memby/server/internal/recommend/engine_test.go

package recommend

import (
	"context"
	"encoding/json"
	"errors"
	"io"
	"log/slog"
	"net/url"
	"strings"
	"sync"
	"testing"

	"github.com/ponzischeme89/memby/server/internal/emby"
)

// fakeSource records the queries the engine makes and replays canned answers.
type fakeSource struct {
	mu sync.Mutex

	itemsByFilter map[string][]json.RawMessage
	similar       map[string][]json.RawMessage
	itemsErr      error
	similarErr    error

	genreQueries []string
	similarSeeds []string
}

func (f *fakeSource) Items(_ context.Context, _ emby.Credentials, params url.Values) (*emby.ItemsResult, error) {
	f.mu.Lock()
	defer f.mu.Unlock()
	if f.itemsErr != nil {
		return nil, f.itemsErr
	}
	if genres := params.Get("Genres"); genres != "" {
		f.genreQueries = append(f.genreQueries, genres)
	}
	key := params.Get("Filters")
	return &emby.ItemsResult{Items: f.itemsByFilter[key]}, nil
}

func (f *fakeSource) Similar(_ context.Context, _ emby.Credentials, itemID string, _ url.Values) (*emby.ItemsResult, error) {
	f.mu.Lock()
	defer f.mu.Unlock()
	f.similarSeeds = append(f.similarSeeds, itemID)
	if f.similarErr != nil {
		return nil, f.similarErr
	}
	return &emby.ItemsResult{Items: f.similar[itemID]}, nil
}

func raw(id, name, itemType string, genres ...string) json.RawMessage {
	quoted := make([]string, 0, len(genres))
	for _, g := range genres {
		quoted = append(quoted, `"`+g+`"`)
	}
	return json.RawMessage(`{"Id":"` + id + `","Name":"` + name + `","Type":"` + itemType +
		`","Genres":[` + strings.Join(quoted, ",") + `],"CommunityRating":7.5}`)
}

func testEngine(source Source) *Engine {
	engine := NewEngine(source, slog.New(slog.NewTextHandler(io.Discard, nil)))
	engine.MinRowItems = 2
	return engine
}

func TestBuildRowsProducesSimilarAndHistoryRows(t *testing.T) {
	source := &fakeSource{
		itemsByFilter: map[string][]json.RawMessage{
			"IsResumable": {raw("ep1", "Good News", "Episode", "Drama")},
			"IsPlayed":    {raw("m1", "Dune", "Movie", "Science Fiction")},
			"IsFavorite":  {raw("m2", "Arrival", "Movie", "Science Fiction")},
			"IsUnplayed": {
				raw("c1", "Blade Runner", "Movie", "Science Fiction"),
				raw("c2", "Solaris", "Movie", "Science Fiction"),
				raw("c3", "Barbie", "Movie", "Comedy"),
			},
		},
		similar: map[string][]json.RawMessage{
			"ep1": {raw("s1", "Devs", "Series", "Drama"), raw("s2", "Mr Robot", "Series", "Drama")},
			"m1":  {raw("s3", "Foundation", "Series", "Science Fiction"), raw("s4", "Arrival II", "Movie", "Science Fiction")},
		},
	}

	rows, err := testEngine(source).BuildRows(context.Background(), emby.Credentials{UserID: "u1"})
	if err != nil {
		t.Fatalf("BuildRows: %v", err)
	}
	if len(rows) != 3 {
		t.Fatalf("expected 2 similar rows + 1 history row, got %d: %+v", len(rows), rowTitles(rows))
	}

	if rows[0].Kind != "similar" || !strings.HasPrefix(rows[0].Title, "Because you watched ") {
		t.Fatalf("unexpected first row: %+v", rows[0])
	}
	last := rows[len(rows)-1]
	if last.Kind != "recommended" || last.Title != "Recommended from your watching history" {
		t.Fatalf("unexpected history row: %+v", last)
	}
	if last.ID != "recommended" {
		t.Fatalf("history row id should be stable, got %q", last.ID)
	}
}

func TestBuildRowsQueriesTheProfilesTopGenres(t *testing.T) {
	source := &fakeSource{
		itemsByFilter: map[string][]json.RawMessage{
			"IsPlayed": {
				raw("m1", "Dune", "Movie", "Science Fiction"),
				raw("m2", "Alien", "Movie", "Science Fiction", "Horror"),
			},
			"IsUnplayed": {raw("c1", "Solaris", "Movie", "Science Fiction")},
		},
	}

	if _, err := testEngine(source).BuildRows(context.Background(), emby.Credentials{UserID: "u1"}); err != nil {
		t.Fatalf("BuildRows: %v", err)
	}

	if len(source.genreQueries) != 1 {
		t.Fatalf("expected a single OR'd genre query, got %v", source.genreQueries)
	}
	// Emby reads "|" as OR, so one query covers every top genre.
	if !strings.HasPrefix(source.genreQueries[0], "Science Fiction") {
		t.Fatalf("heaviest genre should lead the query, got %q", source.genreQueries[0])
	}
}

func TestBuildRowsExcludesAlreadyWatchedFromSimilarRow(t *testing.T) {
	source := &fakeSource{
		itemsByFilter: map[string][]json.RawMessage{
			"IsPlayed": {raw("m1", "Dune", "Movie", "Science Fiction")},
		},
		similar: map[string][]json.RawMessage{
			// Emby suggests something the user already finished; it must not appear.
			"m1": {raw("m1", "Dune", "Movie", "Science Fiction"), raw("s1", "Foundation", "Series", "Science Fiction")},
		},
	}
	engine := testEngine(source)
	engine.MinRowItems = 1

	rows, err := engine.BuildRows(context.Background(), emby.Credentials{UserID: "u1"})
	if err != nil {
		t.Fatalf("BuildRows: %v", err)
	}

	for _, row := range rows {
		for _, item := range row.Items {
			if strings.Contains(string(item), `"Id":"m1"`) {
				t.Fatalf("row %q contained an already-watched item", row.ID)
			}
		}
	}
}

func TestBuildRowsDropsRowsShorterThanTheMinimum(t *testing.T) {
	source := &fakeSource{
		itemsByFilter: map[string][]json.RawMessage{
			"IsPlayed":   {raw("m1", "Dune", "Movie", "Science Fiction")},
			"IsUnplayed": {raw("c1", "Solaris", "Movie", "Science Fiction")},
		},
		similar: map[string][]json.RawMessage{
			"m1": {raw("s1", "Foundation", "Series", "Science Fiction")},
		},
	}
	engine := testEngine(source)
	engine.MinRowItems = 5

	rows, err := engine.BuildRows(context.Background(), emby.Credentials{UserID: "u1"})
	if err != nil {
		t.Fatalf("BuildRows: %v", err)
	}
	if len(rows) != 0 {
		t.Fatalf("expected short rows to be dropped, got %v", rowTitles(rows))
	}
}

func TestBuildRowsReturnsNothingForAUserWithNoHistory(t *testing.T) {
	source := &fakeSource{itemsByFilter: map[string][]json.RawMessage{}}

	rows, err := testEngine(source).BuildRows(context.Background(), emby.Credentials{UserID: "new"})
	if err != nil {
		t.Fatalf("BuildRows: %v", err)
	}
	if len(rows) != 0 {
		t.Fatalf("a new user should get no rows, got %v", rowTitles(rows))
	}
	if len(source.similarSeeds) != 0 {
		t.Fatal("no seeds means no similarity lookups should be attempted")
	}
}

// A failing similarity lookup is one dead row, not a dead home screen.
func TestBuildRowsSurvivesASimilarLookupFailure(t *testing.T) {
	source := &fakeSource{
		itemsByFilter: map[string][]json.RawMessage{
			"IsPlayed": {raw("m1", "Dune", "Movie", "Science Fiction")},
			"IsUnplayed": {
				raw("c1", "Solaris", "Movie", "Science Fiction"),
				raw("c2", "Blade Runner", "Movie", "Science Fiction"),
			},
		},
		similarErr: errors.New("emby is unwell"),
	}

	rows, err := testEngine(source).BuildRows(context.Background(), emby.Credentials{UserID: "u1"})
	if err != nil {
		t.Fatalf("BuildRows should not fail: %v", err)
	}
	if len(rows) != 1 || rows[0].Kind != "recommended" {
		t.Fatalf("expected the history row to survive, got %v", rowTitles(rows))
	}
}

func TestBuildRowsFailsWhenHistoryCannotBeRead(t *testing.T) {
	source := &fakeSource{itemsErr: errors.New("emby down")}

	if _, err := testEngine(source).BuildRows(context.Background(), emby.Credentials{UserID: "u1"}); err == nil {
		t.Fatal("expected an error when the history queries fail")
	}
}

func rowTitles(rows []Row) []string {
	out := make([]string, 0, len(rows))
	for _, row := range rows {
		out = append(out, row.Title)
	}
	return out
}