# roles/thin-client/deployment/snapper.nix
#
# BTRFS snapshots for the root subvolume via snapper. Snapshots taken
# before and after each `nixos-rebuild switch`, plus hourly/daily.
#
# Q18 decision: Generation-Picker + BTRFS-Snapshot.
{config, lib, ...}: let
  inherit (lib) mkIf;
  cfg = config.az.tc;
in {
  config = mkIf cfg.enable {
    services.snapper = {
      snapshotRootOnBoot = true;
      configs = {
        root = {
          SUBVOLUME = "/";
          ALLOW_USERS = ["root"];
          TIMELINE_CREATE = true;
          TIMELINE_CLEANUP = true;
          TIMELINE_LIMIT_HOURLY = "12";
          TIMELINE_LIMIT_DAILY = "7";
          TIMELINE_LIMIT_WEEKLY = "4";
          TIMELINE_LIMIT_MONTHLY = "0";
        };
      };
    };

    # Take a snapshot before any nixos-rebuild switch — hooks into the
    # toplevel system path activation.
    system.activationScripts.snapperPreSwitch = {
      deps = [];
      text = ''
        if [ -d /.snapshots ]; then
          ${config.services.snapper.package}/bin/snapper -c root create \
            -d "pre-switch $(date +%Y-%m-%d-%H%M)" || true
        fi
      '';
    };
  };
}