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A Protocol for Asynchronous Non-Blocking Data Sequence

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/***************************************************
 * Licensed under MIT No Attribution (SPDX: MIT-0) *
 ***************************************************/

package org.reactivestreams.tck.flow.support;

import java.util.Collections;
import java.util.Iterator;
import java.util.concurrent.Executor;

import org.reactivestreams.example.unicast.AsyncIterablePublisher;

public class HelperPublisher extends AsyncIterablePublisher {
  
    public HelperPublisher(final int from, final int to, final Function create, final Executor executor) {
        super(new Iterable() {
          { if(from > to) throw new IllegalArgumentException("from must be equal or greater than to!"); }
          @Override public Iterator iterator() {
            return new Iterator() {
              private int at = from;
              @Override public boolean hasNext() { return at < to; }
              @Override public T next() {
                if (!hasNext()) return Collections.emptyList().iterator().next();
                else try {
                  return create.apply(at++);
                } catch (Throwable t) {
                  throw new IllegalStateException(String.format("Failed to create element for id %d!", at - 1), t);
                }
              }
              @Override public void remove() { throw new UnsupportedOperationException(); }
            };
          }
        }, executor);
    }
}