build: add nix support

I use nix for everything so it felt kinda weird not having it in this project.
Nix will ensure that all colaborators use the exact same version of node, as
well as the docker.

Author: Tygo-van-den-Hurk

.envrc

@@ -0,0 +1,14 @@
+# shellcheck shell=sh
+
+# Load environment variables.
+if [ -f .env ]; then
+  dotenv .env
+fi
+
+# automatically loads a Nix Development environment if nix is installed.
+if has nix; then
+  use flake .
+else
+  echo 'Error: `nix` is not installed.'
+  echo 'Please consider installing nix.'
+fi

default.nix

@@ -0,0 +1,27 @@
+(import
+  (
+    let
+      lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+      node = lock.nodes.flake-compat.locked;
+
+      sha256 = node.narHash;
+      inherit (node) owner;
+      inherit (node) repo;
+      inherit (node) rev;
+      inherit (node) type;
+
+      url =
+        if type == "github" then
+          "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz"
+        else
+          throw "Unknown URL type: ${type}";
+    in
+    fetchTarball {
+      inherit url;
+      inherit sha256;
+    }
+  )
+  {
+    src = ./.;
+  }
+).defaultNix

flake.lock

@@ -0,0 +1,46 @@
+{
+  description = "Make beautifully animated Slydes and presentations from XML with ease!";
+
+  # A collection of packages for the Nix package manager
+  inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+
+  # Generate Github Actions matrices from Nix Flakes
+  inputs.nix-github-actions = {
+    url = "github:nix-community/nix-github-actions";
+    inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  # Flake basics described using the module system
+  inputs.flake-parts.url = "github:hercules-ci/flake-parts";
+
+  # Allow flakes to be used with Nix < 2.4
+  inputs.flake-compat = {
+    url = "github:edolstra/flake-compat";
+    flake = false;
+  };
+
+  # treefmt nix configuration modules
+  inputs.treefmt-nix = {
+    url = "github:numtide/treefmt-nix";
+    inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  # Seamless integration of https://pre-commit.com git hooks with Nix.
+  inputs.git-hooks-nix = {
+    url = "github:cachix/git-hooks.nix";
+    inputs.flake-compat.follows = "flake-compat";
+    inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  outputs =
+    inputs:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [ ./nix ];
+      systems = [
+        "aarch64-darwin"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "x86_64-linux"
+      ];
+    };
+}

flake.nix

@@ -0,0 +1,6 @@
+_:
+{
+  perSystem = _: {
+    # do not set a default, let that be the default package instead.
+  };
+}

nix/apps/default.nix

@@ -0,0 +1,16 @@
+{ inputs, config, ... }:
+let
+  inherit (inputs) nix-github-actions;
+in
+{
+  # Used by GitHub Actions to create a matrix out of this:
+  flake.githubActions = nix-github-actions.lib.mkGithubMatrix {
+    checks = inputs.nixpkgs.lib.getAttrs config.systems (
+      # check whether the packages can be build for every platform,
+      # but for Linux x86_64 also do the other checks. Prevents
+      # duplicated checks for non-package builds as formatting for
+      # example should be platform independent.
+      inputs.self.packages // { inherit (inputs.self.checks) x86_64-linux; }
+    );
+  };
+}

nix/ci/default.nix

@@ -0,0 +1,11 @@
+_: {
+  imports = [
+    ./apps
+    ./ci
+    ./formatting
+    ./hooks
+    ./overlays
+    ./packages
+    ./shells
+  ];
+}

nix/default.nix

@@ -0,0 +1,30 @@
+{ inputs, ... }:
+{
+  imports = [
+    inputs.treefmt-nix.flakeModule
+  ];
+
+  perSystem = _: {
+    treefmt = {
+      enableDefaultExcludes = true;
+      flakeCheck = true;
+      flakeFormatter = true;
+      #// on-unmatched = "warn";
+
+      # nix formatting
+      programs.nixfmt = {
+        enable = true;
+      };
+
+      # nix static analysis
+      programs.statix = {
+        enable = true;
+      };
+
+      # find dead nix code
+      programs.deadnix = {
+        enable = true;
+      };
+    };
+  };
+}

nix/formatting/default.nix

@@ -0,0 +1,6 @@
+{ ... }:
+{
+  imports = [
+    ./git.nix
+  ];
+}