// This program reads a Graphviz file of friendships and finds the distance
// between two people in the graph.

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

public class Friends {
   public static void main(String[] args) throws FileNotFoundException {
      Scanner console = new Scanner(System.in);
      System.out.print("Input file? ");
      String fileName = console.nextLine();
      Scanner input = new Scanner(new File(fileName));
      
      Map<String, Set<String>> friends = processFriends(input);
      // outputFriends(friends);
      
      System.out.print("Starting person? ");
      String origin = console.nextLine().trim();
      if (!friends.containsKey(origin)) {
         System.out.println("That person is not in the data file.");
      } else {   
         System.out.print("Person to find? ");
         String dest = console.nextLine().trim();
         
         findFriend(friends, origin, dest);
      }
   }
   
   // pre: input is open and contains a legal Graphviz file of friendships
   // returns a map from each person in the file to their set of friends
   public static Map<String, Set<String>> processFriends(Scanner input) {
      Map<String, Set<String>> friends = new TreeMap<String, Set<String>>();

      while (input.hasNextLine()) {
         String line = input.nextLine();
         if (line.contains("--")) {
            String[] parts = line.split("--");
            addFriend(friends, parts[0].trim(), parts[1].trim());
            addFriend(friends, parts[1].trim(), parts[0].trim());
         }
      }
      
      return friends;
   }
   
   // pre: friendMap is non-null
   // creates a friendship link in friendMap from friend1 to friend2
   private static void addFriend(Map<String, Set<String>> friendMap, String friend1, String friend2) {
      if (!friendMap.containsKey(friend1)) {
         friendMap.put(friend1, new TreeSet<String>());
      }
      friendMap.get(friend1).add(friend2);
   }
   
   public static void outputFriends(Map<String, Set<String>> friendMap) {
      for (String name : friendMap.keySet()) {
         System.out.println(name + " is friends with " + friendMap.get(name));
      }
   }
   
   // pre: friendMap is non-null
   //      origin is a kay in friendMap
   // prints out the list of friends each distance from origin until either
   //   target is found or no more people are reachable
   public static void findFriend(Map<String, Set<String>> friendMap, String origin, String target) {
      System.out.println(origin + "'s friends:");
      
      Set<String> oldFriends = new TreeSet<String>();
      Set<String> newFriends = new TreeSet<String>();
      newFriends.add(origin);
      int level = 0;
      
      while (!newFriends.contains(target) && !newFriends.isEmpty()) {
         oldFriends.addAll(newFriends);
         level++;         

         Set<String> newNewFriends = new TreeSet<String>();
         for (String person : newFriends) {
            newNewFriends.addAll(friendMap.get(person));
         }
         newNewFriends.removeAll(oldFriends);
         newFriends = newNewFriends;
         System.out.println("    Level " + level + ": " + newFriends);
      }
      
      if (newFriends.contains(target)) {
         System.out.println(target + " found at level " + level);
      } else {
         System.out.println(target + " not found");
      }
   }
}