<?php
$input_file = '../inputs/day12.txt';
if (file_exists($input_file)) {
	$input = file_get_contents($input_file);
	if ($input != null) {
		$instructions = array_map('trim', explode("\n", $input));
		print 'Part 1 answer: ' . solve_part_one($instructions) . "\n";
		print 'Part 2 answer: ' . solve_part_two($instructions) . "\n";
	}
}

function solve_part_one(array $instructions): int
{
	$state = new day12_state();

	foreach (parse_instructions($instructions) as $instruction) {
        $state = move($instruction, $state);
    }

	return abs($state->v_pos) + abs($state->h_pos);
}

function solve_part_two(array $instructions): int
{
	$state = new day12_state();

	foreach (parse_instructions($instructions) as $instruction)
		$state = move_with_waypoint($instruction, $state);

	return abs($state->v_pos) + abs($state->h_pos);
}

function move(array $instruction, day12_state $state): day12_state
{
	switch ($instruction[0]) {
		case 'N':
			$state->v_pos += $instruction[1];
			break;
		case 'S':
			$state->v_pos -= +$instruction[1];
			break;
		case 'E':
			$state->h_pos += $instruction[1];
			break;
		case 'W':
			$state->h_pos -= $instruction[1];
			break;
		case 'F':
			switch ($state->facing_direction % 4) {
				case 0:
					$state->v_pos += $instruction[1];
					break;
				case 1:
					$state->h_pos += $instruction[1];
					break;
				case 2:
					$state->v_pos -= $instruction[1];
					break;
				case 3:
					$state->h_pos -= $instruction[1];
					break;
			}
			break;
		case 'R':
			$state->facing_direction += ($instruction[1] / 90);
			break;
		case 'L':
			$state->facing_direction -= ($instruction[1] / 90);
			break;
	}

    if ($state->facing_direction < 0)
        $state->facing_direction += 4; // NOT THAT EASY, need to wrap around 0

	return $state;
}

function move_with_waypoint(array $instruction, day12_state $state): day12_state
{
	switch ($instruction[0]) {
		case 'N':
			$state->w_v_pos += $instruction[1];
			break;
		case 'S':
			$state->w_v_pos -= +$instruction[1];
			break;
		case 'E':
			$state->w_h_pos += $instruction[1];
			break;
		case 'W':
			$state->w_h_pos -= $instruction[1];
			break;
		case 'F':
			for ($i = 0; $i < $instruction[1]; $i++) {
				$state->v_pos += $state->w_v_pos;
				$state->h_pos += $state->w_h_pos;
			}
			break;
		case 'R':
			for ($i = 0; $i < $instruction[1] / 90; $i++) {
				$new_v_pos = -$state->w_h_pos;
				$new_h_pos = $state->w_v_pos;
				$state->w_v_pos = $new_v_pos;
				$state->w_h_pos = $new_h_pos;
			}
			break;
		case 'L':
			for ($i = 0; $i < $instruction[1] / 90; $i++) {
				$new_v_pos = $state->w_h_pos;
				$new_h_pos = -$state->w_v_pos;
				$state->w_v_pos = $new_v_pos;
				$state->w_h_pos = $new_h_pos;
			}
			break;
	}

	return $state;
}

function parse_instructions(array $instructions): array
{
	$parsed_instructions = [];

	foreach ($instructions as $instruction) {
		if (preg_match('/^([NSEWLRF])(\d+)$/', trim($instruction), $matches)) {
			[, $inst, $arg] = $matches;
			$parsed_instructions[] = [$inst, $arg];
		}
	}

	return $parsed_instructions;
}

class day12_state
{
	public int $v_pos = 0;
	public int $h_pos = 0;
	public int $w_v_pos = 1;
	public int $w_h_pos = 10;
	public int $facing_direction = 1; // N = 0, E = 1, S = 2, W = 3
}