# /etc/nixos/modules/seaweedfs-mount.nix
#
# This module sets up a systemd service to mount a SeaweedFS filer
# via FUSE directly on the NixOS host.

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

let
  # Use lib.mkOption to create configurable settings for our module.
  # This makes it reusable and easy to adjust from configuration.nix.
  cfg = config.services.seaweedfs-mount;
in
{
  # Define the options that can be set in configuration.nix
  options.services.seaweedfs-mount = {
    enable = lib.mkEnableOption "SeaweedFS FUSE mount service";

    filerAddresses = lib.mkOption {
      type = lib.types.listOf lib.types.str;
      example = [ "seaweedfs_filer_nix1:8888" "seaweedfs_filer_nix2:8888" ];
      description = "List of filer addresses (hostname:port) to connect to.";
    };

    mountPoint = lib.mkOption {
      type = lib.types.path;
      default = "/mnt/service/seaweedfs";
      description = "The absolute path where the SeaweedFS volume will be mounted.";
    };

    cacheDir = lib.mkOption {
      type = lib.types.path;
      default = "/data/seaweedfs/cache";
      description = "Directory for local FUSE cache.";
    };

    volumeDir = lib.mkOption {
      type = lib.types.path;
      default = "/data/seaweedfs/volume";
      description = "Directory for local volume.";
    };

    user = lib.mkOption {
      type = lib.types.str;
      default = "root";
      description = "The user to run the mount process as.";
    };

    group = lib.mkOption {
      type = lib.types.str;
      default = "root";
      description = "The group to run the mount process as.";
    };
  };

  # This part of the module will be activated only if services.seaweedfs-mount.enable = true;
  config = lib.mkIf cfg.enable {

    # 1. Ensure the FUSE kernel module is loaded at boot.
    boot.kernelModules = [ "fuse" ];

    # 2. Ensure the seaweedfs package is available in the system path.
    environment.systemPackages = [ pkgs.seaweedfs ];

    # 3. Create the necessary directories before the service starts.
    systemd.tmpfiles.rules = [
      "d ${cfg.mountPoint} 0755 ${cfg.user} ${cfg.group} -"
      "d ${cfg.cacheDir} 0755 ${cfg.user} ${cfg.group} -"
      "d ${cfg.volumeDir} 0755 ${cfg.user} ${cfg.group} -"
    ];

    # 4. Define the systemd service itself.
    systemd.services.seaweedfs-mount = {
      description = "SeaweedFS FUSE Mount Service";

      # Start after the network is fully available.
      wantedBy = [ "multi-user.target" ];
      after = [ "network-online.target" ];
      wants = [ "network-online.target" ];

      # Service configuration details.
      serviceConfig = {
        # The user and group to run the command as.
        User = cfg.user;
        Group = cfg.group;

        # The core command to start the mount process.
        # We build the -filer string by joining the list of addresses with commas.
        ExecStart = ''
          ${pkgs.seaweedfs}/bin/weed mount \
            -dir=${cfg.mountPoint} \
            -cacheDir=${cfg.cacheDir} \
            -filer=${lib.concatStringsSep "," cfg.filerAddresses} \
            -allowOthers=true \
            -map.uid="1000:0" \
            -map.gid="1000:0" \
            -dirAutoCreate \
            -cacheCapacityMB=15000 \
            -filer.path=/
        '';

        # Command to cleanly unmount on service stop.
        ExecStop = "${pkgs.util-linux}/bin/umount ${cfg.mountPoint}";

        # *** This is the key part for your request ***
        # Always restart the service if it fails.
        Restart = "always";
        # Wait 10 seconds before attempting to restart.
        RestartSec = "10s";

        # Required for FUSE mounts to work correctly under systemd.
        Type = "simple";
        KillMode = "process";
      };
    };
  };
}