freeCodeCamp/utils/validate.ts

type Valid = {
  valid: true;
  error: null;
};

type Invalid = {
  valid: false;
  error: string;
};

type Validated = Valid | Invalid;

export const invalidCharError: Invalid = {
  valid: false,
  error: 'contains invalid characters'
};
export const validationSuccess: Valid = { valid: true, error: null };
export const usernameTooShort: Invalid = {
  valid: false,
  error: 'is too short'
};
export const usernameIsHttpStatusCode: Invalid = {
  valid: false,
  error: 'is a reserved error code'
};

const validCharsRE = /^[a-zA-Z0-9\-_+]*$/;
export const isHttpStatusCode = (str: string): boolean => {
  const output = parseInt(str, 10);
  return !isNaN(output) && output >= 100 && output <= 599;
};

export const isValidUsername = (str: string): Validated => {
  if (!validCharsRE.test(str)) return invalidCharError;
  if (str.length < 3) return usernameTooShort;
  if (isHttpStatusCode(str)) return usernameIsHttpStatusCode;
  return validationSuccess;
};