Detect left clicking ranged weapon in hand

I'm making a dart blower. It's going to have normal, poison and wither darts. But I can only use one ammo type per weapon. So I thought I could switch modes of the dart blower to poison and wither dart blower by swinging item in hand. It worked! But right clicking also worked, meaning I can't even shoot with it. I want to shoot with right click and change mode with left click, maybe even shift left click. Can anyone help?