The Irrealis of the past (Irrealis der Vergangenheit) is formed with the compound form of the conjunctive II (with orientation to the past):
conjunctive II of haben + perfect participle in both parts of the sentence. The conjunction that introduces the condition is wenn.

Examples: Ich hätte mir ein Auto gekauft, wenn ich Geld gehabt hätte. = = I would have bought a car if I had had the money. Du hättest dir ein Auto gekauft, wenn du Geld gehabt hättest. = You would have bought a car if you had had the money. Er / Sie / Es hätte sich ein Auto gekauft, wenn er / sie / es Geld gehabt hätte. = He / She / It would have bought a car if he / she / it had had the money. Wir hätten uns ein Auto gekauft, wenn wir Geld gehabt hätten. = We would have bought a car if we had had the money. Ihr hättet euch ein Auto gekauft, wenn ihr Geld gehabt hättet. = You would have bought a car if you had had the money. Sie hätten sich ein Auto gekauft, wenn sie Geld gehabt hätten. = They would have bought a car if they had had the money.