package com.google.sps.data;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableMap.Builder;
import com.google.common.collect.ImmutableSet;
import com.google.sps.data.Book;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.util.Scanner;
import java.util.Set;

/**
 * Class that takes in an InputStream as the constructor parameter
 * and populates a list of Books with title, genre, and reviews.
 */
public class BookReader {
  private final File file;
  public BookReader(String path) {
    this.file = new File(path);
  }

  public ImmutableMap<Integer, Book> makeBookList() throws IOException {
    ImmutableMap.Builder<Integer, Book> allBooks = new Builder<Integer, Book>();
    try (Scanner scanner = new Scanner(file, "utf-8").useDelimiter("\\Z")) {
      String content = scanner.next().replaceAll("[\\r\\n]+", "");
      String[] lines = content.split("NEXTBOOK"); // lines[i] represents one row of the file

      String current_title = "";
      Book.Builder current_builder = Book.builder().title("null");
      int currentId = 0;

      for (int i = 1; i < lines.length; i++) {
        String[] cells = lines[i].split(",");
        String title = cells[0];
        Set<String> genre = getGenreSet(cells[8]);
        String review = cells[13];
        if (current_title.equals(title)) {
          // add review:
          current_builder.addReview(review);
        } else {
          // close old book:
          if (i != 1) {
            Book book = current_builder.build();
            allBooks.put(currentId++, book);
          }
          // start building new book
          current_builder = Book.builder().title(title).genre(genre).addReview(review);
          current_title = title;
        }
      }
      Book book = current_builder.build();
      allBooks.put(currentId, book);
    } catch (Exception ex) {
      throw new IOException("Error reading CSV file", ex);
    }
    return allBooks.build();
  }

  /**
   * Helper method that takes in the list of genres as a ";"-separated string
   * and returns a set of genres
   *
   * @param genreString: ";"-separated string of genres
   * @return ImmutableSet of genres
   */
  private ImmutableSet<String> getGenreSet(String genreString) {
    ImmutableSet.Builder<String> genres = new ImmutableSet.Builder<String>();
    for (String genre : genreString.toLowerCase().split(";")) {
      genres.add(genre);
    }
    return genres.build();
  }
}

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.common.collect.ImmutableMultimap.Builder;
import com.google.common.collect.ImmutableMultimap;
import java. util. Collection;
import com.google.common.collect.ImmutableSetMultimap.Builder;
import com.google.common.collect.ImmutableSetMultimap;
import com.google.common.collect.Multimap;
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 ImmutableSetMultimap<Book, String> bookToGenres;
  private ImmutableSetMultimap<String, 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;
    ImmutableSetMultimap.Builder<Book, String> bookToGenresBuilder = new ImmutableSetMultimap.Builder<Book, String>();
    ImmutableSetMultimap.Builder<String, Book> genreToBooksBuilder = new ImmutableSetMultimap.Builder<String, Book>();
    for (Book book : books) {
      for (String genre: book.genre()) {
          bookToGenresBuilder.put(book, genre);
          genreToBooksBuilder.put(genre, book);
      }
    }
    bookToGenres = bookToGenresBuilder.build();
    genreToBooks = genreToBooksBuilder.build();
  }

  /**
   * 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) {
    ImmutableSet<String> genres = bookToGenres.get(book);
    if (genres == null) {
      return ImmutableSet.of();
    }
    return 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) {
    ImmutableSet.Builder<Book> matchingBooks = new ImmutableSet.Builder<Book>();
    for (Book book : bookToGenres.keySet()) {
      if (bookToGenres.get(book).equals(genres)) {
        matchingBooks.add(book);
      }
    }
    ImmutableSet<Book> matches = matchingBooks.build();
    if (matches.isEmpty()) {
      return ImmutableSet.of();
    }
    return matches;
  }
}
use immutableMultimap