GA pilot reported a near miss with another aircraft during final approach due to other aircraft flying erratically.

Narrative

The tower was closed at the time due to lack of staffing on a busy morning. A student pilot flying Aircraft Y cut off two planes in the pattern by flying an erratic and unsafe traffic pattern. While turning left base from the downwind 20; the student cut off another aircraft who had already turned base-to-final 20. The student flew through the 20 final; and luckily the other plane on final was able to land. A pilot on frequency kept telling the student they needed to go-around and re-enter the pattern. The student ignored the other pilot on frequency and didn't reply.At this point; the student flew to the north for a few minutes and called out on the radio they were entering a right downwind 20 (non standard). I entered a left base 20 (standard pattern). As I am about to turn a left base-to-final; I notice this student is suddenly flying an opposing base directly at me. Had I not made an evasive hard right turn; we would have had a midair. I made a ~120 degree right turn and alerted the other pilots on frequency that I was making a sharp turn on the final of 20. The student continued their final approach and landed 20. I re-entered a stabilized final for 20 and landed uneventfully.