Reduced recommended anime function complexity

pages/recommended/affinity.go

@@ -0,0 +1,48 @@
+package recommended
+
+import (
+	"math"
+
+	"github.com/animenotifier/arn"
+)
+
+func getAnimeAffinity(anime *arn.Anime, animeListItem *arn.AnimeListItem, completed *arn.AnimeList, bestGenres []string) float64 {
+	animeAffinity := anime.Score()
+
+	// Planned anime go higher
+	if animeListItem != nil && animeListItem.Status == arn.AnimeListStatusPlanned {
+		animeAffinity += 10.0
+	}
+
+	// Anime whose high-ranked prequel you did not see are lower ranked
+	prequels := anime.Prequels()
+
+	for _, prequel := range prequels {
+		item := completed.Find(prequel.ID)
+
+		// Filter out unimportant prequels
+		if prequel.Score() < anime.Score()/2 {
+			continue
+		}
+
+		if item == nil {
+			animeAffinity -= 20.0
+		}
+	}
+
+	// Give favorite genre bonus if we have enough completed anime
+	if len(completed.Items) >= genreBonusCompletedAnimeThreshold {
+		bestGenreCount := 0
+
+		for _, genre := range anime.Genres {
+			if arn.Contains(bestGenres, genre) {
+				bestGenreCount++
+			}
+		}
+
+		// Use square root to dampen the bonus of additional best genres
+		animeAffinity += math.Sqrt(float64(bestGenreCount)) * 7.0
+	}
+
+	return animeAffinity
+}