feat: Introduce Flake for development and builds

This PR introduces a Nix flake, allowing for InfiniSim to be built as a
Flake, including a FHS development environment.

We also introduce `flake-compat`, allowing for non-Flake Nix mahcines to
use the project as-is, both for building (`default.nix`), and
development (`shell.nix`).

Additionally, we introduce `.envrc`, meaning that with `direnv`, the Nix
Flake is activated automatically.

Signed-off-by: Dom Rodriguez <shymega@shymega.org.uk>

Author: shymega

.envrc

@@ -0,0 +1 @@
+use flake

default.nix

@@ -0,0 +1,10 @@
+(import
+  (
+    let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
+    fetchTarball {
+      url = lock.nodes.flake-compat.locked.url or "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  { src = ./.; }
+).defaultNix

flake.lock

@@ -0,0 +1,77 @@
+{
+  description = "A very basic flake";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+    infinitime.url = "github:shymega/InfiniTime?ref=shymega-feat/nix-flake&submodules=1";
+    # infinitime.url = "github:InfiniTimeOrg/InfiniTime";
+    flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";
+  };
+
+  outputs = { self, ... }@inputs:
+    let
+      forAllSystems = function:
+        inputs.nixpkgs.lib.genAttrs [
+          "x86_64-linux"
+          "aarch64-linux"
+        ]
+          (system: function (import inputs.nixpkgs {
+            inherit system;
+            config.allowUnfree = true;
+          }));
+    in
+    {
+      packages = forAllSystems (pkgs:
+        let
+          infinitime = inputs.infinitime.packages.${pkgs.system}.default;
+        in
+        with pkgs; {
+          default = stdenv.mkDerivation rec {
+            name = "infinisim";
+            srcs = [
+              (fetchFromGitHub {
+                name = "InfiniTime";
+                owner = "shymega";
+                repo = "InfiniTime";
+                rev = "refs/heads/shymega-feat/nix-flake";
+                fetchSubmodules = true;
+                leaveDotGit = true;
+                sha256 = "sha256-3x4FubKg8xXJf4t1QjSRIE8FKh89/0yT67bStH+a3HQ=";
+              })
+              (lib.cleanSource ./.)
+            ];
+            sourceRoot = ".";
+
+            nativeBuildInputs = with pkgs; [
+              SDL2
+              libpng
+              patch
+              zlib
+            ] ++ infinitime.nativeBuildInputs;
+
+            buildInputs = with pkgs; [
+              cmake
+            ] ++ infinitime.buildInputs;
+
+            preConfigure = ''
+              patchShebangs $sourceRoot/InfiniTime/src/displayapp/fonts/generate.py \
+                  $sourceRoot/InfiniTime/tools/mcuboot/imgtool.py \
+                  $sourceRoot/source/img/convert_bmp_to_header.py
+            '';
+
+            cmakeFlags = [
+              "-DInfiniTime_DIR=${sourceRoot}/InfiniTime"
+            ];
+          };
+        });
+
+      devShells = forAllSystems (pkgs:
+        {
+          default =
+            pkgs.mkShell {
+              packages = [ pkgs.ninja ] ++ self.packages.${pkgs.system}.default.nativeBuildInputs;
+            };
+        });
+    };
+}
+      

flake.nix

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+(import
+  (
+    let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
+    fetchTarball {
+      url = lock.nodes.flake-compat.locked.url or "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  { src = ./.; }
+).shellNix