Model validations for data integrity

                  class User < ApplicationRecord
  has_many :posts, foreign_key: :author_id

  validates :email, presence: true,
                    uniqueness: { case_sensitive: false },
                    format: { with: URI::MailTo::EMAIL_REGEXP }

  validates :username, presence: true,
                       uniqueness: { case_sensitive: false },
                       length: { in: 3..30 },
                       format: { with: /\A[a-zA-Z0-9_]+\z/, message: 'only allows letters, numbers, and underscores' }

  validates :password, length: { minimum: 8 }, if: :password_required?
  validate :password_complexity, if: :password_required?

  private

  def password_required?
    new_record? || password.present?
  end

  def password_complexity
    return if password.blank?

    unless password.match?(/[A-Z]/) && password.match?(/[a-z]/) && password.match?(/[0-9]/)
      errors.add(:password, 'must include uppercase, lowercase, and numbers')
    end
  end
end