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

with lib;

let
  cfg = config.malobeo.autoUpdate;
in
{
  options.malobeo.autoUpdate = {
    enable = mkOption {
      description = ''
        Enables a timer that periodically checks a hydra instance for the last build of the local system, and switches to it if it is different.
  
        Also enables periodical /nix/store GC.
      '';
      type = types.bool;
      default = false;
    };

    # https://hydra.dynamicdiscord.de/job/malobeo/infrastructure/louise/latest
    url = mkOption {
      description = lib.mdDoc ''
        Url to your hydra instace. like https://hydra.example.de
      '';
      type = types.str;
      default = "";
    };

    project = mkOption {
      description = lib.mdDoc ''
        Name of the project at the hydra instace
      '';
      type = types.str;
      default = "";
    };

    jobset = mkOption {
      description = lib.mdDoc ''
        Name of the jobset at the hydra instace
      '';
      type = types.str;
      default = "";
    };

    cacheurl = mkOption {
      description = lib.mdDoc ''
        Url of the binary cache
      '';
      type = types.str;
      default = cfg.url;
    };
  };

  config = {
    # the presence of this .service file signifies that the system is
    # autoupdate-enabled. it is checked to prevent autoupdating back
    # to a system without autoupdate when deploying with autoupdate
    # for the first time.
    systemd.services.autoupdate = lib.mkIf config.malobeo.autoUpdate.enable {
      wantedBy = [ "multi-user.target" ];
      path = with pkgs; [ nix nettools curl jq ];
      serviceConfig = {
        Type = "oneshot";
        # switch-to-configuration may not return. HACK: cap running
        # time so that the timer can be scheduled again.
        TimeoutStartSec = "30min";
      };
      script = ''
        OLD=$(readlink /run/current-system)
        echo Current system: $(basename $OLD)
        NEW=$(curl -sLH "Accept: application/json" ${cfg.url}/job/${cfg.project}/${cfg.jobset}/${config.networking.hostName}/latest | jq -er .buildoutputs.out.path)
        if [ -z "$NEW" ] || [ "$NEW" = "null" ]; then
          echo "Unable to obtain updated system"
          exit 1
        fi
        echo New system: $(basename $NEW)

        if [ "$OLD" != "$NEW" ]; then
          echo "Fetching new system built by ${cfg.url}/job/${cfg.project}/${cfg.jobset}"
          # this should fetch the new system from the binary cache
          nix copy --from ${cfg.cacheurl} "$NEW"
          if [ -e "$NEW/etc/systemd/system/autoupdate.timer" ]; then
            echo "Switch to the new system..."
            nix-env -p /nix/var/nix/profiles/system --set $NEW
            "$NEW/bin/switch-to-configuration" switch
          else
            echo "New system is not yet autoupdate-enabled. Refusing to switch into a dead end."
          fi
        else
          echo "No update required"
        fi
      '';
      # don't let the switch kill this service, aborting the switch
      restartIfChanged = false;
      unitConfig.X-StopOnRemoval = false;
      # create timer
      startAt = "hourly";
    };

    nix = {
      # Show a diff when activating a new system except for microvms which handle this seperately
      #diffSystem = config.malobeo.deployment.server or "" == "";
      #TODO: THIS WIPES HOSTS NIX STORE FROM WITHIN NIXOS-CONTAINER
      #gc = lib.mkIf config.malobeo.autoUpdate.enable {
      #  automatic = true;
      #  randomizedDelaySec = "6h";
      #  options = "--delete-older-than 21d";
      #};
    };

    environment.systemPackages = [ (
      # Provide a manual updating script that fetches the latest
      # updated+built system from Hydra
      pkgs.writeScriptBin "update-from-hydra" ''
        #! ${pkgs.runtimeShell} -e

        OLD=$(readlink /run/current-system)
        echo Current system: $(basename $OLD)
        NEW=$(curl -sLH "Accept: application/json" ${cfg.url}/job/${cfg.project}/${cfg.jobset}/${config.networking.hostName}/latest | ${pkgs.jq}/bin/jq -er .buildoutputs.out.path)
        if [ -z "$NEW" ] || [ "$NEW" = "null" ]; then
          echo "Unable to obtain updated system"
          exit 1
        fi
        echo New system: $(basename $NEW)

        if [ "$OLD" != "$NEW" ]; then
          echo "Fetching new system built by ${cfg.url}/job/${cfg.project}/${cfg.jobset}"
          # this should fetch the new system from the binary cache
          nix copy --from ${cfg.cacheurl} "$NEW"
          echo "Switch to the new system..."
          nix-env -p /nix/var/nix/profiles/system --set $NEW
          "$NEW/bin/switch-to-configuration" switch
        else
          echo "No update required"
        fi
      ''
    ) ];
  };
}