Nix flake (#4)

* Add Nix flake

* Add Nix flake build instructions to README

.gitignore

@@ -22,3 +22,6 @@ go.work
 
 # Goreleaser
 dist/
+
+# Nix build output
+result

README.md

@@ -119,6 +119,42 @@ docker pull ghcr.io/marevers/pleasant-cli:latest
 docker pull ghcr.io/marevers/pleasant-cli:<version>
 ```
 
+## Build
+
+### Nix
+
+To build the project as a *Nix flake* (ensure you have *Nix* installed with flakes enabled):
+```bash
+nix build
+```
+This creates a `result` symlink pointing to the built package in your *Nix* store.
+
+To run it directly:
+```bash
+nix run
+```
+
+To enter a development environment with all necessary dependencies:
+```bash
+nix develop
+```
+
+To install it in your current profile:
+```bash
+nix profile install
+```
+
+You may also want to update the locked dependencies in `flake.lock`:
+```bash
+nix flake update
+```
+
+As *Nix* uses hashes to ensure reproducibility between builds, you may need to update the vendor hash in `flake.nix` when Go dependencies change (for example after `go get -u`).
+
+To do so, run `nix build` as usual: this will fail giving the expected new hash that you can use to update the `vendorHash` variable in `flake.nix`. Once updated, the rebuild should work as expected.
+
+For more information about using flakes in *Nix* and *NixOS* environments please have a look at the [documentation](https://nixos.wiki/wiki/flakes).
+
 ## Roadmap
 
 **Clipboard support**

flake.nix

@@ -0,0 +1,43 @@
+{
+  description = "A command line interface for Pleasant Password Server";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+
+        # Version extraction from source code
+        rootGoContent = builtins.readFile ./cmd/root.go;
+        versionMatch = builtins.match
+          ".*var version = \"([^\"]*)\".*" rootGoContent;
+        version =
+          if versionMatch == null
+          then throw "Version not found in cmd/root.go"
+          else builtins.head versionMatch;
+
+      in
+      {
+        packages.default = pkgs.buildGoModule {
+          pname = "pleasant-cli";
+          inherit version;
+          src = ./.;
+          vendorHash = "sha256-mRAlpDUg+2O/ShhxNVGGfK8YUJvWcR/ojossgZ7rCEY=";
+        };
+
+        apps.default = flake-utils.lib.mkApp {
+          drv = self.packages.${system}.default;
+        };
+
+        devShells.default = pkgs.mkShell {
+          buildInputs = with pkgs; [
+            go
+          ];
+        };
+      }
+    );
+}