feat: add post like

2026-06-09 16:28:40 +05:30
parent da2bbc323d
commit e9299051f5
12 changed files with 658 additions and 8 deletions
@@ -125,6 +125,51 @@ func (h *PostHandler) Get(w http.ResponseWriter, r *http.Request) {
 	response.JSON(w, http.StatusOK, p)
 }

+// likeResp is returned by Like / Unlike — the new viewer state + effective
+// total (likes_count + pending Redis delta) so the client can reconcile.
+type likeResp struct {
+	Liked      bool `json:"liked"`
+	LikesCount int  `json:"likes_count"`
+}
+
+// Like — POST /posts/{id}/like. Idempotent. RequireAuth.
+func (h *PostHandler) Like(w http.ResponseWriter, r *http.Request) {
+	uid := middleware.UserID(r.Context())
+	id := chi.URLParam(r, "id")
+	count, err := h.svc.Like(r.Context(), uid, id)
+	if err != nil {
+		mapSocialErr(w, err)
+		return
+	}
+	response.JSON(w, http.StatusOK, likeResp{Liked: true, LikesCount: count})
+}
+
+// Unlike — DELETE /posts/{id}/like. Idempotent. RequireAuth.
+func (h *PostHandler) Unlike(w http.ResponseWriter, r *http.Request) {
+	uid := middleware.UserID(r.Context())
+	id := chi.URLParam(r, "id")
+	count, err := h.svc.Unlike(r.Context(), uid, id)
+	if err != nil {
+		mapSocialErr(w, err)
+		return
+	}
+	response.JSON(w, http.StatusOK, likeResp{Liked: false, LikesCount: count})
+}
+
+// ListLikes — GET /posts/{id}/likes?limit=&offset=&q=. Paginated "liked by"
+// users with optional name/handle search. Public (OptionalAuth).
+func (h *PostHandler) ListLikes(w http.ResponseWriter, r *http.Request) {
+	id := chi.URLParam(r, "id")
+	limit, offset := parseLimitOffset(r)
+	q := strings.TrimSpace(r.URL.Query().Get("q"))
+	users, total, err := h.svc.Likers(r.Context(), id, q, limit, offset)
+	if err != nil {
+		mapSocialErr(w, err)
+		return
+	}
+	response.JSON(w, http.StatusOK, followListResp{Users: users, Total: total})
+}
+
 func (h *PostHandler) Delete(w http.ResponseWriter, r *http.Request) {
 	uid := middleware.UserID(r.Context())
 	if err := h.svc.Delete(r.Context(), chi.URLParam(r, "id"), uid); err != nil {
@@ -443,10 +488,11 @@ type ProfileHandler struct {
 	posts       *repository.PostRepo
 	collections *repository.CollectionRepo
 	graph       *service.SocialGraphService
+	likes       *repository.LikeRepo
 }

-func NewProfileHandler(users *repository.UserRepo, posts *repository.PostRepo, collections *repository.CollectionRepo, graph *service.SocialGraphService) *ProfileHandler {
-	return &ProfileHandler{users: users, posts: posts, collections: collections, graph: graph}
+func NewProfileHandler(users *repository.UserRepo, posts *repository.PostRepo, collections *repository.CollectionRepo, graph *service.SocialGraphService, likes *repository.LikeRepo) *ProfileHandler {
+	return &ProfileHandler{users: users, posts: posts, collections: collections, graph: graph, likes: likes}
 }

 func (h *ProfileHandler) Get(w http.ResponseWriter, r *http.Request) {
@@ -527,6 +573,17 @@ func (h *ProfileHandler) Feed(w http.ResponseWriter, r *http.Request) {
 			}
 		}
 	}
+	// Like counts (effective) + viewer-liked state for every post in the page.
+	if len(posts) > 0 {
+		ptrs := make([]*model.Post, len(posts))
+		for i := range posts {
+			ptrs[i] = &posts[i]
+		}
+		if err := h.likes.Hydrate(r.Context(), viewerID, ptrs); err != nil {
+			mapSocialErr(w, err)
+			return
+		}
+	}
 	response.JSONWithMeta(w, http.StatusOK, posts, paginationMeta(total, limit, offset))
 }

@@ -39,6 +39,13 @@ type Post struct {
 	// after the repo returns posts; always false for anonymous viewers.
 	// Drives the post-card "Reshare ↔ Send" swap on the frontend.
 	ViewerHasReshared bool `json:"viewer_has_reshared"`
+
+	// Likes. LikesCount is the effective total = the denormalized
+	// posts.likes_count plus any still-pending Redis delta (hydrated by the
+	// like layer). ViewerHasLiked reflects the calling user's membership row;
+	// false for anonymous viewers.
+	LikesCount     int  `json:"likes_count"`
+	ViewerHasLiked bool `json:"viewer_has_liked"`
 }

 // PostImage represents one attached image on a post.
@@ -167,6 +174,13 @@ type Notification struct {
 	CreatedAt time.Time  `json:"created_at"`
 	ReadAt    *time.Time `json:"read_at,omitempty"`

+	// Aggregation: for post_like, PostID is the liked post and ActorCount is
+	// how many likers have aggregated into this single row (the frontend
+	// renders "X and N-1 others liked your post"). Other kinds: PostID nil,
+	// ActorCount 1.
+	PostID     *string `json:"post_id,omitempty"`
+	ActorCount int     `json:"actor_count"`
+
 	ActorName   *string `json:"actor_name,omitempty"`
 	ActorHandle *string `json:"actor_handle,omitempty"`
 	ActorAvatar *string `json:"actor_avatar_url,omitempty"`
@@ -0,0 +1,305 @@
+package repository
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"strings"
+
+	"github.com/prabhupadasays/spsays-bff/internal/model"
+	"go.uber.org/zap"
+)
+
+// likeDeltaPrefix namespaces the per-post pending-like counters in Redis. Each
+// like/unlike INCRBY/DECRBYs likes:delta:{postID}; the LikesWorker folds these
+// into posts.likes_count every 15 minutes (GETDEL + UPDATE). Reads add the
+// still-pending delta on top of likes_count so the displayed total is current.
+const likeDeltaPrefix = "likes:delta:"
+
+// LikeRepo handles post-like membership (Postgres) and the write-behind count
+// delta (Redis). Membership is written synchronously so viewer state and the
+// "liked by" list stay consistent; only the hot counter is batched.
+//
+// `redis` is optional: when nil (Redis unavailable) likes still work, but the
+// count is applied to posts.likes_count directly on each like instead of being
+// batched.
+type LikeRepo struct {
+	pg     *Postgres
+	redis  *Redis
+	logger *zap.Logger
+}
+
+func NewLikeRepo(pg *Postgres, redis *Redis, logger *zap.Logger) *LikeRepo {
+	return &LikeRepo{pg: pg, redis: redis, logger: logger}
+}
+
+func (r *LikeRepo) deltaKey(postID string) string { return likeDeltaPrefix + postID }
+
+// Like records a membership row. Returns whether it was newly liked (false if
+// the user had already liked it — idempotent). On a real change it nudges the
+// pending count up.
+func (r *LikeRepo) Like(ctx context.Context, postID, userID string) (bool, error) {
+	tag, err := r.pg.Pool.Exec(ctx,
+		`INSERT INTO post_likes (post_id, user_id) VALUES ($1, $2)
+		 ON CONFLICT (post_id, user_id) DO NOTHING`,
+		postID, userID,
+	)
+	if err != nil {
+		return false, fmt.Errorf("insert like: %w", err)
+	}
+	if tag.RowsAffected() == 0 {
+		return false, nil // already liked
+	}
+	r.bumpDelta(ctx, postID, 1)
+	return true, nil
+}
+
+// Unlike removes the membership row. Returns whether it actually changed.
+func (r *LikeRepo) Unlike(ctx context.Context, postID, userID string) (bool, error) {
+	tag, err := r.pg.Pool.Exec(ctx,
+		`DELETE FROM post_likes WHERE post_id = $1 AND user_id = $2`,
+		postID, userID,
+	)
+	if err != nil {
+		return false, fmt.Errorf("delete like: %w", err)
+	}
+	if tag.RowsAffected() == 0 {
+		return false, nil // wasn't liked
+	}
+	r.bumpDelta(ctx, postID, -1)
+	return true, nil
+}
+
+// bumpDelta adjusts the pending count. Prefers the Redis write-behind counter;
+// falls back to a direct DB update when Redis is unavailable so the count is
+// never lost.
+func (r *LikeRepo) bumpDelta(ctx context.Context, postID string, d int64) {
+	if r.redis != nil {
+		if err := r.redis.Client.IncrBy(ctx, r.deltaKey(postID), d).Err(); err == nil {
+			return
+		}
+		r.logger.Warn("likes: redis incr failed, applying to DB", zap.String("post", postID))
+	}
+	if _, err := r.pg.Pool.Exec(ctx,
+		`UPDATE posts SET likes_count = GREATEST(0, likes_count + $2) WHERE id = $1`,
+		postID, d,
+	); err != nil {
+		r.logger.Warn("likes: direct count update failed", zap.String("post", postID), zap.Error(err))
+	}
+}
+
+// PostAuthor returns the user id that owns the post (for like notifications).
+func (r *LikeRepo) PostAuthor(ctx context.Context, postID string) (string, error) {
+	var uid string
+	if err := r.pg.Pool.QueryRow(ctx,
+		`SELECT user_id FROM posts WHERE id = $1`, postID,
+	).Scan(&uid); err != nil {
+		return "", fmt.Errorf("post author: %w", err)
+	}
+	return uid, nil
+}
+
+// EffectiveCount returns likes_count + the pending Redis delta for one post.
+func (r *LikeRepo) EffectiveCount(ctx context.Context, postID string) (int, error) {
+	var c int
+	if err := r.pg.Pool.QueryRow(ctx,
+		`SELECT likes_count FROM posts WHERE id = $1`, postID,
+	).Scan(&c); err != nil {
+		return 0, fmt.Errorf("read likes_count: %w", err)
+	}
+	if r.redis != nil {
+		if d, err := r.redis.Client.Get(ctx, r.deltaKey(postID)).Int(); err == nil {
+			c += d
+		}
+	}
+	if c < 0 {
+		c = 0
+	}
+	return c, nil
+}
+
+// Hydrate fills LikesCount (effective) and ViewerHasLiked on the given posts.
+// Used by every post read path. viewerID "" leaves ViewerHasLiked false.
+func (r *LikeRepo) Hydrate(ctx context.Context, viewerID string, posts []*model.Post) error {
+	ids := make([]string, 0, len(posts))
+	for _, p := range posts {
+		if p != nil {
+			ids = append(ids, p.ID)
+		}
+	}
+	if len(ids) == 0 {
+		return nil
+	}
+
+	// Denormalized counts from Postgres.
+	counts := make(map[string]int, len(ids))
+	rows, err := r.pg.Pool.Query(ctx,
+		`SELECT id, likes_count FROM posts WHERE id = ANY($1)`, ids)
+	if err != nil {
+		return fmt.Errorf("hydrate like counts: %w", err)
+	}
+	for rows.Next() {
+		var id string
+		var c int
+		if err := rows.Scan(&id, &c); err != nil {
+			rows.Close()
+			return fmt.Errorf("scan like count: %w", err)
+		}
+		counts[id] = c
+	}
+	rows.Close()
+	if err := rows.Err(); err != nil {
+		return err
+	}
+
+	// Pending deltas from Redis (best-effort).
+	deltas := r.pendingDeltas(ctx, ids)
+
+	// Viewer membership.
+	liked := make(map[string]bool)
+	if viewerID != "" {
+		lr, err := r.pg.Pool.Query(ctx,
+			`SELECT post_id FROM post_likes WHERE user_id = $1 AND post_id = ANY($2)`,
+			viewerID, ids)
+		if err != nil {
+			return fmt.Errorf("hydrate viewer likes: %w", err)
+		}
+		for lr.Next() {
+			var pid string
+			if err := lr.Scan(&pid); err != nil {
+				lr.Close()
+				return fmt.Errorf("scan viewer like: %w", err)
+			}
+			liked[pid] = true
+		}
+		lr.Close()
+		if err := lr.Err(); err != nil {
+			return err
+		}
+	}
+
+	for _, p := range posts {
+		if p == nil {
+			continue
+		}
+		c := counts[p.ID] + deltas[p.ID]
+		if c < 0 {
+			c = 0
+		}
+		p.LikesCount = c
+		p.ViewerHasLiked = liked[p.ID]
+	}
+	return nil
+}
+
+// pendingDeltas returns the Redis like-deltas for the given posts (absent →
+// zero). Best-effort: Redis errors yield an empty map.
+func (r *LikeRepo) pendingDeltas(ctx context.Context, ids []string) map[string]int {
+	out := make(map[string]int)
+	if r.redis == nil || len(ids) == 0 {
+		return out
+	}
+	keys := make([]string, len(ids))
+	for i, id := range ids {
+		keys[i] = r.deltaKey(id)
+	}
+	vals, err := r.redis.Client.MGet(ctx, keys...).Result()
+	if err != nil {
+		return out
+	}
+	for i, v := range vals {
+		s, ok := v.(string)
+		if !ok {
+			continue
+		}
+		if n, err := strconv.Atoi(s); err == nil && n != 0 {
+			out[ids[i]] = n
+		}
+	}
+	return out
+}
+
+// ListLikers returns one page of users who liked the post (newest first),
+// optionally filtered by a name/handle search, plus the total matching count.
+func (r *LikeRepo) ListLikers(ctx context.Context, postID, q string, limit, offset int) ([]model.UserSummary, int, error) {
+	like := "%" + q + "%"
+
+	var total int
+	if err := r.pg.Pool.QueryRow(ctx, `
+		SELECT count(*)
+		FROM post_likes l JOIN users u ON u.id = l.user_id
+		WHERE l.post_id = $1
+		  AND ($2 = '' OR u.name ILIKE $3 OR u.handle ILIKE $3)`,
+		postID, q, like,
+	).Scan(&total); err != nil {
+		return nil, 0, fmt.Errorf("count likers: %w", err)
+	}
+	if total == 0 {
+		return []model.UserSummary{}, 0, nil
+	}
+
+	rows, err := r.pg.Pool.Query(ctx, `
+		SELECT u.handle, u.name, u.avatar_url
+		FROM post_likes l JOIN users u ON u.id = l.user_id
+		WHERE l.post_id = $1
+		  AND ($2 = '' OR u.name ILIKE $3 OR u.handle ILIKE $3)
+		ORDER BY l.created_at DESC, u.handle ASC
+		LIMIT $4 OFFSET $5`,
+		postID, q, like, limit, offset,
+	)
+	if err != nil {
+		return nil, 0, fmt.Errorf("list likers: %w", err)
+	}
+	defer rows.Close()
+
+	out := make([]model.UserSummary, 0, limit)
+	for rows.Next() {
+		var s model.UserSummary
+		if err := rows.Scan(&s.Handle, &s.Name, &s.AvatarURL); err != nil {
+			return nil, 0, fmt.Errorf("scan liker: %w", err)
+		}
+		out = append(out, s)
+	}
+	return out, total, rows.Err()
+}
+
+// FlushDeltas drains every pending Redis like-delta into posts.likes_count.
+// Called periodically by the LikesWorker. Returns how many posts were updated.
+// GETDEL makes each pop atomic; a failed UPDATE restores the delta so it's
+// retried next cycle.
+func (r *LikeRepo) FlushDeltas(ctx context.Context) (int, error) {
+	if r.redis == nil {
+		return 0, nil
+	}
+	var cursor uint64
+	applied := 0
+	for {
+		keys, next, err := r.redis.Client.Scan(ctx, cursor, likeDeltaPrefix+"*", 200).Result()
+		if err != nil {
+			return applied, fmt.Errorf("scan like deltas: %w", err)
+		}
+		for _, key := range keys {
+			postID := strings.TrimPrefix(key, likeDeltaPrefix)
+			v, err := r.redis.Client.GetDel(ctx, key).Int()
+			if err != nil || v == 0 {
+				continue
+			}
+			if _, err := r.pg.Pool.Exec(ctx,
+				`UPDATE posts SET likes_count = GREATEST(0, likes_count + $2) WHERE id = $1`,
+				postID, v,
+			); err != nil {
+				// Restore so the delta isn't lost; retried next cycle.
+				r.redis.Client.IncrBy(ctx, key, int64(v))
+				r.logger.Warn("likes flush: update failed, delta restored",
+					zap.String("post", postID), zap.Error(err))
+				continue
+			}
+			applied++
+		}
+		cursor = next
+		if cursor == 0 {
+			break
+		}
+	}
+	return applied, nil
+}
@@ -319,7 +319,8 @@ func (r *NotificationRepo) Create(ctx context.Context, userID string, actorID *s
 // notifications or since-deleted actors).
 func (r *NotificationRepo) ListByUser(ctx context.Context, userID string, limit, offset int) ([]model.Notification, error) {
 	rows, err := r.pg.Pool.Query(ctx, `
-		SELECT n.id, n.user_id, n.actor_id, n.kind, n.created_at, n.read_at,
+		SELECT n.id, n.user_id, n.actor_id, n.kind, n.post_id, n.actor_count,
+		       n.created_at, n.read_at,
 		       u.name, u.handle, u.avatar_url
 		FROM notifications n
 		LEFT JOIN users u ON u.id = n.actor_id
@@ -334,7 +335,8 @@ func (r *NotificationRepo) ListByUser(ctx context.Context, userID string, limit,
 	out := []model.Notification{}
 	for rows.Next() {
 		var n model.Notification
-		if err := rows.Scan(&n.ID, &n.UserID, &n.ActorID, &n.Kind, &n.CreatedAt, &n.ReadAt,
+		if err := rows.Scan(&n.ID, &n.UserID, &n.ActorID, &n.Kind, &n.PostID, &n.ActorCount,
+			&n.CreatedAt, &n.ReadAt,
 			&n.ActorName, &n.ActorHandle, &n.ActorAvatar); err != nil {
 			return nil, fmt.Errorf("scan notification: %w", err)
 		}
@@ -343,6 +345,29 @@ func (r *NotificationRepo) ListByUser(ctx context.Context, userID string, limit,
 	return out, rows.Err()
 }

+// 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)
+		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)
+	if err != nil {
+		return 0, fmt.Errorf("upsert like notification: %w", err)
+	}
+	return count, nil
+}
+
 // CountUnread returns how many of a recipient's notifications are unread.
 func (r *NotificationRepo) CountUnread(ctx context.Context, userID string) (int, error) {
 	var n int
@@ -162,7 +162,10 @@ func (s *Server) initAuth(cfg *config.Config, logger *zap.Logger) {
 	postRepo := repository.NewPostRepo(s.pg)
 	bookmarkRepo := repository.NewBookmarkRepo(s.pg)
 	collectionRepo := repository.NewCollectionRepo(s.pg)
-	postSvc := service.NewPostService(postRepo, r2)
+	// Likes: membership in Postgres, count delta batched through Redis
+	// (s.redis may be nil — LikeRepo then applies counts directly).
+	likeRepo := repository.NewLikeRepo(s.pg, s.redis, logger)
+	postSvc := service.NewPostService(postRepo, r2, likeRepo)
 	bookmarkSvc := service.NewBookmarkService(userRepo, bookmarkRepo)
 	collectionSvc := service.NewCollectionService(userRepo, collectionRepo, postRepo, r2)

@@ -210,6 +213,9 @@ func (s *Server) initAuth(cfg *config.Config, logger *zap.Logger) {
 	pushSender := service.NewPushSender(pushRepo, cfg.VAPIDPublicKey, cfg.VAPIDPrivateKey, cfg.VAPIDSubject, logger)
 	s.pushH = handler.NewPushHandler(pushSender, pushRepo)
 	notifSvc := service.NewNotificationService(notifRepo, userRepo, mail, rtClient, pushSender, logger, cfg.FrontendURL)
+	// Wire the notification seam into the post service so a new like notifies
+	// the author (push + realtime; not the liker themselves).
+	postSvc.SetNotifier(notifSvc)

 	// Sādhana reminders: a background worker nudges users (email + push +
 	// websocket) to chant / post a quote at their local time. Shares the
@@ -223,11 +229,15 @@ func (s *Server) initAuth(cfg *config.Config, logger *zap.Logger) {
 	}
 	worker.NewReminderWorker(reminderSvc, logger).Run(wctx)

+	// Likes worker: folds the pending Redis like-deltas into posts.likes_count
+	// every 15 minutes (no-op when Redis is unavailable).
+	worker.NewLikesWorker(likeRepo, logger).Run(wctx)
+
 	graphSvc := service.NewSocialGraphService(followRepo, blockRepo, reportRepo, postRepo, userRepo, notifSvc, mail, cfg.FeedbackAdminEmails, logger)
 	s.relationH = handler.NewRelationshipHandler(graphSvc)
 	s.notificationH = handler.NewNotificationHandler(notifSvc)
 	s.postH = handler.NewPostHandler(postSvc, graphSvc)
-	s.profileH = handler.NewProfileHandler(userRepo, postRepo, collectionRepo, graphSvc)
+	s.profileH = handler.NewProfileHandler(userRepo, postRepo, collectionRepo, graphSvc, likeRepo)

 	// Sādhana streak: daily chanting log + the growing-plant state. Reads
 	// the chanting half from sadhna_logs and the posting half from the
@@ -631,6 +641,8 @@ func (s *Server) setupRouter() {
 			r.Group(func(r chi.Router) {
 				r.Use(middleware.OptionalAuth(s.authIssuer, s.userRepo))
 				r.Get("/{id}", s.postH.Get)
+				// Paginated "liked by" list — public, like the count itself.
+				r.Get("/{id}/likes", s.postH.ListLikes)
 			})
 			// Protected — create / delete / image presign / "my posts" /
 			// reshare actions.
@@ -646,6 +658,10 @@ func (s *Server) setupRouter() {
 				// double-clicks don't 4xx.
 				r.Post("/{id}/reshare", s.postH.Reshare)
 				r.Delete("/{id}/reshare", s.postH.Unreshare)
+				// Like / unlike — idempotent; membership is written now, the
+				// count is batched into likes_count via Redis.
+				r.Post("/{id}/like", s.postH.Like)
+				r.Delete("/{id}/like", s.postH.Unlike)
 				// Report a post (category + optional reason) → admin email.
 				r.Post("/{id}/report", s.postH.Report)
 			})
@@ -15,6 +15,7 @@ package service
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"html/template"
 	"strings"

@@ -29,6 +30,7 @@ import (
 const (
 	NotifFollowRequest  = "follow_request"
 	NotifFollowAccepted = "follow_accepted"
+	NotifPostLike       = "post_like"

 	// Reminder kinds are delivered live (email + push + a websocket toast)
 	// but NOT persisted — they're ephemeral nudges, not history.
@@ -96,6 +98,76 @@ func (s *NotificationService) NotifyFollowAccepted(ctx context.Context, recipien
 		"%s accepted your follow request — Prabhupāda Says")
 }

+// NotifyPostLike tells the post author that `likerID` liked their post. Sent
+// only when the liker isn't the author (callers also guard). Unlike follows,
+// likes are high-volume, so this delivers a persisted row + realtime nudge +
+// Web Push but NO email. The push is tagged per-post so repeated likes on the
+// same post collapse into one notification rather than stacking.
+func (s *NotificationService) NotifyPostLike(ctx context.Context, postID, authorID, likerID string) {
+	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)
+	if err != nil {
+		s.logger.Warn("aggregate like notification failed",
+			zap.String("recipient", authorID), zap.Error(err))
+		count = 1
+	}
+
+	actorUser, _ := s.users.FindByID(ctx, likerID)
+	who := "Someone"
+	if actorUser != nil {
+		who = actorDisplay(actorUser)
+	}
+	body := likeMessage(who, count)
+
+	// Realtime nudge — carry actor_count so the toast can read "and N others".
+	if s.rt != nil {
+		payload := map[string]any{"kind": NotifPostLike, "actor_count": count}
+		if actorUser != nil {
+			payload["actor_name"] = actorDisplay(actorUser)
+			payload["actor_handle"] = actorUser.Handle
+			payload["actor_avatar_url"] = actorUser.AvatarURL
+		}
+		if err := s.rt.Trigger(ctx, "notifications."+authorID, "notification", payload); err != nil {
+			s.logger.Warn("realtime like publish failed", zap.String("recipient", authorID), zap.Error(err))
+		}
+	}
+
+	// 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
+	}
+	url := s.frontendURL + "/notifications"
+	if author, err := s.users.FindByID(ctx, authorID); err == nil && 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,
+	})
+}
+
+// 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 {
+	if count <= 1 {
+		return who + " liked your post"
+	}
+	others := count - 1
+	noun := "others"
+	if others == 1 {
+		noun = "other"
+	}
+	return fmt.Sprintf("%s and %d %s liked your post", who, others, noun)
+}
+
 // dispatch persists the notification and sends the matching email. All
 // failures are logged, never propagated.
 func (s *NotificationService) dispatch(ctx context.Context, recipientID, actorID, kind, subjectFmt string) {
@@ -33,12 +33,18 @@ var (
 type PostService struct {
 	posts *repository.PostRepo
 	r2    *repository.R2
+	likes *repository.LikeRepo
+	notif *NotificationService // optional; set via SetNotifier
 }

-func NewPostService(posts *repository.PostRepo, r2 *repository.R2) *PostService {
-	return &PostService{posts: posts, r2: r2}
+func NewPostService(posts *repository.PostRepo, r2 *repository.R2, likes *repository.LikeRepo) *PostService {
+	return &PostService{posts: posts, r2: r2, likes: likes}
 }

+// SetNotifier wires the notification seam after construction (the
+// NotificationService is built later in server wiring than PostService).
+func (s *PostService) SetNotifier(n *NotificationService) { s.notif = n }
+
 // Create persists a new post. The caption is treated as opaque — we trust
 // the frontend to send the exact text the user selected. Source URL must be
 // a same-origin path (e.g. /books/bg/1/1?hl=…) — we strip the host if one
@@ -72,6 +78,9 @@ func (s *PostService) Get(ctx context.Context, id, viewerID string) (*model.Post
 	if err := s.hydrateReshareStates(ctx, viewerID, []*model.Post{p}); err != nil {
 		return nil, err
 	}
+	if err := s.likes.Hydrate(ctx, viewerID, []*model.Post{p}); err != nil {
+		return nil, err
+	}
 	return p, nil
 }

@@ -171,9 +180,58 @@ func (s *PostService) ListByHandle(ctx context.Context, handle, viewerID string,
 	if err := s.hydrateReshareStatesSlice(ctx, viewerID, posts); err != nil {
 		return nil, 0, err
 	}
+	if err := s.hydrateLikesSlice(ctx, viewerID, posts); err != nil {
+		return nil, 0, err
+	}
 	return posts, total, nil
 }

+// hydrateLikesSlice fills LikesCount + ViewerHasLiked on a value slice.
+func (s *PostService) hydrateLikesSlice(ctx context.Context, viewerID string, posts []model.Post) error {
+	if len(posts) == 0 {
+		return nil
+	}
+	ptrs := make([]*model.Post, len(posts))
+	for i := range posts {
+		ptrs[i] = &posts[i]
+	}
+	return s.likes.Hydrate(ctx, viewerID, ptrs)
+}
+
+// Like / Unlike toggle the caller's like on a post and return the effective
+// total (likes_count + pending Redis delta).
+func (s *PostService) Like(ctx context.Context, userID, postID string) (int, error) {
+	changed, err := s.likes.Like(ctx, postID, userID)
+	if err != nil {
+		return 0, err
+	}
+	count, err := s.likes.EffectiveCount(ctx, postID)
+	if err != nil {
+		return 0, err
+	}
+	// Notify the author on a genuinely new like by someone else. Fire-and-
+	// forget on a detached context so it isn't cancelled when the request
+	// returns; NotifyPostLike re-checks self-like internally too.
+	if changed && s.notif != nil {
+		if authorID, aerr := s.likes.PostAuthor(ctx, postID); aerr == nil && authorID != userID {
+			go s.notif.NotifyPostLike(context.Background(), postID, authorID, userID)
+		}
+	}
+	return count, nil
+}
+
+func (s *PostService) Unlike(ctx context.Context, userID, postID string) (int, error) {
+	if _, err := s.likes.Unlike(ctx, postID, userID); err != nil {
+		return 0, err
+	}
+	return s.likes.EffectiveCount(ctx, postID)
+}
+
+// Likers returns one page of users who liked the post + the total count.
+func (s *PostService) Likers(ctx context.Context, postID, q string, limit, offset int) ([]model.UserSummary, int, error) {
+	return s.likes.ListLikers(ctx, postID, q, limit, offset)
+}
+
 // ListMine is the owner's view of their own profile feed. Every post
 // they own — authored or reshared — comes from posts.user_id, so the
 // viewer is by construction the owner. ViewerHasReshared is true for
@@ -195,6 +253,9 @@ func (s *PostService) ListMine(ctx context.Context, userID string, limit, offset
 			posts[i].ViewerHasReshared = true
 		}
 	}
+	if err := s.hydrateLikesSlice(ctx, userID, posts); err != nil {
+		return nil, 0, err
+	}
 	return posts, total, nil
 }

@@ -0,0 +1,55 @@
+package worker
+
+import (
+	"context"
+	"time"
+
+	"github.com/prabhupadasays/spsays-bff/internal/repository"
+	"go.uber.org/zap"
+)
+
+// LikesWorker periodically folds the pending Redis like-deltas into
+// posts.likes_count, so the hot counter is written in batches rather than on
+// every like. It also does a best-effort final flush on shutdown so deltas
+// aren't lost.
+type LikesWorker struct {
+	repo     *repository.LikeRepo
+	interval time.Duration
+	logger   *zap.Logger
+}
+
+func NewLikesWorker(repo *repository.LikeRepo, logger *zap.Logger) *LikesWorker {
+	return &LikesWorker{repo: repo, interval: 15 * time.Minute, logger: logger}
+}
+
+// Run starts the flush loop in its own goroutine; it exits when ctx is done.
+func (w *LikesWorker) Run(ctx context.Context) {
+	go func() {
+		w.logger.Info("likes worker started", zap.Duration("interval", w.interval))
+		defer w.logger.Info("likes worker stopped")
+
+		ticker := time.NewTicker(w.interval)
+		defer ticker.Stop()
+
+		for {
+			select {
+			case <-ctx.Done():
+				// Final flush so a graceful shutdown doesn't drop pending
+				// deltas. Fresh, short-lived context since ctx is cancelled.
+				flushCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+				if _, err := w.repo.FlushDeltas(flushCtx); err != nil {
+					w.logger.Warn("likes worker: final flush failed", zap.Error(err))
+				}
+				cancel()
+				return
+			case <-ticker.C:
+				n, err := w.repo.FlushDeltas(ctx)
+				if err != nil {
+					w.logger.Warn("likes worker: flush failed", zap.Error(err))
+				} else if n > 0 {
+					w.logger.Info("likes worker: flushed", zap.Int("posts", n))
+				}
+			}
+		}
+	}()
+}
@@ -0,0 +1,2 @@
+DROP TABLE IF EXISTS post_likes;
+ALTER TABLE posts DROP COLUMN IF EXISTS likes_count;
@@ -0,0 +1,26 @@
+-- Post likes.
+--
+-- `post_likes` is the membership table (one row per user-per-post like),
+-- written synchronously so a viewer's like state and the "liked by" list are
+-- immediately consistent. The UNIQUE(post_id, user_id) makes liking idempotent.
+--
+-- `posts.likes_count` is a denormalized counter that is NOT updated on every
+-- like (that hot-row UPDATE doesn't scale for popular posts). Instead each
+-- like/unlike nudges a per-post delta in Redis, and a background worker folds
+-- the deltas into this column every 15 minutes. Reads return
+-- likes_count + the still-pending Redis delta, so the displayed total is
+-- always current.
+ALTER TABLE posts ADD COLUMN IF NOT EXISTS likes_count INTEGER NOT NULL DEFAULT 0;
+
+CREATE TABLE IF NOT EXISTS post_likes (
+    id         UUID         PRIMARY KEY DEFAULT gen_random_uuid(),
+    post_id    UUID         NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
+    user_id    UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at TIMESTAMPTZ  NOT NULL DEFAULT now(),
+    UNIQUE (post_id, user_id)
+);
+
+-- Listing "who liked this post", newest first.
+CREATE INDEX IF NOT EXISTS post_likes_post_idx ON post_likes (post_id, created_at DESC);
+-- "Have I liked these posts?" — viewer-state hydration across a feed.
+CREATE INDEX IF NOT EXISTS post_likes_user_idx ON post_likes (user_id);
@@ -0,0 +1,3 @@
+DROP INDEX IF EXISTS notifications_post_like_uq;
+ALTER TABLE notifications DROP COLUMN IF EXISTS actor_count;
+ALTER TABLE notifications DROP COLUMN IF EXISTS post_id;
@@ -0,0 +1,14 @@
+-- Aggregated like notifications.
+--
+-- Likes are high-volume, so instead of one notification row per like we keep a
+-- single row per (recipient, post) and aggregate: actor_id holds the most
+-- recent liker, actor_count how many distinct likers have aggregated into it.
+-- The partial unique index lets the like path UPSERT that one row (bumping the
+-- count, refreshing the actor, re-marking unread) — so the activity list shows
+-- "X and N others liked your post", not a flood.
+ALTER TABLE notifications ADD COLUMN IF NOT EXISTS post_id UUID REFERENCES posts(id) ON DELETE CASCADE;
+ALTER TABLE notifications ADD COLUMN IF NOT EXISTS actor_count INTEGER NOT NULL DEFAULT 1;
+
+CREATE UNIQUE INDEX IF NOT EXISTS notifications_post_like_uq
+    ON notifications (user_id, post_id)
+    WHERE kind = 'post_like';