{ config, pkgs, lib, ... }:

with lib;

let
  cfg = config.services.naxos.selfUpdate;

  updateScript = pkgs.writeShellScriptBin "naxos-self-update" ''
    set -euo pipefail
    CONFIG_DIR="''${CONFIG_DIR:-/etc/naxos/repo}"
    LOG_FILE="/var/log/naxos-update.log"

    echo "[$(date -Iseconds)] Checking for NaxOS updates..." | tee -a "$LOG_FILE"

    if [ ! -d "$CONFIG_DIR/.git" ]; then
      echo "Configuration directory is not a git repository. Skipping." | tee -a "$LOG_FILE"
      exit 0
    fi

    cd "$CONFIG_DIR"
    git fetch origin main

    LOCAL_HASH=$(git rev-parse HEAD)
    REMOTE_HASH=$(git rev-parse origin/main)

    if [ "$LOCAL_HASH" = "$REMOTE_HASH" ]; then
      echo "System is already up to date ($LOCAL_HASH)." | tee -a "$LOG_FILE"
      exit 0
    fi

    echo "New updates detected ($LOCAL_HASH -> $REMOTE_HASH). Updating flake inputs and pulling..." | tee -a "$LOG_FILE"
    git merge origin/main --ff-only

    echo "Rebuilding and applying configuration..." | tee -a "$LOG_FILE"
    naxos-rebuild-safe
  '';

in {
  options.services.naxos.selfUpdate = {
    enable = mkEnableOption "NaxOS Automated Background Self-Update Service";

    schedule = mkOption {
      type = types.str;
      default = "*-*-* 04:00:00"; # Daily at 4:00 AM
      description = "Systemd calendar expression for scheduled update checks.";
    };

    channel = mkOption {
      type = types.enum [ "stable" "beta" "nightly" ];
      default = "stable";
      description = "Update release channel.";
    };
  };

  config = mkIf cfg.enable {
    environment.systemPackages = [ updateScript ];

    systemd.services.naxos-self-update = {
      description = "NaxOS Self-Update Check & Apply";
      path = [ pkgs.git pkgs.nix pkgs.systemd pkgs.bash ];
      serviceConfig = {
        Type = "oneshot";
        ExecStart = "${updateScript}/bin/naxos-self-update";
      };
    };

    systemd.timers.naxos-self-update = {
      description = "NaxOS Scheduled Self-Update Timer";
      wantedBy = [ "timers.target" ];
      timerConfig = {
        OnCalendar = cfg.schedule;
        Persistent = true;
        RandomizedDelaySec = "1800"; # 30 min random jitter
      };
    };
  };
}