Alter Javascript file using PHP - open to bidding

You will write a php method to: * get a javascript file, * alter javascript file to add a line of code to a proper position, * save file to specified path Following items should be considered while writing the code: * Injection should not corrupt the integrity of the javascript file * File content is changing almost every week * Marker is not always in the same position of the file Prototype and target javascript are included to the task.