/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

package org.apache.jena.mem2.store.legacy;

import org.apache.jena.graph.Triple;
import org.apache.jena.mem2.spliterator.ArraySpliterator;
import org.apache.jena.util.iterator.ExtendedIterator;
import org.apache.jena.util.iterator.NiceIterator;

import java.util.ConcurrentModificationException;
import java.util.NoSuchElementException;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.Predicate;

/**
 * An ArrayBunch implements TripleBunch with a linear search of a short-ish
 * array of Triples. The array can grow, but it only grows by 4 elements each time
 * (because, if it gets big enough for this linear growth to be bad, it should always
 * have been replaced by a more efficient set-of-triples implementation).
 */
public class ArrayBunch implements TripleBunch {

    private static final int INITIAL_SIZE = 5;

    protected int size = 0;
    protected Triple[] elements;

    public ArrayBunch() {
        elements = new Triple[INITIAL_SIZE];
    }

    /**
     * Copy constructor.
     * The new bunch will contain all the same triples of the bunch to copy.
     * But it will reserve only the space needed to contain them. Growing is still possible.
     *
     * @param bunchToCopy
     */
    private ArrayBunch(final ArrayBunch bunchToCopy) {
        this.elements = new Triple[bunchToCopy.size];
        System.arraycopy(bunchToCopy.elements, 0, this.elements, 0, bunchToCopy.size);
        this.size = bunchToCopy.size;
    }

    @Override
    public boolean containsKey(Triple t) {
        int i = size;
        while (i > 0) if (t.equals(elements[--i])) return true;
        return false;
    }

    @Override
    public boolean anyMatch(Predicate<Triple> predicate) {
        int i = size;
        while (i > 0) if (predicate.test(elements[--i])) return true;
        return false;
    }

    @Override
    public void clear() {
        this.elements = new Triple[INITIAL_SIZE];
        this.size = 0;
    }

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

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

    @Override
    public boolean tryAdd(Triple t) {
        if (this.containsKey(t)) return false;
        if (size == elements.length) grow();
        elements[size++] = t;
        return true;
    }

    @Override
    public void addUnchecked(Triple t) {
        if (size == elements.length) grow();
        elements[size++] = t;
    }

    /**
     * Note: linear growth is suboptimal (order n<sup>2</sup>) normally, but
     * ArrayBunch's are meant for <i>small</i> sets and are replaced by some
     * sort of hash- or tree- set when they get big; currently "big" means more
     * than 9 elements, so that's only one growth spurt anyway.
     */
    protected void grow() {
        final var oldElements = elements;
        elements = new Triple[size + 4];
        System.arraycopy(oldElements, 0, elements, 0, size);
    }

    @Override
    public boolean tryRemove(Triple t) {
        for (int i = 0; i < size; i += 1) {
            if (t.equals(elements[i])) {
                elements[i] = elements[--size];
                return true;
            }
        }
        return false;
    }

    @Override
    public void removeUnchecked(Triple t) {
        for (int i = 0; i < size; i += 1) {
            if (t.equals(elements[i])) {
                elements[i] = elements[--size];
                return;
            }
        }
    }

    @Override
    public ExtendedIterator<Triple> keyIterator() {
        return new NiceIterator<>() {
            private final int initialSize = size;

            private int i = size;

            @Override
            public boolean hasNext() {
                return 0 < i;
            }

            @Override
            public Triple next() {
                if (size != initialSize) throw new ConcurrentModificationException();
                if (i == 0) throw new NoSuchElementException();
                return elements[--i];
            }

            @Override
            public void forEachRemaining(Consumer<? super Triple> action) {
                while (0 < i--) action.accept(elements[i]);
                if (size != initialSize) throw new ConcurrentModificationException();
            }
        };
    }

    @Override
    public Spliterator<Triple> keySpliterator() {
        final var initialSize = size;
        final Runnable checkForConcurrentModification = () -> {
            if (size != initialSize) throw new ConcurrentModificationException();
        };
        return new ArraySpliterator<>(elements, size, checkForConcurrentModification);
    }

    @Override
    public boolean isArray() {
        return true;
    }

    @Override
    public ArrayBunch copy() {
        return new ArrayBunch(this);
    }
}
