I need an online shop with a custom interface (customizing items with Ajax, with a preview included). Writing it myself does not make too much sense (implementing all the payment options etc.), so I would like to use an existing online shop (OpenSource).
I would like to build my own UI which, for example, tells the shop to add an item to its cart -- i.e. without using the online shop's native UI. More precisely, it should be an online gallery where the user can directly order an image if he likes it. The final checkout/payment page can be native again.
Is there a shop system that supports this? Or is it still faster to write it on my own? Or are there better options?
Finally the image goes to the shopping cart and the user can proceed to checkout. This is where I would like the online shop system to kick in. Not before, i.e. not in the previous paragraph.