gravity-falls-decoder.rb

#!/usr/bin/env ruby

# this script takes a list of encoded words,
# and returns the decoded message. for example:
#
#  gravity-falls-decoder.rb 4-16-19 11-23-10
#

#
# we'll start by setting up some important variables
#

# this will eventually contain our decoded message
# (as a list of letters)
decoded_message = []

# this just says "take encoded messages from the command line"
encoded_words = ARGV

# now we make an array of the letters a-z
# i.e. ['a', 'b', ..., 'z']
letters = ('a'..'z').to_a
# and then we reverse it ("switch a and z")
# i.e. ['z', 'y', ..., 'a']
letters.reverse!

#
# okay here's where we actually decode the message.
#

# start by looping through each encoded message
# (in the form "4-16-19")
encoded_words.each do |encoded_word|
  # split it up by the dash, so we get a list of just the numbers
  numbers = encoded_word.split('-')

  # loop over each number in the message
  numbers.each do |number|
    # convert it to an Integer so we can do math on it
    number = number.to_i
    # this part is a little weird:
    # subtract 1, because in Ruby we address the position of
    # an element in an array starting at 0.
    # i.e. letters[0] = 'z', letters[1] = 'y'
    number = number - 1
    # rotate the alphabet by 3 letters
    # (I arrived here by trial and error)
    # i.e. A->D, B->E, ..., Z->C
    number = number + 3
    # finally, look up the number in our reversed alphabet,
    # and add it to the decoded message
    decoded_message << letters[number]
  end

  # we just finished a word, so add a space to the decoded message
  decoded_message << ' '
end

#
# all done decoding!
#

# now combine all of the decrypted letters into a single string
# i.e. "fonda" instead of ['f', 'o', 'n', 'd', 'a']
decoded_message = decoded_message.join

# print it out
puts decoded_message