package org.davidmoten.kool.internal.operators.maybe;
   
   import java.util.Optional;
   
   import org.davidmoten.kool.Maybe;
   import org.davidmoten.kool.function.Function;
   
   import com.github.davidmoten.guavamini.Preconditions;
   
  public final class MaybeFlatMapMaybe<T, R> implements Maybe<R> {
  
      private final Maybe<T> maybe;
      private final Function<? super T, ? extends Maybe<? extends R>> mapper;
  
      public MaybeFlatMapMaybe(Maybe<T> maybe, Function<? super T, ? extends Maybe<? extends R>> mapper) {
          this.maybe = maybe;
          this.mapper = mapper;
      }
  
      @SuppressWarnings("unchecked")
      @Override
      public Optional<R> get() {
          Optional<T> v = maybe.get();
          if (v.isPresent()) {
              return (Optional<R>) Preconditions.checkNotNull(mapper.applyUnchecked(v.get()), "mapper cannot return null").get();
          } else {
              return Optional.empty();
          }
      }
  
  }