# cmake/MetalShaderCompile.cmake — Compile Metal shaders to metallib
#
# Usage:
#   include(cmake/MetalShaderCompile.cmake)
#   turboquant_add_metal_shader(TARGET shader_target SOURCE ggml-metal-turbo.metal)
#
# On non-macOS platforms, this is a no-op (shader is installed as source).
# If Metal toolchain is not installed, shader compilation is skipped gracefully.

function(turboquant_add_metal_shader)
    cmake_parse_arguments(ARGS "" "TARGET;SOURCE;OUTPUT" "" ${ARGN})

    if(NOT APPLE)
        # On non-Apple platforms, just ensure the .metal file is included
        # in install targets. Runtime compilation is not available.
        message(STATUS "Metal shader compilation skipped (not on Apple platform)")
        return()
    endif()

    find_program(XCRUN_EXECUTABLE xcrun)
    if(NOT XCRUN_EXECUTABLE)
        message(WARNING "xcrun not found — Metal shader compilation disabled")
        return()
    endif()

    # Check if Metal toolchain is actually installed
    execute_process(
        COMMAND "${XCRUN_EXECUTABLE}" -sdk macosx metal --version
        OUTPUT_VARIABLE METAL_VERSION
        ERROR_VARIABLE METAL_VERSION_ERR
        RESULT_VARIABLE METAL_VERSION_RESULT
        TIMEOUT 10
    )
    if(NOT METAL_VERSION_RESULT EQUAL 0)
        message(WARNING "Metal toolchain not installed (xcrun metal failed) — shader compilation disabled")
        message(STATUS "  Install with: xcodebuild -downloadComponent MetalToolchain")
        return()
    endif()

    set(METAL_SOURCE "${CMAKE_CURRENT_SOURCE_DIR}/${ARGS_SOURCE}")
    set(METAL_AIR "${CMAKE_CURRENT_BINARY_DIR}/ggml-metal-turbo.air")
    set(METAL_LIB "${CMAKE_CURRENT_BINARY_DIR}/ggml-metal-turbo.metallib")

    if(ARGS_OUTPUT)
        set(METAL_LIB "${ARGS_OUTPUT}")
    endif()

    # Step 1: Compile .metal → .air (Metal intermediate)
    add_custom_command(
        OUTPUT "${METAL_AIR}"
        COMMAND "${XCRUN_EXECUTABLE}" -sdk macosx metal
            -c "${METAL_SOURCE}"
            -o "${METAL_AIR}"
            -std=metal2.4
            -O2
        DEPENDS "${METAL_SOURCE}"
        COMMENT "Compiling Metal shader: ${ARGS_SOURCE}"
        VERBATIM
    )

    # Step 2: Link .air → .metallib (Metal library)
    add_custom_command(
        OUTPUT "${METAL_LIB}"
        COMMAND "${XCRUN_EXECUTABLE}" -sdk macosx metallib
            "${METAL_AIR}"
            -o "${METAL_LIB}"
        DEPENDS "${METAL_AIR}"
        COMMENT "Linking Metal library: ggml-metal-turbo.metallib"
        VERBATIM
    )

    # Create target
    add_custom_target(${ARGS_TARGET} ALL
        DEPENDS "${METAL_LIB}"
    )

    # Install metallib alongside the binary
    install(FILES "${METAL_LIB}"
        DESTINATION bin
        COMPONENT runtime
    )

    # Also install raw .metal for runtime compilation fallback
    install(FILES "${METAL_SOURCE}"
        DESTINATION bin
        COMPONENT runtime
    )

    message(STATUS "Metal shader compilation configured: ${ARGS_SOURCE} -> ${METAL_LIB}")
endfunction()