<?php

/**
 *
 * Idiorm
 *
 * http://github.com/j4mie/idiorm/
 *
 * A single-class super-simple database abstraction layer for PHP.
 * Provides (nearly) zero-configuration object-relational mapping
 * and a fluent interface for building basic, commonly-used queries.
 *
 * BSD Licensed.
 *
 * Copyright (c) 2010, Jamie Matthews
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright notice, this
 *   list of conditions and the following disclaimer.
 *
 * * Redistributions in binary form must reproduce the above copyright notice,
 *   this list of conditions and the following disclaimer in the documentation
 *   and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

class ORM implements ArrayAccess {

    // ----------------------- //
    // --- CLASS CONSTANTS --- //
    // ----------------------- //

    // WHERE and HAVING condition array keys
    const CONDITION_FRAGMENT = 0;
    const CONDITION_VALUES = 1;

    const DEFAULT_CONNECTION = 'default';

    // Limit clause style
    const LIMIT_STYLE_TOP_N = "top";
    const LIMIT_STYLE_LIMIT = "limit";

    // ------------------------ //
    // --- CLASS PROPERTIES --- //
    // ------------------------ //

    // Class configuration
    protected static $_default_config = array(
        'connection_string' => 'sqlite::memory:',
        'id_column' => 'id',
        'id_column_overrides' => array(),
        'error_mode' => PDO::ERRMODE_EXCEPTION,
        'username' => null,
        'password' => null,
        'driver_options' => null,
        'identifier_quote_character' => null, // if this is null, will be autodetected
        'limit_clause_style' => null, // if this is null, will be autodetected
        'logging' => false,
        'logger' => null,
        'caching' => false,
        'caching_auto_clear' => false,
        'return_result_sets' => false,
    );

    // Map of configuration settings
    protected static $_config = array();

    // Map of database connections, instances of the PDO class
    protected static $_db = array();

    // Last query run, only populated if logging is enabled
    protected static $_last_query;

    // Log of all queries run, mapped by connection key, only populated if logging is enabled
    protected static $_query_log = array();

    // Query cache, only used if query caching is enabled
    protected static $_query_cache = array();

    // Reference to previously used PDOStatement object to enable low-level access, if needed
    protected static $_last_statement = null;

    // --------------------------- //
    // --- INSTANCE PROPERTIES --- //
    // --------------------------- //

    // Key name of the connections in self::$_db used by this instance
    protected $_connection_name;

    // The name of the table the current ORM instance is associated with
    protected $_table_name;

    // Alias for the table to be used in SELECT queries
    protected $_table_alias = null;

    // Values to be bound to the query
    protected $_values = array();

    // Columns to select in the result
    protected $_result_columns = array('*');

    // Are we using the default result column or have these been manually changed?
    protected $_using_default_result_columns = true;

    // Join sources
    protected $_join_sources = array();

    // Should the query include a DISTINCT keyword?
    protected $_distinct = false;

    // Is this a raw query?
    protected $_is_raw_query = false;

    // The raw query
    protected $_raw_query = '';

    // The raw query parameters
    protected $_raw_parameters = array();

    // Array of WHERE clauses
    protected $_where_conditions = array();

    // LIMIT
    protected $_limit = null;

    // OFFSET
    protected $_offset = null;

    // ORDER BY
    protected $_order_by = array();

    // GROUP BY
    protected $_group_by = array();

    // HAVING
    protected $_having_conditions = array();

    // The data for a hydrated instance of the class
    protected $_data = array();

    // Fields that have been modified during the
    // lifetime of the object
    protected $_dirty_fields = array();

    // Fields that are to be inserted in the DB raw
    protected $_expr_fields = array();

    // Is this a new object (has create() been called)?
    protected $_is_new = false;

    // Name of the column to use as the primary key for
    // this instance only. Overrides the config settings.
    protected $_instance_id_column = null;

    // ---------------------- //
    // --- STATIC METHODS --- //
    // ---------------------- //

    /**
     * Pass configuration settings to the class in the form of
     * key/value pairs. As a shortcut, if the second argument
     * is omitted and the key is a string, the setting is
     * assumed to be the DSN string used by PDO to connect
     * to the database (often, this will be the only configuration
     * required to use Idiorm). If you have more than one setting
     * you wish to configure, another shortcut is to pass an array
     * of settings (and omit the second argument).
     * @param string $key
     * @param mixed $value
     * @param string $connection_name Which connection to use
     */
    public static function configure($key, $value = null, $connection_name = self::DEFAULT_CONNECTION) {
        self::_setup_db_config($connection_name); //ensures at least default config is set

        if (is_array($key)) {
            // Shortcut: If only one array argument is passed,
            // assume it's an array of configuration settings
            foreach ($key as $conf_key => $conf_value) {
                self::configure($conf_key, $conf_value, $connection_name);
            }
        } else {
            if (is_null($value)) {
                // Shortcut: If only one string argument is passed,
                // assume it's a connection string
                $value = $key;
                $key = 'connection_string';
            }
            self::$_config[$connection_name][$key] = $value;
        }
    }

    /**
     * Retrieve configuration options by key, or as whole array.
     * @param string $key
     * @param string $connection_name Which connection to use
     */
    public static function get_config($key = null, $connection_name = self::DEFAULT_CONNECTION) {
        if ($key) {
            return self::$_config[$connection_name][$key];
        } else {
            return self::$_config[$connection_name];
        }
    }

    /**
     * Delete all configs in _config array.
     */
    public static function reset_config() {
        self::$_config = array();
    }

    /**
     * Despite its slightly odd name, this is actually the factory
     * method used to acquire instances of the class. It is named
     * this way for the sake of a readable interface, ie
     * ORM::for_table('table_name')->find_one()-> etc. As such,
     * this will normally be the first method called in a chain.
     * @param string $table_name
     * @param string $connection_name Which connection to use
     * @return ORM
     */
    public static function for_table($table_name, $connection_name = self::DEFAULT_CONNECTION) {
        self::_setup_db($connection_name);
        return new self($table_name, array(), $connection_name);
    }

    /**
     * Set up the database connection used by the class
     * @param string $connection_name Which connection to use
     */
    protected static function _setup_db($connection_name = self::DEFAULT_CONNECTION) {
        if (!array_key_exists($connection_name, self::$_db) ||
            !is_object(self::$_db[$connection_name])) {
            self::_setup_db_config($connection_name);

            $db = new PDO(
                self::$_config[$connection_name]['connection_string'],
                self::$_config[$connection_name]['username'],
                self::$_config[$connection_name]['password'],
                self::$_config[$connection_name]['driver_options']
            );

            $db->setAttribute(PDO::ATTR_ERRMODE, self::$_config[$connection_name]['error_mode']);
            self::set_db($db, $connection_name);
        }
    }

    /**
     * Ensures configuration (multiple connections) is at least set to default.
     * @param string $connection_name Which connection to use
     */
    protected static function _setup_db_config($connection_name) {
        if (!array_key_exists($connection_name, self::$_config)) {
            self::$_config[$connection_name] = self::$_default_config;
        }
    }

    /**
     * Set the PDO object used by Idiorm to communicate with the database.
     * This is public in case the ORM should use a ready-instantiated
     * PDO object as its database connection. Accepts an optional string key
     * to identify the connection if multiple connections are used.
     * @param PDO $db
     * @param string $connection_name Which connection to use
     */
    public static function set_db($db, $connection_name = self::DEFAULT_CONNECTION) {
        self::_setup_db_config($connection_name);
        self::$_db[$connection_name] = $db;
        if(!is_null(self::$_db[$connection_name])) {
            self::_setup_identifier_quote_character($connection_name);
            self::_setup_limit_clause_style($connection_name);
        }
    }

    /**
     * Delete all registered PDO objects in _db array.
     */
    public static function reset_db() {
        self::$_db = array();
    }

    /**
     * Detect and initialise the character used to quote identifiers
     * (table names, column names etc). If this has been specified
     * manually using ORM::configure('identifier_quote_character', 'some-char'),
     * this will do nothing.
     * @param string $connection_name Which connection to use
     */
    protected static function _setup_identifier_quote_character($connection_name) {
        if (is_null(self::$_config[$connection_name]['identifier_quote_character'])) {
            self::$_config[$connection_name]['identifier_quote_character'] =
                self::_detect_identifier_quote_character($connection_name);
        }
    }

    /**
     * Detect and initialise the limit clause style ("SELECT TOP 5" /
     * "... LIMIT 5"). If this has been specified manually using
     * ORM::configure('limit_clause_style', 'top'), this will do nothing.
     * @param string $connection_name Which connection to use
     */
    public static function _setup_limit_clause_style($connection_name) {
        if (is_null(self::$_config[$connection_name]['limit_clause_style'])) {
            self::$_config[$connection_name]['limit_clause_style'] =
                self::_detect_limit_clause_style($connection_name);
        }
    }

    /**
     * Return the correct character used to quote identifiers (table
     * names, column names etc) by looking at the driver being used by PDO.
     * @param string $connection_name Which connection to use
     * @return string
     */
    protected static function _detect_identifier_quote_character($connection_name) {
        switch(self::get_db($connection_name)->getAttribute(PDO::ATTR_DRIVER_NAME)) {
            case 'pgsql':
            case 'sqlsrv':
            case 'dblib':
            case 'mssql':
            case 'sybase':
            case 'firebird':
                return '"';
            case 'mysql':
            case 'sqlite':
            case 'sqlite2':
            default:
                return '`';
        }
    }

    /**
     * Returns a constant after determining the appropriate limit clause
     * style
     * @param string $connection_name Which connection to use
     * @return string Limit clause style keyword/constant
     */
    protected static function _detect_limit_clause_style($connection_name) {
        switch(self::get_db($connection_name)->getAttribute(PDO::ATTR_DRIVER_NAME)) {
            case 'sqlsrv':
            case 'dblib':
            case 'mssql':
                return ORM::LIMIT_STYLE_TOP_N;
            default:
                return ORM::LIMIT_STYLE_LIMIT;
        }
    }

    /**
     * Returns the PDO instance used by the the ORM to communicate with
     * the database. This can be called if any low-level DB access is
     * required outside the class. If multiple connections are used,
     * accepts an optional key name for the connection.
     * @param string $connection_name Which connection to use
     * @return PDO
     */
    public static function get_db($connection_name = self::DEFAULT_CONNECTION) {
        self::_setup_db($connection_name); // required in case this is called before Idiorm is instantiated
        return self::$_db[$connection_name];
    }

    /**
     * Executes a raw query as a wrapper for PDOStatement::execute.
     * Useful for queries that can't be accomplished through Idiorm,
     * particularly those using engine-specific features.
     * @example raw_execute('SELECT `name`, AVG(`order`) FROM `customer` GROUP BY `name` HAVING AVG(`order`) > 10')
     * @example raw_execute('INSERT OR REPLACE INTO `widget` (`id`, `name`) SELECT `id`, `name` FROM `other_table`')
     * @param string $query The raw SQL query
     * @param array  $parameters Optional bound parameters
     * @param string $connection_name Which connection to use
     * @return bool Success
     */
    public static function raw_execute($query, $parameters = array(), $connection_name = self::DEFAULT_CONNECTION) {
        self::_setup_db($connection_name);
        return self::_execute($query, $parameters, $connection_name);
    }

    /**
     * Returns the PDOStatement instance last used by any connection wrapped by the ORM.
     * Useful for access to PDOStatement::rowCount() or error information
     * @return PDOStatement
     */
    public static function get_last_statement() {
        return self::$_last_statement;
    }

    /**
     * Internal helper method for executing statments. Logs queries, and
     * stores statement object in ::_last_statment, accessible publicly
     * through ::get_last_statement()
     * @param string $query
     * @param array $parameters An array of parameters to be bound in to the query
     * @param string $connection_name Which connection to use
     * @return bool Response of PDOStatement::execute()
     */
    protected static function _execute($query, $parameters = array(), $connection_name = self::DEFAULT_CONNECTION) {
        $statement = self::get_db($connection_name)->prepare($query);
        self::$_last_statement = $statement;
        $time = microtime(true);

        foreach ($parameters as $key => &$param) {
            if (is_null($param)) {
                $type = PDO::PARAM_NULL;
            } else if (is_bool($param)) {
                $type = PDO::PARAM_BOOL;
            } else if (is_int($param)) {
                $type = PDO::PARAM_INT;
            } else {
                $type = PDO::PARAM_STR;
            }

            $statement->bindParam(is_int($key) ? ++$key : $key, $param, $type);
        }

        $q = $statement->execute();
        self::_log_query($query, $parameters, $connection_name, (microtime(true)-$time));

        return $q;
    }

    /**
     * Add a query to the internal query log. Only works if the
     * 'logging' config option is set to true.
     *
     * This works by manually binding the parameters to the query - the
     * query isn't executed like this (PDO normally passes the query and
     * parameters to the database which takes care of the binding) but
     * doing it this way makes the logged queries more readable.
     * @param string $query
     * @param array $parameters An array of parameters to be bound in to the query
     * @param string $connection_name Which connection to use
     * @param float $query_time Query time
     * @return bool
     */
    protected static function _log_query($query, $parameters, $connection_name, $query_time) {
        // If logging is not enabled, do nothing
        if (!self::$_config[$connection_name]['logging']) {
            return false;
        }

        if (!isset(self::$_query_log[$connection_name])) {
            self::$_query_log[$connection_name] = array();
        }

        // Strip out any non-integer indexes from the parameters
        foreach($parameters as $key => $value) {
            if (!is_int($key)) unset($parameters[$key]);
        }

        if (count($parameters) > 0) {
            // Escape the parameters
            $parameters = array_map(array(self::get_db($connection_name), 'quote'), $parameters);

            // Avoid %format collision for vsprintf
            $query = str_replace("%", "%%", $query);

            // Replace placeholders in the query for vsprintf
            if(false !== strpos($query, "'") || false !== strpos($query, '"')) {
                $query = IdiormString::str_replace_outside_quotes("?", "%s", $query);
            } else {
                $query = str_replace("?", "%s", $query);
            }

            // Replace the question marks in the query with the parameters
            $bound_query = vsprintf($query, $parameters);
        } else {
            $bound_query = $query;
        }

        self::$_last_query = $bound_query;
        self::$_query_log[$connection_name][] = $bound_query;


        if(is_callable(self::$_config[$connection_name]['logger'])){
            $logger = self::$_config[$connection_name]['logger'];
            $logger($bound_query, $query_time);
        }

        return true;
    }

    /**
     * Get the last query executed. Only works if the
     * 'logging' config option is set to true. Otherwise
     * this will return null. Returns last query from all connections if
     * no connection_name is specified
     * @param null|string $connection_name Which connection to use
     * @return string
     */
    public static function get_last_query($connection_name = null) {
        if ($connection_name === null) {
            return self::$_last_query;
        }
        if (!isset(self::$_query_log[$connection_name])) {
            return '';
        }

        return end(self::$_query_log[$connection_name]);
    }

    /**
     * Get an array containing all the queries run on a
     * specified connection up to now.
     * Only works if the 'logging' config option is
     * set to true. Otherwise, returned array will be empty.
     * @param string $connection_name Which connection to use
     */
    public static function get_query_log($connection_name = self::DEFAULT_CONNECTION) {
        if (isset(self::$_query_log[$connection_name])) {
            return self::$_query_log[$connection_name];
        }
        return array();
    }

    /**
     * Get a list of the available connection names
     * @return array
     */
    public static function get_connection_names() {
        return array_keys(self::$_db);
    }

    // ------------------------ //
    // --- INSTANCE METHODS --- //
    // ------------------------ //

    /**
     * "Private" constructor; shouldn't be called directly.
     * Use the ORM::for_table factory method instead.
     */
    protected function __construct($table_name, $data = array(), $connection_name = self::DEFAULT_CONNECTION) {
        $this->_table_name = $table_name;
        $this->_data = $data;

        $this->_connection_name = $connection_name;
        self::_setup_db_config($connection_name);
    }

    /**
     * Create a new, empty instance of the class. Used
     * to add a new row to your database. May optionally
     * be passed an associative array of data to populate
     * the instance. If so, all fields will be flagged as
     * dirty so all will be saved to the database when
     * save() is called.
     */
    public function create($data=null) {
        $this->_is_new = true;
        if (!is_null($data)) {
            return $this->hydrate($data)->force_all_dirty();
        }
        return $this;
    }

    /**
     * Specify the ID column to use for this instance or array of instances only.
     * This overrides the id_column and id_column_overrides settings.
     *
     * This is mostly useful for libraries built on top of Idiorm, and will
     * not normally be used in manually built queries. If you don't know why
     * you would want to use this, you should probably just ignore it.
     */
    public function use_id_column($id_column) {
        $this->_instance_id_column = $id_column;
        return $this;
    }

    /**
     * Create an ORM instance from the given row (an associative
     * array of data fetched from the database)
     */
    protected function _create_instance_from_row($row) {
        $instance = self::for_table($this->_table_name, $this->_connection_name);
        $instance->use_id_column($this->_instance_id_column);
        $instance->hydrate($row);
        return $instance;
    }

    /**
     * Tell the ORM that you are expecting a single result
     * back from your query, and execute it. Will return
     * a single instance of the ORM class, or false if no
     * rows were returned.
     * As a shortcut, you may supply an ID as a parameter
     * to this method. This will perform a primary key
     * lookup on the table.
     */
    public function find_one($id=null) {
        if (!is_null($id)) {
            $this->where_id_is($id);
        }
        $this->limit(1);
        $rows = $this->_run();

        if (empty($rows)) {
            return false;
        }

        return $this->_create_instance_from_row($rows[0]);
    }

    /**
     * Tell the ORM that you are expecting multiple results
     * from your query, and execute it. Will return an array
     * of instances of the ORM class, or an empty array if
     * no rows were returned.
     * @return array|\IdiormResultSet
     */
    public function find_many() {
        if(self::$_config[$this->_connection_name]['return_result_sets']) {
            return $this->find_result_set();
        }
        return $this->_find_many();
    }

    /**
     * Tell the ORM that you are expecting multiple results
     * from your query, and execute it. Will return an array
     * of instances of the ORM class, or an empty array if
     * no rows were returned.
     * @return array
     */
    protected function _find_many() {
        $rows = $this->_run();
        return array_map(array($this, '_create_instance_from_row'), $rows);
    }

    /**
     * Tell the ORM that you are expecting multiple results
     * from your query, and execute it. Will return a result set object
     * containing instances of the ORM class.
     * @return \IdiormResultSet
     */
    public function find_result_set() {
        return new IdiormResultSet($this->_find_many());
    }

    /**
     * Tell the ORM that you are expecting multiple results
     * from your query, and execute it. Will return an array,
     * or an empty array if no rows were returned.
     * @return array
     */
    public function find_array() {
        return $this->_run();
    }

    /**
     * Tell the ORM that you wish to execute a COUNT query.
     * Will return an integer representing the number of
     * rows returned.
     */
    public function count($column = '*') {
        return $this->_call_aggregate_db_function(__FUNCTION__, $column);
    }

    /**
     * Tell the ORM that you wish to execute a MAX query.
     * Will return the max value of the choosen column.
     */
    public function max($column)  {
        return $this->_call_aggregate_db_function(__FUNCTION__, $column);
    }

    /**
     * Tell the ORM that you wish to execute a MIN query.
     * Will return the min value of the choosen column.
     */
    public function min($column)  {
        return $this->_call_aggregate_db_function(__FUNCTION__, $column);
    }

    /**
     * Tell the ORM that you wish to execute a AVG query.
     * Will return the average value of the choosen column.
     */
    public function avg($column)  {
        return $this->_call_aggregate_db_function(__FUNCTION__, $column);
    }

    /**
     * Tell the ORM that you wish to execute a SUM query.
     * Will return the sum of the choosen column.
     */
    public function sum($column)  {
        return $this->_call_aggregate_db_function(__FUNCTION__, $column);
    }

    /**
     * Execute an aggregate query on the current connection.
     * @param string $sql_function The aggregate function to call eg. MIN, COUNT, etc
     * @param string $column The column to execute the aggregate query against
     * @return int
     */
    protected function _call_aggregate_db_function($sql_function, $column) {
        $alias = strtolower($sql_function);
        $sql_function = strtoupper($sql_function);
        if('*' != $column) {
            $column = $this->_quote_identifier($column);
        }
        $result_columns = $this->_result_columns;
        $this->_result_columns = array();
        $this->select_expr("$sql_function($column)", $alias);
        $result = $this->find_one();
        $this->_result_columns = $result_columns;

        $return_value = 0;
        if($result !== false && isset($result->$alias)) {
            if (!is_numeric($result->$alias)) {
                $return_value = $result->$alias;
            }
            elseif((int) $result->$alias == (float) $result->$alias) {
                $return_value = (int) $result->$alias;
            } else {
                $return_value = (float) $result->$alias;
            }
        }
        return $return_value;
    }

    /**
     * This method can be called to hydrate (populate) this
     * instance of the class from an associative array of data.
     * This will usually be called only from inside the class,
     * but it's public in case you need to call it directly.
     */
    public function hydrate($data=array()) {
        $this->_data = $data;
        return $this;
    }

    /**
     * Force the ORM to flag all the fields in the $data array
     * as "dirty" and therefore update them when save() is called.
     */
    public function force_all_dirty() {
        $this->_dirty_fields = $this->_data;
        return $this;
    }

    /**
     * Perform a raw query. The query can contain placeholders in
     * either named or question mark style. If placeholders are
     * used, the parameters should be an array of values which will
     * be bound to the placeholders in the query. If this method
     * is called, all other query building methods will be ignored.
     */
    public function raw_query($query, $parameters = array()) {
        $this->_is_raw_query = true;
        $this->_raw_query = $query;
        $this->_raw_parameters = $parameters;
        return $this;
    }

    /**
     * Add an alias for the main table to be used in SELECT queries
     */
    public function table_alias($alias) {
        $this->_table_alias = $alias;
        return $this;
    }

    /**
     * Internal method to add an unquoted expression to the set
     * of columns returned by the SELECT query. The second optional
     * argument is the alias to return the expression as.
     */
    protected function _add_result_column($expr, $alias=null) {
        if (!is_null($alias)) {
            $expr .= " AS " . $this->_quote_identifier($alias);
        }

        if ($this->_using_default_result_columns) {
            $this->_result_columns = array($expr);
            $this->_using_default_result_columns = false;
        } else {
            $this->_result_columns[] = $expr;
        }
        return $this;
    }

    /**
     * Counts the number of columns that belong to the primary
     * key and their value is null.
     */
    public function count_null_id_columns() {
        if (is_array($this->_get_id_column_name())) {
            return count(array_filter($this->id(), 'is_null'));
        } else {
            return is_null($this->id()) ? 1 : 0;
        }
    }

    /**
     * Add a column to the list of columns returned by the SELECT
     * query. This defaults to '*'. The second optional argument is
     * the alias to return the column as.
     */
    public function select($column, $alias=null) {
        $column = $this->_quote_identifier($column);
        return $this->_add_result_column($column, $alias);
    }

    /**
     * Add an unquoted expression to the list of columns returned
     * by the SELECT query. The second optional argument is
     * the alias to return the column as.
     */
    public function select_expr($expr, $alias=null) {
        return $this->_add_result_column($expr, $alias);
    }

    /**
     * Add columns to the list of columns returned by the SELECT
     * query. This defaults to '*'. Many columns can be supplied
     * as either an array or as a list of parameters to the method.
     *
     * Note that the alias must not be numeric - if you want a
     * numeric alias then prepend it with some alpha chars. eg. a1
     *
     * @example select_many(array('alias' => 'column', 'column2', 'alias2' => 'column3'), 'column4', 'column5');
     * @example select_many('column', 'column2', 'column3');
     * @example select_many(array('column', 'column2', 'column3'), 'column4', 'column5');
     *
     * @return \ORM
     */
    public function select_many() {
        $columns = func_get_args();
        if(!empty($columns)) {
            $columns = $this->_normalise_select_many_columns($columns);
            foreach($columns as $alias => $column) {
                if(is_numeric($alias)) {
                    $alias = null;
                }
                $this->select($column, $alias);
            }
        }
        return $this;
    }

    /**
     * Add an unquoted expression to the list of columns returned
     * by the SELECT query. Many columns can be supplied as either
     * an array or as a list of parameters to the method.
     *
     * Note that the alias must not be numeric - if you want a
     * numeric alias then prepend it with some alpha chars. eg. a1
     *
     * @example select_many_expr(array('alias' => 'column', 'column2', 'alias2' => 'column3'), 'column4', 'column5')
     * @example select_many_expr('column', 'column2', 'column3')
     * @example select_many_expr(array('column', 'column2', 'column3'), 'column4', 'column5')
     *
     * @return \ORM
     */
    public function select_many_expr() {
        $columns = func_get_args();
        if(!empty($columns)) {
            $columns = $this->_normalise_select_many_columns($columns);
            foreach($columns as $alias => $column) {
                if(is_numeric($alias)) {
                    $alias = null;
                }
                $this->select_expr($column, $alias);
            }
        }
        return $this;
    }

    /**
     * Take a column specification for the select many methods and convert it
     * into a normalised array of columns and aliases.
     *
     * It is designed to turn the following styles into a normalised array:
     *
     * array(array('alias' => 'column', 'column2', 'alias2' => 'column3'), 'column4', 'column5'))
     *
     * @param array $columns
     * @return array
     */
    protected function _normalise_select_many_columns($columns) {
        $return = array();
        foreach($columns as $column) {
            if(is_array($column)) {
                foreach($column as $key => $value) {
                    if(!is_numeric($key)) {
                        $return[$key] = $value;
                    } else {
                        $return[] = $value;
                    }
                }
            } else {
                $return[] = $column;
            }
        }
        return $return;
    }

    /**
     * Add a DISTINCT keyword before the list of columns in the SELECT query
     */
    public function distinct() {
        $this->_distinct = true;
        return $this;
    }

    /**
     * Internal method to add a JOIN source to the query.
     *
     * The join_operator should be one of INNER, LEFT OUTER, CROSS etc - this
     * will be prepended to JOIN.
     *
     * The table should be the name of the table to join to.
     *
     * The constraint may be either a string or an array with three elements. If it
     * is a string, it will be compiled into the query as-is, with no escaping. The
     * recommended way to supply the constraint is as an array with three elements:
     *
     * first_column, operator, second_column
     *
     * Example: array('user.id', '=', 'profile.user_id')
     *
     * will compile to
     *
     * ON `user`.`id` = `profile`.`user_id`
     *
     * The final (optional) argument specifies an alias for the joined table.
     */
    protected function _add_join_source($join_operator, $table, $constraint, $table_alias=null) {

        $join_operator = trim("{$join_operator} JOIN");

        $table = $this->_quote_identifier($table);

        // Add table alias if present
        if (!is_null($table_alias)) {
            $table_alias = $this->_quote_identifier($table_alias);
            $table .= " {$table_alias}";
        }

        // Build the constraint
        if (is_array($constraint)) {
            list($first_column, $operator, $second_column) = $constraint;
            $first_column = $this->_quote_identifier($first_column);
            $second_column = $this->_quote_identifier($second_column);
            $constraint = "{$first_column} {$operator} {$second_column}";
        }

        $this->_join_sources[] = "{$join_operator} {$table} ON {$constraint}";
        return $this;
    }

    /**
     * Add a RAW JOIN source to the query
     */
    public function raw_join($table, $constraint, $table_alias, $parameters = array()) {
        // Add table alias if present
        if (!is_null($table_alias)) {
            $table_alias = $this->_quote_identifier($table_alias);
            $table .= " {$table_alias}";
        }

        $this->_values = array_merge($this->_values, $parameters);

        // Build the constraint
        if (is_array($constraint)) {
            list($first_column, $operator, $second_column) = $constraint;
            $first_column = $this->_quote_identifier($first_column);
            $second_column = $this->_quote_identifier($second_column);
            $constraint = "{$first_column} {$operator} {$second_column}";
        }

        $this->_join_sources[] = "{$table} ON {$constraint}";
        return $this;
    }

    /**
     * Add a simple JOIN source to the query
     */
    public function join($table, $constraint, $table_alias=null) {
        return $this->_add_join_source("", $table, $constraint, $table_alias);
    }

    /**
     * Add an INNER JOIN souce to the query
     */
    public function inner_join($table, $constraint, $table_alias=null) {
        return $this->_add_join_source("INNER", $table, $constraint, $table_alias);
    }

    /**
     * Add a LEFT OUTER JOIN souce to the query
     */
    public function left_outer_join($table, $constraint, $table_alias=null) {
        return $this->_add_join_source("LEFT OUTER", $table, $constraint, $table_alias);
    }

    /**
     * Add an RIGHT OUTER JOIN souce to the query
     */
    public function right_outer_join($table, $constraint, $table_alias=null) {
        return $this->_add_join_source("RIGHT OUTER", $table, $constraint, $table_alias);
    }

    /**
     * Add an FULL OUTER JOIN souce to the query
     */
    public function full_outer_join($table, $constraint, $table_alias=null) {
        return $this->_add_join_source("FULL OUTER", $table, $constraint, $table_alias);
    }

    /**
     * Internal method to add a HAVING condition to the query
     */
    protected function _add_having($fragment, $values=array()) {
        return $this->_add_condition('having', $fragment, $values);
    }

    /**
     * Internal method to add a HAVING condition to the query
     */
    protected function _add_simple_having($column_name, $separator, $value) {
        return $this->_add_simple_condition('having', $column_name, $separator, $value);
    }

    /**
     * Internal method to add a HAVING clause with multiple values (like IN and NOT IN)
     */
    public function _add_having_placeholder($column_name, $separator, $values) {
        if (!is_array($column_name)) {
            $data = array($column_name => $values);
        } else {
            $data = $column_name;
        }
        $result = $this;
        foreach ($data as $key => $val) {
            $column = $result->_quote_identifier($key);
            $placeholders = $result->_create_placeholders($val);
            $result = $result->_add_having("{$column} {$separator} ({$placeholders})", $val);
        }
        return $result;
    }

    /**
     * Internal method to add a HAVING clause with no parameters(like IS NULL and IS NOT NULL)
     */
    public function _add_having_no_value($column_name, $operator) {
        $conditions = (is_array($column_name)) ? $column_name : array($column_name);
        $result = $this;
        foreach($conditions as $column) {
            $column = $this->_quote_identifier($column);
            $result = $result->_add_having("{$column} {$operator}");
        }
        return $result;
    }

    /**
     * Internal method to add a WHERE condition to the query
     */
    protected function _add_where($fragment, $values=array()) {
        return $this->_add_condition('where', $fragment, $values);
    }

    /**
     * Internal method to add a WHERE condition to the query
     */
    protected function _add_simple_where($column_name, $separator, $value) {
        return $this->_add_simple_condition('where', $column_name, $separator, $value);
    }

    /**
     * Add a WHERE clause with multiple values (like IN and NOT IN)
     */
    public function _add_where_placeholder($column_name, $separator, $values) {
        if (!is_array($column_name)) {
            $data = array($column_name => $values);
        } else {
            $data = $column_name;
        }
        $result = $this;
        foreach ($data as $key => $val) {
            $column = $result->_quote_identifier($key);
            $placeholders = $result->_create_placeholders($val);
            $result = $result->_add_where("{$column} {$separator} ({$placeholders})", $val);
        }
        return $result;
    }

    /**
     * Add a WHERE clause with no parameters(like IS NULL and IS NOT NULL)
     */
    public function _add_where_no_value($column_name, $operator) {
        $conditions = (is_array($column_name)) ? $column_name : array($column_name);
        $result = $this;
        foreach($conditions as $column) {
            $column = $this->_quote_identifier($column);
            $result = $result->_add_where("{$column} {$operator}");
        }
        return $result;
    }

    /**
     * Internal method to add a HAVING or WHERE condition to the query
     */
    protected function _add_condition($type, $fragment, $values=array()) {
        $conditions_class_property_name = "_{$type}_conditions";
        if (!is_array($values)) {
            $values = array($values);
        }
        array_push($this->$conditions_class_property_name, array(
            self::CONDITION_FRAGMENT => $fragment,
            self::CONDITION_VALUES => $values,
        ));
        return $this;
    }

    /**
     * Helper method to compile a simple COLUMN SEPARATOR VALUE
     * style HAVING or WHERE condition into a string and value ready to
     * be passed to the _add_condition method. Avoids duplication
     * of the call to _quote_identifier
     *
     * If column_name is an associative array, it will add a condition for each column
     */
    protected function _add_simple_condition($type, $column_name, $separator, $value) {
        $multiple = is_array($column_name) ? $column_name : array($column_name => $value);
        $result = $this;

        foreach($multiple as $key => $val) {
            // Add the table name in case of ambiguous columns
            if (count($result->_join_sources) > 0 && strpos($key, '.') === false) {
                $table = $result->_table_name;
                if (!is_null($result->_table_alias)) {
                    $table = $result->_table_alias;
                }

                $key = "{$table}.{$key}";
            }
            $key = $result->_quote_identifier($key);
            $result = $result->_add_condition($type, "{$key} {$separator} ?", $val);
        }
        return $result;
    }

    /**
     * Return a string containing the given number of question marks,
     * separated by commas. Eg "?, ?, ?"
     */
    protected function _create_placeholders($fields) {
        if(!empty($fields)) {
            $db_fields = array();
            foreach($fields as $key => $value) {
                // Process expression fields directly into the query
                if(array_key_exists($key, $this->_expr_fields)) {
                    $db_fields[] = $value;
                } else {
                    $db_fields[] = '?';
                }
            }
            return implode(', ', $db_fields);
        }
    }

    /**
     * Helper method that filters a column/value array returning only those
     * columns that belong to a compound primary key.
     *
     * If the key contains a column that does not exist in the given array,
     * a null value will be returned for it.
     */
    protected function _get_compound_id_column_values($value) {
        $filtered = array();
        foreach($this->_get_id_column_name() as $key) {
            $filtered[$key] = isset($value[$key]) ? $value[$key] : null;
        }
        return $filtered;
    }

    /**
     * Helper method that filters an array containing compound column/value
     * arrays.
     */
    protected function _get_compound_id_column_values_array($values) {
        $filtered = array();
        foreach($values as $value) {
            $filtered[] = $this->_get_compound_id_column_values($value);
        }
        return $filtered;
    }

    /**
     * Add a WHERE column = value clause to your query. Each time
     * this is called in the chain, an additional WHERE will be
     * added, and these will be ANDed together when the final query
     * is built.
     *
     * If you use an array in $column_name, a new clause will be
     * added for each element. In this case, $value is ignored.
     */
    public function where($column_name, $value=null) {
        return $this->where_equal($column_name, $value);
    }

    /**
     * More explicitly named version of for the where() method.
     * Can be used if preferred.
     */
    public function where_equal($column_name, $value=null) {
        return $this->_add_simple_where($column_name, '=', $value);
    }

    /**
     * Add a WHERE column != value clause to your query.
     */
    public function where_not_equal($column_name, $value=null) {
        return $this->_add_simple_where($column_name, '!=', $value);
    }

    /**
     * Special method to query the table by its primary key
     *
     * If primary key is compound, only the columns that
     * belong to they key will be used for the query
     */
    public function where_id_is($id) {
        return (is_array($this->_get_id_column_name())) ?
            $this->where($this->_get_compound_id_column_values($id), null) :
            $this->where($this->_get_id_column_name(), $id);
    }

    /**
     * Allows adding a WHERE clause that matches any of the conditions
     * specified in the array. Each element in the associative array will
     * be a different condition, where the key will be the column name.
     *
     * By default, an equal operator will be used against all columns, but
     * it can be overriden for any or every column using the second parameter.
     *
     * Each condition will be ORed together when added to the final query.
     */
    public function where_any_is($values, $operator='=') {
        $data = array();
        $query = array("((");
        $first = true;
        foreach ($values as $item) {
            if ($first) {
                $first = false;
            } else {
                $query[] = ") OR (";
            }
            $firstsub = true;
            foreach($item as $key => $item) {
                $op = is_string($operator) ? $operator : (isset($operator[$key]) ? $operator[$key] : '=');
                if ($firstsub) {
                    $firstsub = false;
                } else {
                    $query[] = "AND";
                }
                $query[] = $this->_quote_identifier($key);
                $data[] = $item;
                $query[] = $op . " ?";
            }
        }
        $query[] = "))";
        return $this->where_raw(join($query, ' '), $data);
    }

    /**
     * Similar to where_id_is() but allowing multiple primary keys.
     *
     * If primary key is compound, only the columns that
     * belong to they key will be used for the query
     */
    public function where_id_in($ids) {
        return (is_array($this->_get_id_column_name())) ?
            $this->where_any_is($this->_get_compound_id_column_values_array($ids)) :
            $this->where_in($this->_get_id_column_name(), $ids);
    }

    /**
     * Add a WHERE ... LIKE clause to your query.
     */
    public function where_like($column_name, $value=null) {
        return $this->_add_simple_where($column_name, 'LIKE', $value);
    }

    /**
     * Add where WHERE ... NOT LIKE clause to your query.
     */
    public function where_not_like($column_name, $value=null) {
        return $this->_add_simple_where($column_name, 'NOT LIKE', $value);
    }

    /**
     * Add a WHERE ... > clause to your query
     */
    public function where_gt($column_name, $value=null) {
        return $this->_add_simple_where($column_name, '>', $value);
    }

    /**
     * Add a WHERE ... < clause to your query
     */
    public function where_lt($column_name, $value=null) {
        return $this->_add_simple_where($column_name, '<', $value);
    }

    /**
     * Add a WHERE ... >= clause to your query
     */
    public function where_gte($column_name, $value=null) {
        return $this->_add_simple_where($column_name, '>=', $value);
    }

    /**
     * Add a WHERE ... <= clause to your query
     */
    public function where_lte($column_name, $value=null) {
        return $this->_add_simple_where($column_name, '<=', $value);
    }

    /**
     * Add a WHERE ... IN clause to your query
     */
    public function where_in($column_name, $values) {
        return $this->_add_where_placeholder($column_name, 'IN', $values);
    }

    /**
     * Add a WHERE ... NOT IN clause to your query
     */
    public function where_not_in($column_name, $values) {
        return $this->_add_where_placeholder($column_name, 'NOT IN', $values);
    }

    /**
     * Add a WHERE column IS NULL clause to your query
     */
    public function where_null($column_name) {
        return $this->_add_where_no_value($column_name, "IS NULL");
    }

    /**
     * Add a WHERE column IS NOT NULL clause to your query
     */
    public function where_not_null($column_name) {
        return $this->_add_where_no_value($column_name, "IS NOT NULL");
    }

    /**
     * Add a raw WHERE clause to the query. The clause should
     * contain question mark placeholders, which will be bound
     * to the parameters supplied in the second argument.
     */
    public function where_raw($clause, $parameters=array()) {
        return $this->_add_where($clause, $parameters);
    }

    /**
     * Add a LIMIT to the query
     */
    public function limit($limit) {
        $this->_limit = $limit;
        return $this;
    }

    /**
     * Add an OFFSET to the query
     */
    public function offset($offset) {
        $this->_offset = $offset;
        return $this;
    }

    /**
     * Add an ORDER BY clause to the query
     */
    protected function _add_order_by($column_name, $ordering) {
        $column_name = $this->_quote_identifier($column_name);
        $this->_order_by[] = "{$column_name} {$ordering}";
        return $this;
    }

    /**
     * Add an ORDER BY column DESC clause
     */
    public function order_by_desc($column_name) {
        return $this->_add_order_by($column_name, 'DESC');
    }

    /**
     * Add an ORDER BY column ASC clause
     */
    public function order_by_asc($column_name) {
        return $this->_add_order_by($column_name, 'ASC');
    }

    /**
     * Add an unquoted expression as an ORDER BY clause
     */
    public function order_by_expr($clause) {
        $this->_order_by[] = $clause;
        return $this;
    }

    /**
     * Add a column to the list of columns to GROUP BY
     */
    public function group_by($column_name) {
        $column_name = $this->_quote_identifier($column_name);
        $this->_group_by[] = $column_name;
        return $this;
    }

    /**
     * Add an unquoted expression to the list of columns to GROUP BY
     */
    public function group_by_expr($expr) {
        $this->_group_by[] = $expr;
        return $this;
    }

    /**
     * Add a HAVING column = value clause to your query. Each time
     * this is called in the chain, an additional HAVING will be
     * added, and these will be ANDed together when the final query
     * is built.
     *
     * If you use an array in $column_name, a new clause will be
     * added for each element. In this case, $value is ignored.
     */
    public function having($column_name, $value=null) {
        return $this->having_equal($column_name, $value);
    }

    /**
     * More explicitly named version of for the having() method.
     * Can be used if preferred.
     */
    public function having_equal($column_name, $value=null) {
        return $this->_add_simple_having($column_name, '=', $value);
    }

    /**
     * Add a HAVING column != value clause to your query.
     */
    public function having_not_equal($column_name, $value=null) {
        return $this->_add_simple_having($column_name, '!=', $value);
    }

    /**
     * Special method to query the table by its primary key.
     *
     * If primary key is compound, only the columns that
     * belong to they key will be used for the query
     */
    public function having_id_is($id) {
        return (is_array($this->_get_id_column_name())) ?
            $this->having($this->_get_compound_id_column_values($value)) :
            $this->having($this->_get_id_column_name(), $id);
    }

    /**
     * Add a HAVING ... LIKE clause to your query.
     */
    public function having_like($column_name, $value=null) {
        return $this->_add_simple_having($column_name, 'LIKE', $value);
    }

    /**
     * Add where HAVING ... NOT LIKE clause to your query.
     */
    public function having_not_like($column_name, $value=null) {
        return $this->_add_simple_having($column_name, 'NOT LIKE', $value);
    }

    /**
     * Add a HAVING ... > clause to your query
     */
    public function having_gt($column_name, $value=null) {
        return $this->_add_simple_having($column_name, '>', $value);
    }

    /**
     * Add a HAVING ... < clause to your query
     */
    public function having_lt($column_name, $value=null) {
        return $this->_add_simple_having($column_name, '<', $value);
    }

    /**
     * Add a HAVING ... >= clause to your query
     */
    public function having_gte($column_name, $value=null) {
        return $this->_add_simple_having($column_name, '>=', $value);
    }

    /**
     * Add a HAVING ... <= clause to your query
     */
    public function having_lte($column_name, $value=null) {
        return $this->_add_simple_having($column_name, '<=', $value);
    }

    /**
     * Add a HAVING ... IN clause to your query
     */
    public function having_in($column_name, $values=null) {
        return $this->_add_having_placeholder($column_name, 'IN', $values);
    }

    /**
     * Add a HAVING ... NOT IN clause to your query
     */
    public function having_not_in($column_name, $values=null) {
        return $this->_add_having_placeholder($column_name, 'NOT IN', $values);
    }

    /**
     * Add a HAVING column IS NULL clause to your query
     */
    public function having_null($column_name) {
        return $this->_add_having_no_value($column_name, 'IS NULL');
    }

    /**
     * Add a HAVING column IS NOT NULL clause to your query
     */
    public function having_not_null($column_name) {
        return $this->_add_having_no_value($column_name, 'IS NOT NULL');
    }

    /**
     * Add a raw HAVING clause to the query. The clause should
     * contain question mark placeholders, which will be bound
     * to the parameters supplied in the second argument.
     */
    public function having_raw($clause, $parameters=array()) {
        return $this->_add_having($clause, $parameters);
    }

    /**
     * Build a SELECT statement based on the clauses that have
     * been passed to this instance by chaining method calls.
     */
    protected function _build_select() {
        // If the query is raw, just set the $this->_values to be
        // the raw query parameters and return the raw query
        if ($this->_is_raw_query) {
            $this->_values = $this->_raw_parameters;
            return $this->_raw_query;
        }

        // Build and return the full SELECT statement by concatenating
        // the results of calling each separate builder method.
        return $this->_join_if_not_empty(" ", array(
            $this->_build_select_start(),
            $this->_build_join(),
            $this->_build_where(),
            $this->_build_group_by(),
            $this->_build_having(),
            $this->_build_order_by(),
            $this->_build_limit(),
            $this->_build_offset(),
        ));
    }

    /**
     * Build the start of the SELECT statement
     */
    protected function _build_select_start() {
        $fragment = 'SELECT ';
        $result_columns = join(', ', $this->_result_columns);

        if (!is_null($this->_limit) &&
            self::$_config[$this->_connection_name]['limit_clause_style'] === ORM::LIMIT_STYLE_TOP_N) {
            $fragment .= "TOP {$this->_limit} ";
        }

        if ($this->_distinct) {
            $result_columns = 'DISTINCT ' . $result_columns;
        }

        $fragment .= "{$result_columns} FROM " . $this->_quote_identifier($this->_table_name);

        if (!is_null($this->_table_alias)) {
            $fragment .= " " . $this->_quote_identifier($this->_table_alias);
        }
        return $fragment;
    }

    /**
     * Build the JOIN sources
     */
    protected function _build_join() {
        if (count($this->_join_sources) === 0) {
            return '';
        }

        return join(" ", $this->_join_sources);
    }

    /**
     * Build the WHERE clause(s)
     */
    protected function _build_where() {
        return $this->_build_conditions('where');
    }

    /**
     * Build the HAVING clause(s)
     */
    protected function _build_having() {
        return $this->_build_conditions('having');
    }

    /**
     * Build GROUP BY
     */
    protected function _build_group_by() {
        if (count($this->_group_by) === 0) {
            return '';
        }
        return "GROUP BY " . join(", ", $this->_group_by);
    }

    /**
     * Build a WHERE or HAVING clause
     * @param string $type
     * @return string
     */
    protected function _build_conditions($type) {
        $conditions_class_property_name = "_{$type}_conditions";
        // If there are no clauses, return empty string
        if (count($this->$conditions_class_property_name) === 0) {
            return '';
        }

        $conditions = array();
        foreach ($this->$conditions_class_property_name as $condition) {
            $conditions[] = $condition[self::CONDITION_FRAGMENT];
            $this->_values = array_merge($this->_values, $condition[self::CONDITION_VALUES]);
        }

        return strtoupper($type) . " " . join(" AND ", $conditions);
    }

    /**
     * Build ORDER BY
     */
    protected function _build_order_by() {
        if (count($this->_order_by) === 0) {
            return '';
        }
        return "ORDER BY " . join(", ", $this->_order_by);
    }

    /**
     * Build LIMIT
     */
    protected function _build_limit() {
        $fragment = '';
        if (!is_null($this->_limit) &&
            self::$_config[$this->_connection_name]['limit_clause_style'] == ORM::LIMIT_STYLE_LIMIT) {
            if (self::get_db($this->_connection_name)->getAttribute(PDO::ATTR_DRIVER_NAME) == 'firebird') {
                $fragment = 'ROWS';
            } else {
                $fragment = 'LIMIT';
            }
            $fragment .= " {$this->_limit}";
        }
        return $fragment;
    }

    /**
     * Build OFFSET
     */
    protected function _build_offset() {
        if (!is_null($this->_offset)) {
            $clause = 'OFFSET';
            if (self::get_db($this->_connection_name)->getAttribute(PDO::ATTR_DRIVER_NAME) == 'firebird') {
                $clause = 'TO';
            }
            return "$clause " . $this->_offset;
        }
        return '';
    }

    /**
     * Wrapper around PHP's join function which
     * only adds the pieces if they are not empty.
     */
    protected function _join_if_not_empty($glue, $pieces) {
        $filtered_pieces = array();
        foreach ($pieces as $piece) {
            if (is_string($piece)) {
                $piece = trim($piece);
            }
            if (!empty($piece)) {
                $filtered_pieces[] = $piece;
            }
        }
        return join($glue, $filtered_pieces);
    }

    /**
     * Quote a string that is used as an identifier
     * (table names, column names etc). This method can
     * also deal with dot-separated identifiers eg table.column
     */
    protected function _quote_one_identifier($identifier) {
        $parts = explode('.', $identifier);
        $parts = array_map(array($this, '_quote_identifier_part'), $parts);
        return join('.', $parts);
    }

    /**
     * Quote a string that is used as an identifier
     * (table names, column names etc) or an array containing
     * multiple identifiers. This method can also deal with
     * dot-separated identifiers eg table.column
     */
    protected function _quote_identifier($identifier) {
        if (is_array($identifier)) {
            $result = array_map(array($this, '_quote_one_identifier'), $identifier);
            return join(', ', $result);
        } else {
            return $this->_quote_one_identifier($identifier);
        }
    }

    /**
     * This method performs the actual quoting of a single
     * part of an identifier, using the identifier quote
     * character specified in the config (or autodetected).
     */
    protected function _quote_identifier_part($part) {
        if ($part === '*') {
            return $part;
        }

        $quote_character = self::$_config[$this->_connection_name]['identifier_quote_character'];
        // double up any identifier quotes to escape them
        return $quote_character .
        str_replace($quote_character,
            $quote_character . $quote_character,
            $part
        ) . $quote_character;
    }

    /**
     * Create a cache key for the given query and parameters.
     */
    protected static function _create_cache_key($query, $parameters, $table_name = null, $connection_name = self::DEFAULT_CONNECTION) {
        if(isset(self::$_config[$connection_name]['create_cache_key']) and is_callable(self::$_config[$connection_name]['create_cache_key'])){
            return call_user_func_array(self::$_config[$connection_name]['create_cache_key'], array($query, $parameters, $table_name, $connection_name));
        }
        $parameter_string = join(',', $parameters);
        $key = $query . ':' . $parameter_string;
        return sha1($key);
    }

    /**
     * Check the query cache for the given cache key. If a value
     * is cached for the key, return the value. Otherwise, return false.
     */
    protected static function _check_query_cache($cache_key, $table_name = null, $connection_name = self::DEFAULT_CONNECTION) {
        if(isset(self::$_config[$connection_name]['check_query_cache']) and is_callable(self::$_config[$connection_name]['check_query_cache'])){
            return call_user_func_array(self::$_config[$connection_name]['check_query_cache'], array($cache_key, $table_name, $connection_name));
        } elseif (isset(self::$_query_cache[$connection_name][$cache_key])) {
            return self::$_query_cache[$connection_name][$cache_key];
        }
        return false;
    }

    /**
     * Clear the query cache
     */
    public static function clear_cache($table_name = null, $connection_name = self::DEFAULT_CONNECTION) {
        self::$_query_cache = array();
        if(isset(self::$_config[$connection_name]['clear_cache']) and is_callable(self::$_config[$connection_name]['clear_cache'])){
            return call_user_func_array(self::$_config[$connection_name]['clear_cache'], array($table_name, $connection_name));
        }
    }

    /**
     * Add the given value to the query cache.
     */
    protected static function _cache_query_result($cache_key, $value, $table_name = null, $connection_name = self::DEFAULT_CONNECTION) {
        if(isset(self::$_config[$connection_name]['cache_query_result']) and is_callable(self::$_config[$connection_name]['cache_query_result'])){
            return call_user_func_array(self::$_config[$connection_name]['cache_query_result'], array($cache_key, $value, $table_name, $connection_name));
        } elseif (!isset(self::$_query_cache[$connection_name])) {
            self::$_query_cache[$connection_name] = array();
        }
        self::$_query_cache[$connection_name][$cache_key] = $value;
    }

    /**
     * Execute the SELECT query that has been built up by chaining methods
     * on this class. Return an array of rows as associative arrays.
     */
    protected function _run() {
        $query = $this->_build_select();
        $caching_enabled = self::$_config[$this->_connection_name]['caching'];

        if ($caching_enabled) {
            $cache_key = self::_create_cache_key($query, $this->_values, $this->_table_name, $this->_connection_name);
            $cached_result = self::_check_query_cache($cache_key, $this->_table_name, $this->_connection_name);

            if ($cached_result !== false) {
                return $cached_result;
            }
        }

        self::_execute($query, $this->_values, $this->_connection_name);
        $statement = self::get_last_statement();

        $rows = array();
        while ($row = $statement->fetch(PDO::FETCH_ASSOC)) {
            $rows[] = $row;
        }

        if ($caching_enabled) {
            self::_cache_query_result($cache_key, $rows, $this->_table_name, $this->_connection_name);
        }

        // reset Idiorm after executing the query
        $this->_values = array();
        $this->_result_columns = array('*');
        $this->_using_default_result_columns = true;

        return $rows;
    }

    /**
     * Return the raw data wrapped by this ORM
     * instance as an associative array. Column
     * names may optionally be supplied as arguments,
     * if so, only those keys will be returned.
     */
    public function as_array() {
        if (func_num_args() === 0) {
            return $this->_data;
        }
        $args = func_get_args();
        return array_intersect_key($this->_data, array_flip($args));
    }

    /**
     * Return the value of a property of this object (database row)
     * or null if not present.
     *
     * If a column-names array is passed, it will return a associative array
     * with the value of each column or null if it is not present.
     */
    public function get($key) {
        if (is_array($key)) {
            $result = array();
            foreach($key as $column) {
                $result[$column] = isset($this->_data[$column]) ? $this->_data[$column] : null;
            }
            return $result;
        } else {
            return isset($this->_data[$key]) ? $this->_data[$key] : null;
        }
    }

    /**
     * Return the name of the column in the database table which contains
     * the primary key ID of the row.
     */
    protected function _get_id_column_name() {
        if (!is_null($this->_instance_id_column)) {
            return $this->_instance_id_column;
        }
        if (isset(self::$_config[$this->_connection_name]['id_column_overrides'][$this->_table_name])) {
            return self::$_config[$this->_connection_name]['id_column_overrides'][$this->_table_name];
        }
        return self::$_config[$this->_connection_name]['id_column'];
    }

    /**
     * Get the primary key ID of this object.
     */
    public function id($disallow_null = false) {
        $id = $this->get($this->_get_id_column_name());

        if ($disallow_null) {
            if (is_array($id)) {
                foreach ($id as $id_part) {
                    if ($id_part === null) {
                        throw new Exception('Primary key ID contains null value(s)');
                    }
                }
            } else if ($id === null) {
                throw new Exception('Primary key ID missing from row or is null');
            }
        }

        return $id;
    }

    /**
     * Set a property to a particular value on this object.
     * To set multiple properties at once, pass an associative array
     * as the first parameter and leave out the second parameter.
     * Flags the properties as 'dirty' so they will be saved to the
     * database when save() is called.
     */
    public function set($key, $value = null) {
        return $this->_set_orm_property($key, $value);
    }

    /**
     * Set a property to a particular value on this object.
     * To set multiple properties at once, pass an associative array
     * as the first parameter and leave out the second parameter.
     * Flags the properties as 'dirty' so they will be saved to the
     * database when save() is called.
     * @param string|array $key
     * @param string|null $value
     */
    public function set_expr($key, $value = null) {
        return $this->_set_orm_property($key, $value, true);
    }

    /**
     * Set a property on the ORM object.
     * @param string|array $key
     * @param string|null $value
     * @param bool $raw Whether this value should be treated as raw or not
     */
    protected function _set_orm_property($key, $value = null, $expr = false) {
        if (!is_array($key)) {
            $key = array($key => $value);
        }
        foreach ($key as $field => $value) {
            $this->_data[$field] = $value;
            $this->_dirty_fields[$field] = $value;
            if (false === $expr and isset($this->_expr_fields[$field])) {
                unset($this->_expr_fields[$field]);
            } else if (true === $expr) {
                $this->_expr_fields[$field] = true;
            }
        }
        return $this;
    }

    /**
     * Check whether the given field has been changed since this
     * object was saved.
     */
    public function is_dirty($key) {
        return isset($this->_dirty_fields[$key]);
    }

    /**
     * Check whether the model was the result of a call to create() or not
     * @return bool
     */
    public function is_new() {
        return $this->_is_new;
    }

    /**
     * Save any fields which have been modified on this object
     * to the database.
     */
    public function save() {
        $query = array();

        // remove any expression fields as they are already baked into the query
        $values = array_values(array_diff_key($this->_dirty_fields, $this->_expr_fields));

        if (!$this->_is_new) { // UPDATE
            // If there are no dirty values, do nothing
            if (empty($values) && empty($this->_expr_fields)) {
                return true;
            }
            $query = $this->_build_update();
            $id = $this->id(true);
            if (is_array($id)) {
                $values = array_merge($values, array_values($id));
            } else {
                $values[] = $id;
            }
        } else { // INSERT
            $query = $this->_build_insert();
        }

        $success = self::_execute($query, $values, $this->_connection_name);
        $caching_auto_clear_enabled = self::$_config[$this->_connection_name]['caching_auto_clear'];
        if($caching_auto_clear_enabled){
            self::clear_cache($this->_table_name, $this->_connection_name);
        }
        // If we've just inserted a new record, set the ID of this object
        if ($this->_is_new) {
            $this->_is_new = false;
            if ($this->count_null_id_columns() != 0) {
                $db = self::get_db($this->_connection_name);
                if($db->getAttribute(PDO::ATTR_DRIVER_NAME) == 'pgsql') {
                    // it may return several columns if a compound primary
                    // key is used
                    $row = self::get_last_statement()->fetch(PDO::FETCH_ASSOC);
                    foreach($row as $key => $value) {
                        $this->_data[$key] = $value;
                    }
                } else {
                    $column = $this->_get_id_column_name();
                    // if the primary key is compound, assign the last inserted id
                    // to the first column
                    if (is_array($column)) {
                        $column = array_slice($column, 0, 1);
                    }
                    $this->_data[$column] = $db->lastInsertId();
                }
            }
        }

        $this->_dirty_fields = $this->_expr_fields = array();
        return $success;
    }

    /**
     * Add a WHERE clause for every column that belongs to the primary key
     */
    public function _add_id_column_conditions(&$query) {
        $query[] = "WHERE";
        $keys = is_array($this->_get_id_column_name()) ? $this->_get_id_column_name() : array( $this->_get_id_column_name() );
        $first = true;
        foreach($keys as $key) {
            if ($first) {
                $first = false;
            }
            else {
                $query[] = "AND";
            }
            $query[] = $this->_quote_identifier($key);
            $query[] = "= ?";
        }
    }

    /**
     * Build an UPDATE query
     */
    protected function _build_update() {
        $query = array();
        $query[] = "UPDATE {$this->_quote_identifier($this->_table_name)} SET";

        $field_list = array();
        foreach ($this->_dirty_fields as $key => $value) {
            if(!array_key_exists($key, $this->_expr_fields)) {
                $value = '?';
            }
            $field_list[] = "{$this->_quote_identifier($key)} = $value";
        }
        $query[] = join(", ", $field_list);
        $this->_add_id_column_conditions($query);
        return join(" ", $query);
    }

    /**
     * Build an INSERT query
     */
    protected function _build_insert() {
        $query[] = "INSERT INTO";
        $query[] = $this->_quote_identifier($this->_table_name);
        $field_list = array_map(array($this, '_quote_identifier'), array_keys($this->_dirty_fields));
        $query[] = "(" . join(", ", $field_list) . ")";
        $query[] = "VALUES";

        $placeholders = $this->_create_placeholders($this->_dirty_fields);
        $query[] = "({$placeholders})";

        if (self::get_db($this->_connection_name)->getAttribute(PDO::ATTR_DRIVER_NAME) == 'pgsql') {
            $query[] = 'RETURNING ' . $this->_quote_identifier($this->_get_id_column_name());
        }

        return join(" ", $query);
    }

    /**
     * Delete this record from the database
     */
    public function delete() {
        $query = array(
            "DELETE FROM",
            $this->_quote_identifier($this->_table_name)
        );
        $this->_add_id_column_conditions($query);
        return self::_execute(join(" ", $query), is_array($this->id(true)) ? array_values($this->id(true)) : array($this->id(true)), $this->_connection_name);
    }

    /**
     * Delete many records from the database
     */
    public function delete_many() {
        // Build and return the full DELETE statement by concatenating
        // the results of calling each separate builder method.
        $query = $this->_join_if_not_empty(" ", array(
            "DELETE FROM",
            $this->_quote_identifier($this->_table_name),
            $this->_build_where(),
        ));

        return self::_execute($query, $this->_values, $this->_connection_name);
    }

    // --------------------- //
    // ---  ArrayAccess  --- //
    // --------------------- //

    public function offsetExists($key) {
        return array_key_exists($key, $this->_data);
    }

    public function offsetGet($key) {
        return $this->get($key);
    }

    public function offsetSet($key, $value) {
        if(is_null($key)) {
            throw new InvalidArgumentException('You must specify a key/array index.');
        }
        $this->set($key, $value);
    }

    public function offsetUnset($key) {
        unset($this->_data[$key]);
        unset($this->_dirty_fields[$key]);
    }

    // --------------------- //
    // --- MAGIC METHODS --- //
    // --------------------- //
    public function __get($key) {
        return $this->offsetGet($key);
    }

    public function __set($key, $value) {
        $this->offsetSet($key, $value);
    }

    public function __unset($key) {
        $this->offsetUnset($key);
    }


    public function __isset($key) {
        return $this->offsetExists($key);
    }

    /**
     * Magic method to capture calls to undefined class methods.
     * In this case we are attempting to convert camel case formatted
     * methods into underscore formatted methods.
     *
     * This allows us to call ORM methods using camel case and remain
     * backwards compatible.
     *
     * @param  string   $name
     * @param  array    $arguments
     * @return ORM
     */
    public function __call($name, $arguments)
    {
        $method = strtolower(preg_replace('/([a-z])([A-Z])/', '$1_$2', $name));

        if (method_exists($this, $method)) {
            return call_user_func_array(array($this, $method), $arguments);
        } else {
            throw new IdiormMethodMissingException("Method $name() does not exist in class " . get_class($this));
        }
    }

    /**
     * Magic method to capture calls to undefined static class methods.
     * In this case we are attempting to convert camel case formatted
     * methods into underscore formatted methods.
     *
     * This allows us to call ORM methods using camel case and remain
     * backwards compatible.
     *
     * @param  string   $name
     * @param  array    $arguments
     * @return ORM
     */
    public static function __callStatic($name, $arguments)
    {
        $method = strtolower(preg_replace('/([a-z])([A-Z])/', '$1_$2', $name));

        return call_user_func_array(array('ORM', $method), $arguments);
    }
}

/**
 * A class to handle str_replace operations that involve quoted strings
 * @example IdiormString::str_replace_outside_quotes('?', '%s', 'columnA = "Hello?" AND columnB = ?');
 * @example IdiormString::value('columnA = "Hello?" AND columnB = ?')->replace_outside_quotes('?', '%s');
 * @author Jeff Roberson <ridgerunner@fluxbb.org>
 * @author Simon Holywell <treffynnon@php.net>
 * @link http://stackoverflow.com/a/13370709/461813 StackOverflow answer
 */
class IdiormString {
    protected $subject;
    protected $search;
    protected $replace;

    /**
     * Get an easy to use instance of the class
     * @param string $subject
     * @return \self
     */
    public static function value($subject) {
        return new self($subject);
    }

    /**
     * Shortcut method: Replace all occurrences of the search string with the replacement
     * string where they appear outside quotes.
     * @param string $search
     * @param string $replace
     * @param string $subject
     * @return string
     */
    public static function str_replace_outside_quotes($search, $replace, $subject) {
        return self::value($subject)->replace_outside_quotes($search, $replace);
    }

    /**
     * Set the base string object
     * @param string $subject
     */
    public function __construct($subject) {
        $this->subject = (string) $subject;
    }

    /**
     * Replace all occurrences of the search string with the replacement
     * string where they appear outside quotes
     * @param string $search
     * @param string $replace
     * @return string
     */
    public function replace_outside_quotes($search, $replace) {
        $this->search = $search;
        $this->replace = $replace;
        return $this->_str_replace_outside_quotes();
    }

    /**
     * Validate an input string and perform a replace on all ocurrences
     * of $this->search with $this->replace
     * @author Jeff Roberson <ridgerunner@fluxbb.org>
     * @link http://stackoverflow.com/a/13370709/461813 StackOverflow answer
     * @return string
     */
    protected function _str_replace_outside_quotes(){
        $re_valid = '/
                # Validate string having embedded quoted substrings.
                ^                           # Anchor to start of string.
                (?:                         # Zero or more string chunks.
                  "[^"\\\\]*(?:\\\\.[^"\\\\]*)*"  # Either a double quoted chunk,
                | \'[^\'\\\\]*(?:\\\\.[^\'\\\\]*)*\'  # or a single quoted chunk,
                | [^\'"\\\\]+               # or an unquoted chunk (no escapes).
                )*                          # Zero or more string chunks.
                \z                          # Anchor to end of string.
                /sx';
        if (!preg_match($re_valid, $this->subject)) {
            throw new IdiormStringException("Subject string is not valid in the replace_outside_quotes context.");
        }
        $re_parse = '/
                # Match one chunk of a valid string having embedded quoted substrings.
                  (                         # Either $1: Quoted chunk.
                    "[^"\\\\]*(?:\\\\.[^"\\\\]*)*"  # Either a double quoted chunk,
                  | \'[^\'\\\\]*(?:\\\\.[^\'\\\\]*)*\'  # or a single quoted chunk.
                  )                         # End $1: Quoted chunk.
                | ([^\'"\\\\]+)             # or $2: an unquoted chunk (no escapes).
                /sx';
        return preg_replace_callback($re_parse, array($this, '_str_replace_outside_quotes_cb'), $this->subject);
    }

    /**
     * Process each matching chunk from preg_replace_callback replacing
     * each occurrence of $this->search with $this->replace
     * @author Jeff Roberson <ridgerunner@fluxbb.org>
     * @link http://stackoverflow.com/a/13370709/461813 StackOverflow answer
     * @param array $matches
     * @return string
     */
    protected function _str_replace_outside_quotes_cb($matches) {
        // Return quoted string chunks (in group $1) unaltered.
        if ($matches[1]) return $matches[1];
        // Process only unquoted chunks (in group $2).
        return preg_replace('/'. preg_quote($this->search, '/') .'/',
            $this->replace, $matches[2]);
    }
}

/**
 * A result set class for working with collections of model instances
 * @author Simon Holywell <treffynnon@php.net>
 */
class IdiormResultSet implements Countable, IteratorAggregate, ArrayAccess, Serializable {
    /**
     * The current result set as an array
     * @var array
     */
    protected $_results = array();

    /**
     * Optionally set the contents of the result set by passing in array
     * @param array $results
     */
    public function __construct(array $results = array()) {
        $this->set_results($results);
    }

    /**
     * Set the contents of the result set by passing in array
     * @param array $results
     */
    public function set_results(array $results) {
        $this->_results = $results;
    }

    /**
     * Get the current result set as an array
     * @return array
     */
    public function get_results() {
        return $this->_results;
    }

    /**
     * Get the current result set as an array
     * @return array
     */
    public function as_array() {
        return $this->get_results();
    }

    /**
     * Get the number of records in the result set
     * @return int
     */
    public function count() {
        return count($this->_results);
    }

    /**
     * Get an iterator for this object. In this case it supports foreaching
     * over the result set.
     * @return \ArrayIterator
     */
    public function getIterator() {
        return new ArrayIterator($this->_results);
    }

    /**
     * ArrayAccess
     * @param int|string $offset
     * @return bool
     */
    public function offsetExists($offset) {
        return isset($this->_results[$offset]);
    }

    /**
     * ArrayAccess
     * @param int|string $offset
     * @return mixed
     */
    public function offsetGet($offset) {
        return $this->_results[$offset];
    }

    /**
     * ArrayAccess
     * @param int|string $offset
     * @param mixed $value
     */
    public function offsetSet($offset, $value) {
        $this->_results[$offset] = $value;
    }

    /**
     * ArrayAccess
     * @param int|string $offset
     */
    public function offsetUnset($offset) {
        unset($this->_results[$offset]);
    }

    /**
     * Serializable
     * @return string
     */
    public function serialize() {
        return serialize($this->_results);
    }

    /**
     * Serializable
     * @param string $serialized
     * @return array
     */
    public function unserialize($serialized) {
        return unserialize($serialized);
    }

    /**
     * Call a method on all models in a result set. This allows for method
     * chaining such as setting a property on all models in a result set or
     * any other batch operation across models.
     * @example ORM::for_table('Widget')->find_many()->set('field', 'value')->save();
     * @param string $method
     * @param array $params
     * @return \IdiormResultSet
     */
    public function __call($method, $params = array()) {
        foreach($this->_results as $model) {
            if (method_exists($model, $method)) {
                call_user_func_array(array($model, $method), $params);
            } else {
                throw new IdiormMethodMissingException("Method $method() does not exist in class " . get_class($this));
            }
        }
        return $this;
    }
}

/**
 * A placeholder for exceptions eminating from the IdiormString class
 */
class IdiormStringException extends Exception {}

class IdiormMethodMissingException extends Exception {}