SofaDB PHP CouchDB alternative

sofadb.php

<?php
/*
	SofaDB, a pure PHP CouchDB alternative
	Developed by Thomas Hunter
	Released under the LGPL
	May 1st, 2010
	Version 0.0.1
	This was something I started as a joke, basically a document storage system which
	stores files on disk in the form of ID.json. It was never heavily tested...
*/
define('SOFA_DIR', './sofadb/');
define('SOFA_EXT', '.json');
define('SOFA_IND', 'index');

class SofaDB {
	private $auto_increment;
	private $error_message;
	
	public function __construct() {
		$filename = SOFA_DIR . SOFA_IND;
		if (file_exists($filename)) {
			$this->auto_increment = file_get_contents($filename) + 0;
			return true;
		} else {
			$this->error_message = "Index file does not exist.";
			return false;
		}
	}
	
	public function getNext() {
		return $this->auto_increment + 1;
	}
	
	public function getError() {
		return $this->$error_message;
	}
	
	public function repair() {
		# re-determine auto increment value
		# clean up database files?
	}
	
	public function select($id) {
		$id += 0;
		$filename = SOFA_DIR . $id . SOFA_EXT;
		if (file_exists($filename)) {
			$data_string = file_get_contents($filename);
			$data = json_decode($data_string);
			return $data;
		} else {
			$this->error_message = "Record does not exist.";
			return false;
		}
	}
	
	public function update($id, $data) {
		$id += 0;
		$filename = SOFA_DIR . $id . SOFA_EXT;
		$data_string = json_encode($data);
		
		$handle_data = fopen($filename, 'w');
		fwrite($handle_data, $data_string);
		fclose($handle_data);
		
		return true;
	}
	
	public function insert($data) {
		$data_string = json_encode($data);
		$this->auto_increment++;
		
		$handle_ai = fopen(SOFA_DIR . SOFA_IND, 'w');
		fwrite($handle_ai, $this->auto_increment);
		fclose($handle_ai);
		
		$handle_data = fopen(SOFA_DIR . $this->auto_increment . SOFA_EXT, 'w');
		fwrite($handle_data, $data_string);
		fclose($handle_data);
		
		return $this->auto_increment;
	}
	
	public function delete($id) {
		$id += 0;
		$filename = SOFA_DIR . $id . SOFA_EXT;
		if (file_exists($filename)) {
			unlink($filename);
			return true;
		} else {
			return false;
		}
	}
	
	public function truncate() {
		$handle = opendir(SOFA_DIR);
		$i = 0;
		while (false !== ($filename = readdir($handle))) {
			if (strpos($filename, SOFA_EXT)) {
				unlink(SOFA_DIR . $filename);
				$i++;
			}
		}
		$handle_ai = fopen(SOFA_DIR . SOFA_IND, 'w');
		fwrite($handle_ai, '0');
		fclose($handle_ai);
		return $i;
	}
}