feat: add book categorisation in transcripts

internal/handler/transcription.go

@@ -3,6 +3,7 @@ package handler
 import (
 	"net/http"
 	"strconv"
+	"strings"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/prabhupadasays/spsays-bff/internal/repository"
@@ -70,6 +71,29 @@ func (h *TranscriptionHandler) GetByType(w http.ResponseWriter, r *http.Request)
 	response.JSON(w, http.StatusOK, docs)
 }
 
+func (h *TranscriptionHandler) GetBooks(w http.ResponseWriter, r *http.Request) {
+	docs, err := h.repo.GetBooks(r.Context())
+	if err != nil {
+		response.Error(w, http.StatusInternalServerError, "failed to fetch books")
+		return
+	}
+	response.JSON(w, http.StatusOK, docs)
+}
+
+func (h *TranscriptionHandler) GetByBook(w http.ResponseWriter, r *http.Request) {
+	code := strings.ToUpper(chi.URLParam(r, "book"))
+	if h.repo.BookTitle(code) == "" {
+		response.Error(w, http.StatusNotFound, "unknown book")
+		return
+	}
+	docs, err := h.repo.GetByBook(r.Context(), code)
+	if err != nil {
+		response.Error(w, http.StatusInternalServerError, "failed to fetch transcriptions")
+		return
+	}
+	response.JSON(w, http.StatusOK, docs)
+}
+
 func (h *TranscriptionHandler) GetYears(w http.ResponseWriter, r *http.Request) {
 	docs, err := h.repo.GetYears(r.Context())
 	if err != nil {

internal/repository/transcription_repo.go

@@ -180,6 +180,80 @@ func (r *TranscriptionRepo) GetPlaces(ctx context.Context) ([]bson.M, error) {
 	return results, nil
 }
 
+// TranscriptionBooks is the canonical set of scriptures that appear in the
+// free-text `reference` field of transcriptions (Prabhupāda's lectures are
+// commentaries on specific verses). Browsing by "book" is derived from the
+// reference string — there are no structured book/chapter columns. Ordered for
+// display fallbacks; the listing endpoints filter out books with no transcripts.
+var TranscriptionBooks = []struct{ Code, Title string }{
+	{"SB", "Śrīmad-Bhāgavatam"},
+	{"BG", "Bhagavad-gītā"},
+	{"CC", "Caitanya-caritāmṛta"},
+	{"BS", "Brahma-saṁhitā"},
+	{"NOD", "The Nectar of Devotion"},
+	{"ISO", "Śrī Īśopaniṣad"},
+}
+
+// bookTitle returns the display title for a known book code, or "" if unknown.
+func bookTitle(code string) string {
+	for _, b := range TranscriptionBooks {
+		if b.Code == code {
+			return b.Title
+		}
+	}
+	return ""
+}
+
+// bookRefFilter matches published transcriptions whose reference begins with the
+// given book code. The trailing "([^A-Za-z]|$)" is a boundary so e.g. "BS" can't
+// match "BG"; no code is a prefix of another, so this is unambiguous.
+func bookRefFilter(code string) bson.M {
+	return bson.M{
+		"isPublished": true,
+		"reference":   bson.M{"$regex": "^" + code + "([^A-Za-z]|$)"},
+	}
+}
+
+// GetBooks returns the books that have at least one transcript, as
+// {_id, title, count} — mirroring the {_id, count} shape the frontend already
+// consumes for years/places. One count query per book (like GetTypeDistribution).
+func (r *TranscriptionRepo) GetBooks(ctx context.Context) ([]bson.M, error) {
+	results := make([]bson.M, 0, len(TranscriptionBooks))
+	for _, b := range TranscriptionBooks {
+		count, err := r.col.CountDocuments(ctx, bookRefFilter(b.Code))
+		if err != nil {
+			return nil, err
+		}
+		if count > 0 {
+			results = append(results, bson.M{"_id": b.Code, "title": b.Title, "count": count})
+		}
+	}
+	return results, nil
+}
+
+// GetByBook lists the transcript summaries for a book code, sorted
+// chronologically (same projection/sort as GetByType).
+func (r *TranscriptionRepo) GetByBook(ctx context.Context, code string) ([]TranscriptionSummaryDoc, error) {
+	opts := options.Find().
+		SetSort(bson.D{{Key: "year", Value: 1}, {Key: "month", Value: 1}, {Key: "day", Value: 1}}).
+		SetProjection(transcriptionSummaryProjection)
+	cursor, err := r.col.Find(ctx, bookRefFilter(code), opts)
+	if err != nil {
+		return nil, err
+	}
+	defer cursor.Close(ctx)
+	var results []TranscriptionSummaryDoc
+	if err := cursor.All(ctx, &results); err != nil {
+		return nil, err
+	}
+	return results, nil
+}
+
+// BookTitle exposes the registry lookup to the handler for validation.
+func (r *TranscriptionRepo) BookTitle(code string) string {
+	return bookTitle(code)
+}
+
 func (r *TranscriptionRepo) GetTypeDistribution(ctx context.Context) (int64, int64, error) {
 	lectureCount, err := r.col.CountDocuments(ctx, bson.M{"type": "lecture", "isPublished": true})
 	if err != nil {

internal/server/server.go

@@ -626,9 +626,11 @@ func (s *Server) setupRouter() {
 			r.Get("/years", s.transcriptionH.GetYears)
 			r.Get("/places", s.transcriptionH.GetPlaces)
 			r.Get("/types", s.transcriptionH.GetTypeDistribution)
+			r.Get("/books", s.transcriptionH.GetBooks)
 			r.Get("/year/{year}", s.transcriptionH.GetByYear)
 			r.Get("/place/{place}", s.transcriptionH.GetByPlace)
 			r.Get("/type/{type}", s.transcriptionH.GetByType)
+			r.Get("/book/{book}", s.transcriptionH.GetByBook)
 			r.Get("/adjacent/{slug}", s.transcriptionH.GetAdjacent)
 			r.Get("/{slug}", s.transcriptionH.GetBySlug)
 		})