[enemyHp, enemyDamage, enemyArmor] =
  File.stream!("inputs/day21.txt")
  |> Stream.map(fn line ->
    [num] = Regex.run(~r/\d+/, line)
    {num, ""} = Integer.parse(num)
    num
  end)
  |> Enum.take(3)

playerHp = 100
# {cost, damage, armor}

# pick exactly one
weapons = [
  {8, 4, 0},
  {10, 5, 0},
  {25, 6, 0},
  {40, 7, 0},
  {74, 8, 0}
]

# pick 0-1
armors = [
  nil,
  {13, 0, 1},
  {31, 0, 2},
  {53, 0, 3},
  {75, 0, 4},
  {102, 0, 5}
]

# pick 0-2
rings = [
  nil,
  {25, 1, 0},
  {50, 2, 0},
  {100, 3, 0},
  {20, 0, 1},
  {40, 0, 2},
  {80, 0, 3}
]

simulateBattle = fn playerDamage, playerArmor ->
  playerDamagePerHit = max(1, playerDamage - enemyArmor)
  enemyDamagePerHit = max(1, enemyDamage - playerArmor)

  playerHitsToVictory = ceil(enemyHp / playerDamagePerHit)
  enemyHitsToVictory = ceil(playerHp / enemyDamagePerHit)
  playerHitsToVictory <= enemyHitsToVictory
end

allCombinations =
  for weapon <- weapons,
      armor <- armors,
      ring1 <- rings,
      ring2 <- rings,
      is_nil(ring1) || ring1 != ring2 do
    Enum.filter([weapon, armor, ring1, ring2], &(!is_nil(&1)))
    |> Enum.reduce({0, 0, 0}, fn {c1, d1, a1}, {c2, d2, a2} ->
      {c1 + c2, d1 + d2, a1 + a2}
    end)
  end

winningCost =
  Enum.filter(allCombinations, fn {_, damage, armor} -> simulateBattle.(damage, armor) end)
  |> Enum.map(fn {cost, _, _} -> cost end)
  |> Enum.min()

IO.puts("Minimum winning cost: #{winningCost}")

losingCost =
  Enum.filter(allCombinations, fn {_, damage, armor} -> !simulateBattle.(damage, armor) end)
  |> Enum.map(fn {cost, _, _} -> cost end)
  |> Enum.max()

IO.puts("Maximum losing cost: #{losingCost}")