flake: add devShells

exposed via nix registry :D
can be used in nix-direnv like `use flake shells#cs.osu`

shells/cs/default.nix

@@ -0,0 +1,14 @@
+{
+  callPackage,
+  lib,
+  mkShell,
+  dotnetCorePackages
+}:
+mkShell {
+  nativeBuildInputs = [ (with dotnetCorePackages; combinePackages [ sdk_6_0 runtime_6_0 ]) ];
+  DOTNET_CLI_TELEMETRY_OPTOUT = 1;
+
+  passthru = {
+    osu = callPackage ./osu.nix {};
+  };
+}

shells/cs/osu.nix

@@ -0,0 +1,80 @@
+# Flake for development on https://github.com/ppy/osu
+{
+  lib,
+  mkShell,
+  writeScript,
+  stdenv,
+  stdenvNoCC,
+
+  dotnetCorePackages,
+
+  alsa-lib,
+  ffmpeg_4,
+  icu,
+  lltng-ust,
+  numactl,
+  openssl,
+  SDL2
+}:
+let
+  baseBuild = "-f net5.0 -v minimal /property:Version=$OSU_VERSION osu.Desktop -- $@";
+
+  deps = [
+    alsa-lib ffmpeg_4 icu lttng-ust numactl openssl SDL2 
+  ];
+
+  fixSdl = writeScript "osu-fixsdl" ''
+    ln -sft osu.Desktop/bin/Debug/net5.0/linux-x64/ ${SDL2}/lib/libSDL2${stdenv.hostPlatform.extensions.sharedLibrary}
+    ln -sft osu.Desktop/bin/Release/net5.0/linux-x64/ ${SDL2}/lib/libSDL2${stdenv.hostPlatform.extensions.sharedLibrary}
+  '';
+  buildScript = writeScript "osu-build" ''
+    rm -f osu.Desktop/bin/Debug/net5.0/linux-x64/libSDL2.so
+    dotnet build -c Debug -r linux-x64 ${baseBuild} && ${fixSdl}
+  '';
+  buildReleaseScript = writeScript "osu-build-rel" ''
+    rm -f osu.Desktop/bin/Release/net5.0/linux-x64/libSDL2.so
+    dotnet build -c Release -r linux-x64 ${baseBuild} && ${fixSdl}
+  '';
+  publishScript = writeScript "osu-publish" ''
+    rm -f osu.Desktop/bin/Release/net5.0/linux-x64/libSDL2.so
+    dotnet publish -c Release -r linux-x64 --self-contained false ${baseBuild} && ${fixSdl}
+  '';
+  publishWinScript = writeScript "osu-publish-win" ''
+    dotnet publish -c Release -r win-x64 --self-contained false -o build-win ${baseBuild}
+  '';
+  runScript = writeScript "osu-run" ''
+    ${buildScript} && dotnet run --no-build -c Debug -f net5.0 -r linux-x64 -p osu.Desktop -v minimal -- $@
+  '';
+  runReleaseScript = writeScript "osu-run-rel" ''
+    ${buildReleaseScript} && dotnet run --no-build -c Release -f net5.0 -r linux-x64 -p osu.Desktop -v minimal -- $@
+  '';
+
+  scripts = stdenvNoCC.mkDerivation {
+    pname = "osu-scripts";
+    version = "1.0.0";
+    dontUnpack = true;
+    installPhase = ''
+      mkdir $out
+      cp ${fixSdl} $out/osu-fixsdl
+      cp ${buildScript} $out/osu-build
+      cp ${buildReleaseScript} $out/osu-build-rel
+      cp ${publishScript} $out/osu-publish
+      cp ${publishWinScript} $out/osu-publish-win
+      cp ${runScript} $out/osu-run
+      cp ${runReleaseScript} $out/osu-run-rel
+    '';
+  };
+in mkShell {
+  nativeBuildInputs = [
+    icu
+
+    (with dotnetCorePackages; combinePackages [ sdk_5_0 runtime_5_0 ])
+  ];
+
+  DOTNET_CLI_TELEMETRY_OPTOUT = 1;
+  DRI_PRIME = 1;
+  LD_LIBRARY_PATH = lib.makeLibraryPath deps;
+  shellHook = ''
+    export PATH="${scripts}:$PATH"
+  '';
+}