#[===================================================================[
   docs target (optional)
#]===================================================================]

find_package (Doxygen)
if (TARGET Doxygen::doxygen)
  set (doc_srcs docs/source.dox)
  file (GLOB_RECURSE other_docs docs/*.md)
  list (APPEND doc_srcs "${other_docs}")
  # read the source config and make a modified one
  # that points the output files to our build directory
  file (READ "${CMAKE_CURRENT_SOURCE_DIR}/docs/source.dox" dox_content)
  string (REGEX REPLACE "[\t ]*OUTPUT_DIRECTORY[\t ]*=(.*)"
    "OUTPUT_DIRECTORY=${CMAKE_BINARY_DIR}\n\\1"
    new_config "${dox_content}")
  file (WRITE "${CMAKE_BINARY_DIR}/source.dox" "${new_config}")
  add_custom_target (docs
    COMMAND "${DOXYGEN_EXECUTABLE}" "${CMAKE_BINARY_DIR}/source.dox"
    BYPRODUCTS "${CMAKE_BINARY_DIR}/html_doc/index.html"
    WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/docs"
    SOURCES "${doc_srcs}")
  if (is_multiconfig)
    set_property (
      SOURCE ${doc_srcs}
      APPEND
      PROPERTY HEADER_FILE_ONLY
      true)
  endif ()
else ()
  message (STATUS "doxygen executable not found -- skipping docs target")
endif ()