package io.atlassian.fugue.optic.law;
   
   import io.atlassian.fugue.*;
   import io.atlassian.fugue.law.IsEq;
   import io.atlassian.fugue.optic.PTraversal;
   
   import java.util.Collections;
   import java.util.List;
   import java.util.function.Function;
  import java.util.stream.Collectors;
  import java.util.stream.StreamSupport;
  
  import static io.atlassian.fugue.law.IsEq.isEq;
  import static java.util.Spliterator.ORDERED;
  import static java.util.Spliterators.spliteratorUnknownSize;
  import static java.util.stream.Collectors.toList;
  import static java.util.stream.StreamSupport.stream;
  
  public final class TraversalLaws<S, A> {
  
    private final PTraversal<S, S, A, A> traversal;
  
    public TraversalLaws(PTraversal<S, S, A, A> traversal) {
      this.traversal = traversal;
    }
  
    /**
     * get what you set.
     */
    public IsEq<List<A>> setGetAll(S s, A a) {
      return isEq(stream(traversal.getAll(traversal.set(a).apply(s)).spliterator(), false).collect(Collectors.toList()),
        stream(Iterables.map(traversal.getAll(s), __ -> a).spliterator(), false).collect(Collectors.toList()));
    }
  
    /**
     * set idempotent
     */
    public IsEq<S> setIdempotent(S s, A a) {
      return isEq(traversal.set(a).apply(traversal.set(a).apply(s)), traversal.set(a).apply(s));
    }
  
    /**
     * modify id = id
     */
    public IsEq<S> modifyIdentity(S s) {
      return isEq(traversal.modify(Function.<A> identity()).apply(s), s);
    }
  
    /**
     * modifyF Applicative.point(_) = Applicative.point(_)
     */
    public IsEq<S> modifySupplierFPoint(S s) {
      return isEq(traversal.modifySupplierF(Suppliers::ofInstance).apply(s).get(), s);
    }
  
    /**
     * modifyF Applicative.point(_) = Applicative.point(_)
     */
    public IsEq<Either<String, S>> modifyEitherFPoint(S s) {
      return isEq(traversal.<String> modifyEitherF(Eithers.toRight()).apply(s), Either.right(s));
    }
  
    /**
     * modifyF Applicative.point(_) = Applicative.point(_)
     */
    public IsEq<Option<S>> modifyOptionFPoint(S s) {
      return isEq(traversal.modifyOptionF(Options.toOption()).apply(s), Option.some(s));
    }
  
    /**
     * modifyF Applicative.point(_) = Applicative.point(_)
     */
    public IsEq<Pair<S, S>> modifyPairFPoint(S s) {
      return isEq(traversal.modifyPairF(a -> Pair.pair(a, a)).apply(s), Pair.pair(s, s));
    }
  
    /**
     * modifyF Applicative.point(_) = Applicative.point(_)
     */
    public IsEq<S> modifyFunctionFPoint(S s) {
      return isEq(traversal.<String> modifyFunctionF(a -> __ -> a).apply(s).apply(""), s);
    }
  
    /**
     * modifyF Applicative.point(_) = Applicative.point(_)
     */
    public IsEq<List<S>> modifyIterableFPoint(S s) {
      return isEq(
        stream(spliteratorUnknownSize(traversal.modifyIterableF(Collections::singleton).apply(s).iterator(), ORDERED), false).collect(toList()),
        Collections.singletonList(s));
    }
  
    /**
     * headOption returns the first element of getAll
     */
    public IsEq<Option<A>> headOption(S s) {
      return isEq(traversal.headOption(s), Iterables.first(traversal.getAll(s)));
    }
  
 }