package org.davidmoten.kool.internal.operators.stream;
   
   import java.util.Optional;
   
   import org.davidmoten.kool.Maybe;
   import org.davidmoten.kool.StreamIterable;
   import org.davidmoten.kool.StreamIterator;
   import org.davidmoten.kool.function.BiFunction;
   
  import com.github.davidmoten.guavamini.Preconditions;
  
  public final class ReduceNoInitialValue<T> implements Maybe<T> {
  
      private final BiFunction<? super T, ? super T, ? extends T> reducer;
      private final StreamIterable<T> source;
  
      public ReduceNoInitialValue(BiFunction<? super T, ? super T, ? extends T> reducer, StreamIterable<T> source) {
          this.reducer = reducer;
          this.source = source;
      }
  
      @Override
      public Optional<T> get() {
          StreamIterator<T> it = source.iteratorNullChecked();
          T a, b;
          if (it.hasNext()) {
              a = it.nextNullChecked();
          } else {
              return Optional.empty();
          }
          if (it.hasNext()) {
              b = it.nextNullChecked();
          } else {
              return Optional.empty();
          }
          T v = reducer.applyUnchecked(a, b);
          while (it.hasNext()) {
              v = Preconditions.checkNotNull(reducer.applyUnchecked(v, it.nextNullChecked()));
          }
          return Optional.of(v);
      }
  
  }