package com.google.sps.data;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Sets;
import com.google.sps.data.Book;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class GenreRecommender {
  private List<Book> books;
  private Map<Book, Set<String>> bookToGenres;
  private Map<String, Set<Book>> genreToBooks;

  /** 
   * Constructor that takes in a list of books 
   * and populates class variables appropriately.
   *
   * @param books: List of Book objects for the recommendation algorithm
   */ 
  public GenreRecommender(List<Book> books) {
    this.books = books;
    bookToGenres = new HashMap<Book, Set<String>>();
    genreToBooks = new HashMap<String, Set<Book>>();
    for (Book book : books) {
      Set<String> genres = book.genre();
      bookToGenres.put(book, genres);
      for (String genre : genres) {
        if (genreToBooks.containsKey(genre)) {
          genreToBooks.get(genre).add(book);
        } else {
          genreToBooks.put(genre, Sets.newHashSet(book));
        }
      }
    }
  }

  /**
  * Takes in a Book object and returns a set of genres 
  * of that book
  * 
  * @param book: Book object
  * @return ImmutableSet of genres of that book
  */
  public ImmutableSet<String> getGenres(Book book) {
    Set<String> genres = bookToGenres.get(book);
    if (genres == null) {
      return ImmutableSet.of();
    }
    return ImmutableSet.copyOf(genres);
  }

  /**
  * Takes in a set of genres and returns a set of Book objects
  * that have exactly the genres from the set. 
  * 
  * @param genres: Set of genres (as Strings)
  * @return ImmutableSet of books that have exactly these genres
  */
  public ImmutableSet<Book> getBooksWithExactGenres(Set<String> genres) {
    Set<Book> matchingBooks = new HashSet<Book>();
    for (Book book : bookToGenres.keySet()) {
      if (bookToGenres.get(book).equals(genres)) {
        matchingBooks.add(book);
      }
    }
    if (matchingBooks.isEmpty()) {
      return ImmutableSet.of();
    }
    return ImmutableSet.copyOf(matchingBooks);
  }
}

@@ -1918,19 +1918,36 @@
 ) %7B%0A    
-Set
+ImmutableSet.Builder
 %3CBook%3E m
@@ -1965,23 +1965,36 @@
 s = new 
-HashSet
+ImmutableSet.Builder
 %3CBook%3E()
@@ -2147,24 +2147,74 @@
     
-if (matchingBook
+ImmutableSet%3CBook%3E matches = matchingBooks.build();%0A    if (matche
 s.is
@@ -2277,42 +2277,15 @@
 urn 
-ImmutableSet.copyOf(matchingBooks)
+matches
 ;%0A  

use builder where possible