<?php

/*
 * Replace long SQL string with several functions
 * Fixed SQL string is hard to migrate to another DB whose syntax may differ.
 * Using a high level abstract interface makes code clean and easy to migrate.
 * Is is strongly recommended to use prepared statement in order to avoid SQL-injection
 */

class SQLBuilder
{
	private $sql = '';

	/**/
	public function insert($table, array $key_values)
	{
		$this->sql = "INSERT INTO `$table`";
		$keys = array_keys($key_values);
		if (count($keys) && $keys[0] !== 0) { //support `INSERT INTO table VALUES (...)
			$this->sql .= '(';
			foreach ($keys as $key) {
				$this->sql .= "`$key`, ";
			}
			$this->sql = substr($this->sql, 0, strlen($this->sql) - 2);
			$this->sql .= ')';
		}
		$this->sql .= " VALUES(";
		foreach ($key_values as $key => $value) {
			if ($value === null) {
				$this->sql .= "null, ";
			} else if ($value === '?') {// support prepared statment
				$this->sql .= "?, ";
			} else {// FIXME: $value may contains '
				$this->sql .= "'$value', ";
			}
		}
		$this->sql = substr($this->sql, 0, strlen($this->sql) - 2);
		$this->sql .= ")";
	}

	/**/
	public function select($table, array $selected_rows = array())
	{
		$this->sql = 'SELECT ';
		foreach ($selected_rows as $row) {
			if (strpos($row, ' ') || strpos($row, '(')) {//contain functions, not pure row name
				$this->sql .= "$row, ";
			} else {
				$this->sql .= "`$row`, ";
			}
		}
		if (count($selected_rows) === 0) {
			$this->sql .= ' * ';
		} else {
			$this->sql = substr($this->sql, 0, strlen($this->sql) - 2);
		}
		$this->sql .= " FROM `$table` ";
	}

	/**/
	public function update($table, array $key_values)
	{
		if ($key_values === null || count($key_values) === 0) {
			return;
		}
		$this->sql = "UPDATE `$table` SET ";
		foreach ($key_values as $key => $value) {
			if ($value === null) {
				$this->sql .= " `$key` = null, ";
			} else if ($value === '?') {
				$this->sql .= " `$key` = ?, ";
			} else {//FIXME: $value may contain '
				$this->sql .= " `$key` = '$value', ";
			}
		}
		$this->sql = substr($this->sql, 0, strlen($this->sql) - 2);
	}

	/**/
	public function delete($table)
	{
		$this->sql = "DELETE FROM `$table` ";
	}

	/* currently, can only represent AND */
	public function where($key_values, $opts = array())
	{
		$where_clause_cnt = 0;
		$keys = array_keys($key_values);

		foreach ($keys as $key) {
			if (!isset($opts[$key])) {
				$opts[$key] = '=';
			}
			if ($where_clause_cnt == 0) {
				$this->sql .= ' WHERE ';
			} else {
				$this->sql .= ' AND ';
			}
			if ($key_values[$key] === null) {
				if ($opts[$key] === '=') {
					$this->sql .= " `$key` is null ";
				} else {
					$this->sql .= " `$key` is not null ";
				}
				$where_clause_cnt++;
			} else if ($key_values[$key] === '?' || in_array(strtoupper($opts[$key]), array('IN', 'BETWEEN', 'LIKE'))) {
				$this->sql .= " `$key` {$opts[$key]} {$key_values[$key]} ";
				$where_clause_cnt++;
			} else {//FIXME: $key_values[$key] may contain '
				$this->sql .= " `$key` {$opts[$key]} '{$key_values[$key]}' ";
				$where_clause_cnt++;
			}
		}
	}

	/**/
	public function group(array $by_arr)
	{
		if ($by_arr === null || count($by_arr) === 0) {
			return;
		}
		$this->sql .= ' GROUP BY ';
		foreach ($by_arr as $by) {
			$this->sql .= "`$by`, ";
		}
		$this->sql = substr($this->sql, 0, strlen($this->sql) - 2);
	}

	/**/
	public function order(array $by_arr)
	{
		if ($by_arr === null || count($by_arr) === 0) {
			return;
		}
		$this->sql .= ' ORDER BY ';
		foreach ($by_arr as $by => $order) {
			if (strtoupper($order) !== 'DESC') {
				$order = 'ASC';
			}
			$this->sql .= "`$by` $order, ";
		}
		$this->sql = substr($this->sql, 0, strlen($this->sql) - 2);
	}

	/**/
	public function limit($offset, $cnt)
	{
		if ($cnt < 0) {// support LIMIT 0 ,-1 to get all records
			$this->sql .= " LIMIT $offset, 18446744073709551615";
		} else {
			$this->sql .= " LIMIT $offset, $cnt";
		}
	}

	/**/
	public function build()
	{
		return $this->sql;
	}

}