pkgs/nixfiles: add script for installing the last system successfully built by hydra

pkgs/nixfiles/nixfiles-system-sync-to-hydra.nix

@@ -0,0 +1,11 @@
+{ pkgs, ... }:
+
+pkgs.writeShellApplication {
+  name = "nixfiles-system-sync-to-hydra";
+  text = builtins.readFile ./nixfiles-system-sync-to-hydra.sh;
+  runtimeInputs = with pkgs; [
+    curl
+    jq
+    nix
+  ];
+}

pkgs/nixfiles/nixfiles-system-sync-to-hydra.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+HYDRA_JOB_URL="https://hydra.clerie.de/job/nixfiles/nixfiles/nixosConfigurations.$(hostname)/latest-finished"
+
+echo "Fetching job output from ${HYDRA_JOB_URL}"
+STORE_PATH="$(curl --fail -s -L -H "Accept: application/json" "${HYDRA_JOB_URL}" | jq -r ".buildoutputs.out.path")"
+
+echo "Download ${STORE_PATH}"
+nix copy --from "https://nix-cache.clerie.de" "${STORE_PATH}"
+
+echo "Add to system profile"
+nix-env -p "/nix/var/nix/profiles/system" --set "${STORE_PATH}"
+
+echo "Activate system"
+/nix/var/nix/profiles/system/bin/switch-to-configuration switch
+
+echo "Finished system upgrade"