require "./common.cr"

lines = File.read("day13_input").split "\n"
lines.pop

map = lines.map &.chars
carts = [] of Tuple(Int32, Int32, Char, Char)

map.each_with_index do |line, y|
  line.each_with_index do |char, x|
    carts << {x, y, char, 'l'} if char == '>' || char == '<' || char == '^' || char == 'v'
  end
end

def next_turn(char)
  return 'r' if char == 's'
  return 'l' if char == 'r'
  return 's'
end

def turn_dir(char, turn)
  if turn == 'l'
    return '<' if char == '^'
    return 'v' if char == '<'
    return '>' if char == 'v'
    return '^' if char == '>'
  end
  if turn == 'r'
    return '>' if char == '^'
    return '^' if char == '<'
    return '<' if char == 'v'
    return 'v' if char == '>'
  end
  return char 
end

def offset(char)
  case char
  when '^'
    {0, -1}
  when 'v'
    {0, 1}
  when '<'
    {-1, 0}
  when '>'
    {1, 0}
  else
    {0, 0}
  end
end

def turn(cart, turnchar)
  if turnchar == '/'
    return '>' if cart == '^'
    return 'v' if cart == '<'
    return '^' if cart == '>'
    return '<'
  elsif turnchar == '\\'
    return 'v' if cart == '>'
    return '<' if cart == '^'
    return '^' if cart == '<'
    return '>'
  end
  return cart
end

def simulate(map, carts)
  crashed = [] of Int32
  crashed_pos = [] of Tuple(Int32, Int32)

  carts.sort_by! do |cart|
    x, y, c, t = cart
    y * 280 + x
  end

  carts.each_with_index do |cart, index|
    next if crashed.includes? index
    x, y, c, t = cart

    # TRUSTED
    dx, dy = offset(c)
    x += dx
    y += dy
    if map[y][x] == '+'
      c = turn_dir(c, t)
      t = next_turn(t)
    else
      c = turn(c, map[y][x])
    end
    # UNTRUSTED

    carts.each_with_index do |c2, i2|
      next if crashed.includes? i2
      next if (c2[0] != x) || (c2[1] != y)

      puts carts
      crashed << index
      crashed << i2
      crashed_pos << {x, y}
    end

    carts[index] = {x, y, c, t}
  end

  crashed.sort!.reverse!.uniq!.each do |index|
    carts.delete_at index
  end

  unless crashed_pos.empty?
    puts crashed_pos
  end

  return carts.size <= 1
end

count = 0
while !simulate(map, carts)
  count += 1
end
puts carts[0]?