The writers of the song are Adam Levine, Joshua Coleman, Lukasz Gottwald (Dr. Luke

), Jacob Kasher, Hindlin, Mike Posner, and Henry Walter.
The producers are Ammo and Cirkut, both of whom are buddies of Dr. Luke.
Dr. Luke probably reworked the melody of Birthday when writing the song. It's a Tik Tok vs Cali Gurls or Halo vs Already Gone situation.
The music video (while much, much better than Birthday's video) is a blatant rip-off though.
By the way, did anyone else notice that Birthday's lyric video is just labeled as "Katy Perry - Birthday"? Even Katy/her label wants to forget the music video happened
