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/*
 * Copyright (C) Posten Norge AS
 *
 * 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 no.digipost.collection;

import java.util.Iterator;
import java.util.function.Predicate;
import java.util.function.Supplier;

public class BatchedIterable> implements Iterable {

    private Supplier batchFetcher;
    private Predicate canFetchNextBatch;


    public static > Iterable batched(Supplier batchFetcher, Predicate fetchNextBatch) {
        return new BatchedIterable<>(batchFetcher, fetchNextBatch);
    }

    private BatchedIterable(Supplier batchFetcher, Predicate fetchNextBatch) {
        this.batchFetcher = batchFetcher;
        this.canFetchNextBatch = fetchNextBatch;
    }


    @Override
    public Iterator iterator() {
        return new Iterator() {
            BATCH currentBatch = batchFetcher.get();
            Iterator currentIterator = currentBatch.iterator();

            @Override
            public boolean hasNext() {
                if (currentIterator.hasNext()) return true;
                if (canFetchNextBatch.test(currentBatch)) {
                    currentBatch = batchFetcher.get();
                    currentIterator = currentBatch.iterator();
                    return currentIterator.hasNext();
                }
                return false;
            }

            @Override
            public T next() {
                return currentIterator.next();
            }
        };
    }

}