<?php
/*
 * Game of Life in PHP using pure functions
 *
 * Joop Schilder
 */
if (version_compare(PHP_VERSION, '7.0') < 1) {
	throw new RuntimeException('PHP>=7.0 required');
}

const BOARDSIZE = 32;
CONST DELAY_MS = 200;
const DEAD = 0;
const ALIVE = 1;

function get_neighbours(array $board, int $i, int $j): array
{
	$neighbours = [];
	for ($ni = $i - 1; $ni <= $i + 1; $ni++) {
		for ($nj = $j - 1; $nj <= $j + 1; $nj++) {
			if (isset($board[$ni][$nj]) && ($ni !== $i || $nj !== $j)) {
				$neighbours[] = $board[$ni][$nj];
			}
		}
	}

	return $neighbours;
}

function get_next_cell_state(array $board, int $i, int $j): int
{
	$living_neighbours = count(array_filter(get_neighbours($board, $i, $j), function (int $state): bool {
		return $state === ALIVE;
	}));
	$is_alive = $board[$i][$j] === ALIVE ? ($living_neighbours > 1 && $living_neighbours < 4) : $living_neighbours === 3;

	return $is_alive ? ALIVE : DEAD;
}

function get_next_board_state(array $board): array
{
	$next_board = [];
	for ($i = 0; $i < BOARDSIZE; $i++) {
		for ($j = 0; $j < BOARDSIZE; $j++) {
			$next_board[$i][$j] = get_next_cell_state($board, $i, $j);
		}
	}

	return $next_board;
}

function print_board(array $board): void
{
	system('WIN' === strtoupper(substr(PHP_OS, 0, 3)) ? 'cls' : 'clear');
	print('┌' . str_repeat('─', 2 * BOARDSIZE) . '┐' . PHP_EOL);
	for ($i = 0; $i < BOARDSIZE; $i++) {
		print('│');
		for ($j = 0; $j < BOARDSIZE; $j++) {
			print($board[$i][$j] === ALIVE ? '██' : '░░');
		}
		print('│' . PHP_EOL);
	}
	print('└' . str_repeat('─', 2 * BOARDSIZE) . '┘' . PHP_EOL);
}

$board = [];
for ($i = 0; $i < BOARDSIZE; $i++) {
	for ($j = 0; $j < BOARDSIZE; $j++) {
		$board[$i][$j] = DEAD;
	}
}

// Glider
$board[1][3] = ALIVE;
$board[2][4] = ALIVE;
$board[3][2] = ALIVE;
$board[3][3] = ALIVE;
$board[3][4] = ALIVE;

while (true) {
	print_board($board);
	usleep(DELAY_MS * 1000);
	$board = get_next_board_state($board);
}