# cmake/platform.cmake — central OS detection and per-OS source selection.
#
# Owned by PKG/QA (docs/adr/0020-cross-platform-strategy.md §4-5, amended: PORT owns
# **/platform/<os>/** and the macOS/Windows packaging trees, but this file is root build
# infrastructure and lands in Phase 0 — CORE's and DAEMON's own seams need
# velox_platform_sources() to select their platform/linux/*.cpp before PORT ever starts).
#
# Sets exactly one of VELOX_OS_LINUX / VELOX_OS_MACOS / VELOX_OS_WINDOWS. Selection lives
# here and nowhere else — no lane's own CMakeLists.txt should reimplement this check.
if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
    set(VELOX_OS_LINUX TRUE)
elseif(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
    set(VELOX_OS_MACOS TRUE)
elseif(CMAKE_SYSTEM_NAME STREQUAL "Windows")
    set(VELOX_OS_WINDOWS TRUE)
else()
    message(FATAL_ERROR "velox: unsupported CMAKE_SYSTEM_NAME '${CMAKE_SYSTEM_NAME}' — "
                        "expected Linux, Darwin or Windows.")
endif()

# velox_platform_sources(<target> <dir>) adds <dir>/platform/<os>/*.cpp to <target>, where
# <os> is linux, macos or windows to match this file's VELOX_OS_* selection. <dir> is
# relative to the calling lane's own CMakeLists.txt (e.g. src/io, src/rpc) — the seam
# headers themselves (<dir>/platform/*.hpp) are not globbed here, they're ordinary sources
# the owning lane already lists.
function(velox_platform_sources target dir)
    if(VELOX_OS_LINUX)
        set(os_dir "linux")
    elseif(VELOX_OS_MACOS)
        set(os_dir "macos")
    elseif(VELOX_OS_WINDOWS)
        set(os_dir "windows")
    endif()

    file(GLOB platform_sources CONFIGURE_DEPENDS
         "${CMAKE_CURRENT_SOURCE_DIR}/${dir}/platform/${os_dir}/*.cpp")

    if(NOT platform_sources)
        message(WARNING "velox: velox_platform_sources(${target} ${dir}) found no "
                        "sources under ${dir}/platform/${os_dir}/ — is the seam missing "
                        "its ${os_dir} backend?")
    endif()

    target_sources(${target} PRIVATE ${platform_sources})
endfunction()