AttachKeyAssert

type AttachKeyAssert<Key extends string, Host> = Key extends ""
    ? "A plugin key needs a name."
    : Key extends `${infer Group}.${infer Leaf}`
      ? Leaf extends `${string}.${string}`
          ? `'${Key}' has more than one dot. A plugin key takes one dot at most.`
          : "" extends Group | Leaf
            ? `'${Key}' has an empty part. Write a group and a plugin name around the dot, like 'services.users'.`
            : Group extends FrameworkChannel
              ? `'${Group}' is a channel the framework logs on. Pick another group name.`
              : Group extends keyof Host
                ? Host[Group] extends PluginLike
                    ? `'${Group}' already holds a plugin, so '${Leaf}' cannot nest inside it.`
                    : Host[Group] extends Record<
                            string,
                            PluginLike
                        >
                      ? Leaf extends keyof Host[Group]
                          ? `'${Key}' is already attached.`
                          : Key
                      : `'${Group}' is already a member on the bot. Pick another group name.`
                : Group extends HostMember<Host>
                  ? `'${Group}' is already a member on the bot. Pick another group name.`
                  : Key
      : Key extends FrameworkChannel
        ? `'${Key}' is a channel the framework logs on. Pick another plugin key.`
        : Key extends keyof Host
          ? Host[Key] extends PluginLike
              ? `'${Key}' is already attached.`
              : Host[Key] extends Record<
                      string,
                      PluginLike
                  >
                ? `'${Key}' already holds a group of plugins. Attach this one under a name of its own.`
                : `'${Key}' is already a member on the bot. Pick another plugin key.`
          : Key extends HostMember<Host>
            ? `'${Key}' is already a member on the bot. Pick another plugin key.`
            : Key;