add flake

flake.nix

@@ -0,0 +1,52 @@
+{
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+    rainix.url = "github:rainprotocol/rainix";
+  };
+
+  outputs = { self, flake-utils, rainix }:
+
+  flake-utils.lib.eachDefaultSystem (system:
+    let
+      pkgs = rainix.pkgs.${system};
+    in rec {
+      packages = {
+        build = rainix.mkTask.${system} {
+          name = "build";
+          body = ''
+            set -euxo pipefail
+            npm install
+          '';
+          additionalBuildInputs = [
+            pkgs.wasm-bindgen-cli
+            rainix.rust-toolchain.${system}
+            rainix.rust-build-inputs.${system}
+            rainix.node-build-inputs.${system}
+          ];
+        };
+
+        test = rainix.mkTask.${system} {
+          name = "test";
+          body = ''
+            set -euxo pipefail
+            npm test
+          '';
+          additionalBuildInputs = [
+            rainix.node-build-inputs.${system}
+          ];
+        };
+      };
+
+      # For `nix develop`:
+      devShell = pkgs.mkShell {
+        nativeBuildInputs = [
+          rainix.rust-toolchain.${system}
+          rainix.rust-build-inputs.${system}
+          rainix.node-build-inputs.${system}
+        ] ++ (with pkgs; [ 
+          wasm-bindgen-cli
+        ]);
+      };
+    }
+  );
+}