Java M4A atom tagging free space issue

Question

Hey, I've been trying to be able to read and write iTunes style M4A atoms and while I've successfully done the reading part, I've come to a bit of a halt in regards to the free space atoms. I figured that I should be able edit and shift the padding around to accommodate writing an atom with more data than it originally had. I've been stuck on this for about a day now, and I've been trying to figure out how to determine the closest free space atom with enough size to accommodate the new data. so far I have:

private freeAtom acquireFreeSpaceAtom( long position )
{
    long atomStart = Long.MAX_VALUE;

    freeAtom atom = null;
    for( freeAtom a : freeSpace )
    {
        if( Math.abs( position - atomStart ) > Math.abs( position - a.getAtomStart() ) )
            atomStart = ( atom = a ).getAtomStart();
    }

    return atom;
}

That code only takes into account the closest free space atom and completely disregards the fact that it should be greater than or equal to a certain size, but I can't quite figure out how I should check for both closeness and size efficiently.