dotfiles/os/syncthing/default.nix

{
  pkgs,
  lib,
  config,
  ...
}:
let
  cfg = config.services.syncthing;
  service = "syncthing";
  secretsDir = "/etc/secrets/${service}";
  password = {
    path = "syncthing/${config.frogeye.name}";
    selector = "@";
    generator = ''(t="$(mktemp -d)" && ${lib.getExe pkgs.syncthing} generate --home="$t" &> /dev/null && cat "$t"/{cert,key}.pem && rm -rf "$t")'';
  };

  capitalizeFirstLetter =
    str:
    (lib.strings.toUpper (builtins.substring 0 1 str))
    + (builtins.substring 1 (builtins.stringLength str) str);

  nixosDevices = builtins.map (system: system.config.frogeye) (
    builtins.attrValues config.frogeye.toplevel.nixosConfigurations
  );
  allDevices = nixosDevices;
  syncingDevices = builtins.filter (device: device.syncthing.id != null) allDevices;
  peerDevices = builtins.filter (device: device.name != config.frogeye.name) syncingDevices;

  # Can't use the module's folders enable option, as it still requests things somehow
  allFolders = builtins.attrValues config.frogeye.folders;
  syncedFolders = builtins.filter (folder: folder.syncthing.enable) allFolders;

  folderShouldSyncWith =
    folder: device:
    (lib.hasAttrByPath [ folder.name ] device.folders)
    && device.folders.${folder.name}.syncthing.enable;
  folderDeviceEntry = folder: device: { deviceID = device.syncthing.id; };

  enable = (builtins.length syncedFolders) > 0;
in
{
  config = {
    services.${service} = {
      inherit enable;
      openDefaultPorts = true;
      configDir = "/var/lib/${service}";
      databaseDir = "/var/cache/${service}";
      dataDir = cfg.databaseDir; # Don't really care

      key = "${secretsDir}/key.pem";
      cert = "${secretsDir}/cert.pem";

      settings = {
        devices = builtins.listToAttrs (
          builtins.map (device: {
            inherit (device) name;
            value = device.syncthing;
          }) syncingDevices
        );
        folders = builtins.listToAttrs (
          builtins.map (folder: {
            inherit (folder) name;
            value = {
              label = "${capitalizeFirstLetter folder.user} ${folder.label}";
              path = "${config.users.users.${folder.user}.home}/${folder.path}";
              # Despite further in the code indicating this is possible, it is, actually not
              # devices = builtins.map (folderDeviceEntry folder) (builtins.filter (folderShouldSyncWith folder) peerDevices);
              devices = builtins.map (device: device.name) (
                builtins.filter (folderShouldSyncWith folder) peerDevices
              );
              versioning =
                if (config.frogeye.storageSize == "big" && folder.versionsMaxDays != null) then
                  {
                    type = "staggered";
                    params.maxAge = builtins.toString (folder.versionsMaxDays * 24 * 3600);
                    # TODO Increase cleanupIntervalS to 1 day or so
                  }
                else
                  null;
              rescanIntervalS = 10 * 3600; # Using watcher, should be good enough
              copyRangeMethod = "all"; # Prevents duplication
              copyOwnershipFromParent = true;
            } // folder.syncthing;
          }) syncedFolders
        );
        options = rec {
          urAccepted = 3;
          urSeen = urAccepted;
        };
      };
    };
    systemd.services.${service}.serviceConfig = {
      ExecStartPre = [
        "+${pkgs.writeShellScript "syncthing-create-folders" ''
          install -Dm700 -o ${cfg.user} -g ${cfg.group} -d ${cfg.configDir}
          install -Dm700 -o ${cfg.user} -g ${cfg.group} -d ${cfg.databaseDir}
        ''}"
      ];
      PrivateUsers = lib.mkForce false;
      AmbientCapabilities = [
        "CAP_CHOWN"
        "CAP_DAC_OVERRIDE"
        "CAP_FOWNER"
      ];
    };
    vivarium.passwordFiles = {
      ${cfg.key}.password = password // {
        transform = "${lib.getExe pkgs.openssl} pkey";
      };
      ${cfg.cert}.password = password // {
        transform = "${lib.getExe pkgs.openssl} x509";
      };
    };
  };
}