backend/internal/dto/post_converter.go

package dto

import (
	"context"
	"encoding/json"
	"with_you/internal/model"
)

// ==================== Post 转换 ====================

// ConvertPostImageToResponse 将PostImage转换为PostImageResponse
func ConvertPostImageToResponse(img *model.PostImage) PostImageResponse {
	if img == nil {
		return PostImageResponse{}
	}
	return PostImageResponse{
		ID:              img.ID,
		URL:             img.URL,
		ThumbnailURL:    img.ThumbnailURL,
		PreviewURL:      img.PreviewURL,
		PreviewURLLarge: img.PreviewURLLarge,
		Width:           img.Width,
		Height:          img.Height,
	}
}

// ConvertPostImagesToResponse 将PostImage列表转换为响应列表
func ConvertPostImagesToResponse(images []model.PostImage) []PostImageResponse {
	result := make([]PostImageResponse, 0, len(images))
	for i := range images {
		result = append(result, ConvertPostImageToResponse(&images[i]))
	}
	return result
}

func postChannelBrief(post *model.Post, channelByID map[string]*model.Channel) *PostChannelBrief {
	if post == nil || post.ChannelID == nil || *post.ChannelID == "" || channelByID == nil {
		return nil
	}
	ch := channelByID[*post.ChannelID]
	if ch == nil {
		return nil
	}
	return &PostChannelBrief{ID: ch.ID, Name: ch.Name}
}

// CollectPostChannelIDs 从帖子列表收集去重后的频道 ID（用于批量查库填充 channel 名称）
func CollectPostChannelIDs(posts []*model.Post) []string {
	seen := make(map[string]struct{})
	out := make([]string, 0)
	for _, p := range posts {
		if p == nil || p.ChannelID == nil || *p.ChannelID == "" {
			continue
		}
		id := *p.ChannelID
		if _, ok := seen[id]; ok {
			continue
		}
		seen[id] = struct{}{}
		out = append(out, id)
	}
	return out
}

// PostChannelBriefForPost 根据帖子与频道映射生成频道摘要（供 Handler 手动组装响应）
func PostChannelBriefForPost(post *model.Post, channelByID map[string]*model.Channel) *PostChannelBrief {
	return postChannelBrief(post, channelByID)
}

// SegmentsOrDefault 如果 segments 为空但 content 非空，
// 返回降级的单 text segment；否则原样返回。
func SegmentsOrDefault(segments model.MessageSegments, content string) model.MessageSegments {
	if len(segments) > 0 {
		return segments
	}
	if content != "" {
		return model.MessageSegments{
			{Type: string(SegmentTypeText), Data: map[string]any{"text": content}},
		}
	}
	return nil
}

// ConvertPostToResponse 将Post转换为PostResponse（列表用）；channelByID 可为 nil
func ConvertPostToResponse(post *model.Post, channelByID map[string]*model.Channel, isLiked, isFavorited bool) *PostResponse {
	if post == nil {
		return nil
	}

	images := make([]PostImageResponse, 0)
	for _, img := range post.Images {
		images = append(images, ConvertPostImageToResponse(&img))
	}

	var author *UserResponse
	if post.User != nil {
		author = ConvertUserToResponse(post.User)
	}

	return &PostResponse{
		ID:              post.ID,
		UserID:          post.UserID,
		ChannelID:       post.ChannelID,
		Title:           post.Title,
		Content:         post.Content,
		Segments:        SegmentsOrDefault(post.Segments, post.Content),
		Images:          images,
		Status:          string(post.Status),
		LikesCount:      post.LikesCount,
		CommentsCount:   post.CommentsCount,
		FavoritesCount:  post.FavoritesCount,
		SharesCount:     post.SharesCount,
		ViewsCount:      post.ViewsCount,
		IsPinned:        post.IsPinned,
		IsLocked:        post.IsLocked,
		IsVote:          post.IsVote,
		CreatedAt:       FormatTime(post.CreatedAt),
		UpdatedAt:       FormatTime(post.UpdatedAt),
		ContentEditedAt: FormatTimePointer(post.ContentEditedAt),
		Author:          author,
		IsLiked:         isLiked,
		IsFavorited:     isFavorited,
		Channel:         postChannelBrief(post, channelByID),
	}
}

// ConvertPostsToResponse 将Post列表转换为响应列表；channelByID 可为 nil
func ConvertPostsToResponse(posts []*model.Post, channelByID map[string]*model.Channel, isLikedMap, isFavoritedMap map[string]bool) []*PostResponse {
	result := make([]*PostResponse, 0, len(posts))
	for _, post := range posts {
		isLiked := false
		isFavorited := false
		if isLikedMap != nil {
			isLiked = isLikedMap[post.ID]
		}
		if isFavoritedMap != nil {
			isFavorited = isFavoritedMap[post.ID]
		}
		result = append(result, ConvertPostToResponse(post, channelByID, isLiked, isFavorited))
	}
	return result
}

// BuildPostResponse 构建单个帖子响应（包含交互状态）
// 这是一个语义化的辅助函数，便于 Handler 层调用
func BuildPostResponse(post *model.Post, channelByID map[string]*model.Channel, isLiked, isFavorited bool) *PostResponse {
	return ConvertPostToResponse(post, channelByID, isLiked, isFavorited)
}

// BuildPostsWithInteractionResponse 批量构建帖子响应（包含交互状态）
// 这是一个语义化的辅助函数，便于 Handler 层调用
func BuildPostsWithInteractionResponse(posts []*model.Post, channelByID map[string]*model.Channel, isLikedMap, isFavoritedMap map[string]bool) []*PostResponse {
	return ConvertPostsToResponse(posts, channelByID, isLikedMap, isFavoritedMap)
}

// ==================== Comment 转换 ====================

// ConvertCommentToResponse 将Comment转换为CommentResponse
func ConvertCommentToResponse(comment *model.Comment, isLiked bool) *CommentResponse {
	if comment == nil {
		return nil
	}

	var author *UserResponse
	if comment.User != nil {
		author = ConvertUserToResponse(comment.User)
	}

	// 转换子回复（扁平化结构）
	var replies []*CommentResponse
	if len(comment.Replies) > 0 {
		replies = make([]*CommentResponse, 0, len(comment.Replies))
		for _, reply := range comment.Replies {
			replies = append(replies, ConvertCommentToResponse(reply, false))
		}
	}

	// TargetID 就是 ParentID，前端根据这个 ID 找到被回复用户的昵称
	var targetID *string
	if comment.ParentID != nil && *comment.ParentID != "" {
		targetID = comment.ParentID
	}

	// 解析图片JSON
	var images []CommentImageResponse
	if comment.Images != "" {
		var urlList []string
		if err := json.Unmarshal([]byte(comment.Images), &urlList); err == nil {
			images = make([]CommentImageResponse, 0, len(urlList))
			for _, url := range urlList {
				images = append(images, CommentImageResponse{URL: url})
			}
		}
	}

	return &CommentResponse{
		ID:           comment.ID,
		PostID:       comment.PostID,
		UserID:       comment.UserID,
		ParentID:     comment.ParentID,
		RootID:       comment.RootID,
		Content:      comment.Content,
		Segments:     SegmentsOrDefault(comment.Segments, comment.Content),
		Images:       images,
		LikesCount:   comment.LikesCount,
		RepliesCount: comment.RepliesCount,
		CreatedAt:    FormatTime(comment.CreatedAt),
		Author:       author,
		IsLiked:      isLiked,
		TargetID:     targetID,
		Replies:      replies,
	}
}


// IsLikedChecker 点赞状态检查器接口
type IsLikedChecker interface {
	IsLiked(ctx context.Context, commentID, userID string) bool
}

// ConvertCommentToResponseWithUser 将Comment转换为CommentResponse（根据用户ID检查点赞状态）
func ConvertCommentToResponseWithUser(comment *model.Comment, userID string, checker IsLikedChecker) *CommentResponse {
	if comment == nil {
		return nil
	}

	// 检查当前用户是否点赞了该评论
	isLiked := false
	if userID != "" && checker != nil {
		isLiked = checker.IsLiked(context.Background(), comment.ID, userID)
	}

	var author *UserResponse
	if comment.User != nil {
		author = ConvertUserToResponse(comment.User)
	}

	// 转换子回复（扁平化结构），递归检查点赞状态
	var replies []*CommentResponse
	if len(comment.Replies) > 0 {
		replies = make([]*CommentResponse, 0, len(comment.Replies))
		for _, reply := range comment.Replies {
			replies = append(replies, ConvertCommentToResponseWithUser(reply, userID, checker))
		}
	}

	// TargetID 就是 ParentID，前端根据这个 ID 找到被回复用户的昵称
	var targetID *string
	if comment.ParentID != nil && *comment.ParentID != "" {
		targetID = comment.ParentID
	}

	// 解析图片JSON
	var images []CommentImageResponse
	if comment.Images != "" {
		var urlList []string
		if err := json.Unmarshal([]byte(comment.Images), &urlList); err == nil {
			images = make([]CommentImageResponse, 0, len(urlList))
			for _, url := range urlList {
				images = append(images, CommentImageResponse{URL: url})
			}
		}
	}

	return &CommentResponse{
		ID:           comment.ID,
		PostID:       comment.PostID,
		UserID:       comment.UserID,
		ParentID:     comment.ParentID,
		RootID:       comment.RootID,
		Content:      comment.Content,
		Segments:     SegmentsOrDefault(comment.Segments, comment.Content),
		Images:       images,
		LikesCount:   comment.LikesCount,
		RepliesCount: comment.RepliesCount,
		CreatedAt:    FormatTime(comment.CreatedAt),
		Author:       author,
		IsLiked:      isLiked,
		TargetID:     targetID,
		Replies:      replies,
	}
}

// ConvertCommentsToResponseWithUser 将Comment列表转换为响应列表（根据用户ID检查点赞状态）
func ConvertCommentsToResponseWithUser(comments []*model.Comment, userID string, checker IsLikedChecker) []*CommentResponse {
	result := make([]*CommentResponse, 0, len(comments))
	for _, comment := range comments {
		result = append(result, ConvertCommentToResponseWithUser(comment, userID, checker))
	}
	return result
}