find_program(DOXYGEN doxygen
  PATHS "$ENV{ProgramFiles}/doxygen/bin"
        "$ENV{ProgramFiles\(x86\)}/doxygen/bin")
if (NOT DOXYGEN)
  message(STATUS "Target 'doc' disabled (requires doxygen)")
  return ()
endif ()

# Find the Python interpreter and set the PYTHON_EXECUTABLE variable.
if (CMAKE_VERSION VERSION_LESS 3.12)
  # This logic is deprecated in CMake after 3.12.
  find_package(PythonInterp QUIET REQUIRED)
else ()
  find_package(Python QUIET REQUIRED)
  set(PYTHON_EXECUTABLE ${Python_EXECUTABLE})
endif ()

add_custom_target(doc
  COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/build.py
                               ${FMT_VERSION}
  SOURCES api.rst syntax.rst usage.rst build.py conf.py _templates/layout.html)

include(GNUInstallDirs)
install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/html/
        DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/doc/fmt OPTIONAL
        PATTERN ".doctrees" EXCLUDE)