Put mussels in a large pot with a lid. Cover, turn heat to medium-high and when you hear the mussel liquid boiling, reduce heat to maintain a steady bubble; you will hear it and see steam escaping. Shake pot now and then; when mussels open, remove them. Let cool slightly and shuck, reserving cooking liquid. When liquid has cooled, strain it.
Meanwhile, bring a pot of salted water to a boil, cook pasta until not quite done (figure about 2 minutes short of where you would usually cook it), drain and set aside.
Put oil in a large skillet over medium-high heat; add garlic and chile flakes and cook for about 1 minute. Add beans, wine, pasta, and mussels; reduce heat to medium-low and stir to combine. Add as much reserved mussel liquid as mixture can accommodate without becoming too soupy.
Cook, stirring gently, until pasta is fully cooked and everything is warmed through; add more liquid if you like. Adjust seasoning as needed, drizzle with a bit more olive oil if you like, sprinkle with parsley and serve.