Clean up the Nix flake, recommended practices, provide overlay

.pre-commit-config.yaml

@@ -12,3 +12,8 @@ repos:
       - id: ruff-format
       - id: ruff
         args: [ --fix ]
+  - repo: https://github.com/kamadorueda/alejandra
+    rev: 3.0.0
+    hooks:
+       # Requires Alejandra to be previously installed in the system
+      - id: alejandra-system

flake.nix

@@ -1,58 +1,58 @@
 {
-  description = "brain";
-  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+  description = "A script to patch the MonoLisa font with Nerd Fonts glyphs.";
 
-  outputs = inputs @ {
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    systems.url = "github:nix-systems/default";
+  };
+
+  outputs = {
     self,
     nixpkgs,
+    systems,
   }: let
-    inherit (nixpkgs.lib) genAttrs;
-    forAllSystems = f:
-      genAttrs
-      ["x86_64-linux" "x86_64-darwin" "aarch64-linux" "aarch64-darwin"]
-      (system: f nixpkgs.legacyPackages.${system});
+    inherit (nixpkgs) lib;
+    eachSystem = fn:
+      lib.genAttrs (import systems) (system: let
+        pkgs = import nixpkgs {
+          localSystem.system = system;
+          overlays = [self.overlays.default];
+        };
+      in
+        fn system pkgs);
   in {
-    packages = forAllSystems (
-      pkgs:
-      with pkgs; {
-        default = stdenv.mkDerivation {
-        name = "monolisa-nerdfont-patch";
-        src = ./.;
-        nativeBuildInputs = [ makeWrapper ];
-        buildInputs = [
-          fontforge
-          python3
-        ];
-        unpackPhase = ":";
-        buildPhase = ":";
-        installPhase = ''
-          mkdir -p $out/bin
-          install -m755 -D ${./patch-monolisa} $out/bin/monolisa-nerdfont-patch
-          install -m755 -D ${./font-patcher} $out/bin/font-patcher
-          cp -r ${./bin} $out/bin/bin
-          cp -r ${./src} $out/bin/src
-        '';
-        postFixup = ''
-          wrapProgram $out/bin/monolisa-nerdfont-patch \
-            --set PATH ${lib.makeBinPath [
-              fontforge
-            ]}
+    overlays = {
+      default = final: prev: {
+        monolisa-nerdfont-patch = final.stdenv.mkDerivation {
+          name = "monolisa-nerdfont-patch";
+          src = ./.;
+          nativeBuildInputs = with final; [makeWrapper];
+          buildInputs = with final; [fontforge python3];
+          buildPhase = ":";
+          installPhase = ''
+            mkdir -p $out/bin
+            install -m755 -D ${./patch-monolisa} $out/bin/monolisa-nerdfont-patch
+            install -m755 -D ${./font-patcher} $out/bin/font-patcher
+            cp -r ${./bin} $out/bin/bin
+            cp -r ${./src} $out/bin/src
+          '';
+          postFixup = ''
+            wrapProgram $out/bin/monolisa-nerdfont-patch \
+              --set PATH ${lib.makeBinPath (with final; [fontforge])}
           '';
+        };
       };
-    }
-      );
+    };
 
-    devShells = forAllSystems (
-      pkgs:
-        with pkgs; {
-          default = mkShell {
-            buildInputs = [
-              fontforge
-              python3
-              pre-commit
-            ];
-          };
-        }
-    );
+    packages = eachSystem (system: pkgs: {
+      default = self.packages.${system}.monolisa-nerdfont-patch;
+      monolisa-nerdfont-patch = pkgs.monolisa-nerdfont-patch;
+    });
+
+    devShells = eachSystem (_: pkgs: {
+      default = pkgs.mkShell {
+        packages = with pkgs; [fontforge python3 pre-commit];
+      };
+    });
   };
 }