Simple, configureable and lightweight Spam Detector

test.php

<?php
$spamChecker = new SpamChecker();
$spamChecker->addRule(function($spam){
    if (strpos($spam, 'test') !== false) {
        return true;
    }
});

echo "The following should be true" . PHP_EOL;
var_dump($spamChecker->isSpam('this is a test'));

echo "The following should be false" . PHP_EOL;
var_dump($spamChecker->isSpam('hello'));


class SpamChecker
{
    protected $rules = array();
    
    /**
     * Checks the variable for spam.
     *
     * @prams string $potentialSpam can be any of the following:
     *                       -text
     *                       -ip address
     *                       -User Agent
     *                       -URL
     */
    function isSpam($potentialSpam)
    {
        $type = $this->determineType($potentialSpam);
        
        //Do we have rules set for this type?
        if (!isset($this->rules[$type]) || !is_array($this->rules[$type])) {
            return false;
        }
        
        //Check if this is spam
        foreach ($this->rules[$type] as $rule) {
            if ($rule($potentialSpam)) {
                return true;
            }
        }
        
        return false;
    }

    /**
     * Determines the type of potential spam to test against.
     * 
     * @throws Exception
     * 
     * @param $potentialSpam
     * 
     * @return String ('text'|'ip'|'ua'|'url')
     */
    function determineType($potentialSpam)
    {
        if (!is_string($potentialSpam)) {
            throw new Exception('String Required');
        }
        
        //regex to determine type of spam
        
        //If nothing else, it is just text.
        return "text";
    }
    
    /**
     * Adds a rule of a given type.
     * 
     * @throws Exception
     *
     * @param $rule Function 
     * @param $ruleType String ('text'|'ip'|'ua'|'url')
     *
     * @return self
     */
    function addRule($rule, $ruleType = 'text')
    {
        $ruleType = strtolower($ruleType);
        
        if (!in_array($ruleType, array('text', 'ip', 'ua', 'url'))) {
            throw new Exception("Rule types can be 'text', 'ip', 'ua' or 'url'");
        }
        
        if (!is_callable($rule)) {
            throw new Exception("The rule must be a function");
        }
        
        $this->rules[$ruleType][] = $rule;
        return $this;
    }
}