Argument Validation

Arguments values can be validated by placing the @validate() decorator on a method:

@command("factorial")
export class Factorial extends TextCommand {
  @arg()
  input!: number;

  @validate("input")
  mustBePositive() {
    if (this.input < 0) {
      throw new TextArgError("Input must be positive.");
    }
  }

  async execute() {
    const factorial = factorial(this.input);
    return this.reply(`${this.input}! = ${factorial}.`);
  }
}

In this case, the mustBePositive method will be called before the command is executed. If it throws an error, the error will be reported to the user.

Reusable Validators

You can also implement Validator subclasses for reusable validation:

export class NotMeValidator extends Validator {
  @inject(HadesClient)
  client: HadesClient;

  async validate(
    arg: TextArgInstaller,
    context: TextCommandContext,
    value: User,
  ) {
    if (value.id === this.client.user.id) {
      throw new TextArgError("You can't use this command on me.");
    }
  }
}

The NotMeValidator checks that an argument parsed as a User is not the bot itself. It can be used like this:

@command("not-me")
export class NotMeCommand extends TextCommand {
  @arg()
  @parser(UserParser)
  @NotMeValidator.check()
  user!: User;

  async execute() {
    await this.reply(`You used the command on ${this.user.tag}.`);
  }
}