#  Copyright (c) 2024 Isidoros Tsaousis-Seiras
#
#  SPDX-License-Identifier: BSL-1.0
#  Distributed under the Boost Software License, Version 1.0. (See accompanying
#  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

if(HPX_WITH_STDEXEC AND NOT HPX_WITH_CXX20_STD_IDENTITY)
  hpx_error("HPX_WITH_STDEXEC Requires std::identity.")
endif()

if(STDEXEC_ROOT AND NOT Stdexec_ROOT)
  set(Stdexec_ROOT ${STDEXEC_ROOT})
  # remove STDEXEC_ROOT from the cache
  unset(STDEXEC_ROOT CACHE)
endif()

if(HPX_WITH_STDEXEC)
  # prefer HPX_WITH_FETCH_STDEXEC by default
  if(Stdexec_ROOT AND HPX_WITH_FETCH_STDEXEC)
    hpx_warn(
      "Both Stdexec_ROOT and HPX_WITH_FETCH_STDEXEC are provided. HPX_WITH_FETCH_STDEXEC will take precedence."
    )
  endif()

  hpx_add_config_define(HPX_HAVE_STDEXEC)

  if(HPX_WITH_FETCH_STDEXEC)
    hpx_info(
      "HPX_WITH_FETCH_STDEXEC=${HPX_WITH_FETCH_STDEXEC}, Stdexec will be fetched using CMake's FetchContent and installed alongside HPX (HPX_WITH_STDEXEC_TAG=${HPX_WITH_STDEXEC_TAG})"
    )
    if(UNIX)
      include(FetchContent)
      fetchcontent_declare(
        Stdexec
        GIT_REPOSITORY https://github.com/NVIDIA/stdexec.git
        GIT_TAG ${HPX_WITH_STDEXEC_TAG}
      )

      fetchcontent_getproperties(Stdexec)
      if(NOT Stdexec_POPULATED)
        fetchcontent_populate(Stdexec)
      endif()
      set(Stdexec_ROOT ${stdexec_SOURCE_DIR})

      add_library(Stdexec INTERFACE)
      target_include_directories(
        Stdexec INTERFACE $<BUILD_INTERFACE:${stdexec_SOURCE_DIR}/include>
                          $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
      )

      install(
        TARGETS Stdexec
        EXPORT HPXStdexecTarget
        COMPONENT core
      )

      install(
        DIRECTORY ${Stdexec_ROOT}/include/
        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
        COMPONENT core
        FILES_MATCHING
        PATTERN "*.hpp"
      )

      export(
        TARGETS Stdexec
        NAMESPACE Stdexec::
        FILE "${CMAKE_CURRENT_BINARY_DIR}/lib/cmake/${HPX_PACKAGE_NAME}/HPXStdexecTarget.cmake"
      )

      install(
        EXPORT HPXStdexecTarget
        NAMESPACE Stdexec::
        FILE HPXStdexecTarget.cmake
        DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/${HPX_PACKAGE_NAME}
        COMPONENT cmake
      )

      # TODO: Enforce a single spelling
      add_library(Stdexec::Stdexec ALIAS Stdexec)
      add_library(STDEXEC::stdexec ALIAS Stdexec)

    endif()

  else()
    find_package(Stdexec REQUIRED)

    if(Stdexec_FOUND)
      hpx_add_config_define(HPX_HAVE_STDEXEC)
    else()
      hpx_error(
        "Stdexec could not be found, please specify Stdexec_ROOT to point to the correct location or enable HPX_WITH_FETCH_STDEXEC"
      )
    endif()
  endif()
endif()