Wordy

wordy.rb

class WordProblem
  def initialize(string)
    @problem = string
  end

  def answer
    operations = extract_operations @problem
    fail ArgumentError, 'Valid operations: plus, minus, multiplied or divided' if operations.empty?
    numbers = extract_numbers @problem
    index = 0

    numbers.inject do |memo, number|
      memo = memo.send(operation(operations[index]), number)
      index += 1
      memo
    end
  end

  private

  def extract_numbers(problem)
    array_of_strings = problem.scan(/-?\d+/)

    array_of_strings.map(&:to_i)
  end

  def operation(string)
    if string == 'plus'
      :+
    elsif string == 'minus'
      :-
    elsif string == 'multiplied'
      :*
    else
      :/
    end
  end

  def extract_operations(problem)
    problem.scan(/plus|minus|multiplied|divided/)
  end
end