import java.util.*;
import java.io.*;

/**
 * This class does a "degrees of separation" analysis on the given input file.
 * small-twitter.dot consists of twitter communications.  The goal is given
 * two people A and B, find the distance apart those two people are via
 * twitter communications.
 *
 * @author Adam Blank
 */
public class Twitter {
    public static void main(String[] args) throws FileNotFoundException {
       Scanner input = new Scanner(new File("small-twitter.dot"));

       // key: a user (String)
       // value: another map? anyone connected
       //        who is one away from this user?
       //        set of all people one away
       
       Map<String, Set<String>> twitterCommunications = new HashMap<>();
       while (input.hasNextLine()) {
          String line = input.nextLine();
          if (line.contains("--")) {
             Scanner lineData = new Scanner(line);
             String name1 = lineData.next();
             lineData.next(); // skip "--"
             String name2 = lineData.next();
             
             // name1 -- name2
             //  key      value
             addToMap(twitterCommunications, name1, name2);
             addToMap(twitterCommunications, name2, name1);
          }
       }
       findDistance(twitterCommunications);
       
    }
    
    public static void addToMap(Map<String, Set<String>> twitterCommunications, String name1, String name2) {
        if (!twitterCommunications.containsKey(name1)) {
            twitterCommunications.put(name1, new HashSet<String>());
        }
        // add name2 to the set mapped to by name1
        twitterCommunications.get(name1).add(name2);
    }
       
    public static void findDistance(Map<String, Set<String>> twitterCommunications) {
       Scanner console = new Scanner(System.in);
       System.out.print("First person? ");
       String name1 = console.next();

       System.out.print("Second person? ");
       String name2 = console.next();
       
       /* Current is the "frontier" that we are exploring.  The people in this
        * set are our current distance away from the starting person. */
       Set<String> current = new HashSet<>();
       
       /* When we begin, name1 is the only person of zero distance away from
        * name1. */
       current.add(name1);
       
       int distance = 0;
       while (!current.contains(name2)) {
           distance++; // Every time through this loop, we add people of 
                       // distance one further from name1.

           /* Collect all of the people of distance 1 from the people we
            * are currently looking at. */
           Set<String> next = new HashSet<>();
           for (String person: current) {
               next.addAll(twitterCommunications.get(person));
           }


           /* Now that we've added everyone we've seen to our "next" set,
            * those people are the next distance we need to check. */
           current = next;
       }
       System.out.println(name1 + " is " + distance + " away from " + name2);
    }
}