<?php declare(strict_types=1);
/**
 * Query
 *
 * SQL Query Builder / Database Abstraction Layer
 *
 * PHP version 7.1
 *
 * @package     Query
 * @author      Timothy J. Warren <tim@timshomepage.net>
 * @copyright   2012 - 2018 Timothy J. Warren
 * @license     http://www.opensource.org/licenses/mit-license.html  MIT License
 * @link        https://git.timshomepage.net/aviat4ion/Query
 */
namespace Query;

use BadMethodCallException;
use PDOStatement;
use Query\Drivers\{
	AbstractUtil,
	DriverInterface,
	SQLInterface
};

/**
 * Convenience class for creating sql queries
 */
class QueryBuilder implements QueryBuilderInterface {

	// --------------------------------------------------------------------------
	// ! Constants
	// --------------------------------------------------------------------------

	const KEY 	= 0;
	const VALUE = 1;
	const BOTH 	= 2;

	// --------------------------------------------------------------------------
	// ! SQL Clause Strings
	// --------------------------------------------------------------------------

	/**
	 * Compiled 'select' clause
	 * @var string
	 */
	protected $selectString = '';

	/**
	 * Compiled 'from' clause
	 * @var string
	 */
	protected $fromString = '';

	/**
	 * Compiled arguments for insert / update
	 * @var string
	 */
	protected $setString;

	/**
	 * Order by clause
	 * @var string
	 */
	protected $orderString;

	/**
	 * Group by clause
	 * @var string
	 */
	protected $groupString;

	// --------------------------------------------------------------------------
	// ! SQL Clause Arrays
	// --------------------------------------------------------------------------

	/**
	 * Keys for insert/update statement
	 * @var array
	 */
	protected $setArrayKeys = [];

	/**
	 * Key/val pairs for order by clause
	 * @var array
	 */
	protected $orderArray = [];

	/**
	 * Key/val pairs for group by clause
	 * @var array
	 */
	protected $groupArray = [];

	// --------------------------------------------------------------------------
	// ! Other Class vars
	// --------------------------------------------------------------------------

	/**
	 * Values to apply to prepared statements
	 * @var array
	 */
	protected $values = [];

	/**
	 * Values to apply to where clauses in prepared statements
	 * @var array
	 */
	protected $whereValues = [];

	/**
	 * Value for limit string
	 * @var string
	 */
	protected $limit;

	/**
	 * Value for offset in limit string
	 * @var integer
	 */
	protected $offset;

	/**
	 * Query component order mapping
	 * for complex select queries
	 *
	 * Format:
	 * array(
	 *		'type' => 'where',
	 *		'conjunction' => ' AND ',
	 *		'string' => 'k=?'
	 * )
	 *
	 * @var array
	 */
	protected $queryMap = [];

	/**
	 * Map for having clause
	 * @var array
	 */
	protected $havingMap;

	/**
	 * Convenience property for connection management
	 * @var string
	 */
	public $connName = '';

	/**
	 * List of queries executed
	 * @var array
	 */
	public $queries;

	/**
	 * Whether to do only an explain on the query
	 * @var boolean
	 */
	protected $explain;

	/**
	 * The current database driver
	 * @var DriverInterface
	 */
	public $driver;

	/**
	 * Query parser class instance
	 * @var QueryParser
	 */
	protected $parser;

	/**
	 * Alias to driver util class
	 * @var AbstractUtil
	 */
	protected $util;

	/**
	 * Alias to driver sql class
	 * @var SQLInterface
	 */
	protected $sql;

	/**
	 * String class values to be reset
	 *
	 * @var array
	 */
	private $stringVars = [
		'selectString',
		'fromString',
		'setString',
		'orderString',
		'groupString',
		'limit',
		'offset',
		'explain',
	];

	/**
	 * Array class variables to be reset
	 *
	 * @var array
	 */
	private $arrayVars = [
		'setArrayKeys',
		'orderArray',
		'groupArray',
		'values',
		'whereValues',
		'queryMap',
		'havingMap'
	];

	// --------------------------------------------------------------------------
	// ! Methods
	// --------------------------------------------------------------------------

	/**
	 * Constructor
	 *
	 * @param DriverInterface $driver
	 * @param QueryParser $parser
	 */
	public function __construct(DriverInterface $driver, QueryParser $parser)
	{
		// Inject driver and parser
		$this->driver = $driver;
		$this->parser = $parser;

		$this->queries['total_time'] = 0;

		// Alias driver sql and util classes
		$this->sql = $this->driver->getSql();
		$this->util = $this->driver->getUtil();
	}

	/**
	 * Destructor
	 * @codeCoverageIgnore
	 */
	public function __destruct()
	{
		$this->driver = NULL;
	}

	/**
	 * Calls a function further down the inheritance chain
	 *
	 * @param string $name
	 * @param array $params
	 * @return mixed
	 * @throws BadMethodCallException
	 */
	public function __call(string $name, array $params)
	{
		// Alias snake_case method calls
		$camelName = \to_camel_case($name);

		foreach([$this, $this->driver] as $object)
		{
			foreach([$name, $camelName] as $methodName)
			{
				if (method_exists($object, $methodName))
				{
					return \call_user_func_array([$object, $methodName], $params);
				}
			}

		}

		throw new BadMethodCallException('Method does not exist');
	}

	// --------------------------------------------------------------------------
	// ! Select Queries
	// --------------------------------------------------------------------------

	/**
	 * Specifies rows to select in a query
	 *
	 * @param string $fields
	 * @return QueryBuilderInterface
	 */
	public function select(string $fields): QueryBuilderInterface
	{
		// Split fields by comma
		$fieldsArray = explode(',', $fields);
		$fieldsArray = array_map('mb_trim', $fieldsArray);

		// Split on 'As'
		foreach ($fieldsArray as $key => $field)
		{
			if (stripos($field, 'as') !== FALSE)
			{
				$fieldsArray[$key] = preg_split('` as `i', $field);
				$fieldsArray[$key] = array_map('mb_trim', $fieldsArray[$key]);
			}
		}

		// Quote the identifiers
		$safeArray = $this->driver->quoteIdent($fieldsArray);

		unset($fieldsArray);

		// Join the strings back together
		for($i = 0, $c = count($safeArray); $i < $c; $i++)
		{
			if (\is_array($safeArray[$i]))
			{
				$safeArray[$i] = implode(' AS ', $safeArray[$i]);
			}
		}

		$this->selectString .= implode(', ', $safeArray);

		unset($safeArray);

		return $this;
	}

	/**
	 * Selects the maximum value of a field from a query
	 *
	 * @param string $field
	 * @param string|bool $as
	 * @return QueryBuilderInterface
	 */
	public function selectMax(string $field, $as=FALSE): QueryBuilderInterface
	{
		// Create the select string
		$this->selectString .= ' MAX'.$this->_select($field, $as);
		return $this;
	}

	/**
	 * Selects the minimum value of a field from a query
	 *
	 * @param string $field
	 * @param string|bool $as
	 * @return QueryBuilderInterface
	 */
	public function selectMin(string $field, $as=FALSE): QueryBuilderInterface
	{
		// Create the select string
		$this->selectString .= ' MIN'.$this->_select($field, $as);
		return $this;
	}

	/**
	 * Selects the average value of a field from a query
	 *
	 * @param string $field
	 * @param string|bool $as
	 * @return QueryBuilderInterface
	 */
	public function selectAvg(string $field, $as=FALSE): QueryBuilderInterface
	{
		// Create the select string
		$this->selectString .= ' AVG'.$this->_select($field, $as);
		return $this;
	}

	/**
	 * Selects the sum of a field from a query
	 *
	 * @param string $field
	 * @param string|bool $as
	 * @return QueryBuilderInterface
	 */
	public function selectSum(string $field, $as=FALSE): QueryBuilderInterface
	{
		// Create the select string
		$this->selectString .= ' SUM'.$this->_select($field, $as);
		return $this;
	}

	/**
	 * Adds the 'distinct' keyword to a query
	 *
	 * @return QueryBuilderInterface
	 */
	public function distinct(): QueryBuilderInterface
	{
		// Prepend the keyword to the select string
		$this->selectString = ' DISTINCT '.$this->selectString;
		return $this;
	}

	/**
	 * Tell the database to give you the query plan instead of result set
	 *
	 * @return QueryBuilderInterface
	 */
	public function explain(): QueryBuilderInterface
	{
		$this->explain = TRUE;
		return $this;
	}

	/**
	 * Specify the database table to select from
	 *
	 * @param string $tblname
	 * @return QueryBuilderInterface
	 */
	public function from($tblname): QueryBuilderInterface
	{
		// Split identifiers on spaces
		$identArray = explode(' ', \mb_trim($tblname));
		$identArray = array_map('\\mb_trim', $identArray);

		// Quote the identifiers
		$identArray[0] = $this->driver->quoteTable($identArray[0]);
		$identArray = $this->driver->quoteIdent($identArray);

		// Paste it back together
		$this->fromString = implode(' ', $identArray);

		return $this;
	}

	// --------------------------------------------------------------------------
	// ! 'Like' methods
	// --------------------------------------------------------------------------

	/**
	 * Creates a Like clause in the sql statement
	 *
	 * @param string $field
	 * @param mixed $val
	 * @param string $pos
	 * @return QueryBuilderInterface
	 */
	public function like($field, $val, $pos='both'): QueryBuilderInterface
	{
		return $this->_like($field, $val, $pos, 'LIKE', 'AND');
	}

	/**
	 * Generates an OR Like clause
	 *
	 * @param string $field
	 * @param mixed $val
	 * @param string $pos
	 * @return QueryBuilderInterface
	 */
	public function orLike($field, $val, $pos='both'): QueryBuilderInterface
	{
		return $this->_like($field, $val, $pos, 'LIKE', 'OR');
	}

	/**
	 * Generates a NOT LIKE clause
	 *
	 * @param string $field
	 * @param mixed $val
	 * @param string $pos
	 * @return QueryBuilderInterface
	 */
	public function notLike($field, $val, $pos='both'): QueryBuilderInterface
	{
		return $this->_like($field, $val, $pos, 'NOT LIKE', 'AND');
	}

	/**
	 * Generates a OR NOT LIKE clause
	 *
	 * @param string $field
	 * @param mixed $val
	 * @param string $pos
	 * @return QueryBuilderInterface
	 */
	public function orNotLike($field, $val, $pos='both'): QueryBuilderInterface
	{
		return $this->_like($field, $val, $pos, 'NOT LIKE', 'OR');
	}

	// --------------------------------------------------------------------------
	// ! Having methods
	// --------------------------------------------------------------------------

	/**
	 * Generates a 'Having' clause
	 *
	 * @param mixed $key
	 * @param mixed $val
	 * @return QueryBuilderInterface
	 */
	public function having($key, $val=[]): QueryBuilderInterface
	{
		return $this->_having($key, $val, 'AND');
	}

	/**
	 * Generates a 'Having' clause prefixed with 'OR'
	 *
	 * @param mixed $key
	 * @param mixed $val
	 * @return QueryBuilderInterface
	 */
	public function orHaving($key, $val=[]): QueryBuilderInterface
	{
		return $this->_having($key, $val, 'OR');
	}

	// --------------------------------------------------------------------------
	// ! 'Where' methods
	// --------------------------------------------------------------------------

	/**
	 * Specify condition(s) in the where clause of a query
	 * Note: this function works with key / value, or a
	 * passed array with key / value pairs
	 *
	 * @param mixed $key
	 * @param mixed $val
	 * @param mixed $escape
	 * @return QueryBuilderInterface
	 */
	public function where($key, $val=[], $escape=NULL): QueryBuilderInterface
	{
		return $this->_whereString($key, $val, 'AND');
	}

	/**
	 * Where clause prefixed with "OR"
	 *
	 * @param string $key
	 * @param mixed $val
	 * @return QueryBuilderInterface
	 */
	public function orWhere($key, $val=[]): QueryBuilderInterface
	{
		return $this->_whereString($key, $val, 'OR');
	}

	/**
	 * Where clause with 'IN' statement
	 *
	 * @param mixed $field
	 * @param mixed $val
	 * @return QueryBuilderInterface
	 */
	public function whereIn($field, $val=[]): QueryBuilderInterface
	{
		return $this->_whereIn($field, $val);
	}

	/**
	 * Where in statement prefixed with "or"
	 *
	 * @param string $field
	 * @param mixed $val
	 * @return QueryBuilderInterface
	 */
	public function orWhereIn($field, $val=[]): QueryBuilderInterface
	{
		return $this->_whereIn($field, $val, 'IN', 'OR');
	}

	/**
	 * WHERE NOT IN (FOO) clause
	 *
	 * @param string $field
	 * @param mixed $val
	 * @return QueryBuilderInterface
	 */
	public function whereNotIn($field, $val=[]): QueryBuilderInterface
	{
		return $this->_whereIn($field, $val, 'NOT IN', 'AND');
	}

	/**
	 * OR WHERE NOT IN (FOO) clause
	 *
	 * @param string $field
	 * @param mixed $val
	 * @return QueryBuilderInterface
	 */
	public function orWhereNotIn($field, $val=[]): QueryBuilderInterface
	{
		return $this->_whereIn($field, $val, 'NOT IN', 'OR');
	}

	// --------------------------------------------------------------------------
	// ! Other Query Modifier methods
	// --------------------------------------------------------------------------

	/**
	 * Sets values for inserts / updates / deletes
	 *
	 * @param mixed $key
	 * @param mixed $val
	 * @return QueryBuilderInterface
	 */
	public function set($key, $val = NULL): QueryBuilderInterface
	{
		$this->_mixedSet($this->setArrayKeys, $key, $val, self::KEY);
		$this->_mixedSet($this->values, $key, $val, self::VALUE);

		// Use the keys of the array to make the insert/update string
		// Escape the field names
		$this->setArrayKeys = array_map([$this->driver, '_quote'], $this->setArrayKeys);

		// Generate the "set" string
		$this->setString = implode('=?,', $this->setArrayKeys);
		$this->setString .= '=?';

		return $this;
	}

	/**
	 * Creates a join phrase in a compiled query
	 *
	 * @param string $table
	 * @param string $condition
	 * @param string $type
	 * @return QueryBuilderInterface
	 */
	public function join($table, $condition, $type=''): QueryBuilderInterface
	{
		// Prefix and quote table name
		$table = explode(' ', mb_trim($table));
		$table[0] = $this->driver->quoteTable($table[0]);
		$table = $this->driver->quoteIdent($table);
		$table = implode(' ', $table);

		// Parse out the join condition
		$parsedCondition = $this->parser->compileJoin($condition);
		$condition = $table . ' ON ' . $parsedCondition;

		$this->_appendMap("\n" . strtoupper($type) . ' JOIN ', $condition, 'join');

		return $this;
	}

	/**
	 * Group the results by the selected field(s)
	 *
	 * @param mixed $field
	 * @return QueryBuilderInterface
	 */
	public function groupBy($field): QueryBuilderInterface
	{
		if ( ! is_scalar($field))
		{
			$newGroupArray = array_map([$this->driver, 'quoteIdent'], $field);
			$this->groupArray = array_merge($this->groupArray, $newGroupArray);
		}
		else
		{
			$this->groupArray[] = $this->driver->quoteIdent($field);
		}

		$this->groupString = ' GROUP BY ' . implode(',', $this->groupArray);

		return $this;
	}

	/**
	 * Order the results by the selected field(s)
	 *
	 * @param string $field
	 * @param string $type
	 * @return QueryBuilderInterface
	 */
	public function orderBy($field, $type=''): QueryBuilderInterface
	{
		// When ordering by random, do an ascending order if the driver
		// doesn't support random ordering
		if (stripos($type, 'rand') !== FALSE)
		{
			$rand = $this->sql->random();
			$type = $rand ?? 'ASC';
		}

		// Set fields for later manipulation
		$field = $this->driver->quoteIdent($field);
		$this->orderArray[$field] = $type;

		$orderClauses = [];

		// Flatten key/val pairs into an array of space-separated pairs
		foreach($this->orderArray as $k => $v)
		{
			$orderClauses[] = $k . ' ' . strtoupper($v);
		}

		// Set the final string
		$this->orderString = ( ! isset($rand))
			? "\nORDER BY ".implode(', ', $orderClauses)
			: "\nORDER BY".$rand;

		return $this;
	}

	/**
	 * Set a limit on the current sql statement
	 *
	 * @param int $limit
	 * @param int|bool $offset
	 * @return QueryBuilderInterface
	 */
	public function limit($limit, $offset=FALSE): QueryBuilderInterface
	{
		$this->limit = (int) $limit;
		$this->offset = $offset;

		return $this;
	}

	// --------------------------------------------------------------------------
	// ! Query Grouping Methods
	// --------------------------------------------------------------------------

	/**
	 * Adds a paren to the current query for query grouping
	 *
	 * @return QueryBuilderInterface
	 */
	public function groupStart(): QueryBuilderInterface
	{
		$conj = empty($this->queryMap) ? ' WHERE ' : ' ';

		$this->_appendMap($conj, '(', 'group_start');

		return $this;
	}

	/**
	 * Adds a paren to the current query for query grouping,
	 * prefixed with 'NOT'
	 *
	 * @return QueryBuilderInterface
	 */
	public function notGroupStart(): QueryBuilderInterface
	{
		$conj = empty($this->queryMap) ? ' WHERE ' : ' AND ';

		$this->_appendMap($conj, ' NOT (', 'group_start');

		return $this;
	}

	/**
	 * Adds a paren to the current query for query grouping,
	 * prefixed with 'OR'
	 *
	 * @return QueryBuilderInterface
	 */
	public function orGroupStart(): QueryBuilderInterface
	{
		$this->_appendMap('', ' OR (', 'group_start');

		return $this;
	}

	/**
	 * Adds a paren to the current query for query grouping,
	 * prefixed with 'OR NOT'
	 *
	 * @return QueryBuilderInterface
	 */
	public function orNotGroupStart(): QueryBuilderInterface
	{
		$this->_appendMap('', ' OR NOT (', 'group_start');

		return $this;
	}

	/**
	 * Ends a query group
	 *
	 * @return QueryBuilderInterface
	 */
	public function groupEnd(): QueryBuilderInterface
	{
		$this->_appendMap('', ')', 'group_end');

		return $this;
	}

	// --------------------------------------------------------------------------
	// ! Query execution methods
	// --------------------------------------------------------------------------

	/**
	 * Select and retrieve all records from the current table, and/or
	 * execute current compiled query
	 *
	 * @param string $table
	 * @param int|bool $limit
	 * @param int|bool $offset
	 * @return PDOStatement
	 */
	public function get($table='', $limit=FALSE, $offset=FALSE): PDOStatement
	{
		// Set the table
		if ( ! empty($table))
		{
			$this->from($table);
		}

		// Set the limit, if it exists
		if (\is_int($limit))
		{
			$this->limit($limit, $offset);
		}

		return $this->_run('get', $table);
	}

	/**
	 * Convenience method for get() with a where clause
	 *
	 * @param string $table
	 * @param array $where
	 * @param int|bool $limit
	 * @param int|bool $offset
	 * @return PDOStatement
	 */
	public function getWhere($table, $where=[], $limit=FALSE, $offset=FALSE): PDOStatement
	{
		// Create the where clause
		$this->where($where);

		// Return the result
		return $this->get($table, $limit, $offset);
	}

	/**
	 * Retrieve the number of rows in the selected table
	 *
	 * @param string $table
	 * @return int
	 */
	public function countAll($table): int
	{
		$sql = 'SELECT * FROM '.$this->driver->quoteTable($table);
		$res = $this->driver->query($sql);
		return (int) count($res->fetchAll());
	}

	/**
	 * Retrieve the number of results for the generated query - used
	 * in place of the get() method
	 *
	 * @param string $table
	 * @param boolean $reset
	 * @return int
	 */
	public function countAllResults(string $table='', bool $reset = TRUE): int
	{
		// Set the table
		if ( ! empty($table))
		{
			$this->from($table);
		}

		$result = $this->_run('get', $table, NULL, NULL, $reset);
		$rows = $result->fetchAll();

		return (int) count($rows);
	}

	/**
	 * Creates an insert clause, and executes it
	 *
	 * @param string $table
	 * @param mixed $data
	 * @return PDOStatement
	 */
	public function insert($table, $data=[]): PDOStatement
	{
		if ( ! empty($data))
		{
			$this->set($data);
		}

		return $this->_run('insert', $table);
	}

	/**
	 * Creates and executes a batch insertion query
	 *
	 * @param string $table
	 * @param array $data
	 * @return PDOStatement
	 */
	public function insertBatch($table, $data=[]): PDOStatement
	{
		// Get the generated values and sql string
		list($sql, $data) = $this->driver->insertBatch($table, $data);

		return ( ! is_null($sql))
			? $this->_run('', $table, $sql, $data)
			: NULL;
	}

	/**
	 * Creates an update clause, and executes it
	 *
	 * @param string $table
	 * @param mixed $data
	 * @return PDOStatement
	 */
	public function update($table, $data=[]): PDOStatement
	{
		if ( ! empty($data))
		{
			$this->set($data);
		}

		return $this->_run('update', $table);
	}

	/**
	 * Creates a batch update, and executes it.
	 * Returns the number of affected rows
	 *
	 * @param string $table
	 * @param array|object $data
	 * @param string $where
	 * @return int|null
	 */
	public function updateBatch($table, $data, $where)
	{
		// Get the generated values and sql string
		list($sql, $data) = $this->driver->updateBatch($table, $data, $where);

		return ( ! is_null($sql))
			? $this->_run('', $table, $sql, $data)
			: NULL;
	}

	/**
	 * Insertion with automatic overwrite, rather than attempted duplication
	 *
	 * @param string $table
	 * @param array $data
	 * @return \PDOStatement|null
	 */
	public function replace($table, $data=[])
	{
		if ( ! empty($data))
		{
			$this->set($data);
		}

		return $this->_run('replace', $table);
	}

	/**
	 * Deletes data from a table
	 *
	 * @param string $table
	 * @param mixed $where
	 * @return PDOStatement
	 */
	public function delete($table, $where=''): PDOStatement
	{
		// Set the where clause
		if ( ! empty($where))
		{
			$this->where($where);
		}

		return $this->_run('delete', $table);
	}

	// --------------------------------------------------------------------------
	// ! SQL Returning Methods
	// --------------------------------------------------------------------------

	/**
	 * Returns the generated 'select' sql query
	 *
	 * @param string $table
	 * @param bool $reset
	 * @return string
	 */
	public function getCompiledSelect(string $table='', bool $reset=TRUE): string
	{
		// Set the table
		if ( ! empty($table))
		{
			$this->from($table);
		}

		return $this->_getCompile('select', $table, $reset);
	}

	/**
	 * Returns the generated 'insert' sql query
	 *
	 * @param string $table
	 * @param bool $reset
	 * @return string
	 */
	public function getCompiledInsert(string $table, bool $reset=TRUE): string
	{
		return $this->_getCompile('insert', $table, $reset);
	}

	/**
	 * Returns the generated 'update' sql query
	 *
	 * @param string $table
	 * @param bool $reset
	 * @return string
	 */
	public function getCompiledUpdate(string $table='', bool $reset=TRUE): string
	{
		return $this->_getCompile('update', $table, $reset);
	}

	/**
	 * Returns the generated 'delete' sql query
	 *
	 * @param string $table
	 * @param bool $reset
	 * @return string
	 */
	public function getCompiledDelete(string $table='', bool $reset=TRUE): string
	{
		return $this->_getCompile('delete', $table, $reset);
	}

	// --------------------------------------------------------------------------
	// ! Miscellaneous Methods
	// --------------------------------------------------------------------------

	/**
	 * Clear out the class variables, so the next query can be run
	 *
	 * @return void
	 */
	public function resetQuery(): void
	{
		// Reset strings and booleans
		foreach($this->stringVars as $var)
		{
			$this->$var = NULL;
		}

		// Reset arrays
		foreach($this->arrayVars as $var)
		{
			$this->$var = [];
		}
	}

	/**
	 * Set values in the class, with either an array or key value pair
	 *
	 * @param array $var
	 * @param mixed $key
	 * @param mixed $val
	 * @param int $valType
	 * @return array
	 */
	protected function _mixedSet(array &$var, $key, $val=NULL, int $valType=self::BOTH): array
	{
		$arg = (is_scalar($key) && is_scalar($val))
			? [$key => $val]
			: $key;

		foreach($arg as $k => $v)
		{
			if (\in_array($valType, [self::KEY, self::VALUE], TRUE))
			{
				$var[] = ($valType === self::KEY)
					? $k
					: $v;
			}
			else
			{
				$var[$k] = $v;
			}
		}

		return $var;
	}

	/**
	 * Method to simplify select_ methods
	 *
	 * @param string $field
	 * @param string|bool $as
	 * @return string
	 */
	protected function _select(string $field, $as = FALSE): string
	{
		// Escape the identifiers
		$field = $this->driver->quoteIdent($field);

		if ( ! \is_string($as))
		{
			return $field;
		}

		$as = $this->driver->quoteIdent($as);
		return "({$field}) AS {$as} ";
	}

	/**
	 * Helper function for returning sql strings
	 *
	 * @param string $type
	 * @param string $table
	 * @param bool $reset
	 * @return string
	 */
	protected function _getCompile(string $type, string $table, bool $reset): string
	{
		$sql = $this->_compile($type, $table);

		// Reset the query builder for the next query
		if ($reset)
		{
			$this->resetQuery();
		}

		return $sql;
	}

	/**
	 * Simplify 'like' methods
	 *
	 * @param string $field
	 * @param mixed $val
	 * @param string $pos
	 * @param string $like
	 * @param string $conj
	 * @return self
	 */
	protected function _like(string $field, $val, string $pos, string $like='LIKE', string $conj='AND'): self
	{
		$field = $this->driver->quoteIdent($field);

		// Add the like string into the order map
		$like = $field. " {$like} ?";

		if ($pos === 'before')
		{
			$val = "%{$val}";
		}
		elseif ($pos === 'after')
		{
			$val = "{$val}%";
		}
		else
		{
			$val = "%{$val}%";
		}

		$conj = empty($this->queryMap) ? ' WHERE ' : " {$conj} ";
		$this->_appendMap($conj, $like, 'like');

		// Add to the values array
		$this->whereValues[] = $val;

		return $this;
	}

	/**
	 * Simplify building having clauses
	 *
	 * @param mixed $key
	 * @param mixed $values
	 * @param string $conj
	 * @return self
	 */
	protected function _having($key, $values=[], string $conj='AND'): self
	{
		$where = $this->_where($key, $values);

		// Create key/value placeholders
		foreach($where as $f => $val)
		{
			// Split each key by spaces, in case there
			// is an operator such as >, <, !=, etc.
			$fArray = explode(' ', trim($f));

			$item = $this->driver->quoteIdent($fArray[0]);

			// Simple key value, or an operator
			$item .= (count($fArray) === 1) ? '=?' : " {$fArray[1]} ?";

			// Put in the having map
			$this->havingMap[] = [
				'conjunction' => ( ! empty($this->havingMap)) ? " {$conj} " : ' HAVING ',
				'string' => $item
			];
		}

		return $this;
	}

	/**
	 * Do all the redundant stuff for where/having type methods
	 *
	 * @param mixed $key
	 * @param mixed $val
	 * @return array
	 */
	protected function _where($key, $val=[]): array
	{
		$where = [];
		$this->_mixedSet($where, $key, $val);
		$this->_mixedSet($this->whereValues, $key, $val, self::VALUE);
		return $where;
	}

	/**
	 * Simplify generating where string
	 *
	 * @param mixed $key
	 * @param mixed $values
	 * @param string $defaultConj
	 * @return self
	 */
	protected function _whereString($key, $values=[], string $defaultConj='AND'): self
	{
		// Create key/value placeholders
		foreach($this->_where($key, $values) as $f => $val)
		{
			// Split each key by spaces, in case there
			// is an operator such as >, <, !=, etc.
			$fArray = explode(' ', trim($f));

			$item = $this->driver->quoteIdent($fArray[0]);

			// Simple key value, or an operator
			$item .= (count($fArray) === 1) ? '=?' : " {$fArray[1]} ?";
			$lastItem = end($this->queryMap);

			// Determine the correct conjunction
			$conjunctionList = array_column($this->queryMap, 'conjunction');
			if (empty($this->queryMap) || ( ! regex_in_array($conjunctionList, "/^ ?\n?WHERE/i")))
			{
				$conj = "\nWHERE ";
			}
			elseif ($lastItem['type'] === 'group_start')
			{
				$conj = '';
			}
			else
			{
				$conj = " {$defaultConj} ";
			}

			$this->_appendMap($conj, $item, 'where');
		}

		return $this;
	}

	/**
	 * Simplify where_in methods
	 *
	 * @param mixed $key
	 * @param mixed $val
	 * @param string $in - The (not) in fragment
	 * @param string $conj - The where in conjunction
	 * @return self
	 */
	protected function _whereIn($key, $val=[], string $in='IN', string $conj='AND'): self
	{
		$key = $this->driver->quoteIdent($key);
		$params = array_fill(0, count($val), '?');

		foreach($val as $v)
		{
			$this->whereValues[] = $v;
		}

		$conjunction = ( ! empty($this->queryMap)) ? " {$conj} " : ' WHERE ';
		$str = $key . " {$in} (".implode(',', $params).') ';

		$this->_appendMap($conjunction, $str, 'where_in');

		return $this;
	}

	/**
	 * Executes the compiled query
	 *
	 * @param string $type
	 * @param string $table
	 * @param string $sql
	 * @param array|null $vals
	 * @param boolean $reset
	 * @return PDOStatement
	 */
	protected function _run(string $type, string $table, $sql=NULL, $vals=NULL, bool $reset=TRUE): PDOStatement
	{
		if ($sql === NULL)
		{
			$sql = $this->_compile($type, $table);
		}

		if ($vals === NULL)
		{
			$vals = array_merge($this->values, (array) $this->whereValues);
		}

		$startTime = microtime(TRUE);

		$res = empty($vals)
			? $this->driver->query($sql)
			: $this->driver->prepareExecute($sql, $vals);

		$endTime = microtime(TRUE);
		$totalTime = number_format($endTime - $startTime, 5);

		// Add this query to the list of executed queries
		$this->_appendQuery($vals, $sql, (int) $totalTime);

		// Reset class state for next query
		if ($reset)
		{
			$this->resetQuery();
		}

		return $res;
	}

	/**
	 * Add an additional set of mapping pairs to a internal map
	 *
	 * @param string $conjunction
	 * @param string $string
	 * @param string $type
	 * @return void
	 */
	protected function _appendMap(string $conjunction = '', string $string = '', string $type = '')
	{
		$this->queryMap[] = [
			'type' => $type,
			'conjunction' => $conjunction,
			'string' => $string
		];
	}

	/**
	 * Convert the prepared statement into readable sql
	 *
	 * @param array $vals
	 * @param string $sql
	 * @param int $totalTime
	 * @return void
	 */
	protected function _appendQuery($vals, string $sql, int $totalTime)
	{
		$evals = \is_array($vals) ? $vals : [];
		$esql = str_replace('?', "%s", $sql);

		// Quote string values
		foreach($evals as &$v)
		{
			$v = ( ! is_numeric($v))
				? htmlentities($this->driver->quote($v), ENT_NOQUOTES, 'utf-8')
				: $v;
		}

		// Add the query onto the array of values to pass
		// as arguments to sprintf
		array_unshift($evals, $esql);

		// Add the interpreted query to the list of executed queries
		$this->queries[] = [
			'time' => $totalTime,
			'sql' => sprintf(...$evals)
		];

		$this->queries['total_time'] += $totalTime;

		// Set the last query to get rowcounts properly
		$this->driver->setLastQuery($sql);
	}

	/**
	 * Sub-method for generating sql strings
	 *
	 * @param string $type
	 * @param string $table
	 * @return string
	 */
	protected function _compileType(string $type='', string $table=''): string
	{
		switch($type)
		{
			case 'insert':
				$paramCount = count($this->setArrayKeys);
				$params = array_fill(0, $paramCount, '?');
				$sql = "INSERT INTO {$table} ("
					. implode(',', $this->setArrayKeys)
					. ")\nVALUES (".implode(',', $params).')';
				break;

			case 'update':
				$sql = "UPDATE {$table}\nSET {$this->setString}";
				break;

			case 'replace':
				// @TODO implement
				$sql = '';
				break;

			case 'delete':
				$sql = "DELETE FROM {$table}";
				break;

			// Get queries
			default:
				$sql = "SELECT * \nFROM {$this->fromString}";

				// Set the select string
				if ( ! empty($this->selectString))
				{
					// Replace the star with the selected fields
					$sql = str_replace('*', $this->selectString, $sql);
				}
				break;
		}

		return $sql;
	}

	/**
	 * String together the sql statements for sending to the db
	 *
	 * @param string $type
	 * @param string $table
	 * @return string
	 */
	protected function _compile(string $type='', string $table=''): string
	{
		// Get the base clause for the query
		$sql = $this->_compileType($type, $this->driver->quoteTable($table));

		$clauses = [
			'queryMap',
			'groupString',
			'orderString',
			'havingMap',
		];

		// Set each type of subclause
		foreach($clauses as $clause)
		{
			$param = $this->$clause;
			if (\is_array($param))
			{
				foreach($param as $q)
				{
					$sql .= $q['conjunction'] . $q['string'];
				}
			}
			else
			{
				$sql .= $param;
			}
		}

		// Set the limit via the class variables
		if (is_numeric($this->limit))
		{
			$sql = $this->sql->limit($sql, $this->limit, $this->offset);
		}

		// See if the query plan, rather than the
		// query data should be returned
		if ($this->explain === TRUE)
		{
			$sql = $this->sql->explain($sql);
		}

		return $sql;
	}
}