Day 02 part 2

type
  Shape = enum
    rock, papper, scissors
  Outcome = enum
    win, draw, lose
  GameRound = object
    us, them: Shape
    outcome: Outcome

var answer: Natural

proc parseShape(strShape: char): Shape =
  case strShape
  of 'A': return rock
  of 'B': return papper
  of 'C': return scissors
  else:
    raise newException(OSError, "Unable to parse: " & strShape)

proc parseOutcome(expOutcome: char): Outcome =
  case expOutcome
  of 'X': return lose
  of 'Y': return draw
  of 'Z': return win
  else:
    raise newException(OSError, "Unable to parse: " & expOutcome)

proc whatWins(s: Shape): Shape = 
  case s
  of rock: return papper
  of papper: return scissors
  of scissors: return rock

proc whatDraws(s: Shape): Shape = s

proc whatLoses(s: Shape): Shape = 
  case s
  of rock: return scissors
  of papper: return rock
  of scissors: return papper

proc pickForUs(them: Shape, expOutcome: Outcome): Shape =
  case expOutcome
  of win: return whatWins(them)
  of draw: return whatDraws(them)
  of lose: return whatLoses(them)

proc newRound(strThem, expOutcome: char): GameRound =
  result.them = parseShape(strThem)
  result.outcome = parseOutcome(expOutcome)
  result.us = pickForUs(result.them, result.outcome)

func score(g: GameRound): Natural =
  case g.us
  of rock: result.inc 
  of papper: result.inc 2
  of scissors: result.inc 3
  if g.outcome == win: result.inc 6
  elif g.outcome == draw: result.inc 3

for l in "input.txt".lines:
  if l.len != 3:
    continue
  let round = newRound(l[0], l[2])
  answer.inc(round.score)

Answer is: 12424