSet) {
        if (finiteSet.isEmpty()) {
            if (isFinite) {
                return NameSet.EMPTY;
            } else {
                return NameSet.EVERYTHING;
            }
        } else {
            Set<String> fs = new HashSet<>();
            fs.addAll(finiteSet);
            return new NameSet(isFinite, fs);
        }
    }

    private static Set<String> intersectFiniteSets(Set<String> a, Set<String> b) {
        Set<String> intersection = new HashSet<>();
        //compute the intersection of _finiteSet with withSet
        Iterator<String> it = a.iterator();
        while (it.hasNext()) {
            String name = it.next();
            if (b.contains(name)) {
                intersection.add(name);
            }
        }
        return intersection;
    }

    /**
     * Returns the union of this NameSet with the 'with' NameSet.
     */
    public NameSet union(NameSet with) {
        if (_isFinite) {
            if (with._isFinite) {
                Set<String> union = new HashSet<>();
                union.addAll(_finiteSet);
                union.addAll(with._finiteSet);
                return newInstance(true, union);
            } else {
                Set<String> subst = new HashSet<>();
                subst.addAll(with._finiteSet);
                subst.removeAll(_finiteSet);
                return newInstance(false, subst);
            }
        } else {
            if (with._isFinite) {
                Set<String> subst = new HashSet<>();
                subst.addAll(_finiteSet);
                subst.removeAll(with._finiteSet);
                return newInstance(false, subst);
            } else {
                return newInstance(false, intersectFiniteSets(_finiteSet, with._finiteSet));
            }
        }
    }

    /**
     * Returns the intersection of this NameSet with the 'with' NameSet
     */
    public NameSet intersect(NameSet with) {
        if (_isFinite) {
            if (with._isFinite) {
                return newInstance(true, intersectFiniteSets(_finiteSet, with._finiteSet));
            } else {
                Set<String> subst = new HashSet<>();
                subst.addAll(_finiteSet);
                subst.removeAll(with._finiteSet);
                return newInstance(false, subst);
            }
        } else {
            if (with._isFinite) {
                Set<String> subst = new HashSet<>();
                subst.addAll(with._finiteSet);
                subst.removeAll(_finiteSet);
                return newInstance(true, subst);
            } else {
                Set<String> union = new HashSet<>();
                union.addAll(_finiteSet);
                union.addAll(with._finiteSet);
                return newInstance(false, union);
            }
        }
    }

    /**
     * Returns the result of substracting this NameSet from 'from' NameSet
     *
     * @see NameSet#substract
     */
    public NameSet substractFrom(NameSet from) {
        return from.substract(this);
    }

    /**
     * Returns the result of substracting 'what' NameSet from this NameSet
     *
     * @see NameSet#substractFrom
     */
    public NameSet substract(NameSet what) {
        if (_isFinite) {
            if (what._isFinite) {
                // it's the subst of _finiteSet with what._finiteSet
                Set<String> subst = new HashSet<>();
                subst.addAll(_finiteSet);
                subst.removeAll(what._finiteSet);
                return newInstance(true, subst);
            } else {
                return newInstance(true, intersectFiniteSets(_finiteSet, what._finiteSet));
            }
        } else {
            if (what._isFinite) {
                // it's the union of _finiteSet with what._finiteSet
                Set<String> union = new HashSet<>();
                union.addAll(_finiteSet);
                union.addAll(what._finiteSet);
                return newInstance(false, union);
            } else {
                // what's in thisSet and it's not in whatSet
                Set<String> subst = new HashSet<>();
                subst.addAll(what._finiteSet);
                subst.removeAll(_finiteSet);
                return newInstance(true, subst);
            }
        }
    }

    /**
     * Returns an inversion of this NameSet
     */
    public NameSet invert() {
        return newInstance(!_isFinite, _finiteSet);
    }

    public boolean contains(String name) {
        if (_isFinite) {
            return _finiteSet.contains(name);
        } else {
            return !_finiteSet.contains(name);
        }
    }
}
