find_package(Doxygen)

if(DOXYGEN_FOUND)

  set(DOXYGEN_INPUT_DIR ${PROJECT_SOURCE_DIR}/include)
  set(DOXYGEN_OUTPUT_DIR ${CMAKE_CURRENT_BINARY_DIR}/doxygen)
  set(DOXYGEN_INDEX_FILE ${DOXYGEN_OUTPUT_DIR}/xml/index.xml)
  set(DOXYFILE_IN ${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in)
  set(DOXYFILE_OUT ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile)

  configure_file(${DOXYFILE_IN} ${DOXYFILE_OUT} @ONLY)

  file(MAKE_DIRECTORY ${DOXYGEN_OUTPUT_DIR})

  add_custom_command(OUTPUT
    ${DOXYGEN_INDEX_FILE}
    COMMAND ${DOXYGEN_EXECUTABLE} ${DOXYFILE_OUT}
    MAIN_DEPENDENCY ${DOXYFILE_OUT} ${DOXYFILE_IN}
    COMMENT "Generating Doxygen documentation"
    VERBATIM
  )

  add_custom_target(docs DEPENDS ${DOXYGEN_INDEX_FILE})

  # Ensure worker is built before documentation.
  add_dependencies(docs bootstrap)

endif()