{
  config,
  lib,
  pkgs,
  ...
}:
let
  inherit (lib)
    concatStringsSep
    mkIf
    mkMerge
    mkOption
    optionalAttrs
    types
    ;

  cfg = config.services.mbsync;

  isDarwin = pkgs.stdenv.isDarwin;
  isLinux = pkgs.stdenv.isLinux;

  mbsyncOptions = [
    "--all"
  ]
  ++ lib.optional cfg.verbose "--verbose"
  ++ lib.optional (cfg.configFile != null) "--config ${cfg.configFile}";

  mbsyncCommand = "${cfg.package}/bin/mbsync ${concatStringsSep " " mbsyncOptions}";

  # Convert systemd calendar format to launchd interval (approximate)
  # Format like "*:0/5" means every 5 minutes
  # We'll parse simple cases, default to 5 minutes
  parseFrequencyToSeconds =
    freq:
    let
      # Try to extract minute interval from patterns like "*:0/5" or "*:*:0/30"
      parts = builtins.match ".*\\*/([0-9]+).*" freq;
    in
    if parts != null then (lib.toInt (builtins.head parts)) * 60 else 300;

in
{
  meta.maintainers = [ lib.maintainers.pjones ];

  options.services.mbsync = {
    enable = lib.mkEnableOption "mbsync";

    package = lib.mkPackageOption pkgs "isync" { };

    frequency = mkOption {
      type = types.str;
      default = "*:0/5";
      description = ''
        How often to run mbsync. On Linux, this value is passed to the systemd
        timer configuration as the onCalendar option. See
        {manpage}`systemd.time(7)` for more information about the format.
        On Darwin, this is converted to an approximate interval in seconds.
      '';
    };

    verbose = mkOption {
      type = types.bool;
      default = true;
      description = ''
        Whether mbsync should produce verbose output.
      '';
    };

    configFile = mkOption {
      type = types.nullOr types.path;
      default = null;
      description = ''
        Optional configuration file to link to use instead of
        the default file ({file}`~/.mbsyncrc`).
      '';
    };

    preExec = mkOption {
      type = types.nullOr types.str;
      default = null;
      example = "mkdir -p %h/mail";
      description = ''
        An optional command to run before mbsync executes. This is
        useful for creating the directories mbsync is going to use.
      '';
    };

    postExec = mkOption {
      type = types.nullOr types.str;
      default = null;
      example = "\${pkgs.mu}/bin/mu index";
      description = ''
        An optional command to run after mbsync executes successfully.
        This is useful for running mailbox indexing tools.
      '';
    };
  };

  config = mkIf cfg.enable (mkMerge [
    # Linux-specific: systemd user service and timer
    (mkIf isLinux {
      systemd.user.services.mbsync = {
        Unit = {
          Description = "mbsync mailbox synchronization";
        };

        Service = {
          Type = "oneshot";
          ExecStart = mbsyncCommand;
        }
        // (optionalAttrs (cfg.postExec != null) {
          ExecStartPost = cfg.postExec;
        })
        // (optionalAttrs (cfg.preExec != null) {
          ExecStartPre = cfg.preExec;
        });
      };

      systemd.user.timers.mbsync = {
        Unit = {
          Description = "mbsync mailbox synchronization";
        };

        Timer = {
          OnCalendar = cfg.frequency;
          Unit = "mbsync.service";
        };

        Install = {
          WantedBy = [ "timers.target" ];
        };
      };
    })

    # Darwin-specific: launchd agent
    (mkIf isDarwin {
      launchd.agents.mbsync = {
        enable = true;
        config =
          let
            # Build a script that handles pre/post exec
            mbsyncScript = pkgs.writeShellScript "mbsync-wrapper" ''
              set -e
              ${lib.optionalString (cfg.preExec != null) cfg.preExec}
              ${mbsyncCommand}
              ${lib.optionalString (cfg.postExec != null) cfg.postExec}
            '';
          in
          {
            ProgramArguments = [ "${mbsyncScript}" ];
            StartInterval = parseFrequencyToSeconds cfg.frequency;
            RunAtLoad = true;
            StandardErrorPath = "/tmp/mbsync.err.log";
            StandardOutPath = "/tmp/mbsync.out.log";
          };
      };
    })
  ]);
}