include(CheckFunctionExists)

# First check whether the system has kqueue built-in. Prefer that over everything else.
check_function_exists(kqueue HAVE_KQUEUE)

if (NOT HAVE_KQUEUE)

    # If the user passed in a path for libkqueue, see if we can find a copy of it there.
    # If they didn't pass one, build our local copy of it.
    if (LIBKQUEUE_ROOT_DIR)

        find_path(LIBKQUEUE_ROOT_DIR NAMES "include/sys/event.h")

        # Prefer linking statically but look for a shared library version too.
        find_library(
            LIBKQUEUE_LIBRARIES NAMES "libkqueue${CMAKE_STATIC_LIBRARY_SUFFIX}"
                                      "libkqueue${CMAKE_SHARED_LIBRARY_SUFFIX}"
            HINTS ${LIBKQUEUE_ROOT_DIR}/lib)

        find_path(LIBKQUEUE_INCLUDE_DIRS NAMES "sys/event.h"
                  HINTS ${LIBKQUEUE_ROOT_DIR}/include/kqueue)

        include(FindPackageHandleStandardArgs)
        find_package_handle_standard_args(LIBKQUEUE DEFAULT_MSG LIBKQUEUE_LIBRARIES
                                          LIBKQUEUE_INCLUDE_DIRS)

        mark_as_advanced(LIBKQUEUE_ROOT_DIR LIBKQUEUE_LIBRARIES LIBKQUEUE_INCLUDE_DIRS)

        set(HAVE_KQUEUE true)
    else ()

        set(kqueue_build "${CMAKE_CURRENT_BINARY_DIR}/libkqueue-build")
        set(kqueue_src "${CMAKE_CURRENT_SOURCE_DIR}/auxil/libkqueue")
        set(kqueue_ep "${CMAKE_CURRENT_BINARY_DIR}/libkqueue-ep")

        if (MSVC)
            set(LIBKQUEUE_NAME "kqueue_static")
            set(WIN_CONFIG -DCMAKE_POLICY_DEFAULT_CMP0091=NEW
                           -DCMAKE_MSVC_RUNTIME_LIBRARY=${CMAKE_MSVC_RUNTIME_LIBRARY})
            set(kqueue_static_lib
                "${kqueue_build}/kqueueStatic/${LIBKQUEUE_NAME}${CMAKE_STATIC_LIBRARY_SUFFIX}")
        else ()
            set(LIBKQUEUE_NAME "libkqueue")
            set(kqueue_static_lib "${kqueue_build}/${LIBKQUEUE_NAME}${CMAKE_STATIC_LIBRARY_SUFFIX}")
        endif ()

        include(ExternalProject)

        if (${CMAKE_VERSION} VERSION_LESS "3.2.0")
            # Build byproducts is just required by the Ninja generator
            # though it's not available before CMake 3.2 ...
            if (${CMAKE_GENERATOR} STREQUAL Ninja)
                message(FATAL_ERROR "Ninja generator requires CMake >= 3.2")
            endif ()

            set(build_byproducts_arg)
        else ()
            set(build_byproducts_arg BUILD_BYPRODUCTS ${kqueue_static_lib})
        endif ()

        ExternalProject_Add(
            project_kqueue
            PREFIX "${kqueue_ep}"
            BINARY_DIR "${kqueue_build}"
            DOWNLOAD_COMMAND ""
            CONFIGURE_COMMAND ""
            BUILD_COMMAND ""
            INSTALL_COMMAND "" ${build_byproducts_arg})

        if (${CMAKE_VERSION} VERSION_LESS "3.4.0")
            set(use_terminal_arg)
        else ()
            set(use_terminal_arg USES_TERMINAL 1)
        endif ()

        ExternalProject_Add_Step(
            project_kqueue project_kqueue_build_step
            COMMAND ${CMAKE_MAKE_PROGRAM}
            COMMENT "Building libkqueue"
            WORKING_DIRECTORY ${kqueue_build}
            ALWAYS 1
            ${use_terminal_arg})

        if (CMAKE_TOOLCHAIN_FILE)
            set(toolchain_arg -DCMAKE_TOOLCHAIN_FILE=${CMAKE_TOOLCHAIN_FILE})
        else ()
            set(toolchain_arg)
        endif ()

        if (CMAKE_C_COMPILER_LAUNCHER)
            set(cmake_c_compiler_launcher_arg
                -DCMAKE_C_COMPILER_LAUNCHER:path=${CMAKE_C_COMPILER_LAUNCHER})
        else ()
            set(cmake_c_compiler_launcher_arg)
        endif ()

        if (CMAKE_CXX_COMPILER_LAUNCHER)
            set(cmake_cxx_compiler_launcher_arg
                -DCMAKE_CXX_COMPILER_LAUNCHER:path=${CMAKE_CXX_COMPILER_LAUNCHER})
        else ()
            set(cmake_cxx_compiler_launcher_arg)
        endif ()

        execute_process(
            COMMAND
                ${CMAKE_COMMAND} -G${CMAKE_GENERATOR} ${toolchain_arg}
                ${cmake_c_compiler_launcher_arg} ${cmake_cxx_compiler_launcher_arg}
                -DCMAKE_BUILD_TYPE:string=${CMAKE_BUILD_TYPE} ${WIN_CONFIG} ${kqueue_src}
            WORKING_DIRECTORY ${kqueue_build}
            RESULT_VARIABLE kqueue_cmake_result
            ERROR_VARIABLE KQUEUE_CMAKE_OUTPUT
            OUTPUT_VARIABLE KQUEUE_CMAKE_OUTPUT
            ERROR_STRIP_TRAILING_WHITESPACE OUTPUT_STRIP_TRAILING_WHITESPACE)

        message("\n********** Begin libkqueue External Project CMake Output ************")
        message("\n${KQUEUE_CMAKE_OUTPUT}")
        message("\n*********** End libkqueue External Project CMake Output *************")
        message("\n")

        if (kqueue_cmake_result)
            message(FATAL_ERROR "libkqueue CMake configuration failed")
        endif ()

        add_library(libkqueue_a STATIC IMPORTED)
        set_property(TARGET libkqueue_a PROPERTY IMPORTED_LOCATION ${kqueue_static_lib})
        add_dependencies(libkqueue_a project_kqueue)

        set(HAVE_KQUEUE true)
        set(LIBKQUEUE_LIBRARIES libkqueue_a CACHE STRING "libkqueue libs" FORCE)
        set(LIBKQUEUE_INCLUDE_DIRS "${kqueue_src}/include;${kqueue_build}/include"
            CACHE INTERNAL "libkqueue includes" FORCE)
    endif ()
endif ()

if (NOT HAVE_KQUEUE)
    message(FATAL_ERROR "Failed to find a working version of kqueue.")
endif ()