// Core Part about Movie Recommendations 

// at Danube.co.uk

//========================================

object M2 { // for purposes of generating a jar

import io.Source

import scala.util._

// (1) Implement the function get_csv_url which takes an url-string

//     as argument and requests the corresponding file. The two urls

//     of interest are ratings_url and movies_url, which correspond 

//     to CSV-files.

//     The function should return the CSV file appropriately broken

//     up into lines, and the first line should be dropped (that is without

//     the header of the CSV file). The result is a list of strings (lines

//     in the file).

def get_csv_url(url: String) : List[String] = {

  val csv = Source.fromURL(url)("ISO-8859-1")

  csv.mkString.split("\n").toList.drop(1)

}

val ratings_url = """https://nms.kcl.ac.uk/christian.urban/ratings.csv"""

val movies_url = """https://nms.kcl.ac.uk/christian.urban/movies.csv"""

// test cases

//val ratings = get_csv_url(ratings_url)

//val movies = get_csv_url(movies_url)

//ratings.length  // 87313

//movies.length   // 9742

// (2) Implement two functions that process the CSV files. The ratings

//     function filters out all ratings below 4 and returns a list of 

//     (userID, movieID) pairs. The movies function just returns a list 

//     of (movieId, title) pairs.

def process_ratings(lines: List[String]) : List[(String, String)] = {

  for (cols <- lines.map(_.split(",").toList); 

       if (cols(2).toInt >= 4)) yield (cols(0), cols(1))  

}

def process_movies(lines: List[String]) : List[(String, String)] = {

  for (cols <- lines.map(_.split(",").toList)) yield (cols(0), cols(1))  

}

// test cases

//val good_ratings = process_ratings(ratings)

//val movie_names = process_movies(movies)

//good_ratings.length   //48580

//movie_names.length    // 9742

// (3) Implement a grouping function that calulates a map

//     containing the userIds and all the corresponding recommendations 

//     (list of movieIds). This  should be implemented in a tail

//     recursive fashion, using a map m as accumulator. This map

//     is set to Map() at the beginning of the claculation.

def groupById(ratings: List[(String, String)], 

              m: Map[String, List[String]]) : Map[String, List[String]] = ratings match {

  case Nil => m

  case (id, mov) :: rest => {

    val old_ratings = m.getOrElse (id, Nil)

    val new_ratings = m + (id -> (mov :: old_ratings))

    groupById(rest, new_ratings)

  }

}

// test cases

//val ratings_map = groupById(good_ratings, Map())

//val movies_map = movie_names.toMap

//ratings_map.get("414").get.map(movies_map.get(_)) // most prolific recommender with 1227 positive ratings

//ratings_map.get("474").get.map(movies_map.get(_)) // second-most prolific recommender with 787 positive ratings

//ratings_map.get("214").get.map(movies_map.get(_)) // least prolific recommender with only 1 positive rating

//(4) Implement a function that takes a ratings map and a movie_name as argument.

// The function calculates all suggestions containing

// the movie mov in its recommendations. It returns a list of all these

// recommendations (each of them is a list and needs to have mov deleted, 

// otherwise it might happen we recommend the same movie).

def favourites(m: Map[String, List[String]], mov: String) : List[List[String]] = 

  (for (id <- m.keys.toList;

        if m(id).contains(mov)) yield m(id).filter(_ != mov))

// test cases

// movie ID "912" -> Casablanca (1942)

//          "858" -> Godfather

//          "260" -> Star Wars: Episode IV - A New Hope (1977)

//favourites(ratings_map, "912").length  // => 80

// That means there are 80 users that recommend the movie with ID 912.

// Of these 80  users, 55 gave a good rating to movie 858 and

// 52 a good rating to movies 260, 318, 593.

// (5) Implement a suggestions function which takes a rating

// map and a movie_name as arguments. It calculates all the recommended

// movies sorted according to the most frequently suggested movie(s) first.

def suggestions(recs: Map[String, List[String]], 

                    mov_name: String) : List[String] = {

  val favs = favourites(recs, mov_name).flatten

  val favs_counted = favs.groupBy(identity).view.mapValues(_.size).toList

  val favs_sorted = favs_counted.sortBy(_._2).reverse

  favs_sorted.map(_._1)

}

// test cases

//suggestions(ratings_map, "912")

//suggestions(ratings_map, "912").length  

// => 4110 suggestions with List(858, 260, 318, 593, ...)

//    being the most frequently suggested movies

// (6) Implement recommendations functions which generates at most

// *two* of the most frequently suggested movies. It Returns the 

// actual movie names, not the movieIDs.

def recommendations(recs: Map[String, List[String]],

                   movs: Map[String, String],

                   mov_name: String) : List[String] =

  suggestions(recs, mov_name).take(2).map(movs.get(_).get)                 

// testcases

// recommendations(ratings_map, movies_map, "912")

//   => List(Godfather, Star Wars: Episode IV - A NewHope (1977))

//recommendations(ratings_map, movies_map, "260")

//   => List(Star Wars: Episode V - The Empire Strikes Back (1980), 

//           Star Wars: Episode VI - Return of the Jedi (1983))

// recommendations(ratings_map, movies_map, "2")

//   => List(Lion King, Jurassic Park (1993))

// recommendations(ratings_map, movies_map, "0")

//   => Nil

// recommendations(ratings_map, movies_map, "1")

//   => List(Shawshank Redemption, Forrest Gump (1994))

// recommendations(ratings_map, movies_map, "4")

//   => Nil  (there are three ratings for this movie in ratings.csv but they are not positive)     

}