if(NOT DEFINED ASN1C_OUTPUT_DIR)
    message(FATAL_ERROR "Missing ASN.1 output directory (ASN1C_OUTPUT_DIR)")
elseif(NOT DEFINED ASN1C_SOURCE_FILE)
    message(FATAL_ERROR "Missing ASN.1 source file (ASN1C_SOURCE_FILE)")
endif()

if(IS_ABSOLUTE "${ASN1C_OUTPUT_DIR}")
    file(RELATIVE_PATH ASN1C_OUTPUT_DIR ${CMAKE_CURRENT_SOURCE_DIR} ${ASN1C_OUTPUT_DIR})
endif()

file(GLOB _sources RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} ${ASN1C_OUTPUT_DIR}/*.c)
list(REMOVE_ITEM _sources
    ${ASN1C_OUTPUT_DIR}/converter-sample.c
    ${ASN1C_OUTPUT_DIR}/converter-example.c
    ${ASN1C_OUTPUT_DIR}/EXTERNAL.c
)

file(WRITE "${ASN1C_SOURCE_FILE}" "# generated file\n")
foreach(_source ${_sources})
    file(APPEND "${ASN1C_SOURCE_FILE}" "${_source}\n")
endforeach()