module Validator {
  export function required(x: any, name?: string) {
    if (x === undefined || x === null || x === '') {
      throw new Error(`${name} is required.`);
    }

    return true;
  }

  export function string(x: any, name?: string) {
    if (typeof x !== 'string' || x === '') {
      throw new Error(`${name} must be a string.`);
    }

    return true;
  }

  export function number(x: any, name?: string) {
    if (typeof x !== 'number') {
      throw new Error(`${name} must be a number.`);
    }

    return true;
  }

  export function boolean(x: any, name?: string) {
    if (typeof x !== 'boolean') {
      throw new Error(`${name} must be a boolean.`);
    }

    return true;
  }

  export function integer(x: any, name?: string) {
    if (!Number.isInteger(x)) {
      throw new Error(`${name} must be an integer.`);
    }

    return true;
  }

  export function object(x: any, name?: string) {
    if (typeof x !== 'object') {
      throw new Error(`${name} must be an object.`);
    }

    return true;
  }

  export function array(x: any, name?: string) {
    if (!Array.isArray(x)) {
      throw new Error(`${name} must be an array.`);
    }

    return true;
  }

  export function oneOf(x: any, y: any, name?: string) {
    if (!Object.values(y).includes(x)) {
      throw new Error(`${name} must be one of ${Object.values(y).join(', ')}.`);
    }

    return true;
  }

  export function maxLength(x: any, y: number, name?: string) {
    if (x.length > y) {
      throw new Error(
        `${name} must have a length smaller than or equal to ${y}.`
      );
    }

    return true;
  }

  export function max(x: any, y: number, name?: string) {
    if (x > y) {
      throw new Error(`${name} must be lower than or equal to ${y}.`);
    }

    return true;
  }

  export function requiredString(x: any, name?: string) {
    return required(x, name) && string(x, name);
  }
}

export { Validator };