Simple English text readability analyzer in PHP

Design and implement a PHP class, or a set of classes, which takes as an input a string of English text and outputs an array of numeric metrics that tell the readability and quality of the text input. Basically, the PHP class would return the same results as the [login to view URL] website. Bonus Feature: If you can, also include to the returning output array a Spam Score, that is, how spam like the input text seems like, and list the spam keywords that were found from the text which make the text seem like spam. The spam keywords must be provided by you, and can be implemented either as a database or as a hard coded array within the php code. In your bid, let me know if you can implement the Bonus Feature too (if you don't mention it, I assume that your bid does not include it). If any free to use code exists that can do this job, or a part of it, feel free to use it.