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

with lib;

let
  zfssnap = pkgs.stdenv.mkDerivation rec {
    name = "zfssnap";
    src = ./zfssnap.py;

    phases = [ "buildPhase" "checkPhase" "installPhase" ];

    buildInputs = with pkgs; [makeWrapper];

    python = pkgs.python39.withPackages (ps: with ps; [pyxdg pytimeparse dateutil]);

    buildPhase = ''
      substitute $src zfssnap \
        --subst-var-by python ${escapeShellArg python}
    '';

    doCheck = true;
    checkPhase = ''
      ${python}/bin/python -m py_compile zfssnap
    '';

    installPhase = ''
      install -m 0755 -D -t $out/bin \
        zfssnap

      wrapProgram $out/bin/zfssnap \
        --prefix PATH : ${makeBinPath [config.boot.zfs.package]}
    '';
  };

  cfg = config.services.zfssnap;
in {
  options = {
    services.zfssnap = {
      enable = mkEnableOption "zfssnap service";

      config = mkOption {
        type = with types; attrsOf (attrsOf str);
        default = {
          keep = {
            within = "15m";
            "5m" = "48";
            "15m" = "32";
            hourly = "48";
            "4h" = "24";
            "12h" = "12";
            daily = "62";
            halfweekly = "32";
            weekly = "24";
            monthly = "-1";
          };
        };
      };

      snapInterval = mkOption {
        type = types.str;
        default = "*-*-* *:00/5:00";
      };
    };
  };

  config = mkIf cfg.enable {
    systemd.services."zfssnap" = {
      description = "Create automatic ZFS snapshots";
      after = [ "zfs-import.target" ];
      wants = [ "zfssnap-prune.service" ];
      before = [ "zfssnap-prune.service" ];
      serviceConfig = {
        Type = "oneshot";
        ExecStart = "${zfssnap}/bin/zfssnap -v";
      };
    };
    systemd.services."zfssnap-prune" = {
      description = "Prune automatic ZFS snapshots";
      after = [ "zfs-import.target" "zfssnap.service" ];
      serviceConfig = {
        Type = "oneshot";
        ExecStart = let
          mkSectionName = name: strings.escape [ "[" "]" ] (strings.toUpper name);
          zfssnapConfig = generators.toINI { inherit mkSectionName; } cfg.config;
        in "${zfssnap}/bin/zfssnap -vv prune --config=${pkgs.writeText "zfssnap.ini" zfssnapConfig}";
      };
    };

    systemd.timers."zfssnap" = {
      wantedBy = ["timers.target"];
      timerConfig = {
        OnCalendar = cfg.snapInterval;
        Persistent = true;
      };
    };

    environment.systemPackages = [zfssnap];
  };
}