{
  description = "Regolith, a retained mode GUI library for Odin";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

    # Pinned to the latest monthly release tag
    # If you change this, also change odinVersion below
    odin-src = {
      url = "github:odin-lang/Odin/dev-2026-10";
      flake = false;
    };

    # OLS must match the Odin revision
    ols-src = {
      url = "github:DanielGavin/ols/dev-2026-10";
      flake = false;
    };
  };

  outputs = { self, nixpkgs, odin-src, ols-src }:
    let
      lib = nixpkgs.lib;
      systems = [ "x86_64-linux" "aarch64-linux" ];
      forAllSystems = f:
        lib.genAttrs systems (system: f nixpkgs.legacyPackages.${system});

      odinVersion = "2026-10";

      build = pkgs:
        let
          llvmPackages = pkgs.llvmPackages_20;

          odin = llvmPackages.stdenv.mkDerivation {
            pname = "odin";
            version = "dev-${odinVersion}";
            src = odin-src;

            nativeBuildInputs = [ pkgs.makeBinaryWrapper pkgs.which ];
            buildInputs = [ llvmPackages.llvm ];

            LLVM_CONFIG = "${llvmPackages.llvm.dev}/bin/llvm-config";

            # The build script stamps the version from the build date, which is
            # meaningless inside the Nix sandbox. Stamp the tag instead.
            postPatch = ''
              substituteInPlace build_odin.sh \
                --replace-fail '$(date +"%Y-%m")' '${odinVersion}'
              patchShebangs build_odin.sh
            '';

            dontConfigure = true;

            buildPhase = ''
              runHook preBuild
              ./build_odin.sh release
              runHook postBuild
            '';

            installPhase = ''
              runHook preInstall

              mkdir -p $out/bin $out/share
              cp odin $out/bin/odin
              for d in base core vendor shared; do
                if [ -d "$d" ]; then cp -r "$d" $out/share/; fi
              done

              wrapProgram $out/bin/odin \
                --prefix PATH : ${lib.makeBinPath [
                  llvmPackages.bintools
                  llvmPackages.clang
                  llvmPackages.lld
                ]} \
                --set-default ODIN_ROOT $out/share

              # Build the C parts of the vendor collection.
              for v in stb cgltf miniaudio; do
                d="$out/share/vendor/$v/src"
                [ -d "$d" ] || continue
                if [ -f "$d/Makefile" ] || [ -f "$d/makefile" ] || [ -f "$d/GNUmakefile" ]; then
                  make -C "$d"
                elif [ -f "$d/build_$v.sh" ]; then
                  patchShebangs "$d/build_$v.sh"
                  (cd "$d" && "./build_$v.sh") || echo "vendor/$v: build script failed, skipping"
                else
                  echo "vendor/$v/src: no known build entry point, skipping"
                fi
              done

              runHook postInstall
            '';
          };

          ols = pkgs.stdenv.mkDerivation {
            pname = "ols";
            version = "dev-${odinVersion}";
            src = ols-src;

            nativeBuildInputs = [ odin ];
            dontConfigure = true;

            postPatch = ''
              patchShebangs build.sh odinfmt.sh
            '';

            buildPhase = ''
              runHook preBuild
              ./build.sh
              ./odinfmt.sh
              runHook postBuild
            '';

            installPhase = ''
              runHook preInstall
              install -Dm755 ols $out/bin/ols
              install -Dm755 odinfmt $out/bin/odinfmt
              runHook postInstall
            '';
          };
        in
        { inherit odin ols llvmPackages; };
    in
    {
      packages = forAllSystems (pkgs:
        let p = build pkgs; in {
          inherit (p) odin ols;
          default = p.odin;
        });

      devShells = forAllSystems (pkgs:
        let
          p = build pkgs;
          llvmPackages = p.llvmPackages;

          runtimeLibs = with pkgs; [
            sdl3
            wayland
            libxkbcommon
            libdecor
            vulkan-loader
            libGL
          ];
        in
        {
          default = (pkgs.mkShell.override { stdenv = llvmPackages.stdenv; }) {
            name = "regolith";

            packages = [
              # Odin toolchain
              p.odin
              p.ols
              llvmPackages.lld
              llvmPackages.bintools

              # Native build and runtime
              pkgs.pkg-config
              pkgs.sdl3

              # WASM
              pkgs.emscripten
              pkgs.nodejs
              pkgs.python3

              # Lua tooling (the engine builds its own vendored Lua)
              pkgs.lua5_4
              pkgs.lua54Packages.luacheck

              # Debugging
              pkgs.gdb
              pkgs.valgrind
              pkgs.git
            ];

            shellHook = ''
              # Emscripten needs a writable cache, and the store is read only.
              export EM_CACHE="$PWD/.cache/emscripten"
              mkdir -p "$EM_CACHE"

              # SDL3 dlopens these at runtime. nixpkgs SDL3 is patched to find
              # most of them, this is a fallback for anything built outside Nix.
              export LD_LIBRARY_PATH="${lib.makeLibraryPath runtimeLibs}:/run/opengl-driver/lib:''${LD_LIBRARY_PATH:-}"
            '';
          };
        });
    };
}