to_underscore.rb

# Write a method that takes a camelcase string as an argument and converts it into snake case

def to_underscore(string)
  uppercase = ("A".."Z").to_a
  lowercase = ("a".."z").to_a
  letters = string.split('')
  snake_case = []
  letters.each do |letter|
    # first uppercase letter
    if letters.index(letter) == 0 && uppercase.include?(letter)
      lowercase_equiv = lowercase[uppercase.index(letter)]
      snake_case.push(lowercase_equiv)
    # handle uppercase letters in the middle - prepend an _
    elsif letters.index(letter) != 0 && uppercase.include?(letter)
      lowercase_equiv = lowercase[uppercase.index(letter)]
      snake_case.push("_" + lowercase_equiv)
    # handle lowercase letters and numbers
    else
      snake_case.push(letter)
    end
  end
  snake_case.join
end

puts to_underscore("TestController")
puts to_underscore("AmyHenning")
puts to_underscore("Am7Days")