#!/usr/bin/env python3

# https://adventofcode.com/2024/day/5

def get_lines(filename: str) -> list:
    with open(filename, "r") as file:
        return [line.strip() for line in file.readlines()]


def get_rules_and_updates(lines: list) -> tuple:
    rules = {}
    updates = []
    for line in lines:
        if "|" in line:
            a, b = line.split("|")
            if rules.get(b):
                rules[b].append(a)
            else:
                rules[b] = [a]
        elif "," in line:
            updates.append(line.split(","))
    return rules, updates


def check_validity(rules: dict, update: list) -> bool:
    for position, page_number in enumerate(update):
        if page_number not in rules:
            continue
        # if a number that is supposed to come earlier than our current page_number
        # is included in the rest of the update, it breaks the rules
        for earlier_number in rules[page_number]:
            if earlier_number in update[position:]:
                return False
    return True


def get_middle_page_sums(rules: dict, updates: list) -> int:
    middle_page_sum = 0
    for update in updates:
        if check_validity(rules, update):
            middle_page_sum += int(update[int(len(update) / 2)])
    return middle_page_sum


def main():
    # lines = get_lines("sample-input.txt")
    lines = get_lines("input.txt")

    rules, updates = get_rules_and_updates(lines)
    print("Part 1: The sum of valid middle pages is:", get_middle_page_sums(rules, updates))


if __name__ == '__main__':
    main()