all: add easy update script

modules/common/default.nix

@@ -5,6 +5,7 @@
     ../home/default.nix
     ./shell.nix
     ./ssh.nix
+    ./update_scripts.nix
   ];
 
   nix = {

modules/common/update_scripts.nix

@@ -0,0 +1,58 @@
+{ config, pkgs, lib, ... }:
+
+let
+  update = pkgs.writeScriptBin "update" ''
+    #! ${pkgs.runtimeShell}
+    set -e
+
+    if [[ $EUID -ne 0 ]]; then
+      exec sudo ${pkgs.runtimeShell} "$0" "$@"
+    fi
+
+    if [ -n "$1" ]; then
+      BRANCH=$1
+    else
+      BRANCH=main
+    fi
+
+    cd /etc/nixos
+    if [ "$BRANCH" = "main" ]; then
+      ${pkgs.git}/bin/git switch $BRANCH
+      ${pkgs.git}/bin/git pull
+    else
+      ${pkgs.git}/bin/git fetch
+      ${pkgs.git}/bin/git switch --detach origin/$BRANCH
+    fi
+
+    if ! ${pkgs.nixos-rebuild}/bin/nixos-rebuild --flake "/etc/nixos#${config.networking.fqdn}" test; then
+      echo "WARNING: `nixos-rebuild test` failed!"
+    fi
+
+    while true; do
+      read -p "Do you want to boot this configuration? " yn
+      case $yn in
+          [Yy]* ) break;;
+          [Nn]* ) exit;;
+          * ) echo "Please answer yes or no.";;
+      esac
+    done
+
+    ${pkgs.nixos-rebuild}/bin/nixos-rebuild --flake "/etc/nixos#${config.networking.fqdn}" boot
+
+    while true; do
+      read -p "Would you like to reboot now? " yn
+      case $yn in
+          [Yy]* ) reboot;;
+          [Nn]* ) exit;;
+          * ) echo "Please answer yes or no.";;
+      esac
+    done
+  '';
+in
+{
+  config = {
+    environment.systemPackages = [
+      update
+    ];
+  };
+}