{
    description = "Advent of Code";

    inputs = {
        nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
        rust-overlay = {
            url = "github:oxalica/rust-overlay";
            inputs.nixpkgs.follows = "nixpkgs";
        };
    };

    outputs = { nixpkgs, rust-overlay, ... }:
    let
        lib = nixpkgs.lib;
        systems = ["x86_64-linux"];

        forEachSystem = fn: lib.genAttrs systems (system:
        let
            overlays = [ (import rust-overlay) ];
            pkgs = import nixpkgs { inherit system overlays; };
        in fn { inherit pkgs; } );

        mkRustToolchain = pkgs: pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
    in {
        devShells = forEachSystem ({ pkgs }: let
            rustToolchain = mkRustToolchain pkgs;
            rustNightlyToolchain = pkgs.rust-bin.selectLatestNightlyWith (t: t.minimal.override {
                extensions = [ "rustfmt" ];
            });

        rustShell = pkgs.mkShell {
                name = "AoC";

                nativeBuildInputs = [
                    rustToolchain
                    rustNightlyToolchain
                ];
            };
        in {
            default = rustShell;
        });
    };
}