nix: init flake

flake.nix

@@ -0,0 +1,70 @@
+{
+  description = "a mod manager for *hatsune miku: project diva mega mix+* by sega";
+
+  # Nixpkgs / NixOS version to use.
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
+
+  outputs = { self, nixpkgs }:
+    let
+
+      # to work with older version of flakes
+      lastModifiedDate = self.lastModifiedDate or self.lastModified or "19700101";
+
+      # Generate a user-friendly version number.
+      version = builtins.substring 0 8 lastModifiedDate;
+
+      # System types to support.
+      supportedSystems = [ "x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin" ];
+
+      # Helper function to generate an attrset '{ x86_64-linux = f "x86_64-linux"; ... }'.
+      forAllSystems = nixpkgs.lib.genAttrs supportedSystems;
+
+      # Nixpkgs instantiated for supported system types.
+      nixpkgsFor = forAllSystems (system: import nixpkgs { inherit system; });
+
+    in
+    {
+
+      # Provide some binary packages for selected system types.
+      packages = forAllSystems (system:
+        let
+          pkgs = nixpkgsFor.${system};
+        in
+        {
+          diva = pkgs.buildGoModule {
+            pname = "diva";
+            inherit version;
+            # In 'nix develop', we don't need a copy of the source tree
+            # in the Nix store.
+            src = builtins.path { path = ./.; name = "source"; };
+
+            # This hash locks the dependencies of this package. It is
+            # necessary because of how Go requires network access to resolve
+            # VCS.  See https://www.tweag.io/blog/2021-03-04-gomod2nix/ for
+            # details. Normally one can build with a fake hash and rely on native Go
+            # mechanisms to tell you what the hash should be or determine what
+            # it should be "out-of-band" with other tooling (eg. gomod2nix).
+            # To begin with it is recommended to set this, but one must
+            # remember to bump this hash when your dependencies change.
+
+            vendorHash = "sha256-8ggFeZ4UjN2W8XY1dcOzGfpIe4cNcvhikAB4ik5FChY=";
+          };
+        });
+
+      # Add dependencies that are only needed for development
+      devShells = forAllSystems (system:
+        let
+          pkgs = nixpkgsFor.${system};
+        in
+        {
+          default = pkgs.mkShell {
+            buildInputs = with pkgs; [ go gopls gotools go-tools ];
+          };
+        });
+
+      # The default package for 'nix build'. This makes sense if the
+      # flake provides only one package or there is a clear "main"
+      # package.
+      defaultPackage = forAllSystems (system: self.packages.${system}.diva);
+    };
+}