{ pkgs, config, lib, ... }:
let
  cfg = config.sbruder.restic.system;

  sftpTarget = "u313368-sub4@u313368-sub4.your-storagebox.de";
  sftpPort = 23;
  repository = "sftp://${sftpTarget}:${toString sftpPort}/personal";
  excludes = [
    # Caches
    "/home/*/Downloads/"
    "/home/*/.cache/"
    "/home/*/**/cache/"
    "/home/*/.local/share/Trash" # some gui applications use it
    "/root/.cache"
    "/data/cache/"
    "/var/cache/"

    # Rust
    "/home/*/.rustup/toolchains/"
    "/home/*/.cargo"

    # Misc
    "/home/*/mount"
    "/home/*/mounts"

    # Docker (state should be kept somewhere else)
    "/var/lib/docker/"

    # Static configuration (generated from this repository)
    "/etc/static/"
  ] ++ cfg.extraExcludes;
  excludesFile = pkgs.writeText "excludes.txt" (lib.concatStringsSep "\n" excludes);

  # script to use restic as user without dealing with authentication
  authScript = pkgs.writeShellScriptBin "restic-auth" ''
    ${pkgs.restic}/bin/restic \
      --password-command="pass data/backup/restic-nixos" \
      --repo "${repository}" \
      $@
  '';

  # HACK: NixOS’ nftables implementation runs nft -c inside the build sandbox,
  # where the target host’s cgroups are not available,
  # and therefore fails.
  # This is there to allow my home router to put backup traffic into the right qdisc,
  # as the ip address and port are also used for other things.
  # This is somewhat of an abuse of the DSCP mark.
  qosRules = pkgs.writeText "restic-qos.nft" ''
    table inet restic
    delete table inet restic

    table inet restic {
      chain output {
        type filter hook output priority mangle
        ip version 4 socket cgroupv2 level 1 "restic.slice" ip dscp set af12 return
        ip6 version 6 socket cgroupv2 level 1 "restic.slice" ip6 dscp set af12 return
      }
    }
  '';
in
{
  options.sbruder.restic.system = {
    enable = lib.mkEnableOption "restic";
    timerConfig = lib.mkOption {
      type = with lib.types; attrsOf str;
      default = {
        OnCalendar = "18:00";
        RandomizedDelaySec = "2h";
      };
    };
    extraPaths = lib.mkOption {
      type = lib.types.listOf lib.types.str;
      default = [ ];
      example = [ "/data" ];
    };
    extraExcludes = lib.mkOption {
      type = lib.types.listOf lib.types.str;
      default = [ ];
    };
    uploadLimit = lib.mkOption {
      type = lib.types.nullOr lib.types.int;
      default = null;
    };
    qos = (lib.mkEnableOption "QoS marking (DSCP AF12) of outgoing packets") // { default = !(lib.isNull cfg.uploadLimit); };
    prune = lib.mkEnableOption "pruning";
  };

  config = lib.mkIf cfg.enable {
    sops.secrets = {
      restic-password = { };
      restic-repository = { };
    } // lib.optionalAttrs cfg.prune {
      restic-ssh-key = {
        sopsFile = ../../machines/${config.networking.hostName}/secrets.yaml;
      };
    };

    services.restic.backups.system = {
      inherit (cfg) timerConfig;
      repositoryFile = config.sops.secrets.restic-repository.path;
      passwordFile = config.sops.secrets.restic-password.path;
      paths = [
        "/etc"
        "/home"
        "/root"
        "/srv"
        "/var"
      ] ++ cfg.extraPaths;
      extraBackupArgs = [
        "--compression auto"
        "--exclude-caches"
        "--exclude-file=${excludesFile}"
        "--tag system"
        "--verbose"
      ] ++ lib.optional (cfg.uploadLimit != null) "--limit-upload=${toString cfg.uploadLimit}";
      backupPrepareCommand = ''
        ${pkgs.nftables}/bin/nft -f ${qosRules}
      '';
      backupCleanupCommand = ''
        ${pkgs.nftables}/bin/nft delete table inet restic
      '';
    };

    systemd.services."restic-backups-system".serviceConfig = {
      "Nice" = 10;
      "IOSchedulingClass" = "best-effort";
      "IOSchedulingPriority" = 7;
      Slice = "restic.slice";
    };

    services.restic.backups.system-prune = lib.mkIf cfg.prune {
      inherit repository;
      passwordFile = config.sops.secrets.restic-password.path;
      timerConfig = {
        OnCalendar = "*-1/2-07 03:00:00";
        RandomizedDelaySec = "4h";
      };
      paths = [ ];
      extraOptions = [
        "-o"
        "sftp.command='ssh -i ${config.sops.secrets.restic-ssh-key.path} -p ${toString sftpPort} ${sftpTarget} -s sftp'"
      ];
      pruneOpts = [
        "--compression auto"
        "--keep-daily 7"
        "--keep-monthly 12"
        "--keep-weekly 5"
        "--keep-yearly 10"
        "--tag system"
        "--verbose"
      ] ++ lib.optional (cfg.uploadLimit != null) "--limit-upload=${toString cfg.uploadLimit}";
    };

    environment.systemPackages = [
      authScript
    ];
  };
}