add core configuration

modules/containers/default.nix

@@ -0,0 +1,48 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}: let
+  cfg = config.lily.containers;
+in {
+  options.lily.containers = {
+    enable = lib.mkEnableOption "activate containers";
+    docker = lib.mkEnableOption "activate docker";
+    podman = lib.mkEnableOption "activate podman";
+  };
+
+  config = lib.mkMerge [
+    # (lib.mkIf (cfg.enable && cfg.docker && cfg.podman)
+    #   (builtins.throw "You can't enable both docker and podman at the same time"))
+    {
+      assertions = [
+        {
+          assertion = !(cfg.docker && cfg.podman);
+          message = "You cannot enable docker and podman at the same time";
+        }
+      ];
+    }
+    (lib.mkIf (cfg.enable && cfg.docker) {
+      # Enable docker support:
+      virtualisation.containers.enable = true;
+      virtualisation.docker.enable = true;
+    })
+    (lib.mkIf (cfg.enable && cfg.podman) {
+      # Enable podman support:
+      virtualisation.containers.enable = true;
+      virtualisation.podman = {
+        enable = true;
+        dockerCompat = true;
+        dockerSocket.enable = true;
+        defaultNetwork.settings = {
+          dns_enabled = true;
+        };
+      };
+      environment.systemPackages = with pkgs; [
+        podman
+        podman-compose
+      ];
+    })
+  ];
+}