<?php
namespace Elgg;
use Elgg\Database\Config;

/**
 * An object representing a single Elgg database.
 *
 * WARNING: THIS API IS IN FLUX. PLUGIN AUTHORS SHOULD NOT USE. See lib/database.php instead.
 *
 * @access private
 *
 * @package    Elgg.Core
 * @subpackage Database
 */
class Database {

	/** @var string $tablePrefix Prefix for database tables */
	private $tablePrefix;

	/** @var resource[] $dbLinks Database connection resources */
	private $dbLinks = array();

	/** @var int $queryCount The number of queries made */
	private $queryCount = 0;

	/**
	 * Query cache for select queries.
	 *
	 * Queries and their results are stored in this cache as:
	 * <code>
	 * $DB_QUERY_CACHE[query hash] => array(result1, result2, ... resultN)
	 * </code>
	 * @see \Elgg\Database::getResults() for details on the hash.
	 *
	 * @var \Elgg\Cache\LRUCache $queryCache The cache
	 */
	private $queryCache = null;

	/**
	 * @var int $queryCacheSize The number of queries to cache
	 */
	private $queryCacheSize = 50;

	/**
	 * Queries are saved to an array and executed using
	 * a function registered by register_shutdown_function().
	 *
	 * Queries are saved as an array in the format:
	 * <code>
	 * $this->delayedQueries[] = array(
	 * 	'q' => string $query,
	 * 	'l' => string $query_type,
	 * 	'h' => string $handler // a callback function
	 * );
	 * </code>
	 *
	 * @var array $delayedQueries Queries to be run during shutdown
	 */
	private $delayedQueries = array();

	/** @var bool $installed Is the database installed? */
	private $installed = false;

	/** @var \Elgg\Database\Config $config Database configuration */
	private $config;

	/** @var \Elgg\Logger $logger The logger */
	private $logger;

	/**
	 * Constructor
	 *
	 * @param \Elgg\Database\Config $config Database configuration
	 * @param \Elgg\Logger          $logger The logger
	 */
	public function __construct(\Elgg\Database\Config $config, \Elgg\Logger $logger) {

		$this->logger = $logger;
		$this->config = $config;

		$this->tablePrefix = $config->getTablePrefix();

		$this->enableQueryCache();
	}

	/**
	 * Gets (if required, also creates) a database link resource.
	 *
	 * The database link resources are created by
	 * {@link \Elgg\Database::setupConnections()}, which is called if no links exist.
	 *
	 * @param string $type The type of link we want: "read", "write" or "readwrite".
	 *
	 * @return resource Database link
	 * @throws \DatabaseException
	 * @todo make protected once we get rid of get_db_link()
	 */
	public function getLink($type) {
		if (isset($this->dbLinks[$type])) {
			return $this->dbLinks[$type];
		} else if (isset($this->dbLinks['readwrite'])) {
			return $this->dbLinks['readwrite'];
		} else {
			$this->setupConnections();
			return $this->getLink($type);
		}
	}

	/**
	 * Establish database connections
	 *
	 * If the configuration has been set up for multiple read/write databases, set those
	 * links up separately; otherwise just create the one database link.
	 *
	 * @return void
	 * @throws \DatabaseException
	 */
	public function setupConnections() {
		if ($this->config->isDatabaseSplit()) {
			$this->establishLink('read');
			$this->establishLink('write');
		} else {
			$this->establishLink('readwrite');
		}
	}


	/**
	 * Establish a connection to the database server
	 *
	 * Connect to the database server and use the Elgg database for a particular database link
	 *
	 * @param string $dblinkname The type of database connection. Used to identify the
	 * resource: "read", "write", or "readwrite".
	 *
	 * @return void
	 * @throws \DatabaseException
	 */
	public function establishLink($dblinkname = "readwrite") {

		$conf = $this->config->getConnectionConfig($dblinkname);

		// Connect to database
		$this->dbLinks[$dblinkname] = mysql_connect($conf['host'], $conf['user'], $conf['password'], true);
		if (!$this->dbLinks[$dblinkname]) {
			$msg = "Elgg couldn't connect to the database using the given credentials. Check the settings file.";
			throw new \DatabaseException($msg);
		}

		if (!mysql_select_db($conf['database'], $this->dbLinks[$dblinkname])) {
			$msg = "Elgg couldn't select the database '{$conf['database']}'. Please check that the database is created and you have access to it.";
			throw new \DatabaseException($msg);
		}

		// Set DB for UTF8
		mysql_query("SET NAMES utf8", $this->dbLinks[$dblinkname]);
	}

	/**
	 * Retrieve rows from the database.
	 *
	 * Queries are executed with {@link \Elgg\Database::executeQuery()} and results
	 * are retrieved with {@link mysql_fetch_object()}.  If a callback
	 * function $callback is defined, each row will be passed as a single
	 * argument to $callback.  If no callback function is defined, the
	 * entire result set is returned as an array.
	 *
	 * @param mixed  $query    The query being passed.
	 * @param string $callback Optionally, the name of a function to call back to on each row
	 *
	 * @return array An array of database result objects or callback function results. If the query
	 *               returned nothing, an empty array.
	 * @throws \DatabaseException
	 */
	public function getData($query, $callback = '') {
		return $this->getResults($query, $callback, false);
	}

	/**
	 * Retrieve a single row from the database.
	 *
	 * Similar to {@link \Elgg\Database::getData()} but returns only the first row
	 * matched.  If a callback function $callback is specified, the row will be passed
	 * as the only argument to $callback.
	 *
	 * @param mixed  $query    The query to execute.
	 * @param string $callback A callback function
	 *
	 * @return mixed A single database result object or the result of the callback function.
	 * @throws \DatabaseException
	 */
	public function getDataRow($query, $callback = '') {
		return $this->getResults($query, $callback, true);
	}

	/**
	 * Insert a row into the database.
	 *
	 * @note Altering the DB invalidates all queries in the query cache.
	 *
	 * @param mixed $query The query to execute.
	 *
	 * @return int|false The database id of the inserted row if a AUTO_INCREMENT field is
	 *                   defined, 0 if not, and false on failure.
	 * @throws \DatabaseException
	 */
	public function insertData($query) {

		$this->logger->log("DB query $query", \Elgg\Logger::INFO);

		$dblink = $this->getLink('write');

		$this->invalidateQueryCache();

		if ($this->executeQuery("$query", $dblink)) {
			return mysql_insert_id($dblink);
		}

		return false;
	}

	/**
	 * Update the database.
	 *
	 * @note Altering the DB invalidates all queries in the query cache.
	 *
	 * @param string $query      The query to run.
	 * @param bool   $getNumRows Return the number of rows affected (default: false)
	 *
	 * @return bool|int
	 * @throws \DatabaseException
	 */
	public function updateData($query, $getNumRows = false) {

		$this->logger->log("DB query $query", \Elgg\Logger::INFO);

		$dblink = $this->getLink('write');

		$this->invalidateQueryCache();

		if ($this->executeQuery("$query", $dblink)) {
			if ($getNumRows) {
				return mysql_affected_rows($dblink);
			} else {
				return true;
			}
		}

		return false;
	}

	/**
	 * Delete data from the database
	 *
	 * @note Altering the DB invalidates all queries in query cache.
	 *
	 * @param string $query The SQL query to run
	 *
	 * @return int|false The number of affected rows or false on failure
	 * @throws \DatabaseException
	 */
	public function deleteData($query) {

		$this->logger->log("DB query $query", \Elgg\Logger::INFO);

		$dblink = $this->getLink('write');

		$this->invalidateQueryCache();

		if ($this->executeQuery("$query", $dblink)) {
			return mysql_affected_rows($dblink);
		}

		return false;
	}

	/**
	 * Get a string that uniquely identifies a callback during the current request.
	 *
	 * This is used to cache queries whose results were transformed by the callback. If the callback involves
	 * object method calls of the same class, different instances will return different values.
	 *
	 * @param callable $callback The callable value to fingerprint
	 *
	 * @return string A string that is unique for each callable passed in
	 * @since 1.9.4
	 * @access private
	 * @todo Make this protected once we can setAccessible(true) via reflection
	 */
	public function fingerprintCallback($callback) {
		if (is_string($callback)) {
			return $callback;
		}
		if (is_object($callback)) {
			return spl_object_hash($callback) . "::__invoke";
		}
		if (is_array($callback)) {
			if (is_string($callback[0])) {
				return "{$callback[0]}::{$callback[1]}";
			}
			return spl_object_hash($callback[0]) . "::{$callback[1]}";
		}
		// this should not happen
		return "";
	}

	/**
	 * Handles queries that return results, running the results through a
	 * an optional callback function. This is for R queries (from CRUD).
	 *
	 * @param string $query    The select query to execute
	 * @param string $callback An optional callback function to run on each row
	 * @param bool   $single   Return only a single result?
	 *
	 * @return array An array of database result objects or callback function results. If the query
	 *               returned nothing, an empty array.
	 * @throws \DatabaseException
	 */
	protected function getResults($query, $callback = null, $single = false) {

		// Since we want to cache results of running the callback, we need to
		// need to namespace the query with the callback and single result request.
		// https://github.com/elgg/elgg/issues/4049
		$query_id = (int)$single . $query . '|';
		if ($callback) {
			$is_callable = is_callable($callback);
			if ($is_callable) {
				$query_id .= $this->fingerprintCallback($callback);
			} else {
				// TODO do something about invalid callbacks
				$callback = null;
			}
		} else {
			$is_callable = false;
		}
		// MD5 yields smaller mem usage for cache and cleaner logs
		$hash = md5($query_id);

		// Is cached?
		if ($this->queryCache) {
			if (isset($this->queryCache[$hash])) {
				$this->logger->log("DB query $query results returned from cache (hash: $hash)", \Elgg\Logger::INFO);
				return $this->queryCache[$hash];
			}
		}

		$dblink = $this->getLink('read');
		$return = array();

		if ($result = $this->executeQuery("$query", $dblink)) {
			while ($row = mysql_fetch_object($result)) {
				if ($is_callable) {
					$row = call_user_func($callback, $row);
				}

				if ($single) {
					$return = $row;
					break;
				} else {
					$return[] = $row;
				}
			}
		}

		if (empty($return)) {
			$this->logger->log("DB query $query returned no results.", \Elgg\Logger::INFO);
		}

		// Cache result
		if ($this->queryCache) {
			$this->queryCache[$hash] = $return;
			$this->logger->log("DB query $query results cached (hash: $hash)", \Elgg\Logger::INFO);
		}

		return $return;
	}

	/**
	 * Execute a query.
	 *
	 * $query is executed via {@link mysql_query()}.  If there is an SQL error,
	 * a {@link DatabaseException} is thrown.
	 *
	 * @param string   $query  The query
	 * @param resource $dblink The DB link
	 *
	 * @return resource|bool The result of mysql_query()
	 * @throws \DatabaseException
	 * @todo should this be public?
	 */
	public function executeQuery($query, $dblink) {

		if ($query == null) {
			throw new \DatabaseException("Query cannot be null");
		}

		if (!is_resource($dblink)) {
			throw new \DatabaseException("Connection to database was lost.");
		}

		$this->queryCount++;

		$result = mysql_query($query, $dblink);

		if (mysql_errno($dblink)) {
			throw new \DatabaseException(mysql_error($dblink) . "\n\n QUERY: $query");
		}

		return $result;
	}

	/**
	 * Runs a full database script from disk.
	 *
	 * The file specified should be a standard SQL file as created by
	 * mysqldump or similar.  Statements must be terminated with ;
	 * and a newline character (\n or \r\n).
	 *
	 * The special string 'prefix_' is replaced with the database prefix
	 * as defined in {@link $this->tablePrefix}.
	 *
	 * @warning Only single line comments are supported. A comment
	 * must start with '-- ' or '# ', where the comment sign is at the
	 * very beginning of each line.
	 *
	 * @warning Errors do not halt execution of the script.  If a line
	 * generates an error, the error message is saved and the
	 * next line is executed.  After the file is run, any errors
	 * are displayed as a {@link DatabaseException}
	 *
	 * @param string $scriptlocation The full path to the script
	 *
	 * @return void
	 * @throws \DatabaseException
	 */
	public function runSqlScript($scriptlocation) {
		$script = file_get_contents($scriptlocation);
		if ($script) {

			$errors = array();

			// Remove MySQL '-- ' and '# ' style comments
			$script = preg_replace('/^(?:--|#) .*$/m', '', $script);

			// Statements must end with ; and a newline
			$sql_statements = preg_split('/;[\n\r]+/', "$script\n");

			foreach ($sql_statements as $statement) {
				$statement = trim($statement);
				$statement = str_replace("prefix_", $this->tablePrefix, $statement);
				if (!empty($statement)) {
					try {
						$this->updateData($statement);
					} catch (\DatabaseException $e) {
						$errors[] = $e->getMessage();
					}
				}
			}
			if (!empty($errors)) {
				$errortxt = "";
				foreach ($errors as $error) {
					$errortxt .= " {$error};";
				}

				$msg = "There were a number of issues: " . $errortxt;
				throw new \DatabaseException($msg);
			}
		} else {
			$msg = "Elgg couldn't find the requested database script at " . $scriptlocation . ".";
			throw new \DatabaseException($msg);
		}
	}

	/**
	 * Queue a query for execution upon shutdown.
	 *
	 * You can specify a handler function if you care about the result. This function will accept
	 * the raw result from {@link mysql_query()}.
	 *
	 * @param string $query   The query to execute
	 * @param string $type    The query type ('read' or 'write')
	 * @param string $handler A callback function to pass the results array to
	 *
	 * @return boolean Whether registering was successful.
	 * @todo deprecate passing resource for $type as that should not be part of public API
	 */
	public function registerDelayedQuery($query, $type, $handler = "") {

		if (!is_resource($type) && $type != 'read' && $type != 'write') {
			return false;
		}

		// Construct delayed query
		$delayed_query = array();
		$delayed_query['q'] = $query;
		$delayed_query['l'] = $type;
		$delayed_query['h'] = $handler;

		$this->delayedQueries[] = $delayed_query;

		return true;
	}


	/**
	 * Trigger all queries that were registered as "delayed" queries. This is
	 * called by the system automatically on shutdown.
	 *
	 * @return void
	 * @access private
	 * @todo make protected once this class is part of public API
	 */
	public function executeDelayedQueries() {

		foreach ($this->delayedQueries as $query_details) {
			try {
				$link = $query_details['l'];

				if ($link == 'read' || $link == 'write') {
					$link = $this->getLink($link);
				} elseif (!is_resource($link)) {
					$msg = "Link for delayed query not valid resource or db_link type. Query: {$query_details['q']}";
					$this->logger->log($msg, \Elgg\Logger::WARNING);
				}

				$result = $this->executeQuery($query_details['q'], $link);

				if ((isset($query_details['h'])) && (is_callable($query_details['h']))) {
					$query_details['h']($result);
				}
			} catch (\DatabaseException $e) {
				// Suppress all exceptions since page already sent to requestor
				$this->logger->log($e, \Elgg\Logger::ERROR);
			}
		}
	}

	/**
	 * Enable the query cache
	 * 
	 * This does not take precedence over the \Elgg\Database\Config setting.
	 * 
	 * @return void
	 */
	public function enableQueryCache() {
		if ($this->config->isQueryCacheEnabled() && $this->queryCache === null) {
			// @todo if we keep this cache, expose the size as a config parameter
			$this->queryCache = new \Elgg\Cache\LRUCache($this->queryCacheSize);
		}
	}

	/**
	 * Disable the query cache
	 * 
	 * This is useful for special scripts that pull large amounts of data back
	 * in single queries.
	 * 
	 * @return void
	 */
	public function disableQueryCache() {
		$this->queryCache = null;
	}

	/**
	 * Invalidate the query cache
	 *
	 * @return void
	 */
	protected function invalidateQueryCache() {
		if ($this->queryCache) {
			$this->queryCache->clear();
			$this->logger->log("Query cache invalidated", \Elgg\Logger::INFO);
		}
	}

	/**
	 * Test that the Elgg database is installed
	 *
	 * @return void
	 * @throws \InstallationException
	 */
	public function assertInstalled() {

		if ($this->installed) {
			return;
		}

		try {
			$dblink = $this->getLink('read');
			mysql_query("SELECT value FROM {$this->tablePrefix}datalists WHERE name = 'installed'", $dblink);
			if (mysql_errno($dblink) > 0) {
				throw new \DatabaseException();
			}
		} catch (\DatabaseException $e) {
			throw new \InstallationException("Unable to handle this request. This site is not configured or the database is down.");
		}

		$this->installed = true;
	}

	/**
	 * Get the number of queries made to the database
	 *
	 * @return int
	 */
	public function getQueryCount() {
		return $this->queryCount;
	}

	/**
	 * Get the prefix for Elgg's tables
	 *
	 * @return string
	 */
	public function getTablePrefix() {
		return $this->tablePrefix;
	}

	/**
	 * Sanitizes an integer value for use in a query
	 *
	 * @param int  $value  Value to sanitize
	 * @param bool $signed Whether negative values are allowed (default: true)
	 * @return int
	 */
	public function sanitizeInt($value, $signed = true) {
		$value = (int) $value;

		if ($signed === false) {
			if ($value < 0) {
				$value = 0;
			}
		}

		return $value;
	}

	/**
	 * Sanitizes a string for use in a query
	 *
	 * @param string $value Value to escape
	 * @return string
	 */
	public function sanitizeString($value) {

		// use resource if established, but don't open a connection to do it.
		if (isset($this->dbLinks['read'])) {
			return mysql_real_escape_string($value, $this->dbLinks['read']);
		}

		return mysql_real_escape_string($value);
	}

	/**
	 * Get the server version number
	 *
	 * @param string $type Connection type (Config constants, e.g. Config::READ_WRITE)
	 *
	 * @return string
	 */
	public function getServerVersion($type) {
		return mysql_get_server_info($this->getLink($type));
	}
}