day_2.rb

class Position
  attr_accessor :x, :y

  def initialize(x, y)
    @x = x
    @y = y
  end

  def ==(another_position)
    self.x == another_position.x && self.y == another_position.y
  end
end

# Each line of instructions corresponds to one button, starting
# at the previous button (or, for the first line, the "5" button);
# press whatever button you're on at the end of each line.
# If a move doesn't lead to a button, ignore it.
def new_position(old_position, instruction, keypad: DEFAULT_KEYPAD)
  new_position = old_position.dup

  case instruction
  when "U"
    new_position.y -= 1
  when "D"
    new_position.y += 1
  when "L"
    new_position.x -= 1
  when "R"
    new_position.x += 1
  end

  valid_position?(new_position, keypad: keypad) ? new_position : old_position
end

def valid_position?(position, keypad: DEFAULT_KEYPAD)
  position.x.between?(0, keypad.length-1) && position.y.between?(0, keypad.length-1) &&
    get_digit(keypad, position)
end

def determine_next_position(old_position, instructions, keypad: DEFAULT_KEYPAD)
  current_position = old_position

  (0...instructions.length).each do |i|
    current_position = new_position(current_position, instructions[i], keypad: keypad)
  end

  current_position
end

def get_digit(keypad, position)
  keypad[position.y][position.x]
end

DEFAULT_KEYPAD = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
]
DEFAULT_STARTING_POSITION = Position.new(1,1)
def determine_passcode(instructions, keypad: DEFAULT_KEYPAD, starting_position: DEFAULT_STARTING_POSITION)
  current_position = starting_position
  passcode = []

  instructions.each do |line|
    current_position = determine_next_position(current_position.dup, line, keypad: keypad)
    passcode << get_digit(keypad, current_position)
  end

  passcode.join
end

# part A
# input = %w(
#   URULLLLLRLDDUURRRULLLDURRDRDRDLURURURLDLLLLRUDDRRLUDDDDDDLRLRDDDUUDUDLDULUDLDURDULLRDDURLLLRRRLLRURLLUDRDLLRRLDDRUDULRRDDLUUUDRLDLURRRULURRDLLLDDDLUDURDDRLDDDLLRULDRUDDDLUDLURUDLLRURRUURUDLLLUUUUDDURDRDDDLDRRUDURDLLLULUDURURDUUULRULUDRUUUUDLRLUUUUUDDRRDDDURULLLRRLDURLDLDRDLLLUULLRRLLLLDRLRDRRDRRUDDLULUUDDDDRRUUDDLURLRDUUDRRLDUDLRRRLRRUUDURDRULULRDURDRRRDLDUUULRDDLRLRDLUUDDUDDRLRRULLLULULLDDDRRDUUUDDRURDDURDRLRDLDRDRULRLUURUDRLULRLURLRRULDRLRDUDLDURLLRLUDLUDDURDUURLUDRLUL
#   LLLUUURUULDDDULRRDLRLLLLLLLLRURRDLURLUDRRDDULDRRRRRRLDURRULDDULLDDDRUUDLUDULLDLRRLUULULRULURDURLLDULURDUDLRRLRLLDULLRLDURRUULDLDULLRDULULLLULDRLDLDLDLDDLULRLDUDRULUDDRDDRLRLURURRDULLUULLDRRDRRDLDLLRDLDDUUURLUULDDRRRUULDULDDRDDLULUDRURUULLUDRURDRULDRUULLRRDURUDDLDUULLDDRLRRDUDRLRRRLDRLRULDRDRRUDRLLLDDUDLULLURRURRLUURDRLLDLLDUDLUUURRLRDDUDRLUDLLRULLDUUURDLUUUDUDULRLDLDRUUDULRDRRUDLULRLRDLDRRDDDUDLDLDLRUURLDLLUURDLDLRDLDRUDDUURLLLRDRDRRULLRLRDULUDDDLUDURLDUDLLRULRDURDRDLLULRRDLLLDUURRDUDDLDDRULRRRRLRDDRURLLRRLLL
#   DRURLDDDDRLUDRDURUDDULLRRLLRLDDRLULURLDURRLDRRLRLUURDDRRDLRDLDLULDURUDRLRUDULRURURLRUDRLLDDUDDRDLDRLLDDLRRDRUUULDUUDRUULRLLDLLULLLRRDRURDLDDRRDDUDDULLDUUULDRUDLDLURLDRURUDLRDDDURRLRDDUDLLLRRUDRULRULRRLLUUULDRLRRRLLLDLLDUDDUUDRURLDLRRUUURLUDDDRRDDLDDDDLUURDDULDRLRURLULLURRDRLLURLLLURDURLDLUDUUDUULLRLDLLLLULRDDLDUDUDDDUULURRLULDLDRLRDRLULLUDDUUUUURDRURLDUULDRRDULUDUDLDDRDLUDDURUDURLDULRUDRRDLRLRDRRURLDLURLULULDDUUDLRLLLLURRURULDDRUUULLDULDRDULDDDLLLRLULDDUDLRUDUDUDURLURLDDLRULDLURD
#   DRUDRDURUURDLRLUUUUURUDLRDUURLLDUULDUULDLURDDUULDRDDRDULUDDDRRRRLDDUURLRDLLRLRURDRRRDURDULRLDRDURUDLLDDULRDUDULRRLLUDLLUUURDULRDDLURULRURDDLRLLULUDURDRRUDLULLRLDUDLURUDRUULDUDLRDUDRRDULDDLDRLRRULURULUURDULRRLDLDULULRUUUUULUURLURLRDLLRRRRLURRUDLRLDDDLDRDRURLULRDUDLRLURRDRRLRLLDLDDLLRRULRLRLRUDRUUULLDUULLDDRLUDDRURLRLDLULDURLLRRLDLLRDDDUDDUULLUDRUDURLLRDRUDLUDLLUDRUUDLRUURRRLLUULLUUURLLLRURUULLDLLDURUUUULDDDLRLURDRLRRRRRRUDLLLRUUULDRRDLRDLLDRDLDDLDLRDUDLDDRDDDDRULRRLRDULLDULULULRULLRRLLUURUUUDLDLUDUDDDLUUDDDDUDDDUURUUDRDURRLUULRRDUUDDUDRRRDLRDRLDLRRURUUDRRRUUDLDRLRDURD
#   DDDLRURUDRRRURUUDLRLRDULDRDUULRURRRUULUDULDDLRRLLRLDDLURLRUDRLRRLRDLRLLDDLULDLRRURDDRDLLDDRUDRRRURRDUDULUDDULRRDRLDUULDLLLDRLUDRDURDRRDLLLLRRLRLLULRURUUDDRULDLLRULDRDLUDLULDDDLLUULRRLDDUURDLULUULULRDDDLDUDDLLLRRLLLDULRDDLRRUDDRDDLLLLDLDLULRRRDUDURRLUUDLLLLDUUULDULRDRULLRDRUDULRUUDULULDRDLDUDRRLRRDRLDUDLULLUDDLURLUUUDRDUDRULULDRDLRDRRLDDRRLUURDRULDLRRLLRRLDLRRLDLDRULDDRLURDULRRUDURRUURDUUURULUUUDLRRLDRDLULDURUDUDLUDDDULULRULDRRRLRURLRLRLUDDLUUDRRRLUUUDURLDRLRRDRRDURLLL
#   )
# puts determine_passcode(input)

####################################################
# part B

DIAMOND_KEYPAD = [
  [nil,nil,  1,nil,nil],
  [nil,  2,  3,  4,nil],
  [  5,  6,  7,  8,  9],
  [nil,"A","B","C",nil],
  [nil,nil,"D",nil, nil]
]
# starting_position = Position.new(0, 2)
# puts determine_passcode(input, keypad: DIAMOND_KEYPAD, starting_position: starting_position)