feat: added endpoint to find common films of user and his friend

src/main/java/ru/yandex/practicum/filmorate/controller/FilmController.java

@@ -69,6 +69,13 @@ public void deleteLike(@PathVariable @Positive long id,
         filmService.removeLike(id, userId);
     }
 
+    @GetMapping("/common")
+    public Collection<FilmDto> findCommonFilms(@RequestParam(name = "userId") @Positive long userId,
+                                               @RequestParam(name = "friendId") @Positive long friendId) {
+            log.trace("Find common films requested for user {} and friend {}", userId, friendId);
+           return filmService.findCommonFilms(userId, friendId);
+    }
+
     @GetMapping("/popular")
     public Collection<FilmDto> findPopular(@RequestParam(defaultValue = "10") @Positive int count) {
         log.trace("Find popular film requested with count: {}", count);

src/main/java/ru/yandex/practicum/filmorate/repository/film/FilmRepository.java

@@ -17,4 +17,6 @@ public interface FilmRepository {
     void deleteById(long id);
 
     Collection<Film> findTopPopularFilms(int count);
+
+    Collection<Film> findCommonFilms(long userId, long friendId);
 }

src/main/java/ru/yandex/practicum/filmorate/repository/film/JdbcFilmRepository.java

@@ -161,6 +161,40 @@ ORDER BY COUNT(fl.user_id) DESC, f.film_id
         return jdbc.query(selectTopFilmsSql, params, filmResultSetExtractor);
     }
 
+    @Override
+    public Collection<Film> findCommonFilms(long userId, long friendId) {
+        String selectCommonFilmsSql = """
+                SELECT f.film_id,
+                       f.name,
+                       f.description,
+                       f.release_date,
+                       f.duration_in_minutes,
+                       f.mpa_id,
+                       mr.name AS mpa_name,
+                       g.genre_id,
+                       g.name AS genre_name
+                FROM films f
+                JOIN mpa_ratings mr ON f.mpa_id = mr.mpa_id
+                LEFT JOIN film_genres fg ON f.film_id = fg.film_id
+                LEFT JOIN genres g ON g.genre_id = fg.genre_id
+                LEFT JOIN likes fl ON f.film_id = fl.film_id
+                WHERE f.film_id in (SELECT l1.film_id
+                                    FROM likes l1
+                                    WHERE l1.user_id = :user_id
+                                    INTERSECT
+                                    SELECT l2.film_id
+                                    FROM likes l2
+                                    WHERE l2.user_id = :friend_id)
+                GROUP BY f.film_id, f.name, g.genre_id
+                ORDER BY COUNT(fl.user_id) DESC, f.film_id
+                """;
+        MapSqlParameterSource params = new MapSqlParameterSource()
+                .addValue("user_id", userId)
+                .addValue("friend_id", friendId);
+
+        return jdbc.query(selectCommonFilmsSql, params, filmResultSetExtractor);
+    }
+
     private void saveGenres(Set<Genre> genres, long filmId) {
         String insertGenresSql = """
                 INSERT INTO film_genres (film_id, genre_id)

src/main/java/ru/yandex/practicum/filmorate/repository/friendship/FriendshipsRepository.java

@@ -4,4 +4,6 @@ public interface FriendshipsRepository {
     void addFriendship(long userId, long friendId);
 
     void removeFriendship(long userId, long friendId);
+
+    boolean isFriends(long userId, long friendId);
 }

src/main/java/ru/yandex/practicum/filmorate/repository/friendship/JdbcFriendshipsRepository.java

@@ -28,9 +28,23 @@ public void removeFriendship(long userId, long friendId) {
         jdbc.update(deleteFriendshipSql, params);
     }
 
+    @Override
+    public boolean isFriends(long userId, long friendId) {
+        String checkFriendshipSql = """
+                SELECT EXISTS (
+                    SELECT 1
+                    FROM friendships
+                    WHERE user_id1 = :user_id AND user_id2 = :friend_id)""";
+        MapSqlParameterSource params = new MapSqlParameterSource()
+                .addValue("user_id", userId)
+                .addValue("friend_id", friendId);
+
+        return Boolean.TRUE.equals(jdbc.queryForObject(checkFriendshipSql, params, Boolean.class));
+    }
+
     private MapSqlParameterSource getParameterMap(long userId, long friendId) {
         return new MapSqlParameterSource()
-        .addValue("user_id1", userId)
-        .addValue("user_id2", friendId);
+                .addValue("user_id1", userId)
+                .addValue("user_id2", friendId);
     }
 }

src/main/java/ru/yandex/practicum/filmorate/service/FilmService.java

@@ -22,4 +22,6 @@ public interface FilmService {
     void removeLike(long filmId, long userId);
 
     Collection<FilmDto> findFilmsWithTopLikes(int count);
+
+    Collection<FilmDto> findCommonFilms(long userId, long friendId);
 }

src/main/java/ru/yandex/practicum/filmorate/service/FilmServiceImpl.java

@@ -126,6 +126,17 @@ public Collection<FilmDto> findFilmsWithTopLikes(int count) {
                 .toList();
     }
 
+    @Override
+    public Collection<FilmDto> findCommonFilms(long userId, long friendId) {
+        throwIfUserNotFound(userId);
+        throwIfUserNotFound(friendId);
+
+        return filmRepository.findCommonFilms(userId, friendId)
+                .stream()
+                .map(FilmMapper::toFilmDto)
+                .toList();
+    }
+
     private void throwIfUserNotFound(long userId) {
         userRepository.findById(userId)
                 .orElseThrow(NotFoundException.supplier("User with id %d not found", userId));