find_package(Doxygen REQUIRED)

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)