if(NOT INPUT_DIRS)
  message(FATAL_ERROR "INPUT_DIRS must be set to a list of directories.")
endif()
if(NOT OUTPUT_FILE)
  message(FATAL_ERROR "OUTPUT_FILE must be set.")
endif()

set(_all_headers "")
foreach(_dir IN LISTS INPUT_DIRS)
  if(EXISTS "${_dir}")
    file(GLOB_RECURSE _hfiles "${_dir}/*.h")
    list(APPEND _all_headers ${_hfiles})
  endif()
endforeach()

if(NOT _all_headers)
  message(FATAL_ERROR "No .h files found in INPUT_DIRS.")
endif()
list(REMOVE_DUPLICATES _all_headers)
list(SORT _all_headers)

foreach(_h IN LISTS _all_headers)
  get_filename_component(_bn "${_h}" NAME)
  string(TOLOWER "${_bn}" _k)
  set(_idx_${_k} "${_h}")
endforeach()

foreach(_h IN LISTS _all_headers)
  file(STRINGS "${_h}" _ll REGEX "^[ \t]*#[ \t]*include[ \t]+\"")
  get_filename_component(_hd "${_h}" DIRECTORY)

  set(_dd "")
  foreach(_l IN LISTS _ll)
    if(_l MATCHES "^[ \t]*#[ \t]*include[ \t]+\"([^\"]+)\"")
      set(_in "${CMAKE_MATCH_1}")
      set(_rv "")
      set(_try "${_hd}/${_in}")
      get_filename_component(_try "${_try}" ABSOLUTE)
      if(EXISTS "${_try}")
        set(_rv "${_try}")
      else()
        string(TOLOWER "${_in}" _k2)
        if(DEFINED _idx_${_k2})
          set(_rv "${_idx_${_k2}}")
        endif()
      endif()
      if(_rv AND _rv IN_LIST _all_headers)
        list(APPEND _dd "${_rv}")
      endif()
    endif()
  endforeach()
  if(_dd)
    list(REMOVE_DUPLICATES _dd)
  endif()
  set(_de_${_h} "${_dd}")
endforeach()

set(_sorted "")
set(_left ${_all_headers})
while(_left)
  set(_prog 0)
  set(_next "")
  foreach(_h IN LISTS _left)
    set(_rdy 1)
    foreach(_d IN LISTS _de_${_h})
      if(_d IN_LIST _left)
        set(_rdy 0)
        break()
      endif()
    endforeach()
    if(_rdy)
      list(APPEND _sorted "${_h}")
      set(_prog 1)
    else()
      list(APPEND _next "${_h}")
    endif()
  endforeach()
  if(NOT _prog)
    foreach(_h IN LISTS _next)
      list(APPEND _sorted "${_h}")
    endforeach()
    break()
  endif()
  set(_left ${_next})
endwhile()

set(_body "")

foreach(_h IN LISTS _sorted)
  file(STRINGS "${_h}" _ll)

  set(_inbc 0)
  set(_out "")
  foreach(_l IN LISTS _ll)
    if(_l STREQUAL "")
      continue()
    endif()

    if(_inbc)
      string(FIND "${_l}" "*/" _ce)
      if(_ce GREATER -1)
        math(EXPR _ca "${_ce} + 2")
        string(SUBSTRING "${_l}" ${_ca} -1 _l)
        set(_inbc 0)
      else()
        continue()
      endif()
    endif()

    string(FIND "${_l}" "//" _sl)
    if(_sl GREATER -1)
      string(SUBSTRING "${_l}" 0 ${_sl} _l)
    endif()

    while(TRUE)
      string(FIND "${_l}" "/*" _so)
      if(_so EQUAL -1)
        break()
      endif()
      string(SUBSTRING "${_l}" 0 ${_so} _bf)
      string(SUBSTRING "${_l}" ${_so} -1 _ar)
      string(FIND "${_ar}" "*/" _ce)
      if(_ce EQUAL -1)
        set(_l "${_bf}")
        set(_inbc 1)
        break()
      else()
        math(EXPR _ca "${_ce} + 2")
        string(SUBSTRING "${_ar}" ${_ca} -1 _af)
        set(_l "${_bf}${_af}")
      endif()
    endwhile()

    string(STRIP "${_l}" _ls)

    if(_ls MATCHES "^#[ \t]*pragma[ \t]+once")
      continue()
    endif()
    if(_ls MATCHES "^#[ \t]*include[ \t]+\"([^\"]+)\"")
      continue()
    endif()
    if(_ls MATCHES "^#[ \t]*include[ \t]+<")
      continue()
    endif()

    if(_ls STREQUAL "")
      continue()
    endif()

    string(APPEND _out "${_l}\n")
  endforeach()

  if(_out)
    if(_body)
      string(APPEND _body "\n")
    endif()
    string(APPEND _body "${_out}")
  endif()
endforeach()

set(_guard "MINECRAFT_LCE_SDK_H")
set(_tmp "${OUTPUT_FILE}.tmp")

file(WRITE "${_tmp}"
  "#ifndef ${_guard}\n"
  "#define ${_guard}\n"
  "\n"
  "// Auto-generated. Do not edit.\n"
  "// Minecraft Console Edition SDK Header\n"
  "\n"
  "#include <cstddef>\n"
  "#include <cstdint>\n"
  "#include <string>\n"
  "#include <memory>\n"
  "#include <vector>\n"
  "#include <map>\n"
  "#include <unordered_map>\n"
  "#include <functional>\n"
  "#include <algorithm>\n"
  "#include <atomic>\n"
  "#include <mutex>\n"
  "#include <thread>\n"
  "#include <fstream>\n"
  "#include <sstream>\n"
  "#include <iostream>\n"
  "#include <array>\n"
  "#include <set>\n"
  "#include <queue>\n"
  "#include <list>\n"
  "#include <cmath>\n"
  "#include <cassert>\n"
  "#include <cstdio>\n"
  "#include <cstdlib>\n"
  "#include <cstring>\n"
  "#include <cwchar>\n"
  "#include <climits>\n"
  "#include <cfloat>\n"
  "#include <type_traits>\n"
  "#include <initializer_list>\n"
  "#include <exception>\n"
  "#include <tuple>\n"
  "#include <chrono>\n"
  "#include <system_error>\n"
  "#if defined(_WIN32) || defined(_WIN64)\n"
  "#include <Windows.h>\n"
  "#endif\n"
  "\n"
)

file(APPEND "${_tmp}" "${_body}")
file(APPEND "${_tmp}" "\n#endif // ${_guard}\n")

if(EXISTS "${OUTPUT_FILE}")
  execute_process(
    COMMAND ${CMAKE_COMMAND} -E compare_files "${OUTPUT_FILE}" "${_tmp}"
    RESULT_VARIABLE _ch
  )
else()
  set(_ch 1)
endif()

if(_ch)
  file(RENAME "${_tmp}" "${OUTPUT_FILE}")
  message(STATUS "GenerateSdk: wrote ${OUTPUT_FILE}")
else()
  file(REMOVE "${_tmp}")
  message(STATUS "GenerateSdk: ${OUTPUT_FILE} is up-to-date")
endif()