Is Vincent a corrupt cop or an undercover cop trying to catch corrupt cops?

In the French movie Nuit Blanche (Titled Sleepless Night for its English release and recently remade by Hollywood as Sleepless) the lead character, Vincent, is a policeman. But whether he is a heroic character or a dark and corrupt character is unclear.

I recently rewatched the original (I've only seen the trailer for the American remake) and this triggered a major question which seems to have been drastically simplified in the remake if the trailer is a guide.

For most of the movie, Vincent is fighting frantically to retrieve his son from a drug dealer who has kidnapped him. This has happened because Vincent and his partner hijacked a large cocaine haul but Vincent was recognised in the ensuing shootout. Their motive at this point appears to be that they both need the money.

Most of the action happens in a dark nightclub complex owned by the drug dealer where Vincent goes to retrieve his son by returning the drugs. But his plans are disrupted by another cop from internal affairs who seems to be investigating Vincent for potential corruption (she moves his stash of drugs from its hiding place preventing Vincent from returning it). But we also see her boss interacting with Vincent's partner in a way that suggests he is a corrupt policeman who wants the drugs for himself.

Everything gets very complicated and murky but the movie has a refreshing lack of exposition so we don't ever get comfortable about who is a good guy and who isn't. But, during one confrontation between Vincent and the female anti-corruption cop trailing him, he suddenly claims to be part of the same department as her, operating undercover to catch corrupt cops. This comes out of nowhere and, as far as I remember, is not referred to again anywhere in the movie. Nor do we see any obvious evidence to corroborate his claim. Nothing we have seen so far in the movie hints at this.

The trailer for the American remake flags the character as an undercover cop, casting him as a hero even before viewing the film. But was this really true in the French original? Do we have any evidence that Vincent was acting undercover to root out police corruption or was he just a corrupt cop making up a story to get him out of a risky situation?