bob.rb

class Bob
  RESPONSES = {
    :shouting  => "Woah, chill out!",
    :silence   => "Fine. Be that way.",
    :question  => "Sure.",
    :statement => "Whatever.",
  }

  def hey(statement)
    validate_statement(statement)
    begin
      RESPONSES[interpret(statement.to_s)]
    rescue => e
      raise "ERROR #{e.message}"
    end
  end

  private
  
  def validate_statement(statement)
    raise "ERROR invalid class: statment.class => #{statement.class}; statement must be String" unless statement.is_a? String
  end

  def interpret(statement)
    validate_statement(statement)

    case
    when statement.empty? then return :silence
    when all_uppercase?(statement) then return :shouting
    when ends_with_question_mark?(statement) then return :question
    else; return :statement
    end
  end

  def all_uppercase?(statement)
    validate_statement(statement)
    statement =~ /^[A-Z]+$/
  end

  def ends_with_question_mark?(statement)
    validate_statement(statement)
    statement.end_with?("?")
  end
end