How can I build a foldable desk within my window frame?

I have a small home and wanted a desk preferably which does not touch down in extended position and can be folded into the window bracket. Below is how my window looks like

Assuming the width of window is 70 cm. How can I go by building this? The idea that I have is fix a piece of wood (70cm x5cm) on the window with door clamps on it side and attach another piece of wood approx 70cm x 45cm to the door clamps so it opens when pulled down. Then use a belt to hold it up for closing it.

Does that make sense? How can I calculate the wieght it would be able to hold? What are the materials required?

• Wood, what kind?
• Clamps? Hinges? is that the proper name? Would a couple be enough?
• How many hinges/clamps should be used?

I am a complete beginner. If you think I should learn somethings first please direct me. I have gotten so far by spending hours at the hardware store. Any guidance appreciated!