Hou quan kou si (1974)

The is a true story about a Chinese patriot and martial arts instructor Koo Sze who is arrested by a corrupt government official named Chow Li Ming (Shih Kien) for not wanting to join the army. While Koo Sze is locked down in jail, he watches out of his window a "monkey" show. How interesting? Chan then decides to teach himself Monkey kung fu.