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

with lib;

let

  cfg = config.services.nfs.server;

  exports = pkgs.writeText "exports" cfg.exports;

  rpcUser = "statd";

in

{
  imports = [
    (mkRenamedOptionModule [ "services" "nfs" "lockdPort" ] [ "services" "nfs" "server" "lockdPort" ])
    (mkRenamedOptionModule [ "services" "nfs" "statdPort" ] [ "services" "nfs" "server" "statdPort" ])
  ];

  ###### interface

  options = {

    services.nfs = {

      server = {
        enable = mkOption {
          type = types.bool;
          default = false;
          description = ''
            Whether to enable the kernel's NFS server.
          '';
        };

        extraNfsdConfig = mkOption {
          type = types.str;
          default = "";
          description = ''
            Extra configuration options for the [nfsd] section of /etc/nfs.conf.
          '';
        };

        exports = mkOption {
          type = types.lines;
          default = "";
          description = ''
            Contents of the /etc/exports file.  See
            <citerefentry><refentrytitle>exports</refentrytitle>
            <manvolnum>5</manvolnum></citerefentry> for the format.
          '';
        };

        hostName = mkOption {
          type = types.nullOr types.str;
          default = null;
          description = ''
            Hostname or address on which NFS requests will be accepted.
            Default is all.  See the <option>-H</option> option in
            <citerefentry><refentrytitle>nfsd</refentrytitle>
            <manvolnum>8</manvolnum></citerefentry>.
          '';
        };

        nproc = mkOption {
          type = types.int;
          default = 8;
          description = ''
            Number of NFS server threads.  Defaults to the recommended value of 8.
          '';
        };

        createMountPoints = mkOption {
          type = types.bool;
          default = false;
          description = "Whether to create the mount points in the exports file at startup time.";
        };

        mountdPort = mkOption {
          type = types.nullOr types.int;
          default = null;
          example = 4002;
          description = ''
            Use fixed port for rpc.mountd, useful if server is behind firewall.
          '';
        };

        lockdPort = mkOption {
          type = types.nullOr types.int;
          default = null;
          example = 4001;
          description = ''
            Use a fixed port for the NFS lock manager kernel module
            (<literal>lockd/nlockmgr</literal>).  This is useful if the
            NFS server is behind a firewall.
          '';
        };

        statdPort = mkOption {
          type = types.nullOr types.int;
          default = null;
          example = 4000;
          description = ''
            Use a fixed port for <command>rpc.statd</command>. This is
            useful if the NFS server is behind a firewall.
          '';
        };

      };

    };

  };


  ###### implementation

  config = mkIf cfg.enable {

    services.nfs.extraConfig = ''
      [nfsd]
      threads=${toString cfg.nproc}
      ${optionalString (cfg.hostName != null) "host=${cfg.hostName}"}
      ${cfg.extraNfsdConfig}

      [mountd]
      ${optionalString (cfg.mountdPort != null) "port=${toString cfg.mountdPort}"}

      [statd]
      ${optionalString (cfg.statdPort != null) "port=${toString cfg.statdPort}"}

      [lockd]
      ${optionalString (cfg.lockdPort != null) ''
        port=${toString cfg.lockdPort}
        udp-port=${toString cfg.lockdPort}
      ''}
    '';

    services.rpcbind.enable = true;

    boot.supportedFilesystems = [ "nfs" ]; # needed for statd and idmapd

    environment.etc.exports.source = exports;

    systemd.services.nfs-server = {
      enable = true;
      wantedBy = [ "multi-user.target" ];
    };

    systemd.services.nfs-mountd = {
      enable = true;
      restartTriggers = [ exports ];

      preStart = optionalString cfg.createMountPoints ''
        # create export directories:
        # skip comments, take first col which may either be a quoted
        # "foo bar" or just foo (-> man export)
        sed '/^#.*/d;s/^"\([^"]*\)".*/\1/;t;s/[ ].*//' ${exports} \
        | xargs -d '\n' mkdir -p
      '';
    };

    # rpc-statd will drop privileges by changing user from root to the owner of
    # /var/lib/nfs
    systemd.tmpfiles.rules = [
      "d /var/lib/nfs 0700 ${rpcUser} ${rpcUser} - -"
    ] ++ map (e:
      "d /var/lib/nfs/${e} 0755 root root - -"
    ) [ "recovery" "v4recovery" "sm" "sm.bak" ];

    users = {
      groups."${rpcUser}" = {};
      users."${rpcUser}" = {
        description = "NFS RPC user";
        group = rpcUser;
        isSystemUser = true;
      };
    };
  };

}