feat: share post to other apps

internal/service/social_service.go

@@ -61,9 +61,88 @@ func (s *PostService) Create(ctx context.Context, userID, caption, sourceURL, so
 	return s.posts.Create(ctx, userID, caption, sourceURL, sourceTitle, imageURLs)
 }
 
-// Get returns one post (public).
-func (s *PostService) Get(ctx context.Context, id string) (*model.Post, error) {
-	return s.posts.FindByID(ctx, id)
+// Get returns one post (public). `viewerID` is "" for anonymous callers;
+// when set, the returned post carries the viewer's reshare state so the
+// frontend can render the right action button without a second request.
+func (s *PostService) Get(ctx context.Context, id, viewerID string) (*model.Post, error) {
+	p, err := s.posts.FindByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	if err := s.hydrateReshareStates(ctx, viewerID, []*model.Post{p}); err != nil {
+		return nil, err
+	}
+	return p, nil
+}
+
+// Reshare records that the caller has reshared the given post. Idempotent
+// — calling it twice with the same (post, user) is a no-op. Resharing
+// your own post is rejected: there's nothing to bring onto an account
+// that already authored the post.
+func (s *PostService) Reshare(ctx context.Context, postID, callerID string) error {
+	p, err := s.posts.FindByID(ctx, postID)
+	if err != nil {
+		return err
+	}
+	if p.UserID == callerID {
+		return errors.New("cannot reshare your own post")
+	}
+	return s.posts.AddReshare(ctx, postID, callerID)
+}
+
+// Unreshare removes a previously recorded reshare. Idempotent — no-ops
+// when no row exists.
+func (s *PostService) Unreshare(ctx context.Context, postID, callerID string) error {
+	return s.posts.RemoveReshare(ctx, postID, callerID)
+}
+
+// hydrateReshareStates fills in ViewerHasReshared on each post via one
+// batched lookup against post_reshares. Skips the query when the viewer
+// is anonymous (`viewerID == ""`) since the answer is uniformly false.
+// Also fast-paths posts authored by the viewer — they can't be reshared
+// by themselves, so we leave the flag at its zero value.
+func (s *PostService) hydrateReshareStates(ctx context.Context, viewerID string, posts []*model.Post) error {
+	if viewerID == "" || len(posts) == 0 {
+		return nil
+	}
+	ids := make([]string, 0, len(posts))
+	for _, p := range posts {
+		if p == nil || p.UserID == viewerID {
+			continue
+		}
+		ids = append(ids, p.ID)
+	}
+	if len(ids) == 0 {
+		return nil
+	}
+	states, err := s.posts.ReshareStatesFor(ctx, viewerID, ids)
+	if err != nil {
+		return err
+	}
+	for _, p := range posts {
+		if p == nil {
+			continue
+		}
+		if states[p.ID] {
+			p.ViewerHasReshared = true
+		}
+	}
+	return nil
+}
+
+// hydrateReshareStatesSlice is the value-slice variant of
+// hydrateReshareStates. Repository list methods return []model.Post
+// (not pointers) — we wrap each element so the helper can mutate in
+// place via a stable pointer.
+func (s *PostService) hydrateReshareStatesSlice(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.hydrateReshareStates(ctx, viewerID, ptrs)
 }
 
 // Delete checks ownership and removes the post.
@@ -81,19 +160,28 @@ func (s *PostService) ReplaceImages(ctx context.Context, postID, callerID string
 	return s.posts.FindByID(ctx, postID)
 }
 
-// ListByHandle is the public feed view.
-func (s *PostService) ListByHandle(ctx context.Context, handle string, limit, offset int) ([]model.Post, int, error) {
+// ListByHandle is the public feed view. `viewerID` is "" for anonymous
+// callers; when set, each returned post carries the viewer's reshare
+// state.
+func (s *PostService) ListByHandle(ctx context.Context, handle, viewerID string, limit, offset int) ([]model.Post, int, error) {
 	if limit <= 0 || limit > 50 {
 		limit = 20
 	}
 	if offset < 0 {
 		offset = 0
 	}
-	return s.posts.ListByHandle(ctx, handle, limit, offset)
+	posts, total, err := s.posts.ListByHandle(ctx, handle, limit, offset)
+	if err != nil {
+		return nil, 0, err
+	}
+	if err := s.hydrateReshareStatesSlice(ctx, viewerID, posts); err != nil {
+		return nil, 0, err
+	}
+	return posts, total, nil
 }
 
-// ListMine is the owner's view of their own posts (drafts feature isn't a
-// thing yet, so this is equivalent to ListByHandle minus the handle lookup).
+// ListMine is the owner's view of their own posts. Reshare hydration
+// is skipped — the caller can't reshare their own posts.
 func (s *PostService) ListMine(ctx context.Context, userID string, limit, offset int) ([]model.Post, int, error) {
 	if limit <= 0 || limit > 50 {
 		limit = 20
@@ -336,6 +424,20 @@ func (s *CollectionService) Get(ctx context.Context, id, viewerID string) (*mode
 		for i := range posts {
 			posts[i].Images = imgs[posts[i].ID]
 		}
+		// Same batched approach for reshare states so the action footer
+		// on each card swaps Reshare↔Send correctly. Anonymous viewers
+		// (viewerID == "") get all-false at zero cost.
+		if viewerID != "" {
+			states, err := s.posts.ReshareStatesFor(ctx, viewerID, ids)
+			if err != nil {
+				return nil, nil, err
+			}
+			for i := range posts {
+				if states[posts[i].ID] {
+					posts[i].ViewerHasReshared = true
+				}
+			}
+		}
 	}
 	return c, posts, nil
 }