feat: add flake.nix

flake.nix

@@ -0,0 +1,51 @@
+{
+  description = "A Nix-flake-based Java development environment";
+
+  inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1.*.tar.gz";
+
+  outputs = { self, nixpkgs }:
+    let
+      javaVersion = 21; # Change this value to update the whole stack
+
+      supportedSystems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
+        pkgs = import nixpkgs { inherit system; overlays = [ self.overlays.default ]; };
+      });
+    in
+    {
+      overlays.default =
+        final: prev:
+        let
+          jdk = prev."jdk${toString javaVersion}";
+        in
+        {
+          inherit jdk;
+          maven = prev.maven.override { jdk_headless = jdk; };
+          gradle = prev.gradle.override { java = jdk; };
+          lombok = prev.lombok.override { inherit jdk; };
+        };
+
+      devShells = forEachSupportedSystem ({ pkgs }: {
+        default = pkgs.mkShell {
+          packages = with pkgs; [
+            gcc
+            gradle
+            jdk
+            maven
+            ncurses
+            patchelf
+            zlib
+          ];
+
+          shellHook =
+            let
+              loadLombok = "-javaagent:${pkgs.lombok}/share/java/lombok.jar";
+              prev = "\${JAVA_TOOL_OPTIONS:+ $JAVA_TOOL_OPTIONS}";
+            in
+            ''
+              export JAVA_TOOL_OPTIONS="${loadLombok}${prev}"
+            '';
+        };
+      });
+    };
+}