신규 아이디 추천.java

import java.util.*;

class Solution {
    public String solution(String new_id) {
        new_id = new_id.toLowerCase();
        
        new_id = new_id.replaceAll("[^a-z0-9-_.]","");
        
        while(new_id.contains("..")) {
            new_id = new_id.replace("..", ".");    
        }
        
        if (new_id.length() > 0) {
            if (new_id.charAt(0) == '.') {
                new_id = new_id.substring(1, new_id.length());
            }
        }
        if (new_id.length() > 0) {
            if (new_id.charAt(new_id.length() - 1) == '.') {
                new_id = new_id.substring(0, new_id.length() - 1);
            }
        }
        
        if(new_id.length()==0) {
            new_id = "a";
        }
        
        if(new_id.length()>=16) {
            new_id = new_id.substring(0, 15);
            if (new_id.charAt(new_id.length() - 1) == '.') {
                new_id = new_id.substring(0, new_id.length() - 1);
            }
        }
        
        if(new_id.length()<=2) {
            char last = new_id.charAt(new_id.length() - 1);
            while (new_id.length() < 3) {
                new_id += last;
            }
        }
        return new_id;
    }
}