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

with lib;

let
  cfg = config.services.syncoid;

  # Extract pool names of local datasets (ones that don't contain "@") that
  # have the specified type (either "source" or "target")
  getPools = type: unique (map (d: head (builtins.match "([^/]+).*" d)) (
    # Filter local datasets
    filter (d: !hasInfix "@" d)
    # Get datasets of the specified type
    (catAttrs type (attrValues cfg.commands))
  ));
in {

    # Interface

    options.services.syncoid = {
      enable = mkEnableOption "Syncoid ZFS synchronization service";

      interval = mkOption {
        type = types.str;
        default = "hourly";
        example = "*-*-* *:15:00";
        description = ''
          Run syncoid at this interval. The default is to run hourly.

          The format is described in
          <citerefentry><refentrytitle>systemd.time</refentrytitle>
          <manvolnum>7</manvolnum></citerefentry>.
        '';
      };

      user = mkOption {
        type = types.str;
        default = "syncoid";
        example = "backup";
        description = ''
          The user for the service. ZFS privilege delegation will be
          automatically configured for any local pools used by syncoid if this
          option is set to a user other than root. The user will be given the
          "hold" and "send" privileges on any pool that has datasets being sent
          and the "create", "mount", "receive", and "rollback" privileges on
          any pool that has datasets being received.
        '';
      };

      group = mkOption {
        type = types.str;
        default = "syncoid";
        example = "backup";
        description = "The group for the service.";
      };

      sshKey = mkOption {
        type = types.nullOr types.path;
        # Prevent key from being copied to store
        apply = mapNullable toString;
        default = null;
        description = ''
          SSH private key file to use to login to the remote system. Can be
          overridden in individual commands.
        '';
      };

      commonArgs = mkOption {
        type = types.listOf types.str;
        default = [];
        example = [ "--no-sync-snap" ];
        description = ''
          Arguments to add to every syncoid command, unless disabled for that
          command. See
          <link xlink:href="https://github.com/jimsalterjrs/sanoid/#syncoid-command-line-options"/>
          for available options.
        '';
      };

      commands = mkOption {
        type = types.attrsOf (types.submodule ({ name, ... }: {
          options = {
            source = mkOption {
              type = types.str;
              example = "pool/dataset";
              description = ''
                Source ZFS dataset. Can be either local or remote. Defaults to
                the attribute name.
              '';
            };

            target = mkOption {
              type = types.str;
              example = "user@server:pool/dataset";
              description = ''
                Target ZFS dataset. Can be either local
                (<replaceable>pool/dataset</replaceable>) or remote
                (<replaceable>user@server:pool/dataset</replaceable>).
              '';
            };

            recursive = mkOption {
              type = types.bool;
              default = false;
              description = ''
                Whether to also transfer child datasets.
              '';
            };

            sshKey = mkOption {
              type = types.nullOr types.path;
              # Prevent key from being copied to store
              apply = mapNullable toString;
              description = ''
                SSH private key file to use to login to the remote system.
                Defaults to <option>services.syncoid.sshKey</option> option.
              '';
            };

            sendOptions = mkOption {
              type = types.separatedString " ";
              default = "";
              example = "Lc e";
              description = ''
                Advanced options to pass to zfs send. Options are specified
                without their leading dashes and separated by spaces.
              '';
            };

            recvOptions = mkOption {
              type = types.separatedString " ";
              default = "";
              example = "ux recordsize o compression=lz4";
              description = ''
                Advanced options to pass to zfs recv. Options are specified
                without their leading dashes and separated by spaces.
              '';
            };

            useCommonArgs = mkOption {
              type = types.bool;
              default = true;
              description = ''
                Whether to add the configured common arguments to this command.
              '';
            };

            extraArgs = mkOption {
              type = types.listOf types.str;
              default = [];
              example = [ "--sshport 2222" ];
              description = "Extra syncoid arguments for this command.";
            };
          };
          config = {
            source = mkDefault name;
            sshKey = mkDefault cfg.sshKey;
          };
        }));
        default = {};
        example = literalExample ''
          {
            "pool/test".target = "root@target:pool/test";
          }
        '';
        description = "Syncoid commands to run.";
      };
    };

    # Implementation

    config = mkIf cfg.enable {
      users =  {
        users = mkIf (cfg.user == "syncoid") {
          syncoid = {
            group = cfg.group;
            isSystemUser = true;
          };
        };
        groups = mkIf (cfg.group == "syncoid") {
          syncoid = {};
        };
      };

      systemd.services.syncoid = {
        description = "Syncoid ZFS synchronization service";
        script = concatMapStringsSep "\n" (c: lib.escapeShellArgs
          ([ "${pkgs.sanoid}/bin/syncoid" ]
            ++ (optionals c.useCommonArgs cfg.commonArgs)
            ++ (optional c.recursive "-r")
            ++ (optionals (c.sshKey != null) [ "--sshkey" c.sshKey ])
            ++ c.extraArgs
            ++ [ "--sendoptions" c.sendOptions
                 "--recvoptions" c.recvOptions
                 "--no-privilege-elevation"
                 c.source c.target
               ])) (attrValues cfg.commands);
        after = [ "zfs.target" ];
        serviceConfig = {
          ExecStartPre = (map (pool: lib.escapeShellArgs [
            "+/run/booted-system/sw/bin/zfs" "allow"
            cfg.user "hold,send" pool
          ]) (getPools "source")) ++
          (map (pool: lib.escapeShellArgs [
            "+/run/booted-system/sw/bin/zfs" "allow"
            cfg.user "create,mount,receive,rollback" pool
          ]) (getPools "target"));
          User = cfg.user;
          Group = cfg.group;
        };
        startAt = cfg.interval;
      };
    };

    meta.maintainers = with maintainers; [ lopsided98 ];
  }