build: add nix flake

Author: echozio

.gitignore

@@ -1 +1,3 @@
 .env
+vendor
+result

flake.lock

@@ -0,0 +1,43 @@
+{
+  inputs = {
+    nixpkgs.url = "nixpkgs/nixos-23.05";
+    systems.url = "github:nix-systems/default";
+  };
+
+  outputs = { self, nixpkgs, systems }:
+  let
+    version = "v1.0.1";
+    lib = nixpkgs.lib;
+    eachSystem = lib.genAttrs (import systems);
+    pkgsFor = eachSystem (system: nixpkgs.legacyPackages.${system});
+  in {
+    devShell = eachSystem(system: pkgsFor.${system}.mkShell {
+      buildInputs = with pkgsFor.${system}; [ go ];
+    });
+    packages = eachSystem (system:
+    let
+      pkgs = pkgsFor.${system};
+    in {
+      default = pkgs.buildGoModule {
+        pname = "commit-status-poster";
+        version = version;
+        src = ./.;
+        vendorHash = "sha256-e3l8lZqbjb7ZaUUM2MipYqilkkxI+BsVac+22OdOpz8=";
+      };
+      dockerImage = pkgs.dockerTools.buildImage {
+        name = "commit-status-poster";
+        tag = version;
+        copyToRoot = pkgs.buildEnv {
+          name = "commit-status-poster";
+          paths = with pkgs; [
+            self.packages.${system}.default
+            dockerTools.caCertificates
+          ];
+        };
+        config = {
+          Entrypoint = [ "/bin/commit-status-poster" ];
+        };
+      };
+    });
+  };
+}