set(BREATHE_FOUND AUTO CACHE STRING "Enable Breathe documentation generator")
set_property(CACHE BREATHE_FOUND
             PROPERTY STRINGS
                      ON
                      OFF
                      AUTO)

find_package(Doxygen)
find_package(Perl)
set(Python_ADDITIONAL_VERSIONS
    3.7
    3.6
    3.5
    3.4
    3.3
    3.2)
find_package(PythonInterp)
if(PYTHONINTERP_FOUND)
  find_package(Sphinx)
  include(FindPythonModule)
  find_python_module(breathe)
  find_python_module(recommonmark)
  if(DOXYGEN_FOUND
     AND PERL_FOUND
     AND PYTHONINTERP_FOUND
     AND SPHINX_EXECUTABLE
     AND breathe
     AND recommonmark)
    set(BREATHE_FOUND ON CACHE STRING "Breathe documentation generator enabled" FORCE)
  else()
    set(BREATHE_FOUND OFF CACHE STRING "Breathe documentation generator disabled" FORCE)
  endif()
else()
  set(BREATHE_FOUND OFF CACHE STRING "Breathe documentation generator disabled" FORCE)
endif()

function(add_breathe_target)
  set(options)
  set(oneValueArgs
      TARGET_NAME
      SOURCE_DIR
      DOXY_FILE
      CONF_FILE
      OUTPUT_DIR
      COMMENT)
  set(multiValueArgs)

  cmake_parse_arguments(_BREATHE
                        "${options}"
                        "${oneValueArgs}"
                        "${multiValueArgs}"
                        ${ARGN})
  if(BREATHE_FOUND)
    set(WORK_DIR ${CMAKE_BINARY_DIR}/_breathe)
    set(BREATHE_DOCS_BUILD_DIR ${WORK_DIR})
    set(GENERATE_XML YES)
    set(GENERATE_HTML NO)
    set(GENERATE_LATEX NO)
    set(OUTPUT_DIRECTORY ${WORK_DIR})

    configure_file(${_BREATHE_CONF_FILE} ${WORK_DIR}/conf.py @ONLY)
    configure_file(${_BREATHE_DOXY_FILE} ${WORK_DIR}/Doxyfile @ONLY)

    add_custom_target(${_BREATHE_TARGET_NAME} VERBATIM
                      COMMAND ${SPHINX_EXECUTABLE}
                              -q
                              -b
                              html
                              -c
                              ${WORK_DIR}
                              -d
                              ${WORK_DIR}/cache
                              ${_BREATHE_SOURCE_DIR}
                              ${_BREATHE_OUTPUT_DIR}
                      COMMENT "Building ${_BREATHE_TARGET_NAME} documentation with Breathe")
  else()
    add_custom_target(${_BREATHE_TARGET_NAME} VERBATIM
                      COMMENT "Breathe is not found. Skipping target ${_BREATHE_TARGET_NAME} build")
  endif()
endfunction()