# GNU Virtual Private Ethernet

{config, pkgs, ...}: 

let 
  inherit (pkgs.lib) mkOption mkIf;
  cfg = config.services.gvpe;
  finalConfig = if cfg.configFile != null then 
    cfg.configFile
  else if cfg.configText != null then
    pkgs.writeTextFile {
      name = "gvpe.conf";
      text = cfg.configText;
    }
  else 
    throw "You must either specify contents of the config file or the config file itself for GVPE";
  ifupScript = if cfg.ipAddress == null || cfg.subnet == null then 
     throw "Specify IP address and subnet (with mask) for GVPE" 
   else if cfg.nodename == null then 
     throw "You must set node name for GVPE" 
   else
   (pkgs.writeTextFile { 
    name = "gvpe-if-up";
    text = ''
      #! /bin/sh
      
      export PATH=$PATH:${pkgs.iproute}/sbin

      ip link set $IFNAME up
      ip address add ${cfg.ipAddress} dev $IFNAME
      ip route add ${cfg.subnet} dev $IFNAME

      ${cfg.customIFSetup}
    '';
    executable = true;
  });
  exec = "${pkgs.gvpe}/sbin/gvpe -c /var/gvpe -D ${cfg.nodename} "
    + " ${cfg.nodename}.pid-file=/var/gvpe/gvpe.pid"
    + " ${cfg.nodename}.if-up=if-up"
    + " &> /var/log/gvpe";
  inherit (cfg) startOn stopOn;
in

{
  options = {
    services.gvpe = {
      enable = mkOption {
        default = false;
        description = ''
          Whether to run gvpe
        '';
      };
      startOn = mkOption {
        default = "network-interfaces/started";
        description = ''
          Condition to start GVPE
        '';
      };
      stopOn = mkOption {
        default = "network-interfaces/stop";
        description = ''
          Condition to stop GVPE
        '';
      };
      nodename = mkOption {
        default = null;
        description =''
          GVPE node name
        '';
      };
      configText = mkOption {
        default = null;
        example = ''
          tcp-port = 655
          udp-port = 655
          mtu = 1480
          ifname = vpn0
          
          node = alpha
          hostname = alpha.example.org
          connect = always
          enable-udp = true
          enable-tcp = true
          on alpha if-up = if-up-0
          on alpha pid-file = /var/gvpe/gvpe.pid
        '';
        description = ''
          GVPE config contents
        '';
      };
      configFile = mkOption {
        default = null;
        example = "/root/my-gvpe-conf";
        description = ''
          GVPE config file, if already present
        '';
      };
      ipAddress = mkOption {
        default = null;
        description = ''
          IP address to assign to GVPE interface
        '';
      };
      subnet = mkOption {
        default = null;
        example = "10.0.0.0/8";
        description = ''
          IP subnet assigned to GVPE network
        '';
      };
      customIFSetup = mkOption {
        default = "";
        description = ''
          Additional commands to apply in ifup script
        '';
      };
    };
  };
  config = mkIf cfg.enable 
  {
    jobs.gvpe = {
      description = "GNU Virtual Private Ethernet node";
      
      inherit startOn stopOn;

      preStart = ''
        mkdir -p /var/gvpe
        mkdir -p /var/gvpe/pubkey
        chown root /var/gvpe
        chmod 700 /var/gvpe
        cp ${finalConfig} /var/gvpe/gvpe.conf
	cp ${ifupScript} /var/gvpe/if-up
      '';

      inherit exec;

      respawn = true;
    };
  };
}