<?php


function get_new_state($grid, $y, $x)
{


    $xmin = max(0, $x - 1);
    $xmax = min(count($grid[$y]) - 1, $x + 1);
    $ymin = max(0, $y - 1);
    $ymax = min(count($grid) - 1, $y + 1);

    $found = array('.'=>0, '|'=>0, '#'=>0);

    for ($yy = $ymin; $yy <= $ymax; $yy++) {
        for ($xx = $xmin; $xx <= $xmax; $xx++) {
            if($x !== $xx || $y !== $yy)
            {
                $found[$grid[$yy][$xx]]++;
            }
        }
    }

    $current_state = $grid[$y][$x];

    switch ($current_state)
    {
        case '.':
            if($found['|']>2)
            {
                return '|';
            }
            break;
        case '|':
            if($found['#']>2)
            {
                return '#';
            }
            break;
        case '#':
            if($found['#']<1 || $found['|']<1)
            {
                return '.';
            }
    }

    return $current_state;
}

function get_value($grid)
{
    $lumber = 0;
    $trees = 0;

    foreach ($grid as $key=>$line)
    {
        $values = array_count_values($line);
        if (isset($values['#'])) {
            $lumber += $values['#'];
        }
        if (isset($values['|'])) {
            $trees += $values['|'];
        }
    }

    return $lumber * $trees;
}

function print_grid($grid)
{

    foreach ($grid as $key=>$line)
    {
        printf('%4d : ', $key);
        echo implode('', $line);
        echo PHP_EOL;
    }
}

$input = file('input.txt');

$original_grid = array();

foreach ($input as $line) {
    $original_grid[] = str_split(trim($line));
}


$iterations = 10;

$grid = $original_grid;


for($i = 0 ; $i < $iterations ; $i++) {
    $new_grid = array();
    for ($y = 0; $y < count($grid); $y++)
    {
        $new_grid[$y] = array();
        for ($x = 0; $x < count($grid[$y]); $x++)
        {
            $new_grid[$y][$x] = get_new_state($grid, $y,$x);
        }
    }
    $grid = $new_grid;
}

printf('Part 1: %d', get_value($grid));
echo PHP_EOL;

$grid = $original_grid;

$iterations = 1000;
$last_diff = 0;
$values = array();
$found_index = 0;
$found_diff = 0;
for($i = 0 ; $i < $iterations ; $i++) {
    $new_grid = array();
    for ($y = 0; $y < count($grid); $y++)
    {
        $new_grid[$y] = array();
        for ($x = 0; $x < count($grid[$y]); $x++)
        {
            $new_grid[$y][$x] = get_new_state($grid, $y,$x);
        }
    }
    $grid = $new_grid;
    $val = get_value($grid);

    $index = array_search($val, $values);
    if($index) {
        $diff = count($values) - $index;
        if ($diff === $last_diff && $found_index === 0) {
            $found_index = $index;
            $found_diff = $diff;
        }
        $last_diff = $diff;
    }
    $values[$i] = $val;
}

$start = 1000000000;
$start -= $found_index;
$start %= $found_diff;
$start += $found_index-1;

printf('Part 2: %d', $values[$start]);
echo PHP_EOL;