<?php
$input_file = '../inputs/day3.txt';
if (file_exists($input_file)) {
	$input = file_get_contents($input_file);
	if ($input != null) {
		$coordinates = explode("\n", $input);
		print 'Part 1 answer: ' . solve_part_one($coordinates) . "\n";
		print 'Part 2 answer: ' . solve_part_two($coordinates) . "\n";
	}
}

function solve_part_one(array $coords): int
{
	return solve_for_slope($coords, 3, 1);
}

function solve_part_two(array $coords): int
{
	return solve_for_slope($coords, 1, 1)
		* solve_for_slope($coords, 3, 1)
		* solve_for_slope($coords, 5, 1)
		* solve_for_slope($coords, 7, 1)
		* solve_for_slope($coords, 1, 2);
}

function solve_for_slope(array $coords, int $incr_x, int $incr_y): int
{
	$current_coords = ['x' => 0, 'y' => 0];
	$trees = 0;
	while ($current_coords['y'] < (count($coords) - 1)) {
		$current_coords['x'] += $incr_x;
		$current_coords['y'] += $incr_y;

		$current_line = trim($coords[$current_coords['y']]);
		$actual_x = $current_coords['x'] % strlen($current_line);
		if ($current_line[$actual_x] === '#')
			$trees += 1;
	}
	return $trees;
}