joining a PF game, what class covers the party's biggest weakness?

[NumberKruncher]

I have very limited experience with pathfinder, which is why I'm asking.

So far, the party has:

Barbarian
Alchemist
Oracle
Rogue

Please let me know some classes that would compliment this party. TIA.

[NumberKruncher]

I'm leaning towards a gunslinger, monk, paladin, cleric, bard, or wizard.

My real D&D experience is in 2e or 5e, and I have very limited pathfinder experience.

Thanks!

[Rags]

The party has no real arcane input, so I'd suggest the Arcanist, Sorcerer, Witch, or Wizard. Maybe there are more classes to fit the bill, I haven't been keeping up with the latest books...

[Blightersbane]

that party isnt the most optimized group
playing a buffing/debuffing heal-bot is soooo very boring - but your party probably gonna need one, less the Oracle is?
also need arcanist wizard or Sorcerer,
oh and a archer there isn't one here
that being said you only have 1 front liner, the Barbarian, probably could use 2 of these or 1 support (like an archer)
the rogue is the skill monkey but not so great at outdoors so you probably need somebody with good outdoors skills like a ranger

ok so a ranger archer could fill in nicely
a paladin archer same, no skills but healing and combat and a archer pali is really kinda slick
Druid combat support, outdoors, spells versatility probably a good solid choice