{ lib, pkgs, config, ... }:
#
# cp -avl (to create hardlinks instead of copy)
# =============================================
#
#┌──────────────────────────────────┐      ┌──────────────────────────────────────┐
#│/media/torrent2/downloads/music    ├─────►│/media/syncthing/music/incomming      │
#└──────────────────────────────────┘      └──────────────────────────────────────┘
#┌──────────────────────────────────┐      ┌──────────────────────────────────────┐
#│/media/torrent2/downloads/movies   ├─────►│/media/syncthing/movies/incoming      │
#└──────────────────────────────────┘      └──────────────────────────────────────┘
#┌──────────────────────────────────┐      ┌──────────────────────────────────────┐
#│/media/torrent2/downloads          ├─────►│/media/torrent/incoming               │
#└──────────────────────────────────┘      └──────────────────────────────────────┘

let
  uiPort = 9091;

  #############################################
  # These are inherited from Transmission.    #
  # Do not declare these. Just use as needed. #
  #                                           #
  # TR_APP_VERSION                            #
  # TR_TIME_LOCALTIME                         #
  # TR_TORRENT_DIR                            #
  # TR_TORRENT_HASH                           #
  # TR_TORRENT_ID                             #
  # TR_TORRENT_NAME                           #
  #                                           #
  #############################################
  completionScript =
    let
      copy_map = {
        "/media/torrent/downloads/series" = "/media/syncthing/series/incoming";
        "/media/torrent/downloads/music" = "/media/syncthing/music/incoming";
        "/media/torrent/downloads/movies" = "/media/syncthing/movies/incoming";
        "/media/torrent/downloads" = "/media/torrent/incoming";
      };
      copy_script = lib.concatStringsSep "\n" (lib.mapAttrsToList
        (source: target: ''
          if [[ "$TR_TORRENT_DIR" == "${source}" ]]
          then
            cp -val "$TR_TORRENT_DIR/$TR_TORRENT_NAME" "${target}/$TR_TORRENT_NAME"
          fi
        '')
        copy_map);
    in
    pkgs.writers.writeBash "torrent-finished" copy_script;
in
{

  containers.torrent2 = {

    # mount host folders
    bindMounts = {
      media = {
        hostPath = "/media";
        mountPoint = "/media"; # must be here otherwise transmission can't see the folder
        isReadOnly = false;
      };
      lib = {
        hostPath = "/media/torrent/torrent2_config";
        mountPoint = "/var/lib/transmission/.config";
        isReadOnly = false;
      };
    };

    # container network setup
    # see also nating on host system.
    autoStart = true;

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

      system.stateVersion = "21.05";
      services.journald.extraConfig = "SystemMaxUse=1G";

      # allow transmission to write in syncthing folders
      users.groups.syncthing = {
        gid = config.ids.gids.syncthing;
        members = [ "transmission" ];
      };

      services.transmission = {
        enable = true;
        settings = {
          download-dir = "/media/torrent/downloads";
          incomplete-dir = "/media/torrent/incomplete";
          incomplete-dir-enabled = true;
          message-level = 1;
          umask = 2;
          rpc-whitelist-enabled = false;
          rpc-host-whitelist-enabled = false;
          rpc-port = uiPort;
          rpc-enable = true;
          rpc-bind-address = "127.0.0.1";

          # "normal" speed limits
          speed-limit-down-enabled = false;
          speed-limit-down = 800;
          speed-limit-up-enabled = true;
          speed-limit-up = 3000;
          upload-slots-per-torrent = 8;
          # Queuing
          # When true, Transmission will only download
          # download-queue-size non-stalled torrents at once.
          download-queue-enabled = true;
          download-queue-size = 3;

          # When true, torrents that have not shared data for
          # queue-stalled-minutes are treated as 'stalled'
          # and are not counted against the queue-download-size
          # and seed-queue-size limits.
          queue-stalled-enabled = true;
          queue-stalled-minutes = 60;

          # When true. Transmission will only seed seed-queue-size
          # non-stalled torrents at once.
          seed-queue-enabled = false;
          seed-queue-size = 10;

          # Enable UPnP or NAT-PMP.
          peer-port = 51413;
          port-forwarding-enabled = false;
          # Start torrents as soon as they are added

          start-added-torrents = true;

          # notify me when download finished
          script-torrent-done-enabled = true;
          script-torrent-done-filename = completionScript;

          # Encryption preference.
          # 0 = Prefer unencrypted connections,
          # 1 = Prefer encrypted connections,
          # 2 = Require encrypted connections;
          # default = 1
          # Encryption may help get around some ISP filtering, but at the cost of slightly
          # higher CPU use
          encryption = 2;
        };
      };

      networking.firewall = {
        allowedTCPPorts = [ 51413 ];
        allowedUDPPorts = [ 51413 ];
      };

      # bind transmission to openvpn
      systemd.services.transmission = {
        serviceConfig = {
          Restart = "always";
          BindPaths = lib.mkForce [
            "/media" # this is needed otherwise cp -l is not working
            "/var/lib/transmission/.config/transmission-daemon"
          ];
        };
      };
    };
  };

  networking.firewall = {
    allowedTCPPorts = [ 51413 ];
    allowedUDPPorts = [ 51413 ];
  };

  # host nginx setup
  # ----------------

  # curl -H "Host: transmission.robi.private" https://robi.private/  < will work
  # curl -H "Host: transmission.robi.private" https://144.76.13.147/ < wont work
  services.nginx = {
    enable = true;
    recommendedProxySettings = true;
    virtualHosts = {
      "transmission2.${config.networking.hostName}.private" = {
        extraConfig = ''
          allow ${config.tinc.private.subnet};
          deny all;
        '';
        locations."/" = {
          proxyPass = "http://127.0.0.1:${toString uiPort}";
        };
      };
    };
  };

}