//@HEADER
// ************************************************************************
//
//                        Kokkos v. 4.0
//       Copyright (2022) National Technology & Engineering
//               Solutions of Sandia, LLC (NTESS).
//
// Under the terms of Contract DE-NA0003525 with NTESS,
// the U.S. Government retains certain rights in this software.
//
// Part of Kokkos, under the Apache License v2.0 with LLVM Exceptions.
// See https://kokkos.org/LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//@HEADER

#ifndef KOKKOS_IMPL_PUBLIC_INCLUDE
#include <Kokkos_Macros.hpp>
static_assert(false,
              "Including non-public Kokkos header files is not allowed.");
#endif
#ifndef KOKKOS_KOKKOS_GRAPHNODE_HPP
#define KOKKOS_KOKKOS_GRAPHNODE_HPP

#include <Kokkos_Macros.hpp>

#include <impl/Kokkos_Error.hpp>  // contract macros

#include <Kokkos_Core_fwd.hpp>
#include <Kokkos_Graph_fwd.hpp>
#include <impl/Kokkos_GraphImpl_fwd.hpp>
#include <Kokkos_Parallel_Reduce.hpp>
#include <impl/Kokkos_GraphImpl_Utilities.hpp>
#include <impl/Kokkos_GraphImpl.hpp>  // GraphAccess

#include <memory>  // std::shared_ptr

namespace Kokkos {
namespace Experimental {

template <class ExecutionSpace, class Kernel /*= TypeErasedTag*/,
          class Predecessor /*= TypeErasedTag*/>
class GraphNodeRef {
  //----------------------------------------------------------------------------
  // <editor-fold desc="template parameter constraints"> {{{2

  // Note: because of these assertions, instantiating this class template is not
  //       intended to be SFINAE-safe, so do validation before you instantiate.

  static_assert(
      std::is_same<Predecessor, TypeErasedTag>::value ||
          Kokkos::Impl::is_specialization_of<Predecessor, GraphNodeRef>::value,
      "Invalid predecessor template parameter given to GraphNodeRef");

  static_assert(
      Kokkos::is_execution_space<ExecutionSpace>::value,
      "Invalid execution space template parameter given to GraphNodeRef");

  static_assert(std::is_same<Predecessor, TypeErasedTag>::value ||
                    Kokkos::Impl::is_graph_kernel<Kernel>::value,
                "Invalid kernel template parameter given to GraphNodeRef");

  static_assert(!Kokkos::Impl::is_more_type_erased<Kernel, Predecessor>::value,
                "The kernel of a graph node can't be more type-erased than the "
                "predecessor");

  // </editor-fold> end template parameter constraints }}}2
  //----------------------------------------------------------------------------

 public:
  //----------------------------------------------------------------------------
  // <editor-fold desc="public member types"> {{{2

  using execution_space   = ExecutionSpace;
  using graph_kernel      = Kernel;
  using graph_predecessor = Predecessor;

  // </editor-fold> end public member types }}}2
  //----------------------------------------------------------------------------

 private:
  //----------------------------------------------------------------------------
  // <editor-fold desc="Friends"> {{{2

  template <class, class, class>
  friend class GraphNodeRef;
  friend struct Kokkos::Impl::GraphAccess;

  // </editor-fold> end Friends }}}2
  //----------------------------------------------------------------------------

  //----------------------------------------------------------------------------
  // <editor-fold desc="Private Data Members"> {{{2

  using graph_impl_t = Kokkos::Impl::GraphImpl<ExecutionSpace>;
  std::weak_ptr<graph_impl_t> m_graph_impl;

  // TODO @graphs figure out if we can get away with a weak reference here?
  //              GraphNodeRef instances shouldn't be stored by users outside
  //              of the create_graph closure, and so if we restructure things
  //              slightly, we could make it so that the graph owns the
  //              node_impl_t instance and this only holds a std::weak_ptr to
  //              it.
  using node_impl_t =
      Kokkos::Impl::GraphNodeImpl<ExecutionSpace, Kernel, Predecessor>;
  std::shared_ptr<node_impl_t> m_node_impl;

  // </editor-fold> end Private Data Members }}}2
  //----------------------------------------------------------------------------

  //----------------------------------------------------------------------------
  // <editor-fold desc="Implementation detail accessors"> {{{2

  // Internally, use shallow constness
  node_impl_t& get_node_impl() const { return *m_node_impl.get(); }
  std::shared_ptr<node_impl_t> const& get_node_ptr() const& {
    return m_node_impl;
  }
  std::shared_ptr<node_impl_t> get_node_ptr() && {
    return std::move(m_node_impl);
  }
  std::weak_ptr<graph_impl_t> get_graph_weak_ptr() const {
    return m_graph_impl;
  }

  // </editor-fold> end Implementation detail accessors }}}2
  //----------------------------------------------------------------------------

  // TODO kernel name propagation and exposure

  template <class NextKernelDeduced>
  auto _then_kernel(NextKernelDeduced&& arg_kernel) const {
    // readability note:
    //   std::remove_cvref_t<NextKernelDeduced> is a specialization of
    //   Kokkos::Impl::GraphNodeKernelImpl:
    static_assert(Kokkos::Impl::is_specialization_of<
                      Kokkos::Impl::remove_cvref_t<NextKernelDeduced>,
                      Kokkos::Impl::GraphNodeKernelImpl>::value,
                  "Kokkos internal error");

    auto graph_ptr = m_graph_impl.lock();
    KOKKOS_EXPECTS(bool(graph_ptr))

    using next_kernel_t = Kokkos::Impl::remove_cvref_t<NextKernelDeduced>;

    using return_t = GraphNodeRef<ExecutionSpace, next_kernel_t, GraphNodeRef>;

    auto rv = Kokkos::Impl::GraphAccess::make_graph_node_ref(
        m_graph_impl,
        Kokkos::Impl::GraphAccess::make_node_shared_ptr<
            typename return_t::node_impl_t>(
            m_node_impl->execution_space_instance(),
            Kokkos::Impl::_graph_node_kernel_ctor_tag{},
            (NextKernelDeduced &&) arg_kernel,
            // *this is the predecessor
            Kokkos::Impl::_graph_node_predecessor_ctor_tag{}, *this));

    // Add the node itself to the backend's graph data structure, now that
    // everything is set up.
    graph_ptr->add_node(rv.m_node_impl);
    // Add the predecessaor we stored in the constructor above in the backend's
    // data structure, now that everything is set up.
    graph_ptr->add_predecessor(rv.m_node_impl, *this);
    KOKKOS_ENSURES(bool(rv.m_node_impl))
    return rv;
  }

  //----------------------------------------------------------------------------
  // <editor-fold desc="Private constructors"> {{{2

  GraphNodeRef(std::weak_ptr<graph_impl_t> arg_graph_impl,
               std::shared_ptr<node_impl_t> arg_node_impl)
      : m_graph_impl(std::move(arg_graph_impl)),
        m_node_impl(std::move(arg_node_impl)) {}

  // </editor-fold> end Private constructors }}}2
  //----------------------------------------------------------------------------

 public:
  //----------------------------------------------------------------------------
  // <editor-fold desc="Constructors, destructors, and assignment"> {{{2

  //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  // <editor-fold desc="rule of 6 ctors"> {{{3

  // Copyable and movable (basically just shared_ptr semantics
  GraphNodeRef() noexcept               = default;
  GraphNodeRef(GraphNodeRef const&)     = default;
  GraphNodeRef(GraphNodeRef&&) noexcept = default;
  GraphNodeRef& operator=(GraphNodeRef const&) = default;
  GraphNodeRef& operator=(GraphNodeRef&&) noexcept = default;
  ~GraphNodeRef()                                  = default;

  // </editor-fold> end rule of 6 ctors }}}3
  //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

  //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
  // <editor-fold desc="Type-erasing converting ctor and assignment"> {{{3

  template <
      class OtherKernel, class OtherPredecessor,
      std::enable_if_t<
          // Not a copy/move constructor
          !std::is_same<GraphNodeRef, GraphNodeRef<execution_space, OtherKernel,
                                                   OtherPredecessor>>::value &&
              // must be an allowed type erasure of the kernel
              Kokkos::Impl::is_compatible_type_erasure<OtherKernel,
                                                       graph_kernel>::value &&
              // must be an allowed type erasure of the predecessor
              Kokkos::Impl::is_compatible_type_erasure<
                  OtherPredecessor, graph_predecessor>::value,
          int> = 0>
  /* implicit */
  GraphNodeRef(
      GraphNodeRef<execution_space, OtherKernel, OtherPredecessor> const& other)
      : m_graph_impl(other.m_graph_impl), m_node_impl(other.m_node_impl) {}

  // Note: because this is an implicit conversion (as is supposed to be the
  //       case with most type-erasing wrappers like this), we don't also need
  //       a converting assignment operator.

  // </editor-fold> end Type-erasing converting ctor and assignment }}}3
  //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

  // </editor-fold> end Constructors, destructors, and assignment }}}2
  //----------------------------------------------------------------------------

  //----------------------------------------------------------------------------
  // <editor-fold desc="then_parallel_for"> {{{2

  template <
      class Policy, class Functor,
      std::enable_if_t<
          // equivalent to:
          //   requires Kokkos::ExecutionPolicy<remove_cvref_t<Policy>>
          is_execution_policy<Kokkos::Impl::remove_cvref_t<Policy>>::value,
          // --------------------
          int> = 0>
  auto then_parallel_for(std::string arg_name, Policy&& arg_policy,
                         Functor&& functor) const {
    //----------------------------------------
    KOKKOS_EXPECTS(!m_graph_impl.expired())
    KOKKOS_EXPECTS(bool(m_node_impl))
    // TODO @graph restore this expectation once we add comparability to space
    //      instances
    // KOKKOS_EXPECTS(
    //   arg_policy.space() == m_graph_impl->get_execution_space());

    // needs to static assert constraint: DataParallelFunctor<Functor>

    using policy_t = Kokkos::Impl::remove_cvref_t<Policy>;
    // constraint check: same execution space type (or defaulted, maybe?)
    static_assert(
        std::is_same<typename policy_t::execution_space,
                     execution_space>::value,
        // TODO @graph make defaulted execution space work
        //|| policy_t::execution_space_is_defaulted,
        "Execution Space mismatch between execution policy and graph");

    auto policy = Experimental::require((Policy &&) arg_policy,
                                        Kokkos::Impl::KernelInGraphProperty{});

    using next_policy_t = decltype(policy);
    using next_kernel_t =
        Kokkos::Impl::GraphNodeKernelImpl<ExecutionSpace, next_policy_t,
                                          std::decay_t<Functor>,
                                          Kokkos::ParallelForTag>;
    return this->_then_kernel(next_kernel_t{std::move(arg_name), policy.space(),
                                            (Functor &&) functor,
                                            (Policy &&) policy});
  }

  template <
      class Policy, class Functor,
      std::enable_if_t<
          // equivalent to:
          //   requires Kokkos::ExecutionPolicy<remove_cvref_t<Policy>>
          is_execution_policy<Kokkos::Impl::remove_cvref_t<Policy>>::value,
          // --------------------
          int> = 0>
  auto then_parallel_for(Policy&& policy, Functor&& functor) const {
    // needs to static assert constraint: DataParallelFunctor<Functor>
    return this->then_parallel_for("", (Policy &&) policy,
                                   (Functor &&) functor);
  }

  template <class Functor>
  auto then_parallel_for(std::string name, std::size_t n,
                         Functor&& functor) const {
    // needs to static assert constraint: DataParallelFunctor<Functor>
    return this->then_parallel_for(std::move(name),
                                   Kokkos::RangePolicy<execution_space>(0, n),
                                   (Functor &&) functor);
  }

  template <class Functor>
  auto then_parallel_for(std::size_t n, Functor&& functor) const {
    // needs to static assert constraint: DataParallelFunctor<Functor>
    return this->then_parallel_for("", n, (Functor &&) functor);
  }

  // </editor-fold> end then_parallel_for }}}2
  //----------------------------------------------------------------------------

  //----------------------------------------------------------------------------
  // <editor-fold desc="then_parallel_reduce"> {{{2

  template <
      class Policy, class Functor, class ReturnType,
      std::enable_if_t<
          // equivalent to:
          //   requires Kokkos::ExecutionPolicy<remove_cvref_t<Policy>>
          is_execution_policy<Kokkos::Impl::remove_cvref_t<Policy>>::value,
          // --------------------
          int> = 0>
  auto then_parallel_reduce(std::string arg_name, Policy&& arg_policy,
                            Functor&& functor,
                            ReturnType&& return_value) const {
    auto graph_impl_ptr = m_graph_impl.lock();
    KOKKOS_EXPECTS(bool(graph_impl_ptr))
    KOKKOS_EXPECTS(bool(m_node_impl))
    // TODO @graph restore this expectation once we add comparability to space
    //      instances
    // KOKKOS_EXPECTS(
    //   arg_policy.space() == m_graph_impl->get_execution_space());

    // needs static assertion of constraint:
    //   DataParallelReductionFunctor<Functor, ReturnType>

    using policy_t = std::remove_cv_t<std::remove_reference_t<Policy>>;
    static_assert(
        std::is_same<typename policy_t::execution_space,
                     execution_space>::value,
        // TODO @graph make defaulted execution space work
        // || policy_t::execution_space_is_defaulted,
        "Execution Space mismatch between execution policy and graph");

    // This is also just an expectation, but it's one that we expect the user
    // to interact with (even in release mode), so we should throw an exception
    // with an explanation rather than just doing a contract assertion.
    // We can't static_assert this because of the way that Reducers store
    // whether or not they point to a View as a runtime boolean rather than part
    // of the type.
    if (Kokkos::Impl::parallel_reduce_needs_fence(
            graph_impl_ptr->get_execution_space(), return_value)) {
      Kokkos::Impl::throw_runtime_exception(
          "Parallel reductions in graphs can't operate on Reducers that "
          "reference a scalar because they can't complete synchronously. Use a "
          "Kokkos::View instead and keep in mind the result will only be "
          "available once the graph is submitted (or in tasks that depend on "
          "this one).");
    }

    //----------------------------------------
    // This is a disaster, but I guess it's not a my disaster to fix right now
    using return_type_remove_cvref =
        std::remove_cv_t<std::remove_reference_t<ReturnType>>;
    static_assert(Kokkos::is_view<return_type_remove_cvref>::value ||
                      Kokkos::is_reducer<return_type_remove_cvref>::value,
                  "Output argument to parallel reduce in a graph must be a "
                  "View or a Reducer");
    using return_type =
        // Yes, you do really have to do this...
        std::conditional_t<Kokkos::is_reducer<return_type_remove_cvref>::value,
                           return_type_remove_cvref,
                           const return_type_remove_cvref>;
    using functor_type = Kokkos::Impl::remove_cvref_t<Functor>;
    // see Kokkos_Parallel_Reduce.hpp for how these details are used there;
    // we're just doing the same thing here
    using return_value_adapter =
        Kokkos::Impl::ParallelReduceReturnValue<void, return_type,
                                                functor_type>;
    // End of Kokkos reducer disaster
    //----------------------------------------

    auto policy = Experimental::require((Policy &&) arg_policy,
                                        Kokkos::Impl::KernelInGraphProperty{});

    using passed_reducer_type = typename return_value_adapter::reducer_type;

    using reducer_selector = Kokkos::Impl::if_c<
        std::is_same<InvalidType, passed_reducer_type>::value, functor_type,
        passed_reducer_type>;
    using analysis = Kokkos::Impl::FunctorAnalysis<
        Kokkos::Impl::FunctorPatternInterface::REDUCE, Policy,
        typename reducer_selector::type,
        typename return_value_adapter::value_type>;
    typename analysis::Reducer final_reducer(
        reducer_selector::select(functor, return_value));
    Kokkos::Impl::CombinedFunctorReducer<functor_type,
                                         typename analysis::Reducer>
        functor_reducer(functor, final_reducer);

    using next_policy_t = decltype(policy);
    using next_kernel_t =
        Kokkos::Impl::GraphNodeKernelImpl<ExecutionSpace, next_policy_t,
                                          decltype(functor_reducer),
                                          Kokkos::ParallelReduceTag>;

    return this->_then_kernel(next_kernel_t{
        std::move(arg_name), graph_impl_ptr->get_execution_space(),
        functor_reducer, (Policy &&) policy,
        return_value_adapter::return_value(return_value, functor)});
  }

  template <
      class Policy, class Functor, class ReturnType,
      std::enable_if_t<
          // equivalent to:
          //   requires Kokkos::ExecutionPolicy<remove_cvref_t<Policy>>
          is_execution_policy<Kokkos::Impl::remove_cvref_t<Policy>>::value,
          // --------------------
          int> = 0>
  auto then_parallel_reduce(Policy&& arg_policy, Functor&& functor,
                            ReturnType&& return_value) const {
    return this->then_parallel_reduce("", (Policy &&) arg_policy,
                                      (Functor &&) functor,
                                      (ReturnType &&) return_value);
  }

  template <class Functor, class ReturnType>
  auto then_parallel_reduce(std::string label,
                            typename execution_space::size_type idx_end,
                            Functor&& functor,
                            ReturnType&& return_value) const {
    return this->then_parallel_reduce(
        std::move(label), Kokkos::RangePolicy<execution_space>{0, idx_end},
        (Functor &&) functor, (ReturnType &&) return_value);
  }

  template <class Functor, class ReturnType>
  auto then_parallel_reduce(typename execution_space::size_type idx_end,
                            Functor&& functor,
                            ReturnType&& return_value) const {
    return this->then_parallel_reduce("", idx_end, (Functor &&) functor,
                                      (ReturnType &&) return_value);
  }

  // </editor-fold> end then_parallel_reduce }}}2
  //----------------------------------------------------------------------------

  // TODO @graph parallel scan, deep copy, etc.
};

}  // end namespace Experimental
}  // end namespace Kokkos

#endif  // KOKKOS_KOKKOS_GRAPHNODE_HPP