How do chemists create diphenhydramine?

Diphenhydamine is the active ingredient in sleep aids. It has minor hallucinogenic effects and can be deadly if taken in large quantities. I know these things; duh. This is not a scam nor do I really want to say why I'm asking this question but I will.

Let's just say the world was going to end in 10 years, It's not an asteroid it's not a volcano it's not aliens. Diphenhydramine would be in high demand if you know what I mean. I do not plan to process sell or even make this substance but If anybody knows how to extract the substances needed to make this compound please enlighten me.