<?php

use JetBrains\PhpStorm\Pure;

$input_file = '../inputs/day9.txt';
if (file_exists($input_file)) {
	$input = file_get_contents($input_file);
	if ($input != null) {
		$preamble = 25;
		$numbers = array_map('trim', explode("\n", $input));
		print 'Part 1 answer: ' . solve_part_one($numbers, $preamble) . "\n";
		print 'Part 2 answer: ' . solve_part_two($numbers, $preamble) . "\n";
	}
}

#[Pure] function solve_part_one(array $numbers, int $preamble): int
{
	return get_first_error($numbers, $preamble);
}

function solve_part_two(array $numbers, int $preamble): int
{
	return get_weakness($numbers, get_first_error($numbers, $preamble));
}

function get_first_error(array $numbers, int $preamble): int
{
	$error = 0;

	for ($i = $preamble; $i < count($numbers); $i++) {
		$correctly_encoded = false;

		for ($j = $i - $preamble; $j < $i; $j++) {
			for ($k = $i - $preamble; $k < $i; $k++) {
				if ($numbers[$j] + $numbers[$k] == $numbers[$i]) {
					$correctly_encoded = true;
					break;
				}
			}
			if ($correctly_encoded)
				break;
		}

		if ($correctly_encoded === false) {
			return $numbers[$i];
		}
	}

	return $error;
}

function get_weakness(array $numbers, int $result): int
{
	$min_pos = 0;
	$length = 2;

	while ($min_pos < count($numbers)) {
		while ($length < count($numbers) - 2) {
			$test = array_slice($numbers, $min_pos, $length);
			if (array_sum($test) == $result) {
				sort($test);
				return $test[0] + $test[count($test) - 1];
			} else if (array_sum($test) > $result) {
				$min_pos += 1;
				$length = 2;
				break;
			}

			$length += 1;
		}
	}

	return 0;
}