# Usage:
#   compile_slang_shaders(
#       TARGET compile_shaders                # custom target name to create
#       SRC_DIR "${CMAKE_SOURCE_DIR}/assets_src/shaders"
#       OUT_DIR "${CMAKE_SOURCE_DIR}/assets_runtime/shaders"
#       # Optional:
#       GLOB_PATTERN "*.slang"                # default: "*.slang"
#       EXTRA_ARGS -O3                        # forwarded to slangc
#       ALL                                   # if present: target is built by default
#   )
#
function(compile_slang_shaders)
    set(options ALL)
    set(oneValueArgs TARGET SRC_DIR OUT_DIR GLOB_PATTERN)
    set(multiValueArgs EXTRA_ARGS)
    cmake_parse_arguments(CSS "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})

    if(NOT CSS_TARGET)
        message(FATAL_ERROR "compile_slang_shaders: TARGET is required")
    endif()
    if(NOT CSS_SRC_DIR)
        message(FATAL_ERROR "compile_slang_shaders: SRC_DIR is required")
    endif()
    if(NOT CSS_OUT_DIR)
        message(FATAL_ERROR "compile_slang_shaders: OUT_DIR is required")
    endif()

    if(NOT CSS_GLOB_PATTERN)
        set(CSS_GLOB_PATTERN "*.slang")
    endif()

    find_program(SLANGC_EXE NAMES slangc slangc.exe REQUIRED)

    # Collect shader sources recursively
    file(GLOB_RECURSE _SLANG_SOURCES
            CONFIGURE_DEPENDS
            "${CSS_SRC_DIR}/${CSS_GLOB_PATTERN}"
    )

    if(_SLANG_SOURCES STREQUAL "")
        message(STATUS "compile_slang_shaders: No sources found in ${CSS_SRC_DIR} (pattern: ${CSS_GLOB_PATTERN})")
    endif()

    # Ensure base output directory exists at configure time (nice-to-have)
    file(MAKE_DIRECTORY "${CSS_OUT_DIR}")

    set(_SPV_OUTPUTS "")

    foreach(_SLANG_FILE IN LISTS _SLANG_SOURCES)
        file(RELATIVE_PATH _REL_PATH "${CSS_SRC_DIR}" "${_SLANG_FILE}")
        get_filename_component(_REL_DIR "${_REL_PATH}" DIRECTORY)
        get_filename_component(_FILE_WE "${_SLANG_FILE}" NAME_WE)

        set(_OUT_SUBDIR "${CSS_OUT_DIR}/${_REL_DIR}")
        set(_OUT_SPV    "${_OUT_SUBDIR}/${_FILE_WE}.spv")

        add_custom_command(
                OUTPUT "${_OUT_SPV}"
                COMMAND "${CMAKE_COMMAND}" -E make_directory "${_OUT_SUBDIR}"
                COMMAND "${SLANGC_EXE}"
                "${_SLANG_FILE}"
                -target spirv
                -o "${_OUT_SPV}"
                ${CSS_EXTRA_ARGS}
                DEPENDS "${_SLANG_FILE}"
                COMMENT "Compiling Slang: ${_REL_PATH} -> ${_OUT_SPV}"
                VERBATIM
        )

        list(APPEND _SPV_OUTPUTS "${_OUT_SPV}")
    endforeach()

    # Create target
    if(CSS_ALL)
        add_custom_target(${CSS_TARGET} ALL DEPENDS ${_SPV_OUTPUTS})
    else()
        add_custom_target(${CSS_TARGET} DEPENDS ${_SPV_OUTPUTS})
    endif()

    # Export outputs to caller if they want them (optional convenience)
    set(${CSS_TARGET}_OUTPUTS "${_SPV_OUTPUTS}" PARENT_SCOPE)
endfunction()