feat: add email notification for post like

internal/handler/notification.go

@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"encoding/json"
 	"net/http"
 
 	"github.com/prabhupadasays/spsays-bff/internal/middleware"
@@ -49,3 +50,36 @@ func (h *NotificationHandler) MarkAllRead(w http.ResponseWriter, r *http.Request
 	}
 	response.NoContent(w)
 }
+
+type emailPrefsResp struct {
+	LikeEmails bool `json:"like_emails"`
+}
+
+// GetEmailPrefs — GET /notifications/email-prefs. The caller's email-notification
+// preferences (currently just aggregated like emails).
+func (h *NotificationHandler) GetEmailPrefs(w http.ResponseWriter, r *http.Request) {
+	uid := middleware.UserID(r.Context())
+	enabled, err := h.svc.LikeEmailPref(r.Context(), uid)
+	if err != nil {
+		response.Error(w, http.StatusInternalServerError, "could not load email preferences")
+		return
+	}
+	response.JSON(w, http.StatusOK, emailPrefsResp{LikeEmails: enabled})
+}
+
+// UpdateEmailPrefs — PUT /notifications/email-prefs { like_emails }.
+func (h *NotificationHandler) UpdateEmailPrefs(w http.ResponseWriter, r *http.Request) {
+	uid := middleware.UserID(r.Context())
+	var req struct {
+		LikeEmails bool `json:"like_emails"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		response.Error(w, http.StatusBadRequest, "invalid JSON body")
+		return
+	}
+	if err := h.svc.SetLikeEmailPref(r.Context(), uid, req.LikeEmails); err != nil {
+		response.Error(w, http.StatusInternalServerError, "could not update email preferences")
+		return
+	}
+	response.JSON(w, http.StatusOK, emailPrefsResp{LikeEmails: req.LikeEmails})
+}

internal/repository/social_graph_repo.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"time"
 
 	"github.com/jackc/pgx/v5"
 	"github.com/prabhupadasays/spsays-bff/internal/model"
@@ -347,25 +348,57 @@ func (r *NotificationRepo) ListByUser(ctx context.Context, userID string, limit,
 
 // UpsertLike records (or aggregates) a like notification: one row per
 // (recipient, post). On a repeat like it refreshes the most-recent actor,
-// bumps actor_count, and re-marks the row unread + most-recent. Returns the
-// new actor_count.
-func (r *NotificationRepo) UpsertLike(ctx context.Context, userID, actorID, postID string) (int, error) {
-	var count int
-	err := r.pg.Pool.QueryRow(ctx, `
-		INSERT INTO notifications (user_id, actor_id, kind, post_id, actor_count)
-		VALUES ($1, $2, 'post_like', $3, 1)
+// bumps actor_count, and re-marks the row unread + most-recent.
+//
+// It also throttles the aggregated like *email*: like_email_sent_at is stamped
+// to now() on the first like and again only once `throttle` has elapsed since
+// the last email. Returns the new actor_count and whether an email is due this
+// call (i.e. the stamp was (re)set now) — decided atomically in one statement
+// to avoid double-emailing under concurrent likes.
+func (r *NotificationRepo) UpsertLike(ctx context.Context, userID, actorID, postID string, throttle time.Duration) (count int, emailDue bool, err error) {
+	secs := int(throttle.Seconds())
+	err = r.pg.Pool.QueryRow(ctx, `
+		INSERT INTO notifications (user_id, actor_id, kind, post_id, actor_count, like_email_sent_at)
+		VALUES ($1, $2, 'post_like', $3, 1, now())
 		ON CONFLICT (user_id, post_id) WHERE kind = 'post_like'
 		DO UPDATE SET actor_id    = EXCLUDED.actor_id,
 		              actor_count  = notifications.actor_count + 1,
 		              read_at      = NULL,
-		              created_at   = now()
-		RETURNING actor_count`,
-		userID, actorID, postID,
-	).Scan(&count)
+		              created_at   = now(),
+		              like_email_sent_at = CASE
+		                  WHEN notifications.like_email_sent_at IS NULL
+		                    OR notifications.like_email_sent_at < now() - make_interval(secs => $4)
+		                  THEN now()
+		                  ELSE notifications.like_email_sent_at
+		              END
+		RETURNING actor_count, (like_email_sent_at = now())`,
+		userID, actorID, postID, secs,
+	).Scan(&count, &emailDue)
 	if err != nil {
-		return 0, fmt.Errorf("upsert like notification: %w", err)
+		return 0, false, fmt.Errorf("upsert like notification: %w", err)
 	}
-	return count, nil
+	return count, emailDue, nil
+}
+
+// LikeEmailsEnabled reports whether the user wants aggregated like emails.
+func (r *NotificationRepo) LikeEmailsEnabled(ctx context.Context, userID string) (bool, error) {
+	var enabled bool
+	if err := r.pg.Pool.QueryRow(ctx,
+		`SELECT like_emails_enabled FROM users WHERE id = $1`, userID,
+	).Scan(&enabled); err != nil {
+		return false, fmt.Errorf("get like-email pref: %w", err)
+	}
+	return enabled, nil
+}
+
+// SetLikeEmailsEnabled flips the user's like-email opt-in.
+func (r *NotificationRepo) SetLikeEmailsEnabled(ctx context.Context, userID string, enabled bool) error {
+	if _, err := r.pg.Pool.Exec(ctx,
+		`UPDATE users SET like_emails_enabled = $1 WHERE id = $2`, enabled, userID,
+	); err != nil {
+		return fmt.Errorf("set like-email pref: %w", err)
+	}
+	return nil
 }
 
 // CountUnread returns how many of a recipient's notifications are unread.

internal/server/server.go

@@ -791,6 +791,8 @@ func (s *Server) setupRouter() {
 			r.Get("/", s.notificationH.List)
 			r.Get("/unread-count", s.notificationH.UnreadCount)
 			r.Post("/read", s.notificationH.MarkAllRead)
+			r.Get("/email-prefs", s.notificationH.GetEmailPrefs)
+			r.Put("/email-prefs", s.notificationH.UpdateEmailPrefs)
 		})
 
 		// --- Web Push --- VAPID key + per-user subscription management.

internal/service/notification_service.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"html/template"
 	"strings"
+	"time"
 
 	"github.com/prabhupadasays/spsays-bff/internal/model"
 	"github.com/prabhupadasays/spsays-bff/internal/repository"
@@ -83,6 +84,16 @@ func (s *NotificationService) MarkAllRead(ctx context.Context, userID string) er
 	return s.notifs.MarkAllRead(ctx, userID)
 }
 
+// LikeEmailPref / SetLikeEmailPref back the Settings → Notifications toggle
+// for aggregated like emails.
+func (s *NotificationService) LikeEmailPref(ctx context.Context, userID string) (bool, error) {
+	return s.notifs.LikeEmailsEnabled(ctx, userID)
+}
+
+func (s *NotificationService) SetLikeEmailPref(ctx context.Context, userID string, enabled bool) error {
+	return s.notifs.SetLikeEmailsEnabled(ctx, userID, enabled)
+}
+
 // NotifyFollowRequest tells `recipientID` that `actorID` asked to follow
 // them. Persists the row and emails the recipient (if they have an email
 // on file).
@@ -107,13 +118,13 @@ func (s *NotificationService) NotifyPostLike(ctx context.Context, postID, author
 	if authorID == "" || likerID == "" || authorID == likerID {
 		return
 	}
-	// Aggregate into the single (author, post) like-notification row, getting
-	// back how many likers it now represents.
-	count, err := s.notifs.UpsertLike(ctx, authorID, likerID, postID)
+	// Aggregate into the single (author, post) like-notification row. Returns
+	// the new liker count and whether an aggregated email is due (throttled).
+	count, emailDue, err := s.notifs.UpsertLike(ctx, authorID, likerID, postID, likeEmailThrottle)
 	if err != nil {
 		s.logger.Warn("aggregate like notification failed",
 			zap.String("recipient", authorID), zap.Error(err))
-		count = 1
+		count, emailDue = 1, false
 	}
 
 	actorUser, _ := s.users.FindByID(ctx, likerID)
@@ -136,24 +147,51 @@ func (s *NotificationService) NotifyPostLike(ctx context.Context, postID, author
 		}
 	}
 
-	// Web Push — tapping opens the author's own feed anchored to the post.
-	// Tagged per-post so repeated likes collapse into one notification.
-	if s.push == nil {
-		return
-	}
+	// Tapping a notification opens the author's own feed anchored to the post.
+	author, _ := s.users.FindByID(ctx, authorID)
 	url := s.frontendURL + "/notifications"
-	if author, err := s.users.FindByID(ctx, authorID); err == nil && author != nil {
+	if author != nil {
 		url = s.frontendURL + "/u/" + author.Handle + "/posts#post-" + postID
 	}
-	s.push.SendToUser(ctx, authorID, PushPayload{
-		Title: "New Like",
-		Body:  body,
-		URL:   url,
-		Icon:  s.iconURL(),
-		Tag:   NotifPostLike + ":" + postID,
-	})
+
+	// Web Push — tagged per-post so repeated likes collapse into one.
+	if s.push != nil {
+		s.push.SendToUser(ctx, authorID, PushPayload{
+			Title: "New Like",
+			Body:  body,
+			URL:   url,
+			Icon:  s.iconURL(),
+			Tag:   NotifPostLike + ":" + postID,
+		})
+	}
+
+	// Aggregated email — only when the throttle says one is due (so a burst of
+	// likes yields a single email), the author has an address, and they
+	// haven't opted out. `body` already aggregates ("X and N others …").
+	if !emailDue || author == nil || author.Email == nil || strings.TrimSpace(*author.Email) == "" {
+		return
+	}
+	if enabled, perr := s.notifs.LikeEmailsEnabled(ctx, authorID); perr != nil || !enabled {
+		return
+	}
+	var buf bytes.Buffer
+	if err := likeEmailTpl.Execute(&buf, map[string]any{
+		"RecipientName": author.Name,
+		"Message":       body,
+		"URL":           url,
+	}); err != nil {
+		s.logger.Warn("render like email failed", zap.Error(err))
+		return
+	}
+	if err := s.mail.Send(strings.TrimSpace(*author.Email), "New likes on your post — Prabhupāda Says", buf.String()); err != nil {
+		s.logger.Warn("like email send failed", zap.String("to", *author.Email), zap.Error(err))
+	}
 }
 
+// likeEmailThrottle is the minimum gap between aggregated like emails for a
+// single post — a burst of likes within the window produces one email.
+const likeEmailThrottle = 6 * time.Hour
+
 // likeMessage renders the aggregated like text: "X liked your post" or
 // "X and N others liked your post".
 func likeMessage(who string, count int) string {
@@ -402,3 +440,20 @@ var reminderEmailTpl = template.Must(template.New("reminder").Parse(`<div style=
   <p style="margin-top:1em">Your servants,<br>
   <strong>The Prabhupāda Says team</strong></p>
 </div>`))
+
+// Aggregated like email. Message is "X and N others liked your post"; the CTA
+// opens the author's post.
+var likeEmailTpl = template.Must(template.New("postLike").Parse(`<div style="font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,Helvetica,Arial,sans-serif;color:#2a2118;max-width:560px;margin:0 auto;font-size:17px;line-height:1.7">
+  <p style="font-size:18px;color:#9a6b2f;letter-spacing:0.04em;margin-bottom:1em">Hare Kṛṣṇa{{if .RecipientName}}, {{.RecipientName}}{{end}} 🙏</p>
+
+  <p>{{.Message}}.</p>
+
+  <p style="margin:1.25em 0">
+    <a href="{{.URL}}" style="display:inline-block;background:#9a6b2f;color:#fff;text-decoration:none;padding:0.6em 1.3em;border-radius:8px;font-weight:600">View your post</a>
+  </p>
+
+  <p style="margin-top:1.5em;font-size:14px;color:#7a6a55">You can turn off like emails any time in Settings → Notifications.</p>
+
+  <p style="margin-top:1em">Your servants,<br>
+  <strong>The Prabhupāda Says team</strong></p>
+</div>`))