How do I write PSD with MINIMAL CODE

For reading PSD (photoshop native image) files, one's parser should be able to handle every possible type of PSD (be it 8bpp 1bpp 24bpp, whether it has no layers other than "background" or whether it has 100 layers, etc) It is a VERY complex format which basically saves the internal state of photoshop to a file!

However I need to know what are only the MANDATORY header and metadata fields. This official Adobe page lists ALL of the possible headers, and subsections, and metadata, and other junk I don't even need to worry about. http://www.adobe.com/devnet-apps/pho...50577409_72092
And it doesn't even specify which parts are MANDATORY versus OPTIONAL.

Well I want to not create a PSD reader, I want to create a VERY SIMPLE PSD WRITER. A compliant reader should be able to parse every possible PSD file that exists. But a writer only needs to create a file using the part of the specification that it will need (such as only 24bpp images). And making a WRITER is what I want to do. I want it to contain only the ABSOLUTE BARE MINIMUM amount of header and metadata needed to get Photoshop to recognize it as a valid PSD file, and therefore display the image. And I only care about 24bpp images (the standard for most image files anyway). When completed this would hopefully be able to convert BMP or other common image types to 24bpp PSD files. This should not require a lot of code to do.

Can someone tell me what are the MINIMUM requirements to get a valid PSD file? Thanks for any help you can provide in this way.