/*
 * Copyright 2022 Red Hat, Inc. and/or its affiliates.
 *
 * 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.
 */
package org.drools.ruleunits.impl.datasources;

import java.util.Iterator;

import org.drools.ruleunits.api.DataProcessor;
import org.drools.ruleunits.api.DataStream;

public class BufferedDataStream<T> extends AbstractDataSource<T> implements DataStream<T> {

    private final LimitedBufferedList<T> list;

    protected BufferedDataStream(int size) {
        this.list = new LimitedBufferedList<>(size);
    }

    @Override
    public void append(T value) {
        list.add(value);
        forEachSubscriber(s -> s.insert(value));
    }

    @Override
    public void subscribe(DataProcessor<T> subscriber) {
        super.subscribe(subscriber);
        list.forEach(subscriber::insert);
    }

    private static class LimitedBufferedList<T> implements Iterable<T> {
        private final T[] array;

        private int head = 0;

        LimitedBufferedList(int size) {
            this.array = (T[]) new Object[size];
        }

        void add(T value) {
            array[head++ % array.length] = value;
        }

        int size() {
            return Math.min(head, array.length);
        }

        @Override
        public Iterator<T> iterator() {
            return new BufferedIterator();
        }

        private class BufferedIterator implements Iterator<T> {

            private int cursor = 0;

            @Override
            public boolean hasNext() {
                return cursor < size();
            }

            @Override
            public T next() {
                return head < array.length ? array[cursor++] : array[(head + cursor++) % array.length];
            }
        }
    }
}
