from puzzle1 import *


verbose = False

def swap(lst, idx_a, idx_b):
	temp = lst[idx_a]
	lst[idx_a] = lst[idx_b]
	lst[idx_b] = temp

def fix_update(update, rules):
	"""Fixes update according to rules by reference."""

	# Allow the loop to be restared after a fix.
	i = 0
	swap_free = False
	while not swap_free:
		swap_free = True
		for rule in rules:
			lhs, rhs = rule

			if not lhs in update or not rhs in update:
				continue

			idx_lhs, idx_rhs = update.index(lhs), update.index(rhs)
			if idx_lhs > idx_rhs:
				if verbose:
					print(f"swapping as {lhs} < {rhs}")
				swap(update, idx_lhs, idx_rhs)
				swap_free = False

if __name__ == "__main__":
	rules, updates = load_input()

	middle_sum = 0
	# Let's assume numbers can only occur once (although the checker does not
	# make this assumption), and every update CAN be fixed.
	for idx, update in enumerate(updates):
		if verbose:
			print(f"{idx:5d}/{len(updates)}:", update)
		if is_update_legal(update, rules):
			if verbose:
				print(update, " is legal")
		else:
			if verbose:
				print(update, " is illegal")
			fix_update(update, rules)
			middle_sum += middle_page_num(update)

	print(f"The sum of middle page numbers of legal updates is {middle_sum}.")