<?php
// vim:et:ts=2:sw=2

define('TOKEN', 'P6HPuPxjwneEWmTK1dEeaSsC');
define('EMPTY_BOARD', '.........');
define('CHANNEL_PATTERN', '/^[a-zA-Z0-9]*$/');
define('USERNAME_PATTERN', '/^[a-z0-9_\\-\\.]*$/');

// I'm using PHP5 on this server, and PHP5 doesn't support arrays in define
// constants, so I have to use const here instead.
const WINNER_LINES = array(
  // horizontal lines
  array(0, 1, 2),
  array(3, 4, 5),
  array(6, 7, 8),
  // vertical lines
  array(0, 3, 6),
  array(1, 4, 7),
  array(2, 5, 8),
  // diagonal lines
  array(0, 4, 8),
  array(2, 4, 6),
);
// Indices of WINNER_LINES to check for board indices
const LINES_TO_CHECK = array(
  array(0, 3, 6),
  array(0, 4),
  array(0, 5, 7),
  array(1, 3),
  array(1, 4, 6, 7),
  array(1, 5),
  array(2, 3, 7),
  array(2, 4),
  array(2, 5, 6),
);

// Defines:
// MYSQL_HOST, MYSQL_DATABASE, MYSQL_TABLE_PREFIX, MYSQL_USER, MYSQL_PASSWORD
include('db.inc.php');

define('TABLE_MOVES', MYSQL_TABLE_PREFIX . 'moves');
define('TABLE_STATUS', MYSQL_TABLE_PREFIX . 'status');

/**
 * Wrapper to die function to also send 500 error.
 */
function error($msg, $db = null) {
  header($_SERVER['SERVER_PROTOCOL'] . ' 500 Internal Server Error', true, 500);
  if ($db) {
    $db->close();
  }
  die($msg);
}

/**
 * The database wrapper class.
 *
 * Database is MySQL, created as:
 *
 * CREATE TABLE `<MYSQL_DATABASE>`.`<MYSQL_TABLE_PREFIX>moves` (
 *   `channel` TINYTEXT NOT NULL,
 *   `step` TINYINT NOT NULL,
 *   `board` CHAR(9) NOT NULL DEFAULT '.........',
 *   PRIMARY KEY (`channel`(255), `step`),
 *   KEY `channel` (`channel`(255))
 * ) ENGINE = InnoDB;
 *
 * CREATE TABLE `<MYSQL_DATABASE>`.`<MYSQL_TABLE_PREFIX>status` (
 *   `channel` TINYTEXT NOT NULL,
 *   `userO` TINYTEXT NOT NULL,
 *   `userX` TINYTEXT NOT NULL,
 *   `ongoing` BOOLEAN NOT NULL DEFAULT TRUE,
 *   `nextstep` TINYINT NOT NULL DEFAULT 0,
 *   PRIMARY KEY (`channel`(255))
 * ) ENGINE = InnoDB;
 */
class Db {
  var $db_link;

  function Db() {
    $this->db_link = mysqli_connect(MYSQL_HOST, MYSQL_USER, MYSQL_PASSWORD)
        or error('Could not connect: ' . mysqli_connect_error());
    $this->execute("SET NAMES 'utf8'");
    mysqli_select_db($this->db_link, MYSQL_DATABASE);
  }

  function query($sql) {
    $result = mysqli_query($this->db_link, $sql);
    if (!$result) {
      return false;
    }
    $array = array();
    while ($row = mysqli_fetch_array($result)) {
      $array[] = $row;
    }
    return $array;
  }

  function execute($sql) {
    mysqli_query($this->db_link, $sql);
  }

  function close() {
    mysqli_close($this->db_link);
  }
}

/**
 * Format a string or an array of strings by adding \n after each string.
 */
function format_array($string_or_array) {
  if (is_array($string_or_array)) {
    $result = '';
    foreach($string_or_array as $line) {
      $result .= "$line\n";
    }
    return $result;
  }
  return "$string_or_array\n";
}

/**
 * Return the message to slack and die.
 *
 * $formatted, $prefix and $suffix can be either array of strings or a string.
 *
 * @param $formatted array of strings to be wrapped with ```, one each line.
 * @param $db database to close before dying.
 * @param $prefix array of strings before $formatted.
 * @param $suffix array of strings after $formatted.
 */
function return_msg($formatted, $db = null, $prefix = null, $suffix = null) {
  $json['response_type'] = 'in_channel';
  $json['text'] = '';
  if ($prefix) {
    $json['text'] .= format_array($prefix);
  }
  if ($formatted) {
    $json['text'] .= "```\n";
    $json['text'] .= format_array($formatted);
    $json['text'] .= "```\n";
  }
  if ($suffix) {
    $json['text'] .= format_array($suffix);
  }
  header('Content-Type: application/json');
  echo(json_encode($json));

  if ($db != null) {
    $db->close();
  }
  die();
}

/**
 * Show command usage and die.
 */
function show_help() {
  $arg0 = $_POST['command'];
  return_msg(array(
    'Slack Tic-Tac-Toe game.',
    '',
    "Usage: $arg0 help|show|stop|@username|move x y",
    '',
    'Subcommands:',
    "    help:      This help message.",
    "    show:      Show the current game on this channel.",
    "    stop:      Stop the current game on this channel.",
    "    replay:    Replay the current or last game on this channel.",
    "    @username: Start a new game on this channel between yourself and @username.",
    "               @username moves first.",
    "    move x y:  Make your next move on x,y (0 <= x,y <= 2)",
  ));
}

/**
 * Get the status table result for $channel.
 */
function get_status($db, $channel) {
  $table = TABLE_STATUS;
  $result = $db->query(
    'SELECT `userO`, `userX`, `ongoing`, `nextstep` FROM ' .
    "`$table` WHERE `channel` = '$channel' LIMIT 1");
  if ($result) {
    $result = $result[0];
  }
  return $result;
}

/**
 * Check whether there's an ongoing game from a channel's status.
 */
function is_ongoing($status) {
  if ($status) {
    return $status['ongoing'];
  }
  return false;
}

/**
 * Render the header of the board.
 */
function draw_board_header($userO, $userX) {
  return "O: @$userO, X: @$userX";
}

/**
 * Render the board of game.
 *
 * @param $board the board, a string with 9 characters.
 * @param $userO
 * @param $userX if both $userO and $userX are set, draw the header as well.
 */
function draw_board($board, $userO = null, $userX = null) {
  $result = '';
  if ($userO && $userX) {
    $result = draw_board_header($userO, $userX) . "\n";
  }
  $board = str_replace('.', ' ', $board);
  $newline = '|---+---+---|';
  for ($i = 0; $i < 3; $i++) {
    $line = '|';
    for ($j = 0; $j < 3; $j++) {
      $index = $i * 3 + $j;
      $char = substr($board, $index, 1);
      $line .= " $char |";
    }
    $result .= "$newline\n";
    $result .= "$line\n";
  }
  $result .= $newline;
  return $result;
}

function starts_with($string, $prefix) {
  return strpos($string, $prefix) === 0;
}

/**
 * Make a SQL query to get the board.
 */
function get_board($db, $channel, $step) {
  $table = TABLE_MOVES;
  $result = $db->query(
    "SELECT `board` from `$table` WHERE " .
    "`channel` = '$channel' AND `step` = '$step' LIMIT 1");
  if ($result) {
    return $result[0]['board'];
  }
  return false;
}

/**
 * Get the token at ($x, $y) from $board.
 */
function get_token($board, $x, $y) {
  return substr($board, $x * 3 + $y, 1);
}

/**
 * Set the token at ($x, $y) to $token from $board.
 */
function set_token($board, $x, $y, $token) {
  $board[$x * 3 + $y] = $token;
  return $board;
}

/**
 * Check if we have a winner at $board on $line coordinates.
 *
 * @param $board the board, must be a string of 9 characters
 * @param $line the coordinates, must be an array of 3 integers
 * @param $userO
 * @param $userX
 *
 * @return winner username, or false if no winner yet.
 */
function check_winner_line($board, $line, $userO, $userX) {
  $token = $board[$line[0]];
  if ($token == '.') {
    return false;
  }
  if ($token != $board[$line[1]] || $token != $board[$line[2]]) {
    return false;
  }
  switch($token) {
  case 'O':
    return $userO;
  case 'X':
    return $userX;
  }
}

/**
 * Check if we have a winner at $board.
 *
 * @return true if it's a draw, false if no winner yet, or winner username.
 */
function check_winner($board, $userO, $userX, $index = null) {
  if ($index === null) {
    foreach(WINNER_LINES as $line) {
      $winner = check_winner_line($board, $line, $userO, $userX);
      if ($winner) {
        return $winner;
      }
    }
  } else {
    foreach(LINES_TO_CHECK[$index] as $i) {
      $line = WINNER_LINES[$i];
      $winner = check_winner_line($board, $line, $userO, $userX);
      if ($winner) {
        return $winner;
      }
    }
  }
  return strpos($board, '.') === false;
}

/**
 * Get the latest board on $channel
 */
function get_latest_board($db, $status, $channel) {
  $board = EMPTY_BOARD;
  $nextstep = $status['nextstep'];
  if ($nextstep > 0) {
    $board = get_board($db, $channel, $nextstep - 1);
  }
  return $board;
}

// Subcommand handling functions

function do_stop($db, $status, $channel) {
  if (is_ongoing($status)) {
    $table = TABLE_STATUS;
    $db->execute(
      "UPDATE `$table` SET `ongoing` = FALSE WHERE `channel` = '$channel'");
    $user1 = $status['userO'];
    $user2 = $status['userX'];
    return_msg(null, $db, array(
      "Stopped the game between @$user1 and @$user2.",
      'Use replay subcommand to replay the game.',
    ));
  } else {
    return_msg(null, $db, 'Error: No game ongoing on this channel.');
  }
}

function do_show($db, $status, $channel) {
  if (is_ongoing($status)) {
    $table = TABLE_MOVES;
    $board = get_latest_board($db, $status, $channel);
    $userO = $status['userO'];
    $userX = $status['userX'];
    if ($status['nextstep'] % 2 == 0) {
      $nextuser = $status['userO'];
    } else {
      $nextuser = $status['userX'];
    }
    return_msg(
      draw_board($board, $userO, $userX),
      $db,
      "@$userX is challenging @$userO:",
      "It's @$nextuser's turn.");
  } else {
    return_msg(null, $db, 'Error: No game ongoing on this channel.');
  }
}

function do_replay($db, $status, $channel) {
  if (!$status) {
    return_msg(null, $db, 'No game on this board to replay.');
  }
  $userO = $status['userO'];
  $userX = $status['userX'];
  $formatted = array();
  $formatted[] = draw_board_header($userO, $userX);
  $lastboard = EMPTY_BOARD;

  $table = TABLE_MOVES;
  $result = $db->query(
    "SELECT `step`, `board` FROM `$table` WHERE `channel` = '$channel' " .
    "ORDER BY `step` ASC");
  foreach($result as $row) {
    $step = $row['step'];
    $board = $row['board'];
    $lastboard = $board;
    $formatted[] = "Step $step:";
    $formatted[] = draw_board($board);
  }
  if ($lastboard == EMPTY_BOARD) {
    $formatted[] = draw_board($lastboard);
    $formatted[] = '(No moves.)';
  }
  $suffix = null;
  $winner = check_winner($lastboard, $userO, $userX);
  if ($winner) {
    if ($winner === true) {
      $suffix = 'It\'s a draw.';
    } else {
      $suffix = "@$winner won.";
    }
  }
  return_msg($formatted, $db, "@$userX challenged @$userO.", $suffix);
}

function do_at($db, $status, $channel, $command) {
  if (strpos($command, ' ')) {
    return_msg(null, $db, array(
      "Error: Invalid command \"$command\".",
      'You cannot add anything after @username.',
    ));
  }
  if (is_ongoing($status)) {
    return_msg(null, $db, array(
      'Error: There is an ongoing game on this channel.',
      'Please either finish it or use stop subcommand to stop it first.',
    ));
  }
  $table = TABLE_MOVES;
  $db->execute("DELETE FROM `$table` WHERE `channel` = '$channel'");
  $table = TABLE_STATUS;
  if ($status) {
    $db->execute("DELETE FROM `$table` WHERE `channel` = '$channel'");
  }
  $userO = substr($command, 1);
  if (preg_match(USERNAME_PATTERN, $userO) != 1) {
    return_msg(null, $db, "Error: Invalid username \"@$userO\"");
  }
  $userX = $_POST['user_name'];
  $db->execute(
    "INSERT INTO `$table` SET " .
    "`channel` = '$channel', `userO` = '$userO', `userX` = '$userX'");
  return_msg(
    draw_board(EMPTY_BOARD, $userO, $userX),
    $db,
    array(
      "@$userX challenges @$userO for a Tic-Tac-Toe game!",
      'There can be only one!',
      '(Or zero. The only winning move is not to play.)',
    ),
    "Now it's @$userO's move.");
}

function do_move($db, $status, $channel, $command) {
  if (!is_ongoing($status)) {
    return_msg(null, $db, 'Error: No game ongoing on this channel.');
  }
  if ($status['nextstep'] % 2 == 0) {
    $nextuser = $status['userO'];
    $nexttoken = 'O';
    $otheruser = $status['userX'];
  } else {
    $nextuser = $status['userX'];
    $nexttoken = 'X';
    $otheruser = $status['userO'];
  }
  if ($nextuser != $_POST['user_name']) {
    return_msg(null, $db, array(
      'Error: It\'s not your turn.',
      "(It's @$nextuser's turn.)",
    ));
  }
  $moves = explode(' ', $command);
  if (sizeof($moves) != 3) {
    return_msg(null, $db, array(
      'Error: Invalid move subcommand.',
      '(Please use "move x y" whith 0 <= x,y <= 2)',
    ));
  }
  $x = $moves[1];
  $y = $moves[2];
  $xx = (string) ((int) $x);
  $yy = (string) ((int) $y);
  if ($x != $xx || $y != $yy) {
    return_msg(null, $db, array(
      'Error: Invalid move subcommand.',
      '(Please use "move x y" whith 0 <= x,y <= 2)',
    ));
  }
  if ($x < 0 || $x > 2 || $y < 0 || $y > 2) {
    return_msg(null, $db, "Error: Move subcommand \"$command\" out of range.");
  }
  $board = get_latest_board($db, $status, $channel);
  $nextstep = $status['nextstep'];
  $userO = $status['userO'];
  $userX = $status['userX'];
  if (get_token($board, $x, $y) != '.') {
    return_msg(
      draw_board($board, $userO, $userX),
      $db,
      array(
        'Error: Invalid move.',
        "($x, $y) is already occupied:",
      ));
  }
  $board = set_token($board, $x, $y, $nexttoken);
  $db->execute('START TRANSACTION');
  $db->execute(
    'INSERT INTO `' . TABLE_MOVES .
    "` VALUES('$channel', $nextstep, '$board')");
  $winner = check_winner($board, $userO, $userX, $x * 3 + $y);
  if ($winner) {
    $db->execute(
      'UPDATE `' . TABLE_STATUS . '` SET `nextstep` = ' . ($nextstep + 1) .
      ", `ongoing` = FALSE WHERE `channel` = '$channel'");
    $db->execute('COMMIT');
    if ($winner === true) {
      $msg = array(
        'It\'s a draw.',
        'The only winning move is not to play.',
      );
    } else {
      $msg = array(
        "Congratulations! @$winner won the game!",
        'There can be only one!',
      );
    }
    return_msg(draw_board($board, $userO, $userX), $db, $msg);
  } else {
    $db->execute(
      'UPDATE `' . TABLE_STATUS . '` SET `nextstep` = ' . ($nextstep + 1) .
      " WHERE `channel` = '$channel'");
    $db->execute('COMMIT');
    return_msg(
      draw_board($board, $userO, $userX),
      $db,
      "@$nextuser just made a move on ($x, $y):",
      "Now it's @$otheruser's turn.");
  }
}

// Main code starts here.

if ($_POST['token'] != TOKEN) {
  error('Invalid token.');
}

$channel = $_POST['channel_id'];
if (!$channel) {
  error('Missing channel_id.');
}
if (preg_match(CHANNEL_PATTERN, $channel) != 1) {
  error('Invalid channel_id.');
}
if (preg_match(USERNAME_PATTERN, $_POST['user_name']) != 1) {
  error('Invalid user_name.');
}
$command = $_POST['text'];
if (!$command) {
  // Default command is to show the current game
  $command = 'show';
}
$command = trim($command);

if ($command == 'help') {
  show_help();
}

$db = new Db();
$status = get_status($db, $channel);

if ($command == 'stop') {
  do_stop($db, $status, $channel);
}

if ($command == 'show') {
  do_show($db, $status, $channel);
}

if ($command == 'replay') {
  do_replay($db, $status, $channel);
}

if (starts_with($command, '@')) {
  do_at($db, $status, $channel, $command);
}

if (starts_with($command, 'move ')) {
  do_move($db, $status, $channel, $command);
}

return_msg(null, $db, array(
  "Error: Unrecognized subcommand \"$command\".",
  "You can use help subcommand to get help.",
));

// Won't reach here, but just in case.
$db->close();

?>