<?php namespace CodeIgniter\Database;

/**
 * CodeIgniter
 *
 * An open source application development framework for PHP
 *
 * This content is released under the MIT License (MIT)
 *
 * Copyright (c) 2014 - 2016, British Columbia Institute of Technology
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 *
 * @package	CodeIgniter
 * @author	CodeIgniter Dev Team
 * @copyright	Copyright (c) 2014 - 2016, British Columbia Institute of Technology (http://bcit.ca/)
 * @license	http://opensource.org/licenses/MIT	MIT License
 * @link	http://codeigniter.com
 * @since	Version 3.0.0
 * @filesource
 */

use CodeIgniter\DatabaseException;

/**
 * Class BaseConnection
 */
abstract class BaseConnection implements ConnectionInterface
{
	/**
	 * Data Source Name / Connect string
	 *
	 * @var    string
	 */
	public $DSN;

	/**
	 * Database port
	 *
	 * @var    int
	 */
	public $port = '';

	/**
	 * Hostname
	 *
	 * @var    string
	 */
	public $hostname;

	/**
	 * Username
	 *
	 * @var    string
	 */
	public $username;

	/**
	 * Password
	 *
	 * @var    string
	 */
	public $password;

	/**
	 * Database name
	 *
	 * @var    string
	 */
	public $database;

	/**
	 * Database driver
	 *
	 * @var    string
	 */
	public $DBDriver = 'MySQLi';

	/**
	 * Sub-driver
	 *
	 * @used-by    CI_DB_pdo_driver
	 * @var    string
	 */
	public $subdriver;

	/**
	 * Table prefix
	 *
	 * @var    string
	 */
	public $DBPrefix = '';

	/**
	 * Persistent connection flag
	 *
	 * @var    bool
	 */
	public $pConnect = false;

	/**
	 * Debug flag
	 *
	 * Whether to display error messages.
	 *
	 * @var    bool
	 */
	public $DBDebug = false;

	/**
	 * Should we cache results?
	 *
	 * @var bool
	 */
	public $cacheOn = false;

	/**
	 * Path to store cache files.
	 *
	 * @var string
	 */
	public $cacheDir;

	/**
	 * Character set
	 *
	 * @var    string
	 */
	public $charset = 'utf8';

	/**
	 * Collation
	 *
	 * @var    string
	 */
	public $DBCollat = 'utf8_general_ci';

	/**
	 * Swap Prefix
	 *
	 * @var    string
	 */
	public $swapPre = '';

	/**
	 * Encryption flag/data
	 *
	 * @var    mixed
	 */
	public $encrypt = false;

	/**
	 * Compression flag
	 *
	 * @var    bool
	 */
	public $compress = false;

	/**
	 * Strict ON flag
	 *
	 * Whether we're running in strict SQL mode.
	 *
	 * @var    bool
	 */
	public $strictOn;

	/**
	 * Settings for a failover connection.
	 *
	 * @var array
	 */
	public $failover = [];

	/**
	 * Whether to keep an in-memory history of queries
	 * for debugging and timeline purposes.
	 *
	 * @var bool
	 */
	public $saveQueries = false;

	//--------------------------------------------------------------------

	/**
	 * Array of query objects that have executed
	 * on this connection.
	 *
	 * @var array
	 */
	protected $queries = [];

	/**
	 * Connection ID
	 *
	 * @var    object|resource
	 */
	public $connID = false;

	/**
	 * Result ID
	 *
	 * @var    object|resource
	 */
	public $resultID = false;

	/**
	 * Protect identifiers flag
	 *
	 * @var    bool
	 */
	public $protectIdentifiers = true;

	/**
	 * List of reserved identifiers
	 *
	 * Identifiers that must NOT be escaped.
	 *
	 * @var    string[]
	 */
	protected $reservedIdentifiers = ['*'];

	/**
	 * Identifier escape character
	 *
	 * @var    string
	 */
	public $escapeChar = '"';

	/**
	 * ESCAPE statement string
	 *
	 * @var    string
	 */
	public $likeEscapeStr = " ESCAPE '%s' ";

	/**
	 * ESCAPE character
	 *
	 * @var    string
	 */
	public $likeEscapeChar = '!';

	/**
	 * Holds previously looked up data
	 * for performance reasons.
	 *
	 * @var array
	 */
	protected $dataCache = [];

	/**
	 * Microtime when connection was made
	 * @var float
	 */
	protected $connectTime;

	/**
	 * How long it took to establish connection.
	 *
	 * @var float
	 */
	protected $connectDuration;

	//--------------------------------------------------------------------

	/**
	 * Saves our connection settings.
	 *
	 * @param array $params
	 */
	public function __construct(array $params)
	{
	    foreach ($params as $key => $value)
	    {
		    $this->$key = $value;
	    }
	}

	//--------------------------------------------------------------------


	/**
	 * Initializes the database connection/settings.
	 *
	 * @return mixed
	 */
	public function initialize()
	{
		/* If an established connection is available, then there's
		 * no need to connect and select the database.
		 *
		 * Depending on the database driver, conn_id can be either
		 * boolean TRUE, a resource or an object.
		 */
		if ($this->connID)
		{
			return;
		}

		//--------------------------------------------------------------------

		$this->connectTime = microtime(true);

		// Connect to the database and set the connection ID
		$this->connID = $this->connect($this->pConnect);

		// No connection resource? Check if there is a failover else throw an error
		if ( ! $this->connID)
		{
			// Check if there is a failover set
			if ( ! empty($this->failover) && is_array($this->failover))
			{
				// Go over all the failovers
				foreach ($this->failover as $failover)
				{
					// Replace the current settings with those of the failover
					foreach ($failover as $key => $val)
					{
						$this->$key = $val;
					}

					// Try to connect
					$this->connID = $this->connect($this->pConnect);

					// If a connection is made break the foreach loop
					if ($this->connID)
					{
						break;
					}
				}
			}

			// We still don't have a connection?
			if ( ! $this->connID)
			{
				throw new DatabaseException('Unable to connect to the database.');
			}
		}

		$this->connectDuration = microtime(true) - $this->connectTime;
	}

	//--------------------------------------------------------------------

	/**
	 * Connect to the database.
	 *
	 * @param bool $persistent
	 * @return mixed
	 */
	abstract public function connect($persistent = false);

	//--------------------------------------------------------------------

	/**
	 * Create a persistent database connection.
	 *
	 * @return mixed
	 */
	public function persistentConnect()
	{
		return $this->connect(true);
	}

	//--------------------------------------------------------------------

	/**
	 * Keep or establish the connection if no queries have been sent for
	 * a length of time exceeding the server's idle timeout.
	 *
	 * @return mixed
	 */
	abstract public function reconnect();

	//--------------------------------------------------------------------

	/**
	 * Returns the actual connection object. If both a 'read' and 'write'
	 * connection has been specified, you can pass either term in to
	 * get that connection. If you pass either alias in and only a single
	 * connection is present, it must return the sole connection.
	 *
	 * @param string|null $alias
	 *
	 * @return mixed
	 */
	public function getConnection(string $alias = null)
	{
		//@todo work with read/write connections
		return $this->connID;
	}

	//--------------------------------------------------------------------

	/**
	 * Select a specific database table to use.
	 *
	 * @param string $databaseName
	 *
	 * @return mixed
	 */
	abstract public function setDatabase(string $databaseName);

	//--------------------------------------------------------------------

	/**
	 * Returns the name of the current database being used.
	 *
	 * @return string
	 */
	public function getDatabase(): string
	{
		return empty($this->database) ? '' : $this->database;
	}

	//--------------------------------------------------------------------

	/**
	 * Returns the last error encountered by this connection.
	 *
	 * @return mixed
	 */
	public function getError()
	{
	}

	//--------------------------------------------------------------------

	/**
	 * The name of the platform in use (MySQLi, mssql, etc)
	 *
	 * @return mixed
	 */
	public function getPlatform()
	{
		return $this->DBDriver;
	}

	//--------------------------------------------------------------------

	/**
	 * Returns a string containing the version of the database being used.
	 *
	 * @return mixed
	 */
	abstract public function getVersion();

	//--------------------------------------------------------------------

	/**
	 * Specifies whether this connection should keep queries objects or not.
	 *
	 * @param bool $save
	 */
	public function saveQueries($save = false)
	{
		$this->saveQueries = $save;

		return $this;
	}

	//--------------------------------------------------------------------

	/**
	 * Executes the query against the database.
	 *
	 * @param $sql
	 *
	 * @return mixed
	 */
	abstract protected function execute($sql);

	//--------------------------------------------------------------------


	/**
	 * Orchestrates a query against the database. Queries must use
	 * Database\Statement objects to store the query and build it.
	 * This method works with the cache.
	 *
	 * Should automatically handle different connections for read/write
	 * queries if needed.
	 *
	 * @param string $sql
	 * @param array  ...$binds
	 * @param $queryClass
	 * @return mixed
	 */
	public function query(string $sql, $binds = null, $queryClass = 'CodeIgniter\\Database\\Query')
	{
		if (empty($this->connID))
		{
			$this->initialize();
		}

		$resultClass = str_replace('Connection', 'Result', get_class($this));

		$query = new $queryClass($this);

		$query->setQuery($sql, $binds);

		if (! empty($this->swapPre) && ! empty($this->DBPrefix))
		{
			$query->swapPrefix($this->DBPrefix, $this->swapPre);
		}

		$startTime = microtime(true);

		// Run the query
		if (false === ($this->resultID = $this->simpleQuery($query->getQuery())))
		{
			$query->setDuration($startTime, $startTime);

			// @todo deal with errors

			if ($this->saveQueries)
			{
				$this->queries[] = $query;
			}

			return new $resultClass($this->connID, $this->resultID);
		}

		$query->setDuration($startTime);

		if ($this->saveQueries)
		{
			$this->queries[] = $query;
		}

		return new $resultClass($this->connID, $this->resultID);
	}

	//--------------------------------------------------------------------

	/**
	 * Performs a basic query against the database. No binding or caching
	 * is performed, nor are transactions handled. Simply takes a raw
	 * query string and returns the database-specific result id.
	 *
	 * @param string $sql
	 *
	 * @return mixed
	 */
	public function simpleQuery(string $sql)
	{
		if (empty($this->connID))
		{
			$this->initialize();
		}

		return $this->execute($sql);
	}

	//--------------------------------------------------------------------

	/**
	 * Returns an instance of the query builder for this connection.
	 *
	 * @param string $tableName
	 *
	 * @return BaseBuilder
	 * @throws DatabaseException
	 */
	public function table($tableName)
	{
		if (empty($tableName))
		{
			throw new DatabaseException('You must set the database table to be used with your query.');
		}

		$className = str_replace('Connection', 'Builder', get_class($this));

		return new $className($tableName, $this);
	}

	//--------------------------------------------------------------------

	/**
	 * Returns an array containing all of the
	 *
	 * @return array
	 */
	public function getQueries(): array
	{
		return $this->queries;
	}

	//--------------------------------------------------------------------

	/**
	 * Returns the total number of queries that have been performed
	 * on this connection.
	 *
	 * @return mixed
	 */
	public function getQueryCount()
	{
		return count($this->queries);
	}

	//--------------------------------------------------------------------

	/**
	 * Returns the last query's statement object.
	 *
	 * @return mixed
	 */
	public function getLastQuery()
	{
		return end($this->queries);
	}

	//--------------------------------------------------------------------

	/**
	 * Returns a string representation of the last query's statement object.
	 *
	 * @return string
	 */
	public function showLastQuery()
	{
	    return (string)end($this->queries);
	}

	//--------------------------------------------------------------------


	/**
	 * Returns the time we started to connect to this database in
	 * seconds with microseconds.
	 *
	 * Used by the Debug Toolbar's timeline.
	 *
	 * @return float
	 */
	public function getConnectStart()
	{
	    return $this->connectTime;
	}

	//--------------------------------------------------------------------

	/**
	 * Returns the number of seconds with microseconds that it took
	 * to connect to the database.
	 *
	 * Used by the Debug Toolbar's timeline.
	 *
	 * @param int $decimals
	 *
	 * @return mixed
	 */
	public function getConnectDuration($decimals = 6)
	{
	    return number_format($this->connectDuration, $decimals);
	}

	//--------------------------------------------------------------------

	/**
	 * Protect Identifiers
	 *
	 * This function is used extensively by the Query Builder class, and by
	 * a couple functions in this class.
	 * It takes a column or table name (optionally with an alias) and inserts
	 * the table prefix onto it. Some logic is necessary in order to deal with
	 * column names that include the path. Consider a query like this:
	 *
	 * SELECT hostname.database.table.column AS c FROM hostname.database.table
	 *
	 * Or a query with aliasing:
	 *
	 * SELECT m.member_id, m.member_name FROM members AS m
	 *
	 * Since the column name can include up to four segments (host, DB, table, column)
	 * or also have an alias prefix, we need to do a bit of work to figure this out and
	 * insert the table prefix (if it exists) in the proper position, and escape only
	 * the correct identifiers.
	 *
	 * @param    string|array
	 * @param    bool
	 * @param    mixed
	 * @param    bool
	 *
	 * @return    string
	 */
	public function protectIdentifiers($item, $prefixSingle = false, $protectIdentifiers = null, $fieldExists = true)
	{
		if ( ! is_bool($protectIdentifiers))
		{
			$protectIdentifiers = $this->protectIdentifiers;
		}

		if (is_array($item))
		{
			$escaped_array = [];
			foreach ($item as $k => $v)
			{
				$escaped_array[$this->protectIdentifiers($k)] = $this->protectIdentifiers($v, $prefixSingle,
					$protectIdentifiers, $fieldExists);
			}

			return $escaped_array;
		}

		// This is basically a bug fix for queries that use MAX, MIN, etc.
		// If a parenthesis is found we know that we do not need to
		// escape the data or add a prefix. There's probably a more graceful
		// way to deal with this, but I'm not thinking of it -- Rick
		//
		// Added exception for single quotes as well, we don't want to alter
		// literal strings. -- Narf
		if (strcspn($item, "()'") !== strlen($item))
		{
			return $item;
		}

		// Convert tabs or multiple spaces into single spaces
		$item = preg_replace('/\s+/', ' ', trim($item));

		// If the item has an alias declaration we remove it and set it aside.
		// Note: strripos() is used in order to support spaces in table names
		if ($offset = strripos($item, ' AS '))
		{
			$alias = ($protectIdentifiers)
				? substr($item, $offset, 4).$this->escapeIdentifiers(substr($item, $offset + 4))
				: substr($item, $offset);
			$item  = substr($item, 0, $offset);
		}
		elseif ($offset = strrpos($item, ' '))
		{
			$alias = ($protectIdentifiers)
				? ' '.$this->escapeIdentifiers(substr($item, $offset + 1))
				: substr($item, $offset);
			$item  = substr($item, 0, $offset);
		}
		else
		{
			$alias = '';
		}

		// Break the string apart if it contains periods, then insert the table prefix
		// in the correct location, assuming the period doesn't indicate that we're dealing
		// with an alias. While we're at it, we will escape the components
		if (strpos($item, '.') !== false)
		{
			$parts = explode('.', $item);

			// Does the first segment of the exploded item match
			// one of the aliases previously identified? If so,
			// we have nothing more to do other than escape the item
			//
			// NOTE: The ! empty() condition prevents this method
			//       from breaking when QB isn't enabled.
			if ( ! empty($this->qb_aliased_tables) && in_array($parts[0], $this->qb_aliased_tables))
			{
				if ($protectIdentifiers === true)
				{
					foreach ($parts as $key => $val)
					{
						if ( ! in_array($val, $this->reservedIdentifiers))
						{
							$parts[$key] = $this->escapeIdentifiers($val);
						}
					}

					$item = implode('.', $parts);
				}

				return $item.$alias;
			}

			// Is there a table prefix defined in the config file? If not, no need to do anything
			if ($this->DBPrefix !== '')
			{
				// We now add the table prefix based on some logic.
				// Do we have 4 segments (hostname.database.table.column)?
				// If so, we add the table prefix to the column name in the 3rd segment.
				if (isset($parts[3]))
				{
					$i = 2;
				}
				// Do we have 3 segments (database.table.column)?
				// If so, we add the table prefix to the column name in 2nd position
				elseif (isset($parts[2]))
				{
					$i = 1;
				}
				// Do we have 2 segments (table.column)?
				// If so, we add the table prefix to the column name in 1st segment
				else
				{
					$i = 0;
				}

				// This flag is set when the supplied $item does not contain a field name.
				// This can happen when this function is being called from a JOIN.
				if ($fieldExists === false)
				{
					$i++;
				}

				// Verify table prefix and replace if necessary
				if ($this->swapPre !== '' && strpos($parts[$i], $this->swapPre) === 0)
				{
					$parts[$i] = preg_replace('/^'.$this->swapPre.'(\S+?)/', $this->DBPrefix.'\\1', $parts[$i]);
				}
				// We only add the table prefix if it does not already exist
				elseif (strpos($parts[$i], $this->DBPrefix) !== 0)
				{
					$parts[$i] = $this->DBPrefix.$parts[$i];
				}

				// Put the parts back together
				$item = implode('.', $parts);
			}

			if ($protectIdentifiers === true)
			{
				$item = $this->escapeIdentifiers($item);
			}

			return $item.$alias;
		}

		// Is there a table prefix? If not, no need to insert it
		if ($this->DBPrefix !== '')
		{
			// Verify table prefix and replace if necessary
			if ($this->swapPre !== '' && strpos($item, $this->swapPre) === 0)
			{
				$item = preg_replace('/^'.$this->swapPre.'(\S+?)/', $this->DBPrefix.'\\1', $item);
			}
			// Do we prefix an item with no segments?
			elseif ($prefixSingle === true && strpos($item, $this->DBPrefix) !== 0)
			{
				$item = $this->DBPrefix.$item;
			}
		}

		if ($protectIdentifiers === true && ! in_array($item, $this->reservedIdentifiers))
		{
			$item = $this->escapeIdentifiers($item);
		}

		return $item.$alias;
	}

	//--------------------------------------------------------------------

	/**
	 * Escape the SQL Identifiers
	 *
	 * This function escapes column and table names
	 *
	 * @param    mixed
	 *
	 * @return    mixed
	 */
	public function escapeIdentifiers($item)
	{
		if ($this->escapeChar === '' OR empty($item) OR in_array($item, $this->reservedIdentifiers))
		{
			return $item;
		}
		elseif (is_array($item))
		{
			foreach ($item as $key => $value)
			{
				$item[$key] = $this->escapeIdentifiers($value);
			}

			return $item;
		}
		// Avoid breaking functions and literal values inside queries
		elseif (ctype_digit($item) OR $item[0] === "'" OR ($this->escapeChar !== '"' && $item[0] === '"') OR
		        strpos($item, '(') !== false
		)
		{
			return $item;
		}

		static $preg_ec = [];

		if (empty($preg_ec))
		{
			if (is_array($this->escapeChar))
			{
				$preg_ec = [
					preg_quote($this->escapeChar[0], '/'),
					preg_quote($this->escapeChar[1], '/'),
					$this->escapeChar[0],
					$this->escapeChar[1],
				];
			}
			else
			{
				$preg_ec[0] = $preg_ec[1] = preg_quote($this->escapeChar, '/');
				$preg_ec[2] = $preg_ec[3] = $this->escapeChar;
			}
		}

		foreach ($this->reservedIdentifiers as $id)
		{
			if (strpos($item, '.'.$id) !== false)
			{
				return preg_replace('/'.$preg_ec[0].'?([^'.$preg_ec[1].'\.]+)'.$preg_ec[1].'?\./i',
					$preg_ec[2].'$1'.$preg_ec[3].'.', $item);
			}
		}

		return preg_replace('/'.$preg_ec[0].'?([^'.$preg_ec[1].'\.]+)'.$preg_ec[1].'?(\.)?/i',
			$preg_ec[2].'$1'.$preg_ec[3].'$2', $item);
	}

	//--------------------------------------------------------------------

	/**
	 * DB Prefix
	 *
	 * Prepends a database prefix if one exists in configuration
	 *
	 * @param    string    the table
	 *
	 * @return    string
	 */
	public function prefixTable($table = '')
	{
		if ($table === '')
		{
			throw new DatabaseException('A table name is required for that operation.');
		}

		return $this->DBPrefix.$table;
	}

	//--------------------------------------------------------------------

	/**
	 * Set DB Prefix
	 *
	 * Set's the DB Prefix to something new without needing to reconnect
	 *
	 * @param    string    the prefix
	 *
	 * @return    string
	 */
	public function setPrefix($prefix = '')
	{
		return $this->DBPrefix = $prefix;
	}

	//--------------------------------------------------------------------

	/**
	 * Returns the total number of rows affected by this query.
	 *
	 * @return mixed
	 */
	abstract public function affectedRows(): int;

	//--------------------------------------------------------------------

	/**
	 * "Smart" Escape String
	 *
	 * Escapes data based on type.
	 * Sets boolean and null types
	 *
	 * @param $str
	 *
	 * @return mixed
	 */
	public function escape($str)
	{
		if (is_array($str))
		{
			$str = array_map([&$this, 'escape'], $str);

			return $str;
		}
		else if (is_string($str) OR (is_object($str) && method_exists($str, '__toString')))
		{
			return "'".$this->escapeString($str)."'";
		}
		else if (is_bool($str))
		{
			return ($str === false) ? 0 : 1;
		}
		else if ($str === null)
		{
			return 'NULL';
		}

		return $str;
	}

	//--------------------------------------------------------------------

	/**
	 * Escape String
	 *
	 * @param	string|string[]	$str	Input string
	 * @param	bool	$like	Whether or not the string will be used in a LIKE condition
	 * @return	string
	 */
	public function escapeString($str, $like = FALSE)
	{
		if (is_array($str))
		{
			foreach ($str as $key => $val)
			{
				$str[$key] = $this->escapeString($val, $like);
			}

			return $str;
		}

		$str = $this->_escapeString($str);

		// escape LIKE condition wildcards
		if ($like === true)
		{
			return str_replace(
				[$this->likeEscapeChar, '%', '_'],
				[$this->likeEscapeChar.$this->likeEscapeChar, $this->likeEscapeChar.'%', $this->likeEscapeChar.'_'],
				$str
			);
		}

		return $str;
	}

	//--------------------------------------------------------------------

	/**
	 * Escape LIKE String
	 *
	 * Calls the individual driver for platform
	 * specific escaping for LIKE conditions
	 *
	 * @param	string|string[]
	 * @return	mixed
	 */
	public function escapeLikeString($str)
	{
		return $this->escapeString($str, TRUE);
	}

	//--------------------------------------------------------------------


	/**
	 * Platform independent string escape.
	 *
	 * Will likely be overridden in child classes.
	 *
	 * @param string $str
	 *
	 * @return string
	 */
	protected function _escapeString(string $str): string
	{
		return str_replace("'", "\\'", remove_invisible_characters($str));
	}

	//--------------------------------------------------------------------

	/**
	 * This function enables you to call PHP database functions that are not natively included
	 * in CodeIgniter, in a platform independent manner.
	 *
	 * @param string $functionName
	 * @param array  ...$params
	 *
	 * @return bool
	 * @throws DatabaseException
	 */
	public function callFunction(string $functionName, ...$params)
	{
		$driver = ($this->DBDriver === 'postgre' ? 'pg' : strtolower($this->DBDriver)).'_';

		if (FALSE === strpos($driver, $functionName))
		{
			$functionName = $driver.$functionName;
		}

		if ( ! function_exists($functionName))
		{
			if ($this->DBDebug)
			{
				throw new DatabaseException('This feature is not available for the database you are using.');
			}

			return false;
		}

		return $functionName(...$params);
	}

	//--------------------------------------------------------------------

	//--------------------------------------------------------------------
	// META Methods
	//--------------------------------------------------------------------

	/**
	 * Returns an array of table names
	 *
	 * @param	string	$constrain_by_prefix = FALSE
	 * @return	array
	 */
	public function listTables($constrain_by_prefix = FALSE)
	{
		// Is there a cached result?
		if (isset($this->dataCache['table_names']))
		{
			return $this->dataCache['table_names'];
		}

		if (FALSE === ($sql = $this->_listTables($constrain_by_prefix)))
		{
			if ($this->DBDebug)
			{
				throw new DatabaseException('This feature is not available for the database you are using.');
			}
			return false;
		}

		$this->dataCache['table_names'] = array();
		$query = $this->query($sql);

		foreach ($query->getResultArray() as $row)
		{
			// Do we know from which column to get the table name?
			if ( ! isset($key))
			{
				if (isset($row['table_name']))
				{
					$key = 'table_name';
				}
				elseif (isset($row['TABLE_NAME']))
				{
					$key = 'TABLE_NAME';
				}
				else
				{
					/* We have no other choice but to just get the first element's key.
					 * Due to array_shift() accepting its argument by reference, if
					 * E_STRICT is on, this would trigger a warning. So we'll have to
					 * assign it first.
					 */
					$key = array_keys($row);
					$key = array_shift($key);
				}
			}

			$this->dataCache['table_names'][] = $row[$key];
		}

		return $this->dataCache['table_names'];
	}

	//--------------------------------------------------------------------

	/**
	 * Determine if a particular table exists
	 *
	 * @param	string	$table_name
	 * @return	bool
	 */
	public function tableExists($table_name)
	{
		return in_array($this->protectIdentifiers($table_name, TRUE, FALSE, FALSE), $this->listTables());
	}

	//--------------------------------------------------------------------

	/**
	 * Fetch Field Names
	 *
	 * @param    string $table Table name
	 *
	 * @return array
	 * @throws DatabaseException
	 */
	public function getFieldNames($table)
	{
		// Is there a cached result?
		if (isset($this->dataCache['field_names'][$table]))
		{
			return $this->dataCache['field_names'][$table];
		}

		if (FALSE === ($sql = $this->_listColumns($table)))
		{
			if ($this->DBDebug)
			{
				throw new DatabaseException('This feature is not available for the database you are using.');
			}
			return false;
		}

		$query = $this->query($sql);
		$this->dataCache['field_names'][$table] = array();

		foreach ($query->getResultArray() as $row)
		{
			// Do we know from where to get the column's name?
			if ( ! isset($key))
			{
				if (isset($row['column_name']))
				{
					$key = 'column_name';
				}
				elseif (isset($row['COLUMN_NAME']))
				{
					$key = 'COLUMN_NAME';
				}
				else
				{
					// We have no other choice but to just get the first element's key.
					$key = key($row);
				}
			}

			$this->dataCache['field_names'][$table][] = $row[$key];
		}

		return $this->dataCache['field_names'][$table];
	}

	//--------------------------------------------------------------------

	/**
	 * Determine if a particular field exists
	 *
	 * @param	string
	 * @param	string
	 * @return	bool
	 */
	public function fieldExists($fieldName, $tableName)
	{
		return in_array($fieldName, $this->listFields($tableName));
	}

	//--------------------------------------------------------------------

	/**
	 * Returns an object with field data
	 *
	 * @param	string	$table	the table name
	 * @return	array
	 */
	public function getFieldData(string $table)
	{
		$query = $this->query($this->_fieldData($this->protect_identifiers($table, TRUE, NULL, FALSE)));
		return ($query) ? $query->field_data() : FALSE;
	}

	//--------------------------------------------------------------------

	/**
	 * Returns the last error code and message.
	 *
	 * Must return an array with keys 'code' and 'message':
	 *
	 *  return ['code' => null, 'message' => null);
	 *
	 * @return	array
	 */
	abstract public function error();

	//--------------------------------------------------------------------

	/**
	 * Insert ID
	 *
	 * @return	int
	 */
	abstract public function insertID();

	//--------------------------------------------------------------------

	/**
	 * Generates the SQL for listing tables in a platform-dependent manner.
	 *
	 * @param bool $constrainByPrefix
	 *
	 * @return string
	 */
	abstract protected function _listTables($constrainByPrefix = false): string;

	//--------------------------------------------------------------------

	/**
	 * Generates a platform-specific query string so that the column names can be fetched.
	 *
	 * @param string $table
	 *
	 * @return string
	 */
	abstract protected function _listColumns(string $table = ''): string;

	//--------------------------------------------------------------------


}