Answer:
You use a knife to slice my head but you weep beside me when I am dead
Keep doing me to avoid lens dryness
I encourage people to run home and steal
I lose my head in the morning and regain back it at night.
I am a precious stone as clear as diamond. Seek me out while the sun's near the horizon. Though you can walk on water with my power try to keep me and I'll vanish in an hour.
James has 98 chocolate bars, he eats 91 of them. What does he have now?