feat(api): add tab-based post feed endpoints with cursor pagination

Add support for different post feed types via tab parameter:
- follow: posts from followed users (requires authentication)
- hot: trending posts using Gorse most_liked_weekly or database fallback
- recommend: personalized recommendations with random offset for diversity
- latest: default chronological feed

The cursor pagination detection is also improved to check for parameter
existence rather than non-empty string value.

internal/service/post_service.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"log"
 	"math/rand"
+	"strconv"
 	"strings"
 	"time"
 
@@ -45,6 +46,9 @@ type PostService interface {
 	ListByCursor(ctx context.Context, userID string, includePending bool, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error)
 	SearchByCursor(ctx context.Context, keyword string, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error)
 	GetUserPostsByCursor(ctx context.Context, userID string, includePending bool, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error)
+	GetFollowingPostsByCursor(ctx context.Context, userID string, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error)
+	GetHotPostsByCursor(ctx context.Context, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error)
+	GetRecommendedPostsByCursor(ctx context.Context, userID string, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error)
 
 	// 关注和推荐
 	GetFollowingPosts(ctx context.Context, userID string, page, pageSize int) ([]*model.Post, int64, error)
@@ -792,3 +796,126 @@ func (s *postServiceImpl) GetUserPostsByCursor(ctx context.Context, userID strin
 
 	return s.postRepo.GetUserPostsByCursor(ctx, userID, includePending, req)
 }
+
+// GetFollowingPostsByCursor 游标分页获取关注用户的帖子
+func (s *postServiceImpl) GetFollowingPostsByCursor(ctx context.Context, userID string, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error) {
+	// 规范化请求参数
+	req.Normalize()
+
+	return s.postRepo.GetFollowingPostsByCursor(ctx, userID, req)
+}
+
+// GetHotPostsByCursor 游标分页获取热门帖子
+func (s *postServiceImpl) GetHotPostsByCursor(ctx context.Context, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error) {
+	// 规范化请求参数
+	req.Normalize()
+
+	// 如果Gorse启用，使用自定义的非个性化推荐器
+	if s.gorseClient.IsEnabled() {
+		// 计算偏移量
+		offset := 0
+		if req.Cursor != "" {
+			// 尝试解析游标作为偏移量
+			if parsed, err := strconv.Atoi(req.Cursor); err == nil {
+				offset = parsed
+			}
+		}
+
+		// 使用 most_liked_weekly 推荐器获取周热门
+		// 多取1条用于判断是否还有下一页
+		itemIDs, err := s.gorseClient.GetNonPersonalized(ctx, "most_liked_weekly", req.PageSize+1, offset, "")
+		if err != nil {
+			log.Printf("[WARN] Gorse GetNonPersonalized failed: %v, fallback to database", err)
+			return s.getHotPostsByCursorFromDB(ctx, req)
+		}
+		if len(itemIDs) > 0 {
+			hasMore := len(itemIDs) > req.PageSize
+			if hasMore {
+				itemIDs = itemIDs[:req.PageSize]
+			}
+			posts, err := s.postRepo.GetByIDs(itemIDs)
+			if err != nil {
+				return nil, err
+			}
+			// 下一页的游标是当前偏移量 + 已获取数量
+			nextCursor := ""
+			if hasMore {
+				nextCursor = strconv.Itoa(offset + req.PageSize)
+			}
+			return &cursor.CursorPageResult[*model.Post]{
+				Items:      posts,
+				NextCursor: nextCursor,
+				PrevCursor: "",
+				HasMore:    hasMore,
+			}, nil
+		}
+	}
+
+	// 降级：从数据库获取
+	return s.getHotPostsByCursorFromDB(ctx, req)
+}
+
+// getHotPostsByCursorFromDB 从数据库游标分页获取热门帖子（降级路径）
+func (s *postServiceImpl) getHotPostsByCursorFromDB(ctx context.Context, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error) {
+	return s.postRepo.GetHotPostsByCursor(ctx, req)
+}
+
+// GetRecommendedPostsByCursor 游标分页获取推荐帖子
+func (s *postServiceImpl) GetRecommendedPostsByCursor(ctx context.Context, userID string, req *cursor.PageRequest) (*cursor.CursorPageResult[*model.Post], error) {
+	// 规范化请求参数
+	req.Normalize()
+
+	// 如果Gorse未启用或用户未登录，降级为热门帖子
+	if !s.gorseClient.IsEnabled() || userID == "" {
+		return s.GetHotPostsByCursor(ctx, req)
+	}
+
+	// 计算偏移量：第一页使用随机偏移量，增加推荐多样性
+	var offset int
+	if req.Cursor == "" {
+		// 第一页随机偏移 0-50，让每次刷新看到不同的推荐内容
+		offset = rand.Intn(51)
+	} else {
+		// 尝试解析游标作为偏移量
+		if parsed, err := strconv.Atoi(req.Cursor); err == nil {
+			offset = parsed
+		}
+	}
+
+	// 从Gorse获取推荐列表
+	// 多取1条用于判断是否还有下一页
+	itemIDs, err := s.gorseClient.GetRecommend(ctx, userID, req.PageSize+1, offset)
+	if err != nil {
+		log.Printf("[WARN] Gorse recommendation failed: %v, fallback to hot posts", err)
+		return s.GetHotPostsByCursor(ctx, req)
+	}
+
+	// 如果没有推荐结果，降级为热门帖子
+	if len(itemIDs) == 0 {
+		return s.GetHotPostsByCursor(ctx, req)
+	}
+
+	hasMore := len(itemIDs) > req.PageSize
+	if hasMore {
+		itemIDs = itemIDs[:req.PageSize]
+	}
+
+	// 根据ID列表查询帖子详情
+	posts, err := s.postRepo.GetByIDs(itemIDs)
+	if err != nil {
+		return nil, err
+	}
+
+	// 下一页的游标是当前偏移量 + 已获取数量
+	nextCursor := ""
+	if hasMore {
+		nextCursor = strconv.Itoa(offset + req.PageSize)
+	}
+
+	return &cursor.CursorPageResult[*model.Post]{
+		Items:      posts,
+		NextCursor: nextCursor,
+		PrevCursor: "",
+		HasMore:    hasMore,
+	}, nil
+}