Armada by Ernest Cline

In this science fiction novel, a teenage gamer named Zack Lightman discovers that the video game he excels at is actually a training simulation designed by the government to prepare humanity for an impending alien invasion. As Zack is recruited into a real-life battle against extraterrestrial forces, he learns about his father's mysterious past and uncovers hidden truths about the world and his own identity. The story blends elements of adventure, nostalgia, and pop culture references as Zack and his allies strive to save Earth from destruction.