# SPDX-FileCopyrightText: 2016-2017 Friedrich W. H. Kossebau <kossebau@kde.org>
#
# SPDX-License-Identifier: BSD-3-Clause

#[=======================================================================[.rst:
ECMAddQch
------------------

This module provides the ``ecm_add_qch`` function for generating API
documentation files in the QCH format, and the ``ecm_install_qch_export``
function for generating and installing exported CMake targets for such
generated QCH files to enable builds of other software with generation of
QCH files to create links into the given QCH files.

::

  ecm_add_qch(<target_name>
      NAME <name>
      VERSION <version>
      QCH_INSTALL_DESTINATION <qchfile_install_path>
      TAGFILE_INSTALL_DESTINATION <tagsfile_install_path>
      [COMPONENT <component>]
      [BASE_NAME <basename>]
      [SOURCE_DIRS <dir> [<dir2> [...]]]
      [SOURCES <file> [<file2> [...]]]
      |MD_MAINPAGE <md_file>]
      [INCLUDE_DIRS <incdir> [<incdir2> [...]]]
      [IMAGE_DIRS <idir> [<idir2> [...]]]
      [EXAMPLE_DIRS <edir> [<edir2> [...]]]
      [ORG_DOMAIN <domain>]
      [NAMESPACE <namespace>]
      [LINK_QCHS <qch> [<qch2> [...]]]
      [PREDEFINED_MACROS <macro[=content]> [<macro2[=content]> [...]]]
      [BLANK_MACROS <macro> [<macro2> [...]]]
      [CONFIG_TEMPLATE <configtemplate_file>]
      [VERBOSE]
  )

This macro adds a target called <target_name> for the creation of an API
documentation manual in the QCH format from the given sources.
It currently uses doxygen, future versions might optionally also allow other
tools.
Next to the QCH file the target will generate a corresponding doxygen tag
file, which enables creating links from other documentation into the
generated QCH file.

It is recommended to make the use of this macro optional, by depending
the call to ``ecm_add_qch`` on a CMake option being set, with a name like
``BUILD_QCH`` and being ``TRUE`` by default. This will allow the developers to
saves resources on normal source development build cycles by setting this
option to FALSE.

The macro will set the target properties ``DOXYGEN_TAGFILE``, ``QHP_NAMESPACE``,
``QHP_NAMESPACE_VERSIONED``, ``QHP_VIRTUALFOLDER`` and ``LINK_QCHS`` to the respective
values, to allow other code access to them, e.g. the macro
``ecm_install_qch_export``.
To enable the use of the target <target_name> as item for ``LINK_QCHS``
in further ``ecm_add_qch`` calls in the current build,
additionally a target property ``DOXYGEN_TAGFILE_BUILD`` is set, with the path
of the created doxygen tag file in the build dir.
If existing, ``ecm_add_qch`` will use this property instead of
``DOXYGEN_TAGFILE`` for access to the tags file.

``NAME`` specifies the name for the generated documentation.

``VERSION`` specifies the version of the library for which the documentation is
created.

``BASE_NAME`` specifies the base name for the generated files.
The default basename is ``<name>``.

``SOURCE_DIRS`` specifies the dirs (incl. subdirs) with the source files for
which the API documentation should be generated.  Dirs can be relative to
the current source dir. Dependencies to the files in the dirs are not
tracked currently, other than with the ``SOURCES`` argument. So do not use for
sources generated during the build.
Needs to be used when ``SOURCES`` or ``CONFIG_TEMPLATE`` are not used.

``SOURCES`` specifies the source files for which the API documentation should be
generated.
Needs to be used when ``SOURCE_DIRS`` or ``CONFIG_TEMPLATE`` are not used.

``MD_MAINPAGE`` specifies a file in Markdown format that should be used as main
page. This page will overrule any ``\mainpage`` command in the included
sources.

``INCLUDE_DIRS`` specifies the dirs which should be searched for included
headers. Dirs can be relative to the current source dir. Since 5.63.

``IMAGE_DIRS`` specifies the dirs which contain images that are included in the
documentation. Dirs can be relative to the current source dir.

``EXAMPLE_DIRS`` specifies the dirs which contain examples that are included in
the documentation. Dirs can be relative to the current source dir.

``QCH_INSTALL_DESTINATION`` specifies where the generated QCH file will be
installed.

``TAGFILE_INSTALL_DESTINATION`` specifies where the generated tag file will be
installed.

``COMPONENT`` specifies the installation component name with which the install
rules for the generated QCH file and tag file are associated.

``NAMESPACE`` can be used to set a custom namespace <namespace> of the generated
QCH file. The namepspace is used as the unique id by QHelpEngine (cmp.
https://doc.qt.io/qt-5/qthelpproject.html#namespace).
The default namespace is ``<domain>.<name>``.
Needs to be used when ``ORG_DOMAIN`` is not used.

``ORG_DOMAIN`` can be used to define the organization domain prefix for the
default namespace of the generated QCH file.
Needs to be used when ``NAMESPACE`` is not used.

``LINK_QCHS`` specifies a list of other QCH targets which should be used for
creating references to API documentation of code in external libraries.
For each target <qch> in the list these target properties are expected to be
defined: ``DOXYGEN_TAGFILE``, ``QHP_NAMESPACE`` and ``QHP_VIRTUALFOLDER``.
If any of these is not existing, <qch> will be ignored.
Use the macro ``ecm_install_qch_export`` for exporting a target with these
properties with the CMake config of a library.
Any target <qch> can also be one created before in the same buildsystem by
another call of ``ecm_add_qch``.

``PREDEFINED_MACROS`` specifies a list of C/C++ macros which should be handled as
given by the API dox generation tool.
Examples are macros only defined in generated files, so whose
definition might be not available to the tool.

``BLANK_MACROS`` specifies a list of C/C++ macro names which should be ignored by
the API dox generation tool and handled as if they resolve to empty strings.
Examples are export macros only defined in generated files, so whose
definition might be not available to the tool.

``CONFIG_TEMPLATE`` specifies a custom cmake template file for the config file
that is created to control the execution of the API dox generation tool.
The following CMake variables need to be used:
- ``ECM_QCH_DOXYGEN_QHELPGENERATOR_EXECUTABLE``
- ``ECM_QCH_DOXYGEN_FILEPATH, ECM_QCH_DOXYGEN_TAGFILE``
The following CMake variables can be used:
- ``ECM_QCH_DOXYGEN_PROJECTNAME``
- ``ECM_QCH_DOXYGEN_PROJECTVERSION``
- ``ECM_QCH_DOXYGEN_VIRTUALFOLDER``
- ``ECM_QCH_DOXYGEN_FULLNAMESPACE``
- ``ECM_QCH_DOXYGEN_TAGFILES``
- ``ECM_QCH_DOXYGEN_WARN_LOGFILE``
- ``ECM_QCH_DOXYGEN_QUIET``
There is no guarantue that the other CMake variables currently used in the
default config file template will also be present with the same semantics
in future versions of this macro.

``VERBOSE`` tells the API dox generation tool to be more verbose about its
activity.

The default config file for the API dox generation tool, so the one when not
using ``CONFIG_TEMPLATE``, allows code to handle the case of being processed by
the tool by defining the C/C++ preprocessor macro ``K_DOXYGEN`` when run
(since v5.67.0). For backward-compatibility also the definition
``DOXYGEN_SHOULD_SKIP_THIS`` is set, but its usage is deprecated.

Example usage:

.. code-block:: cmake

  ecm_add_qch(
      MyLib_QCH
      NAME MyLib
      VERSION "0.42.0"
      ORG_DOMAIN org.myorg
      SOURCE_DIRS
          src
      LINK_QCHS
          Qt5Core_QCH
          Qt5Xml_QCH
          Qt5Gui_QCH
          Qt5Widgets_QCH
      BLANK_MACROS
          MyLib_EXPORT
          MyLib_DEPRECATED
      TAGFILE_INSTALL_DESTINATION ${CMAKE_INSTALL_PREFIX}/share/docs/tags
      QCH_INSTALL_DESTINATION ${CMAKE_INSTALL_PREFIX}/share/docs/qch
      COMPONENT Devel
  )

Example usage (with two QCH files, second linking first):

.. code-block:: cmake

  ecm_add_qch(
      MyLib_QCH
      NAME MyLib
      VERSION ${MyLib_VERSION}
      ORG_DOMAIN org.myorg
      SOURCES ${MyLib_PUBLIC_HEADERS}
      MD_MAINPAGE src/mylib/README.md
      LINK_QCHS Qt5Core_QCH
      TAGFILE_INSTALL_DESTINATION ${CMAKE_INSTALL_PREFIX}/share/docs/tags
      QCH_INSTALL_DESTINATION ${CMAKE_INSTALL_PREFIX}/share/docs/qch
      COMPONENT Devel
  )
  ecm_add_qch(
      MyOtherLib_QCH
      NAME MyOtherLib
      VERSION ${MyOtherLib_VERSION}
      ORG_DOMAIN org.myorg
      SOURCES ${MyOtherLib_PUBLIC_HEADERS}
      MD_MAINPAGE src/myotherlib/README.md
      LINK_QCHS Qt5Core_QCH MyLib_QCH
      TAGFILE_INSTALL_DESTINATION ${CMAKE_INSTALL_PREFIX}/share/docs/tags
      QCH_INSTALL_DESTINATION ${CMAKE_INSTALL_PREFIX}/share/docs/qch
      COMPONENT Devel
  )

::

  ecm_install_qch_export(
      TARGETS [<name> [<name2> [...]]]
      FILE <file>
      DESTINATION <dest>
      [COMPONENT <component>]
  )

This macro creates and installs a CMake file <file> which exports the given
QCH targets <name> etc., so they can be picked up by CMake-based builds of
other software that also generate QCH files (using ``ecm_add_qch``) and
which should include links to the QCH files created by the given targets.
The installed CMake file <file> is expected to be included by the CMake
config file created for the software the related QCH files are documenting.

``TARGETS`` specifies the QCH targets which should be exported. If a target does
not exist or does not have all needed properties, a warning will be
generated and the target skipped.
This behaviour might change in future versions to result in a fail instead.

``FILE`` specifies the name of the created CMake file, typically with a .cmake
extension.

``DESTINATION`` specifies the directory on disk to which the file will be
installed. It usually is the same as the one where the CMake config files
for this software are installed.

``COMPONENT`` specifies the installation component name with which the
install rule is associated.

Example usage:

.. code-block:: cmake

  ecm_install_qch_export(
      TARGETS MyLib_QCH
      FILE MyLibQCHTargets.cmake
      DESTINATION "${CMAKE_INSTALL_PREFIX}/lib/cmake/MyLib"
      COMPONENT Devel
  )

Since 5.36.0.
#]=======================================================================]

include(${CMAKE_CURRENT_LIST_DIR}/../modules/QtVersionOption.cmake)
include(ECMQueryQt)


# Helper method: adding the LINK_QCHS property to a Qt QCH targets, from module base names ("Core" etc.)
# if target does not exist (e.g. because no tagsfile was found), this is a no-op
macro(_ecm_setup_qt_qch_links _module)
    set(_target "Qt${QT_MAJOR_VERSION}${_module}_QCH")
    if(TARGET ${_target})
        set(_linkqchs)
        foreach(_linkqch ${ARGN})
            list(APPEND _linkqchs "Qt${QT_MAJOR_VERSION}${_linkqch}_QCH")
        endforeach()
        set_property(TARGET ${_target} PROPERTY LINK_QCHS ${_linkqchs})
    endif()
endmacro()

# Helper method: ensure Qt QCH targets are created
function(_ecm_ensure_qt_qch_targets)
    # create QCH targets for Qt
    # Ideally one day Qt CMake Config files provide these
    if(NOT TARGET Qt${QT_MAJOR_VERSION}Core_QCH)
        # get Qt version, if any
        find_package(Qt${QT_MAJOR_VERSION}Core CONFIG QUIET)
        # lookup tag files
        ecm_query_qt(qt_docs_dir QT_INSTALL_DOCS TRY)
        find_path(_qtcoreTagsPath qtcore/qtcore.tags
            PATHS
                ${qt_docs_dir}
        )

        if(Qt${QT_MAJOR_VERSION}Core_FOUND AND _qtcoreTagsPath)
            string(REPLACE "." "" _version ${Qt${QT_MAJOR_VERSION}Core_VERSION})
            # TODO: properly find each tag file
            # TODO: complete list of Qt modules
            if (QT_MAJOR_VERSION EQUAL "6")
                set(_module_list
                    3D Bluetooth Concurrent Core DBus Gui Location
                    Network Nfc Pdf Positioning PrintSupport Qml Quick
                    Sensors SerialBus SerialPort Sql StateMachine Svg
                    Test TextToSpeech WebChannel WebEngine WebSockets Widgets Xml)
            else()
                set(_module_list
                    3D Bluetooth Concurrent Core DBus Gui Location
                    Network Positioning PrintSupport Qml Quick
                    Sensors SerialPort Sql Svg
                    WebChannel WebEngine WebSockets Widgets Xml XmlPatterns)
            endif()
            foreach(_module ${_module_list})
                string(TOLOWER ${_module} _lowermodule)

                set(_tagfile "${_qtcoreTagsPath}/qt${_lowermodule}/qt${_lowermodule}.tags")
                if(EXISTS "${_tagfile}")
                    add_custom_target(Qt${QT_MAJOR_VERSION}${_module}_QCH)
                    set_target_properties(Qt${QT_MAJOR_VERSION}${_module}_QCH PROPERTIES
                        DOXYGEN_TAGFILE         "${_tagfile}"
                        QHP_NAMESPACE           "org.qt-project.qt${_lowermodule}"
                        QHP_NAMESPACE_VERSIONED "org.qt-project.qt${_lowermodule}.${_version}"
                        QHP_VIRTUALFOLDER       "qt${_lowermodule}"
                    )
                endif()
            endforeach()
            _ecm_setup_qt_qch_links(3D           Gui Core)
            _ecm_setup_qt_qch_links(Bluetooth    DBus Core)
            _ecm_setup_qt_qch_links(Concurrent   Gui Core)
            _ecm_setup_qt_qch_links(DBus         Core)
            _ecm_setup_qt_qch_links(Gui          Core)
            _ecm_setup_qt_qch_links(Location     Positioning Gui Core)
            _ecm_setup_qt_qch_links(Network      Core)
            if (QT_MAJOR_VERSION EQUAL "6")
                _ecm_setup_qt_qch_links(Nfc      Core)
                _ecm_setup_qt_qch_links(Pdf      Gui Core)
            endif()
            _ecm_setup_qt_qch_links(Positioning  Core)
            _ecm_setup_qt_qch_links(PrintSupport Widgets Gui Core)
            _ecm_setup_qt_qch_links(Qml          Network Core)
            _ecm_setup_qt_qch_links(Quick        Qml Network Gui Core)
            _ecm_setup_qt_qch_links(Sensors      Core)
            if (QT_MAJOR_VERSION EQUAL "6")
                _ecm_setup_qt_qch_links(SerialBus   Core)
            endif()
            _ecm_setup_qt_qch_links(SerialPort   Core)
            _ecm_setup_qt_qch_links(Sql          Core)
            if (QT_MAJOR_VERSION EQUAL "6")
                _ecm_setup_qt_qch_links(StateMachine   Core)
            endif()
            _ecm_setup_qt_qch_links(Svg          Widgets Gui Core)
            _ecm_setup_qt_qch_links(Test         Core)
            if (QT_MAJOR_VERSION EQUAL "6")
                _ecm_setup_qt_qch_links(TextToSpeech   Core)
            endif()
            _ecm_setup_qt_qch_links(WebChannel   Qml Core)
            _ecm_setup_qt_qch_links(WebEngine    Quick Qml Gui Core)
            _ecm_setup_qt_qch_links(WebSockets   Network Core)
            _ecm_setup_qt_qch_links(Widgets      Gui Core)
            _ecm_setup_qt_qch_links(Xml          Core)
            if (QT_MAJOR_VERSION EQUAL "5")
                _ecm_setup_qt_qch_links(XmlPatterns  Network Core)
            endif()
        endif()
    endif()
endfunction()

# Helper method: collect all qch targets from the LINK_QCHS dependency tree and set result to <var>
function(_ecm_collect_linkable_qch_targets name)
    set(_candidate_qchs ${ARGN})
    set(_handled_qchs)
    set(_good_qchs)
    # while unhandled qch targets
    while(_candidate_qchs)
        # get another unhandled qch target
        list(GET _candidate_qchs 0 _qch)
        list(REMOVE_AT _candidate_qchs 0)
        list(FIND _handled_qchs ${_qch} _index)
        # if not already handled
        if(_index EQUAL -1)
            list(APPEND _handled_qchs ${_qch})
            if(TARGET ${_qch})
                # always look at other linked qch targets, also for incomplete targets
                get_property(_link_qchs TARGET ${_qch} PROPERTY LINK_QCHS)
                if(_link_qchs)
                    list(APPEND _candidate_qchs ${_link_qchs})
                endif()
                # check if this target has all needed properties
                set(_target_usable TRUE)
                foreach(_propertyname
                    DOXYGEN_TAGFILE
                    QHP_NAMESPACE
                    QHP_VIRTUALFOLDER
                )
                    get_target_property(_property ${_qch} ${_propertyname})
                    if(NOT _property)
                        message(STATUS "No property ${_propertyname} set on ${_qch} when calling ecm_add_qch(). <<${_property}>>")
                        set(_target_usable FALSE)
                    endif()
                endforeach()
                get_target_property(_tagfile_build ${_qch} DOXYGEN_TAGFILE_BUILD)
                if (NOT _tagfile_build)
                    get_target_property(_tagfile ${_qch} DOXYGEN_TAGFILE)
                    if(NOT EXISTS ${_tagfile})
                        message(STATUS "No such tag file \"${_tagfile}\" found for ${_qch} when calling ecm_add_qch().")
                        set(_target_usable FALSE)
                    endif()
                endif()
                if(_target_usable)
                    list(APPEND _good_qchs ${_qch})
                else()
                    message(WARNING "No linking to API dox of ${_qch}.")
                endif()
            else()
                message(STATUS "No such target ${_qch} defined when calling ecm_add_qch(), ignored.")
            endif()
        endif()
    endwhile()
    set(${name} ${_good_qchs} PARENT_SCOPE)
endfunction()


function(ecm_add_qch target_name)
    # Parse arguments
    set(options VERBOSE)
    set(oneValueArgs NAME BASE_NAME QCH_INSTALL_DESTINATION TAGFILE_INSTALL_DESTINATION COMPONENT VERSION NAMESPACE MD_MAINPAGE ORG_DOMAIN CONFIG_TEMPLATE)
    set(multiValueArgs SOURCE_DIRS SOURCES INCLUDE_DIRS IMAGE_DIRS EXAMPLE_DIRS PREDEFINED_MACROS BLANK_MACROS LINK_QCHS)
    cmake_parse_arguments(ARGS "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})

    # check required args
    foreach(_arg_name NAME QCH_INSTALL_DESTINATION TAGFILE_INSTALL_DESTINATION VERSION)
        if(NOT DEFINED ARGS_${_arg_name})
            message(FATAL_ERROR "${_arg_name} needs to be defined when calling ecm_add_qch")
        endif()
    endforeach()
    if(NOT DEFINED ARGS_SOURCE_DIRS AND NOT DEFINED ARGS_SOURCES AND NOT DEFINED ARGS_CONFIG_TEMPLATE)
        message(FATAL_ERROR "SOURCE_DIRS or SOURCES needs to be defined when calling ecm_add_qch")
    endif()
    if(DEFINED ARGS_SOURCE_DIRS AND DEFINED ARGS_SOURCES)
        message(FATAL_ERROR "Either SOURCE_DIRS or SOURCES, not both, needs to be defined when calling ecm_add_qch")
    endif()
    if(NOT DEFINED ARGS_ORG_DOMAIN AND NOT DEFINED ARGS_NAMESPACE)
        message(FATAL_ERROR "ORG_DOMAIN or NAMESPACE needs to be defined when calling ecm_add_qch")
    endif()

    # find required tools
    if (NOT DOXYGEN_PATCHED_JSFILESADDED)
        set(REQUIRED_DOXYGEN_VERSION 1.8.13)
    endif()
    find_package(Doxygen ${REQUIRED_DOXYGEN_VERSION} REQUIRED)
    if (NOT DOXYGEN_FOUND AND NOT DOXYGEN_PATCHED_JSFILESADDED)
        set(doxygen_description_addition " (Or older version patched with https://github.com/doxygen/doxygen/commit/bf9415698e53d79b, pass -DDOXYGEN_PATCHED_JSFILESADDED=ON to cmake if patched)")
    endif()
    set_package_properties(Doxygen PROPERTIES
        TYPE REQUIRED
        PURPOSE "Needed for API dox QCH file generation${doxygen_description_addition}"
    )

    if (QT_MAJOR_VERSION EQUAL "5")
        find_package(QHelpGenerator REQUIRED)
        set_package_properties(QHelpGenerator PROPERTIES
            TYPE REQUIRED
            PURPOSE "Needed for API dox QCH file generation"
            DESCRIPTION "Part of Qt5 tools"
        )
    else()
        find_package(Qt6 COMPONENTS ToolsTools CONFIG REQUIRED)
        set_package_properties(Qt6ToolsTools PROPERTIES
            TYPE REQUIRED
            PURPOSE "Needed for API dox QCH file generation"
            DESCRIPTION "qhelpgenerator from Qt6 tools"
        )
        if(TARGET Qt6::qhelpgenerator)
            get_target_property(QHelpGenerator_EXECUTABLE Qt6::qhelpgenerator LOCATION)
        endif()
    endif()

    set(_missing_tools)
    if (NOT DOXYGEN_FOUND)
        list(APPEND _missing_tools "Doxygen")
    endif()
    if (NOT QHelpGenerator_FOUND AND NOT TARGET Qt6::qhelpgenerator)
        list(APPEND _missing_tools "qhelpgenerator")
    endif()

    if (_missing_tools)
        message(WARNING "API dox QCH file will not be generated, tools missing: ${_missing_tools}!")
    else()
        _ecm_ensure_qt_qch_targets()

        # prepare base dirs, working file names and other vars
        if (DEFINED ARGS_BASE_NAME)
            set(_basename ${ARGS_BASE_NAME})
        else()
            set(_basename ${ARGS_NAME})
        endif()
        set(_qch_file_basename "${_basename}.qch")
        set(_tags_file_basename "${_basename}.tags")
        set(_qch_buildpath "${CMAKE_CURRENT_BINARY_DIR}/${_qch_file_basename}")
        set(_tags_buildpath "${CMAKE_CURRENT_BINARY_DIR}/${_tags_file_basename}")
        set(_apidox_builddir "${CMAKE_CURRENT_BINARY_DIR}/${_basename}_ECMQchDoxygen")
        if (DEFINED ARGS_NAMESPACE)
            set(_namespace "${ARGS_NAMESPACE}")
        else()
            set(_namespace "${ARGS_ORG_DOMAIN}.${ARGS_NAME}")
        endif()
        string(REPLACE "." "_" _dotLessVersion ${ARGS_VERSION})
        set(_versioned_namespace "${_namespace}.${_dotLessVersion}")
        set(_sources)
        set(_dep_tagfiles)
        set(_dep_qch_targets)

        ### Create doxygen config file
        set(_doxygenconfig_file "${CMAKE_CURRENT_BINARY_DIR}/${_basename}_ECMQchDoxygen.config")
        if (DEFINED ARGS_CONFIG_TEMPLATE)
            set(_doxygenconfig_template_file "${ARGS_CONFIG_TEMPLATE}")
        else()
            set(_doxygenconfig_template_file "${ECM_MODULE_DIR}/ECMQchDoxygen.config.in")
        endif()
        set(_doxygen_layout_file "${ECM_MODULE_DIR}/ECMQchDoxygenLayout.xml")
        # Setup variables used in config file template, ECM_QCH_DOXYGEN_*
        set(ECM_QCH_DOXYGEN_OUTPUTDIR "\"${_apidox_builddir}\"")
        set(ECM_QCH_DOXYGEN_TAGFILE "\"${_tags_buildpath}\"")
        set(ECM_QCH_DOXYGEN_LAYOUTFILE "\"${_doxygen_layout_file}\"")
        set(ECM_QCH_DOXYGEN_INCLUDE_PATH)
        foreach(_include_DIR IN LISTS ARGS_INCLUDE_DIRS)
            if (NOT IS_ABSOLUTE ${_include_DIR})
                set(_include_DIR "${CMAKE_CURRENT_SOURCE_DIR}/${_include_DIR}")
            endif()
            # concat dirs separated by a break, it is no issue that first has also a leading break
            set(ECM_QCH_DOXYGEN_INCLUDE_PATH "${ECM_QCH_DOXYGEN_INCLUDE_PATH} \\\n\"${_include_DIR}\"")
        endforeach()
        set(ECM_QCH_DOXYGEN_IMAGEDIRS)
        foreach(_image_DIR IN LISTS ARGS_IMAGE_DIRS)
            if (NOT IS_ABSOLUTE ${_image_DIR})
                set(_image_DIR "${CMAKE_CURRENT_SOURCE_DIR}/${_image_DIR}")
            endif()
            # concat dirs separated by a break, it is no issue that first has also a leading break
            set(ECM_QCH_DOXYGEN_IMAGEDIRS "${ECM_QCH_DOXYGEN_IMAGEDIRS} \\\n\"${_image_DIR}\"")
        endforeach()
        set(ECM_QCH_DOXYGEN_EXAMPLEDIRS)
        foreach(_example_DIR IN LISTS ARGS_EXAMPLE_DIRS)
            if (NOT IS_ABSOLUTE ${_example_DIR})
                set(_example_DIR "${CMAKE_CURRENT_SOURCE_DIR}/${_example_DIR}")
            endif()
            # concat dirs separated by a break, it is no issue that first has also a leading break
            set(ECM_QCH_DOXYGEN_EXAMPLEDIRS "${ECM_QCH_DOXYGEN_EXAMPLEDIRS} \\\n\"${_example_DIR}\"")
        endforeach()
        if (ARGS_MD_MAINPAGE)
            if (NOT IS_ABSOLUTE ${ARGS_MD_MAINPAGE})
                set(ARGS_MD_MAINPAGE "${CMAKE_CURRENT_SOURCE_DIR}/${ARGS_MD_MAINPAGE}")
            endif()
            set(ECM_QCH_DOXYGEN_MAINPAGE_MDFILE "\"${ARGS_MD_MAINPAGE}\"")
        else()
            set(ECM_QCH_DOXYGEN_MAINPAGE_MDFILE)
        endif()
        set(ECM_QCH_DOXYGEN_INPUT)
        if (ARGS_SOURCE_DIRS)
            foreach(_source_DIR IN LISTS ARGS_SOURCE_DIRS)
                if (NOT IS_ABSOLUTE ${_source_DIR})
                    set(_source_DIR "${CMAKE_CURRENT_SOURCE_DIR}/${_source_DIR}")
                endif()
                # concat dirs separated by a break, it is no issue that first has also a leading break
                set(ECM_QCH_DOXYGEN_INPUT "${ECM_QCH_DOXYGEN_INPUT} \\\n\"${_source_DIR}\"")
            endforeach()
            if (ARGS_MD_MAINPAGE)
                set(ECM_QCH_DOXYGEN_INPUT "${ECM_QCH_DOXYGEN_INPUT} \\\n\"${ARGS_MD_MAINPAGE}\"")
            endif()
            set(ECM_QCH_DOXYGEN_FILE_PATTERNS "*.h *.cpp *.hpp *.hh *.cc *.h++ *.c++ *.hxx *.cxx *.dox *.md")
        else()
            foreach(_source IN LISTS ARGS_SOURCES)
                if (NOT IS_ABSOLUTE ${_source})
                    set(_source "${CMAKE_CURRENT_SOURCE_DIR}/${_source}")
                endif()
                list(APPEND _sources "${_source}")
            endforeach()
            if (ARGS_MD_MAINPAGE)
                list(FIND _sources ${ARGS_MD_MAINPAGE} _mainpage_index)
                if (_mainpage_index STREQUAL -1)
                    list(APPEND _sources "${ARGS_MD_MAINPAGE}")
                endif()
            endif()
            foreach(_source IN LISTS _sources)
                # concat sources separated by a break, it is no issue that first has also a leading break
                set(ECM_QCH_DOXYGEN_INPUT "${ECM_QCH_DOXYGEN_INPUT} \\\n\"${_source}\"")
            endforeach()
            set(ECM_QCH_DOXYGEN_FILE_PATTERNS "")
        endif()

        set(ECM_QCH_DOXYGEN_PROJECTNAME ${ARGS_NAME})
        file(RELATIVE_PATH _builddirrelative_filepath "${_apidox_builddir}/html"  ${_qch_buildpath})
        set(ECM_QCH_DOXYGEN_FILEPATH "\"${_builddirrelative_filepath}\"")
        set(ECM_QCH_DOXYGEN_PROJECTVERSION ${ARGS_VERSION})
        string(TOLOWER ${ARGS_NAME} ECM_QCH_DOXYGEN_VIRTUALFOLDER)
        set(ECM_QCH_DOXYGEN_FULLNAMESPACE ${_versioned_namespace})
        set(ECM_QCH_DOXYGEN_PREDEFINED_MACROS)
        foreach(_macro IN LISTS ARGS_PREDEFINED_MACROS)
            # concat dirs separated by a break, it is no issue that first has also a leading break
            # wrap each macro in quotes, to handle potential blanks and commas
            string(REPLACE "\"" "\\\"" _macro "${_macro}")
            set(ECM_QCH_DOXYGEN_PREDEFINED_MACROS "${ECM_QCH_DOXYGEN_PREDEFINED_MACROS} \\\n\"${_macro}\"")
        endforeach()
        set(ECM_QCH_DOXYGEN_BLANK_MACROS)
        foreach(_macro IN LISTS ARGS_BLANK_MACROS)
            # concat dirs separated by a break, it is no issue that first has also a leading break
            # wrap each macro in quotes, to handle potential blanks and commas
            string(REPLACE "\"" "\\\"" _macro "${_macro}")
            set(ECM_QCH_DOXYGEN_BLANK_MACROS "${ECM_QCH_DOXYGEN_BLANK_MACROS} \\\n\"${_macro}=\"")
        endforeach()

        # create list of tag files for linking other QCH files
        set(ECM_QCH_DOXYGEN_TAGFILES)
        _ecm_collect_linkable_qch_targets(_link_qchs ${ARGS_LINK_QCHS})
        foreach(_link_qch IN LISTS _link_qchs)
            list(APPEND _dep_qch_targets ${_link_qch})
            get_target_property(_link_qch_tagfile ${_link_qch} DOXYGEN_TAGFILE)
            get_target_property(_link_qch_tagfile_build ${_link_qch} DOXYGEN_TAGFILE_BUILD)
            get_target_property(_link_qch_namespace ${_link_qch} QHP_NAMESPACE)
            get_target_property(_link_qch_virtualfolder ${_link_qch} QHP_VIRTUALFOLDER)
            # if same build, then prefer build version over any installed one
            if (_link_qch_tagfile_build)
                set(_link_qch_tagfile ${_link_qch_tagfile_build})
                list(APPEND _dep_tagfiles "${_link_qch_tagfile}")
            endif()
            get_property(_linkqchs TARGET ${_link_qch} PROPERTY LINK_QCHS)
            set(_tagfile_entry "\"${_link_qch_tagfile}=qthelp://${_link_qch_namespace}/${_link_qch_virtualfolder}/\"")
            # concat dirs separated by a break, it is no issue that first has also a leading break
            set(ECM_QCH_DOXYGEN_TAGFILES "${ECM_QCH_DOXYGEN_TAGFILES} \\\n${_tagfile_entry}")
        endforeach()

        set(ECM_QCH_DOXYGEN_WARN_LOGFILE "\"${_doxygenconfig_file}.log\"")
        if(ARGS_VERBOSE)
            set(ECM_QCH_DOXYGEN_QUIET "NO")
        else()
            set(ECM_QCH_DOXYGEN_QUIET "YES")
        endif()
        set(ECM_QCH_DOXYGEN_QHELPGENERATOR_EXECUTABLE ${QHelpGenerator_EXECUTABLE})

        # finally create doxygen config file
        configure_file(
            "${_doxygenconfig_template_file}"
            "${_doxygenconfig_file}"
            @ONLY
        )
        # Doxygen warns verbosely about outdated config entries.
        # To spare custom code here to generate configuration with no out-dated entries,
        # instead make use of the doxygen feature to update configuration files.
        execute_process(
            COMMAND ${DOXYGEN_EXECUTABLE} -u "${_doxygenconfig_file}"
            ERROR_VARIABLE _doxygen_update_error
            RESULT_VARIABLE _doxygen_update_result
        )
        if(NOT ${_doxygen_update_result} STREQUAL "0")
            message(WARNING "Updating the doxygen config file failed: ${_doxygen_update_error}")
        endif()

        # setup make target
        set(_qch_INSTALLPATH ${ARGS_QCH_INSTALL_DESTINATION})
        set(_tags_INSTALLPATH ${ARGS_TAGFILE_INSTALL_DESTINATION})
        file(RELATIVE_PATH _relative_qch_file ${CMAKE_BINARY_DIR}  ${_qch_buildpath})
        file(RELATIVE_PATH _relative_tags_file ${CMAKE_BINARY_DIR}  ${_tags_buildpath})
        add_custom_command(
            OUTPUT ${_qch_buildpath} ${_tags_buildpath}
            COMMENT "Generating ${_relative_qch_file}, ${_relative_tags_file}"
            COMMAND cmake -E remove_directory "${ECM_QCH_DOXYGEN_OUTPUTDIR}"
            COMMAND cmake -E make_directory "${ECM_QCH_DOXYGEN_OUTPUTDIR}"
            COMMAND ${DOXYGEN_EXECUTABLE} "${_doxygenconfig_file}"
            DEPENDS
                ${_doxygenconfig_file}
                ${_doxygen_layout_file}
                ${_sources}
                ${_dep_tagfiles}
                ${_dep_qch_targets}
        )
        add_custom_target(${target_name} ALL DEPENDS ${_qch_buildpath} ${_tags_buildpath})
        set_target_properties(${target_name} PROPERTIES
            DOXYGEN_TAGFILE "${_qch_INSTALLPATH}/${_tags_file_basename}"
            DOXYGEN_TAGFILE_NAME "${_tags_file_basename}"
            DOXYGEN_TAGFILE_INSTALLDIR "${_qch_INSTALLPATH}"
            DOXYGEN_TAGFILE_BUILD "${_tags_buildpath}"
            QHP_NAMESPACE "${_namespace}"
            QHP_NAMESPACE_VERSIONED  "${_versioned_namespace}"
            QHP_VIRTUALFOLDER "${ECM_QCH_DOXYGEN_VIRTUALFOLDER}"
        )
        # list as value does not work with set_target_properties
        set_property(TARGET ${target_name} PROPERTY LINK_QCHS "${ARGS_LINK_QCHS}")

        if (DEFINED ARGS_COMPONENT)
            set(_component COMPONENT ${ARGS_COMPONENT})
        else()
            set(_component)
        endif()

        # setup installation
        install(FILES
            ${_qch_buildpath}
            DESTINATION ${_qch_INSTALLPATH}
            ${_component}
        )

        install(FILES
            ${_tags_buildpath}
            DESTINATION ${_tags_INSTALLPATH}
            ${_component}
        )
    endif()

endfunction()


function(ecm_install_qch_export)
    set(options )
    set(oneValueArgs FILE DESTINATION COMPONENT)
    set(multiValueArgs TARGETS)

    cmake_parse_arguments(ARGS "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})

    if(NOT DEFINED ARGS_FILE)
        message(FATAL_ERROR "FILE needs to be defined when calling ecm_install_qch_export().")
    endif()

    if(NOT DEFINED ARGS_DESTINATION)
        message(FATAL_ERROR "DESTINATION needs to be defined when calling ecm_install_qch_export().")
    endif()

    # TARGETS may be empty (and ARGS_TARGETS will not be defined then by cmake_parse_arguments)

    set(_content
"# This file was generated by ecm_install_qch_export(). DO NOT EDIT!
"
    )

    foreach(_target IN LISTS ARGS_TARGETS)
        set(_target_usable TRUE)

        if (NOT TARGET ${_target})
            message(STATUS "No such target ${_target} when calling ecm_install_qch_export().")
            set(_target_usable FALSE)
        else()
            foreach(_propertyname
                DOXYGEN_TAGFILE_NAME
                DOXYGEN_TAGFILE_INSTALLDIR
                QHP_NAMESPACE
                QHP_NAMESPACE_VERSIONED
                QHP_VIRTUALFOLDER
            )
                get_target_property(_property ${_target} ${_propertyname})
                if(NOT _property)
                    message(STATUS "No property ${_propertyname} set on ${_target} when calling ecm_install_qch_export(). <${_property}>")
                    set(_target_usable FALSE)
                endif()
            endforeach()
        endif()
        if(_target_usable)
            get_target_property(_tagfile_name ${_target} DOXYGEN_TAGFILE_NAME)
            get_target_property(_tagfile_installdir ${_target} DOXYGEN_TAGFILE_INSTALLDIR)
            if (NOT IS_ABSOLUTE ${_tagfile_installdir})
                set(_tagfile_installdir "${CMAKE_INSTALL_PREFIX}/${_tagfile_installdir}")
            endif()
            get_target_property(_namespace ${_target} QHP_NAMESPACE)
            get_target_property(_namespace_versioned ${_target} QHP_NAMESPACE_VERSIONED)
            get_target_property(_virtualfolder ${_target} QHP_VIRTUALFOLDER)
            get_property(_linkqchs TARGET ${_target} PROPERTY LINK_QCHS)
            set(_content "${_content}
if (NOT TARGET ${_target})

add_custom_target(${_target})
set_target_properties(${_target} PROPERTIES
    DOXYGEN_TAGFILE \"${_tagfile_installdir}/${_tagfile_name}\"
    QHP_NAMESPACE \"${_namespace}\"
    QHP_NAMESPACE_VERSIONED \"${_namespace_versioned}\"
    QHP_VIRTUALFOLDER \"${_virtualfolder}\"
)
set_property(TARGET ${_target} PROPERTY LINK_QCHS ${_linkqchs})

endif()
"
            )
        else()
            message(STATUS "No target exported for ${_target}.")
        endif()
    endforeach()

    if (NOT IS_ABSOLUTE ${ARGS_FILE})
        set(ARGS_FILE "${CMAKE_CURRENT_BINARY_DIR}/${ARGS_FILE}")
    endif()

    file(GENERATE
        OUTPUT "${ARGS_FILE}"
        CONTENT "${_content}"
    )

    if (DEFINED ARGS_COMPONENT)
        set(_component COMPONENT ${ARGS_COMPONENT})
    else()
        set(_component)
    endif()
    install(
        FILES "${ARGS_FILE}"
        DESTINATION "${ARGS_DESTINATION}"
        ${_component}
    )

endfunction()
