feat: add feed

2026-06-13 23:55:02 +05:30
parent 2135ec334c
commit 8a2bdf945a
7 changed files with 232 additions and 0 deletions
@@ -213,6 +213,103 @@ func (r *PostRepo) ListByUser(ctx context.Context, userID string, limit, offset
 	return r.collectPosts(ctx, total, q, userID, limit, offset)
 }

+// FeedForViewer returns one page of the global home feed for `viewerID`,
+// newest-first within a two-tier priority:
+//
+//	tier 0 — posts by people the viewer follows that they haven't liked yet
+//	tier 1 — everything else (followed-and-liked, followers', strangers')
+//
+// The viewer's own posts and anything involving a block (either direction)
+// are excluded. The tier is computed in ORDER BY via correlated EXISTS, so no
+// extra columns leak into scanPost. No total is computed (infinite scroll
+// infers "more" from a full page); offset paging keeps it simple. At larger
+// scale this would move to a precomputed fan-out / keyset cursor.
+func (r *PostRepo) FeedForViewer(ctx context.Context, viewerID string, limit, offset int) ([]model.Post, error) {
+	q := `SELECT ` + postSelectColumns + postSelectFrom + `
+		WHERE p.user_id <> $1
+		  AND NOT EXISTS (
+		      SELECT 1 FROM user_blocks b
+		      WHERE (b.blocker_id = $1 AND b.blocked_id = p.user_id)
+		         OR (b.blocker_id = p.user_id AND b.blocked_id = $1)
+		  )
+		ORDER BY
+		  (CASE
+		     WHEN EXISTS (
+		            SELECT 1 FROM follows f
+		            WHERE f.follower_id = $1 AND f.following_id = p.user_id
+		              AND f.status = 'accepted'
+		          )
+		      AND NOT EXISTS (
+		            SELECT 1 FROM post_likes pl
+		            WHERE pl.post_id = p.id AND pl.user_id = $1
+		          )
+		     THEN 0 ELSE 1
+		   END) ASC,
+		  p.created_at DESC, p.id DESC
+		LIMIT $2 OFFSET $3`
+	posts, _, err := r.collectPosts(ctx, 0, q, viewerID, limit, offset)
+	return posts, err
+}
+
+// HydrateViewerRelationships fills ViewerFollowsAuthor / AuthorFollowsViewer
+// across a page of feed posts in two batched queries (one per direction).
+// No-op for anonymous viewers.
+func (r *PostRepo) HydrateViewerRelationships(ctx context.Context, viewerID string, posts []model.Post) error {
+	if viewerID == "" || len(posts) == 0 {
+		return nil
+	}
+	seen := map[string]bool{}
+	authorIDs := make([]string, 0, len(posts))
+	for i := range posts {
+		id := posts[i].UserID
+		if id != "" && id != viewerID && !seen[id] {
+			seen[id] = true
+			authorIDs = append(authorIDs, id)
+		}
+	}
+	if len(authorIDs) == 0 {
+		return nil
+	}
+
+	following, err := r.followEdges(ctx,
+		`SELECT following_id FROM follows
+		 WHERE follower_id = $1 AND status = 'accepted' AND following_id = ANY($2)`,
+		viewerID, authorIDs)
+	if err != nil {
+		return err
+	}
+	followers, err := r.followEdges(ctx,
+		`SELECT follower_id FROM follows
+		 WHERE following_id = $1 AND status = 'accepted' AND follower_id = ANY($2)`,
+		viewerID, authorIDs)
+	if err != nil {
+		return err
+	}
+	for i := range posts {
+		posts[i].ViewerFollowsAuthor = following[posts[i].UserID]
+		posts[i].AuthorFollowsViewer = followers[posts[i].UserID]
+	}
+	return nil
+}
+
+// followEdges runs a one-column follow query and collects the ids into a set.
+func (r *PostRepo) followEdges(ctx context.Context, query, viewerID string, ids []string) (map[string]bool, error) {
+	rows, err := r.pg.Pool.Query(ctx, query, viewerID, ids)
+	if err != nil {
+		return nil, fmt.Errorf("hydrate follow edges: %w", err)
+	}
+	defer rows.Close()
+	out := map[string]bool{}
+	for rows.Next() {
+		var id string
+		if err := rows.Scan(&id); err != nil {
+			return nil, fmt.Errorf("scan follow edge: %w", err)
+		}
+		out[id] = true
+	}
+	return out, rows.Err()
+}
+
 // Delete removes a post only if it belongs to the caller. Cascades:
 //   - the post's images (post_images.post_id FK)
 //   - any reshares of this post made by other users (posts.reshared_from_post_id FK)