refactor: split recommendation engine into subpackage

internal/anime/recommendations/recommendations_test.go

@@ -0,0 +1,226 @@
+package recommendations
+
+import (
+	"database/sql"
+	"mal/integrations/jikan"
+	"mal/internal/db"
+	"mal/internal/domain"
+	"testing"
+	"time"
+)
+
+func TestRecommendationEntryWeightPrioritizesCommittedRecentHistory(t *testing.T) {
+	now := time.Date(2026, time.June, 4, 12, 0, 0, 0, time.UTC)
+
+	completed := recommendationEntryWeight(now, db.GetUserWatchListRow{
+		Status:         "completed",
+		UpdatedAt:      now.Add(-24 * time.Hour),
+		CurrentEpisode: sql.NullInt64{Int64: 12, Valid: true},
+	})
+	planned := recommendationEntryWeight(now, db.GetUserWatchListRow{
+		Status:    "plan_to_watch",
+		UpdatedAt: now.Add(-24 * time.Hour),
+	})
+
+	if completed <= planned {
+		t.Fatalf("expected completed history to outrank planned history, got completed=%f planned=%f", completed, planned)
+	}
+}
+
+func TestBuildRecommendationSeedsFiltersUnsupportedStatuses(t *testing.T) {
+	now := time.Date(2026, time.June, 4, 12, 0, 0, 0, time.UTC)
+
+	seeds := buildRecommendationSeeds(now, []db.GetUserWatchListRow{
+		{AnimeID: 1, Status: "dropped", UpdatedAt: now},
+		{AnimeID: 2, Status: "watching", UpdatedAt: now},
+		{AnimeID: 3, Status: "completed", UpdatedAt: now},
+	})
+
+	if len(seeds) != 2 {
+		t.Fatalf("expected 2 valid seeds, got %d", len(seeds))
+	}
+	if seeds[0].animeID != 2 || seeds[1].animeID != 3 {
+		t.Fatalf("unexpected seed ordering: %+v", seeds)
+	}
+}
+
+func TestScoreRecommendationCandidateRewardsProfileOverlap(t *testing.T) {
+	now := time.Date(2026, time.June, 4, 12, 0, 0, 0, time.UTC)
+	profile := userTasteProfile{
+		genres: map[int]float64{
+			1: 2.0,
+		},
+		themes:       map[int]float64{},
+		studios:      map[int]float64{},
+		demographics: map[int]float64{},
+	}
+
+	matching := scoreRecommendationCandidate(now, profile, jikan.Anime{
+		MalID:      10,
+		Genres:     []jikan.NamedEntity{{MalID: 1, Name: "Action"}},
+		Popularity: 100,
+		Score:      8.0,
+	}, 5.0, 0)
+	nonMatching := scoreRecommendationCandidate(now, profile, jikan.Anime{
+		MalID:      11,
+		Genres:     []jikan.NamedEntity{{MalID: 2, Name: "Drama"}},
+		Popularity: 100,
+		Score:      8.0,
+	}, 5.0, 0)
+
+	if matching.score <= nonMatching.score {
+		t.Fatalf("expected matching candidate to score higher, got matching=%f nonMatching=%f", matching.score, nonMatching.score)
+	}
+}
+
+func TestBuildTasteProfileUsesSeedWeights(t *testing.T) {
+	now := time.Date(2026, time.June, 4, 12, 0, 0, 0, time.UTC)
+
+	profile := buildTasteProfile(
+		now,
+		[]recommendationSeed{
+			{animeID: 1, weight: 2.0},
+			{animeID: 2, weight: 0.5},
+		},
+		[]jikan.Anime{
+			{
+				MalID:        1,
+				Airing:       true,
+				Year:         2026,
+				Genres:       []jikan.NamedEntity{{MalID: 1, Name: "Action"}},
+				Themes:       []jikan.NamedEntity{{MalID: 10, Name: "Team Sports"}},
+				Studios:      []jikan.NamedEntity{{MalID: 20, Name: "Production I.G"}},
+				Demographics: []jikan.NamedEntity{{MalID: 30, Name: "Shounen"}},
+			},
+			{
+				MalID:        2,
+				Year:         2001,
+				Genres:       []jikan.NamedEntity{{MalID: 2, Name: "Drama"}},
+				Themes:       []jikan.NamedEntity{{MalID: 11, Name: "School"}},
+				Studios:      []jikan.NamedEntity{{MalID: 21, Name: "Madhouse"}},
+				Demographics: []jikan.NamedEntity{{MalID: 31, Name: "Seinen"}},
+			},
+		},
+	)
+
+	if profile.genres[1] <= profile.genres[2] {
+		t.Fatalf("expected stronger seed genre to carry more weight, got profile=%+v", profile.genres)
+	}
+	if !profile.prefersAiring {
+		t.Fatal("expected weighted profile to prefer airing anime")
+	}
+	if !profile.prefersRecent {
+		t.Fatal("expected weighted profile to prefer recent anime")
+	}
+}
+
+func TestBuildProfileSearchQueriesIncludesTasteSignals(t *testing.T) {
+	profile := userTasteProfile{
+		genres: map[int]float64{
+			1: 2.0,
+			2: 1.5,
+			3: 0.2,
+		},
+		themes: map[int]float64{
+			10: 1.4,
+		},
+		studios: map[int]float64{
+			20: 1.0,
+		},
+		demographics: map[int]float64{
+			30: 1.2,
+		},
+	}
+
+	queries := buildProfileSearchQueries(profile)
+
+	if !hasGenreSearchQuery(queries, 1) {
+		t.Fatalf("expected strongest genre query, got %+v", queries)
+	}
+	if !hasGenreSearchQuery(queries, 10) {
+		t.Fatalf("expected theme query, got %+v", queries)
+	}
+	if !hasGenreSearchQuery(queries, 30) {
+		t.Fatalf("expected demographic query, got %+v", queries)
+	}
+	if !hasStudioSearchQuery(queries, 20) {
+		t.Fatalf("expected studio query, got %+v", queries)
+	}
+}
+
+func TestRerankRecommendationCandidatesSpreadsRepeatedGenres(t *testing.T) {
+	const sportsGenreID = 30
+
+	candidates := []recommendationCandidate{
+		{anime: testRecommendationAnime(1, sportsGenreID), score: 10},
+		{anime: testRecommendationAnime(2, sportsGenreID), score: 9.9},
+		{anime: testRecommendationAnime(3, sportsGenreID), score: 9.8},
+		{anime: testRecommendationAnime(4, sportsGenreID), score: 9.7},
+		{anime: testRecommendationAnime(5, sportsGenreID), score: 9.6},
+		{anime: testRecommendationAnime(6, 1), score: 9.5},
+		{anime: testRecommendationAnime(7, 2), score: 9.4},
+		{anime: testRecommendationAnime(8, 3), score: 9.3},
+	}
+
+	reranked := rerankRecommendationCandidates(candidates, 8)
+	if len(reranked) < 5 {
+		t.Fatalf("expected enough reranked candidates, got %d", len(reranked))
+	}
+
+	for i := 0; i <= len(reranked)-5; i++ {
+		if allHaveGenre(reranked[i:i+5], sportsGenreID) {
+			t.Fatalf("expected reranker to avoid five sports anime in a row, got %+v", animeIDs(reranked))
+		}
+	}
+}
+
+func testRecommendationAnime(id int, genreID int) jikan.Anime {
+	return jikan.Anime{
+		MalID:  id,
+		Genres: []jikan.NamedEntity{{MalID: genreID, Name: "Genre"}},
+	}
+}
+
+func allHaveGenre(animes []domain.Anime, genreID int) bool {
+	for _, anime := range animes {
+		hasGenre := false
+		for _, genre := range anime.Genres {
+			if genre.MalID == genreID {
+				hasGenre = true
+				break
+			}
+		}
+		if !hasGenre {
+			return false
+		}
+	}
+	return true
+}
+
+func animeIDs(animes []domain.Anime) []int {
+	ids := make([]int, 0, len(animes))
+	for _, anime := range animes {
+		ids = append(ids, anime.MalID)
+	}
+	return ids
+}
+
+func hasGenreSearchQuery(queries []profileSearchQuery, genreID int) bool {
+	for _, query := range queries {
+		for _, id := range query.genreIDs {
+			if id == genreID {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func hasStudioSearchQuery(queries []profileSearchQuery, studioID int) bool {
+	for _, query := range queries {
+		if query.studioID == studioID {
+			return true
+		}
+	}
+	return false
+}