<?php

/**
 * Object representing a SQL query.
 * The various parts of the SQL query can be manipulated individually.
 */
class SQLQuery extends Object {
	/**
	 * An array of fields to select.
	 * @var array
	 */
	public $select;
	
	/**
	 * An array of join clauses. The first one is just the table name.
	 * @var array
	 */
	public $from;
	
	/**
	 * An array of filters.
	 * @var array
	 */
	public $where;
	
	/**
	 * An ORDER BY clause.
	 * @var string
	 */
	public $orderby;
	
	/**
	 * An array of fields to group by.
	 * @var array
	 */
	public $groupby;
	
	/**
	 * An array of having clauses.
	 * @var array
	 */
	public $having;
	
	/**
	 * A limit clause.
	 * @var string
	 */
	public $limit;
	
	/**
	 * If this is true DISTINCT will be added to the SQL.
	 * @var boolean
	 */
	public $distinct;
	
	/**
	 * If this is true, this statement will delete rather than select.
	 * @var boolean
	 */
	public $delete;
	
	/**
	 * Construct a new SQLQuery.
	 * @param array $select An array of fields to select.
	 * @param array $from An array of join clauses. The first one should be just the table name.
	 * @param array $where An array of filters, to be inserted into the WHERE clause.
	 * @param string $orderby An ORDER BY clause.
	 * @param array $groupby An array of fields to group by.
	 * @param array $having An array of having clauses.
	 * @param string $limit A LIMIT clause.
	 */
	function __construct($select = array(), $from = array(), $where = "", $orderby = "", $groupby = "", $having = "", $limit = "") {
		if($select) $this->select = is_array($select) ? $select : array($select);
		if($from) $this->from = is_array($from) ? $from : array(str_replace('`','',$from) => $from);
		if($where) $this->where = is_array($where) ? $where : array($where);
		$this->orderby = $orderby;
		if($groupby) $this->groupby = is_array($groupby) ? $groupby : array($groupby);
		if($having) $this->having = is_array($having) ? $having : array($having);
		$this->limit = $limit;

		parent::__construct();
	}
	
	/**
	 * Swap the use of one table with another.
	 * @param string $old Name of the old table.
	 * @param string $new Name of the new table.
	 */
	function renameTable($old, $new) {
		$this->replaceText("`$old`", "`$new`");
	}
	
	/**
	 * Swap some text in the SQL query with another.
	 * @param string $old The old text.
	 * @param string $new The new text.
	 */
	function replaceText($old, $new) {
		if($this->select) foreach($this->select as $i => $item)
			$this->select[$i] = str_replace($old, $new, $item);

		if($this->from) foreach($this->from as $i => $item)
			$this->from[$i] = str_replace($old, $new, $item);

		if($this->where) {
			foreach($this->where as $i => $item)
				$this->where[$i] = str_replace($old, $new, $item);
		}
		
		$this->orderby = str_replace($old, $new, $this->orderby);

		if($this->groupby) {
			foreach($this->groupby as $i => $item)
				$this->groupby[$i] = str_replace($old, $new, $item);
		}

		if($this->having) {
			foreach($this->having as $i => $item)
				$this->having[$i] = str_replace($old, $new, $item);
		}
	}

	/**
	 * Generate the SQL statement for this query.
	 * @return string
	 */
	function sql() {
		$distinct = $this->distinct ? "DISTINCT " : "";
		if($this->select) {
			$text = "SELECT $distinct" . implode(", ", $this->select);
		} else {
			if($this->delete) $text = "DELETE ";
		}
		$text .= " FROM " . implode(" ", $this->from);
		
		if($this->where) $text .= " WHERE (" . implode(") AND (" , $this->where) . ")";
		if($this->groupby) $text .= " GROUP BY " . implode(", ", $this->groupby);
		if($this->having) $text .= " HAVING ( " . implode(" ) AND ( ", $this->having) . " )";
		if($this->orderby) $text .= " ORDER BY " . $this->orderby;
		if($this->limit) $text .= " LIMIT " . $this->limit;
		
		return $text;
	}
	
	/**
	 * Execute this query.
	 * @return Query
	 */
	function execute() {
		return DB::query($this->sql());
	}
	
	/// VARIOUS TRANSFORMATIONS BELOW
	
	/**
	 * Return the number of rows in this query if the limit were removed.  Useful in paged data sets.
	 * @return int
	 */
	function unlimitedRowCount( $column = "*" ) {
		$clone = clone $this;
		$clone->select = array("count($column)");
		$clone->limit = null;
		$clone->orderby = null;
		$clone->groupby = null;
		return $clone->execute()->value();
	}
}

?>