nfsroot: add reinstallDacbert command

hosts/nfsroot/default.nix

@@ -1,10 +1,29 @@
-{ lib, ... }:
+{ config, lib, pkgs, ... }:
 let
   nfsExports = [
     "var/lib/nfsroot/dacbert"
     "var/lib/nfsroot/riscbert"
     "var/lib/dump-dvb/whoopsie"
   ];
+
+  reinstallDacbert = pkgs.writeScriptBin "reinstall-dacbert" ''
+    SYSTEM=$(${pkgs.curl}/bin/curl -sLH "Accept: application/json" \
+      https://hydra.hq.c3d2.de/job/c3d2/nix-config/dacbert/latest \
+      | ${pkgs.jq}/bin/jq -er .buildoutputs.out.path
+    )
+    BOOT=$(${pkgs.curl}/bin/curl -sLH "Accept: application/json" \
+      https://hydra.hq.c3d2.de/job/c3d2/nix-config/dacbert-tftproot/latest \
+      | ${pkgs.jq}/bin/jq -er .buildoutputs.out.path
+    )
+    ${config.nix.package}/bin/nix --extra-experimental-features nix-command \
+      copy \
+      --from https://nix-cache.hq.c3d2.de \
+      --to /var/lib/nfsroot/dacbert \
+      --no-check-sigs \
+      $SYSTEM $BOOT
+    cp /var/lib/nfsroot/dacbert/$BOOT/* /var/lib/nfsroot/dacbert/boot/
+  '';
+
 in {
   imports = [
     ./tftp.nix
@@ -37,5 +56,7 @@ in {
     firewall.enable = false;
   };
 
+  environment.systemPackages = [ reinstallDacbert ];
+
   system.stateVersion = "22.05";
 }