Run cmake-init and setup flake.nix and default.nix

cmake/docs.cmake

@@ -0,0 +1,46 @@
+# ---- Dependencies ----
+
+set(extract_timestamps "")
+if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.24")
+  set(extract_timestamps DOWNLOAD_EXTRACT_TIMESTAMP YES)
+endif()
+
+include(FetchContent)
+FetchContent_Declare(
+    mcss URL
+    https://github.com/friendlyanon/m.css/releases/download/release-1/mcss.zip
+    URL_MD5 00cd2757ebafb9bcba7f5d399b3bec7f
+    SOURCE_DIR "${PROJECT_BINARY_DIR}/mcss"
+    UPDATE_DISCONNECTED YES
+    ${extract_timestamps}
+)
+FetchContent_MakeAvailable(mcss)
+
+find_package(Python3 3.6 REQUIRED)
+
+# ---- Declare documentation target ----
+
+set(
+    DOXYGEN_OUTPUT_DIRECTORY "${PROJECT_BINARY_DIR}/docs"
+    CACHE PATH "Path for the generated Doxygen documentation"
+)
+
+set(working_dir "${PROJECT_BINARY_DIR}/docs")
+
+foreach(file IN ITEMS Doxyfile conf.py)
+  configure_file("docs/${file}.in" "${working_dir}/${file}" @ONLY)
+endforeach()
+
+set(mcss_script "${mcss_SOURCE_DIR}/documentation/doxygen.py")
+set(config "${working_dir}/conf.py")
+
+add_custom_target(
+    docs
+    COMMAND "${CMAKE_COMMAND}" -E remove_directory
+    "${DOXYGEN_OUTPUT_DIRECTORY}/html"
+    "${DOXYGEN_OUTPUT_DIRECTORY}/xml"
+    COMMAND "${Python3_EXECUTABLE}" "${mcss_script}" "${config}"
+    COMMENT "Building documentation using Doxygen and m.css"
+    WORKING_DIRECTORY "${working_dir}"
+    VERBATIM
+)