nix: add flake

flake.lock

@@ -0,0 +1,69 @@
+{
+  "nodes": {
+    "futils": {
+      "locked": {
+        "lastModified": 1638122382,
+        "narHash": "sha256-sQzZzAbvKEqN9s0bzWuYmRaA03v40gaJ4+iL1LXjaeI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "74f7e4319258e287b0f9cb95426c9853b282730b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "ref": "master",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1638286143,
+        "narHash": "sha256-A+rgjbIpz3uPRKHPXwdmouVcVn5pZqLnaZHymjkraG4=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "29d1f6e1f625d246dcf84a78ef97b4da3cafc6ea",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "pre-commit-hooks": {
+      "inputs": {
+        "flake-utils": [
+          "futils"
+        ],
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1637745948,
+        "narHash": "sha256-DmQG1bZk24eS+BAHwnHPyYIadMLKbq0d1b//iapYIPU=",
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "rev": "c3b4f94350b0e59c2546fa85890cc70d03616b9c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "ref": "master",
+        "repo": "pre-commit-hooks.nix",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "futils": "futils",
+        "nixpkgs": "nixpkgs",
+        "pre-commit-hooks": "pre-commit-hooks"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,65 @@
+{
+  description = "My Advent of Code solutions";
+
+  inputs = {
+    futils = {
+      type = "github";
+      owner = "numtide";
+      repo = "flake-utils";
+      ref = "master";
+    };
+
+    nixpkgs = {
+      type = "github";
+      owner = "NixOS";
+      repo = "nixpkgs";
+      ref = "nixos-unstable";
+    };
+
+    pre-commit-hooks = {
+      type = "github";
+      owner = "cachix";
+      repo = "pre-commit-hooks.nix";
+      ref = "master";
+      inputs = {
+        flake-utils.follows = "futils";
+        nixpkgs.follows = "nixpkgs";
+      };
+    };
+  };
+
+  outputs = { self, futils, nixpkgs, pre-commit-hooks }:
+    futils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+      in
+      {
+        checks = {
+          pre-commit = pre-commit-hooks.lib.${system}.run {
+            src = self;
+
+            hooks = {
+              black = {
+                enable = true;
+              };
+
+              isort = {
+                enable = true;
+              };
+
+              nixpkgs-fmt = {
+                enable = true;
+              };
+            };
+          };
+        };
+
+        devShell = pkgs.mkShell {
+          buildInputs = with pkgs; [
+            python3
+          ];
+
+          inherit (self.checks.${system}.pre-commit) shellHook;
+        };
+      });
+}