if(NOT BASIC_PROJECT_CONFIG_DONE)
    message(FATAL_ERROR "Before including the Doxygen module, the BasicConfig module must be included.")
endif()

option(NO_DOXYGEN "whether creation of Doxygen targets is disabled (enabled by default)" OFF)

if(NOT NO_DOXYGEN)
    # find doxygen.h template
    include(TemplateFinder)
    find_template_file("doxygen" CPP_UTILITIES DOXYGEN_TEMPLATE_FILE)

    # find executables
    find_program(DOXYGEN_BIN doxygen)
    find_program(PERL_BIN perl)
    find_program(DIA_BIN dia)
    if(DIA_BIN)
        set(HAVE_DIA "YES")
    else()
        set(HAVE_DIA "NO")
    endif()
    find_program(DOT_BIN dot)
    if(DOT_BIN)
        set(HAVE_DOT "YES")
    else()
        set(HAVE_DOT "NO")
    endif()

    if(NOT DOXYGEN_BIN)
        message(WARNING "Doxygen not found, unable to add target for generating API documentation for ${TARGET_PREFIX}${META_PROJECT_NAME}${TARGET_SUFFIX}")
    else()
        # load cached configuration and other variables
        set(DOXY_LANGUAGE "English" CACHE STRING "specifies the language of the API documentation generated with Doxygen")
        set(DOXY_CUSTOM_CONFIG "" CACHE STRING "specifies extra options for Doxygen")
        set(DOXY_NUMBER "${META_APP_VERSION}")
        set(DOXY_INPUT_FILES
            ${HEADER_FILES} ${SRC_FILES} ${TEST_HEADER_FILES} ${TEST_SRC_FILES} ${WIDGETS_HEADER_FILES} ${WIDGETS_SRC_FILES}
            ${QML_HEADER_FILES} ${QML_SRC_FILES} ${DOC_ONLY_FILES}
        )
        set(DOXY_PATH_PREFIX "${CMAKE_CURRENT_SOURCE_DIR}/")
        list(GET DOC_FILES 0 DOXY_MAIN_PAGE_FILE)
        set(DOXY_MAIN_PAGE_FILE "${DOXY_PATH_PREFIX}${DOXY_MAIN_PAGE_FILE}")

        # convert DOXY_INPUT_FILES to whitespace-separated list
        include(ListToString)
        list_to_string(" " "\"${DOXY_PATH_PREFIX}" "\"" "${DOXY_INPUT_FILES}" DOXY_INPUT_FILES_WHITESPACE_SEPARATED)

        # generate Doxygen configuration
        configure_file(
            "${DOXYGEN_TEMPLATE_FILE}"
            "${CMAKE_CURRENT_BINARY_DIR}/doxygen.config"
        )

        # add target for generating API documentation
        add_custom_target(${TARGET_PREFIX}${META_PROJECT_NAME}${TARGET_SUFFIX}_apidoc
            COMMAND "${DOXYGEN_BIN}" "${CMAKE_CURRENT_BINARY_DIR}/doxygen.config"
            SOURCES ${DOXY_INPUT_FILES}
        )

        # add install target for API documentation
        install(DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/api-doc"
                DESTINATION "share/${META_PROJECT_NAME}"
                COMPONENT api-doc
                OPTIONAL
        )

        if(NOT TARGET install-api-doc)
            add_custom_target(install-api-doc
                COMMAND "${CMAKE_COMMAND}" -DCMAKE_INSTALL_COMPONENT=api-doc -P "${CMAKE_BINARY_DIR}/cmake_install.cmake"
            )
        endif()

        message(STATUS "Generating target for generating API documentation for ${TARGET_PREFIX}${META_PROJECT_NAME}${TARGET_SUFFIX} with Doxygen")

    endif()
endif()