jiang13-bbs/backend/service/snippet.go

package service

import (
	"errors"
	"fmt"
	"strings"
	"sync"
	"time"
	"unicode/utf8"

	"github.com/freefire/jiang13-bbs/model"
	"gorm.io/gorm"
)

// 代码片段语言白名单（与前端 highlight.js 注册表对齐）
var snippetLanguages = map[string]struct{}{
	"plaintext": {}, "bash": {}, "c": {}, "cpp": {}, "csharp": {}, "css": {},
	"dart": {}, "diff": {}, "dockerfile": {}, "go": {}, "graphql": {}, "html": {},
	"ini": {}, "java": {}, "javascript": {}, "json": {}, "jsonc": {}, "jsx": {},
	"kotlin": {}, "lua": {}, "makefile": {}, "markdown": {}, "nginx": {}, "php": {},
	"powershell": {}, "prisma": {}, "python": {}, "r": {}, "regex": {}, "ruby": {},
	"rust": {}, "scss": {}, "shell": {}, "sql": {}, "swift": {}, "toml": {},
	"tsx": {}, "typescript": {}, "vue": {}, "xml": {}, "yaml": {},
}

const (
	snippetTitleMaxRunes = 120
	snippetDescMaxBytes  = 8 << 10  // 8KB
	snippetCodeMaxBytes  = 64 << 10 // 64KB
	snippetCommentMaxLen = 2000
	snippetCopyThrottle  = 10 * time.Second
)

var (
	ErrSnippetNotFound  = errors.New("代码片段不存在")
	ErrSnippetForbidden = errors.New("无权操作该代码片段")
	ErrSnippetBadInput  = errors.New("代码片段参数无效")
)

// SnippetLanguages 返回支持的语言白名单（排序固定，便于前端渲染）
func SnippetLanguages() []string {
	out := make([]string, 0, len(snippetLanguages))
	for k := range snippetLanguages {
		out = append(out, k)
	}
	// 固定排序：plaintext 置顶，其余按字典序
	plaintext := []string{"plaintext"}
	var rest []string
	for _, v := range out {
		if v != "plaintext" {
			rest = append(rest, v)
		}
	}
	for i := 0; i < len(rest)-1; i++ {
		for j := i + 1; j < len(rest); j++ {
			if rest[i] > rest[j] {
				rest[i], rest[j] = rest[j], rest[i]
			}
		}
	}
	return append(plaintext, rest...)
}

// normalizeSnippetLanguage 空值回落 plaintext，不在白名单则报错
func normalizeSnippetLanguage(lang string) (string, error) {
	lang = strings.ToLower(strings.TrimSpace(lang))
	if lang == "" {
		return "plaintext", nil
	}
	if _, ok := snippetLanguages[lang]; !ok {
		return "", ErrSnippetBadInput
	}
	return lang, nil
}

// SnippetInput 创建/更新代码片段入参
type SnippetInput struct {
	Title       string `json:"title"`
	Language    string `json:"language"`
	Description string `json:"description"`
	Code        string `json:"code"`
	Visibility  string `json:"visibility"`
}

// badInput 输入校验错误（wrap ErrSnippetBadInput，handler 据此返回 400）
func badInput(msg string) error {
	return fmt.Errorf("%w: %s", ErrSnippetBadInput, msg)
}

func (in *SnippetInput) normalize() error {
	in.Title = strings.TrimSpace(in.Title)
	if in.Title == "" {
		return badInput("标题不能为空")
	}
	if utf8.RuneCountInString(in.Title) > snippetTitleMaxRunes {
		return badInput("标题不能超过 120 字")
	}
	lang, err := normalizeSnippetLanguage(in.Language)
	if err != nil {
		return badInput("不支持的语言")
	}
	in.Language = lang
	if strings.TrimSpace(in.Code) == "" {
		return badInput("代码不能为空")
	}
	if len(in.Code) > snippetCodeMaxBytes {
		return badInput("代码不能超过 64KB")
	}
	in.Description = strings.TrimSpace(in.Description)
	if len(in.Description) > snippetDescMaxBytes {
		return badInput("描述不能超过 8KB")
	}
	in.Visibility = model.NormalizeSnippetVisibility(in.Visibility)
	return nil
}

// SnippetOwner 片段所有者摘要
type SnippetOwner struct {
	ID       uint   `json:"id"`
	Username string `json:"username"`
	Nickname string `json:"nickname"`
	Avatar   string `json:"avatar"`
}

// SnippetForkedFrom 源片段摘要
type SnippetForkedFrom struct {
	ID    uint   `json:"id"`
	Title string `json:"title"`
}

// SnippetDetail 片段详情（含所有者与源片段摘要）
type SnippetDetail struct {
	model.CodeSnippet
	User        *SnippetOwner      `json:"user,omitempty"`
	ForkedFrom  *SnippetForkedFrom `json:"forked_from,omitempty"`
}

// SnippetListItem 广场/我的列表项（不含 code 全文，仅前 300 字符作预览）
type SnippetListItem struct {
	ID           uint          `json:"id"`
	Title        string        `json:"title"`
	Language     string        `json:"language"`
	Description  string        `json:"description"`
	Preview      string        `json:"preview"` // code 前 300 字符
	Visibility   string        `json:"visibility"`
	UserID       uint          `json:"user_id"`
	CopyCount    int           `json:"copy_count"`
	ViewCount    int           `json:"view_count"`
	CommentCount int           `json:"comment_count"`
	ForkCount    int           `json:"fork_count"`
	ForkedFromID *uint          `json:"forked_from_id,omitempty"`
	User         *SnippetOwner  `json:"user,omitempty"`
	CreatedAt    time.Time      `json:"created_at"`
	UpdatedAt    time.Time      `json:"updated_at"`
}

// SnippetCommentNode 片段评论节点（主评带 replies，软删 tombstone 占位）
type SnippetCommentNode struct {
	model.SnippetComment
	Floor   int                  `json:"floor"`   // 主评楼层号（含软删）
	Deleted bool                 `json:"deleted"` // 软删标记
	Edited  bool                 `json:"edited"`  // 相对创建已编辑
	User    *SnippetOwner        `json:"user,omitempty"`
	Replies []SnippetCommentNode `json:"replies,omitempty"`
}

// SnippetService 代码片段服务
type SnippetService struct {
	db          *gorm.DB
	copyMu      sync.Mutex
	copyRecords map[string]time.Time // key=userID 或 IP，10s 内只计一次
	statsMu     sync.Mutex
	statsCache  *SnippetStats
	statsAt     time.Time
}

func NewSnippetService(db *gorm.DB) *SnippetService {
	return &SnippetService{db: db, copyRecords: make(map[string]time.Time)}
}

// escapeILike 转义 ILIKE 特殊字符 % 和 _
func escapeILike(s string) string {
	s = strings.ReplaceAll(s, `\`, `\\`)
	s = strings.ReplaceAll(s, `%`, `\%`)
	s = strings.ReplaceAll(s, `_`, `\_`)
	return s
}

// SnippetLangStat 语言分布项
type SnippetLangStat struct {
	Language string `json:"language"`
	Count    int64  `json:"count"`
}

// SnippetStats 片段广场聚合统计（仅公开片段）
type SnippetStats struct {
	TotalSnippets int64             `json:"total_snippets"`
	TotalCopies   int64             `json:"total_copies"`
	TotalViews    int64             `json:"total_views"`
	TotalComments int64             `json:"total_comments"`
	TotalForks    int64             `json:"total_forks"`
	Contributors  int64             `json:"contributors"`
	TopLanguages  []SnippetLangStat `json:"top_languages"`
}

const snippetStatsTTL = 30 * time.Second

// Stats 广场聚合统计（30s 内存缓存）
func (s *SnippetService) Stats() (*SnippetStats, error) {
	s.statsMu.Lock()
	if s.statsCache != nil && time.Since(s.statsAt) < snippetStatsTTL {
		cached := s.statsCache
		s.statsMu.Unlock()
		return cached, nil
	}
	s.statsMu.Unlock()

	pub := func() *gorm.DB {
		return s.db.Model(&model.CodeSnippet{}).Where("visibility = ?", model.SnippetVisibilityPublic)
	}

	var agg struct {
		Total    int64
		Copies   int64
		Views    int64
		Comments int64
		Forks    int64
	}
	if err := pub().
		Select("COUNT(*) AS total, COALESCE(SUM(copy_count),0) AS copies, COALESCE(SUM(view_count),0) AS views, COALESCE(SUM(comment_count),0) AS comments, COALESCE(SUM(fork_count),0) AS forks").
		Scan(&agg).Error; err != nil {
		return nil, err
	}

	var contributors int64
	if err := pub().Distinct("user_id").Count(&contributors).Error; err != nil {
		return nil, err
	}

	langs := make([]SnippetLangStat, 0, 6)
	if err := pub().
		Select("language, COUNT(*) AS count").
		Group("language").
		Order("count DESC, language ASC").
		Limit(6).
		Scan(&langs).Error; err != nil {
		return nil, err
	}

	st := &SnippetStats{
		TotalSnippets: agg.Total,
		TotalCopies:   agg.Copies,
		TotalViews:    agg.Views,
		TotalComments: agg.Comments,
		TotalForks:    agg.Forks,
		Contributors:  contributors,
		TopLanguages:  langs,
	}

	s.statsMu.Lock()
	s.statsCache = st
	s.statsAt = time.Now()
	s.statsMu.Unlock()
	return st, nil
}

// toListItem 模型转列表项（截断 code 生成 preview）
func toSnippetListItem(s model.CodeSnippet, owner *SnippetOwner) SnippetListItem {
	preview := s.Code
	if len(preview) > 300 {
		preview = preview[:300]
	}
	return SnippetListItem{
		ID:           s.ID,
		Title:        s.Title,
		Language:     s.Language,
		Description:  s.Description,
		Preview:      preview,
		Visibility:   s.Visibility,
		UserID:       s.UserID,
		CopyCount:    s.CopyCount,
		ViewCount:    s.ViewCount,
		CommentCount: s.CommentCount,
		ForkCount:    s.ForkCount,
		ForkedFromID: s.ForkedFromID,
		User:         owner,
		CreatedAt:    s.CreatedAt,
		UpdatedAt:    s.UpdatedAt,
	}
}

// ownerMap 批量取所有者摘要（避免 N+1）
func (s *SnippetService) ownerMap(ids []uint) map[uint]*SnippetOwner {
	if len(ids) == 0 {
		return map[uint]*SnippetOwner{}
	}
	uniq := make([]uint, 0, len(ids))
	seen := map[uint]bool{}
	for _, id := range ids {
		if !seen[id] {
			seen[id] = true
			uniq = append(uniq, id)
		}
	}
	var users []model.User
	if err := s.db.Select("id, username, nickname, avatar").Where("id IN ?", uniq).Find(&users).Error; err != nil {
		return map[uint]*SnippetOwner{}
	}
	m := make(map[uint]*SnippetOwner, len(users))
	for i := range users {
		u := &users[i]
		m[u.ID] = &SnippetOwner{ID: u.ID, Username: u.Username, Nickname: u.Nickname, Avatar: u.Avatar}
	}
	return m
}

// Create 创建代码片段
func (s *SnippetService) Create(in *SnippetInput, userID uint) (*model.CodeSnippet, error) {
	if err := in.normalize(); err != nil {
		return nil, err
	}
	snippet := &model.CodeSnippet{
		Title:       in.Title,
		Language:    in.Language,
		Description: in.Description,
		Code:        in.Code,
		Visibility:  in.Visibility,
		UserID:      userID,
	}
	if err := s.db.Create(snippet).Error; err != nil {
		return nil, err
	}
	return snippet, nil
}

// Update 更新代码片段（仅 owner 或 staff；编辑前落 SnippetVersion）
func (s *SnippetService) Update(id uint, in *SnippetInput, editorID uint, isStaff bool) (*model.CodeSnippet, error) {
	var snippet model.CodeSnippet
	if err := s.db.First(&snippet, id).Error; err != nil {
		return nil, ErrSnippetNotFound
	}
	if snippet.UserID != editorID && !isStaff {
		return nil, ErrSnippetForbidden
	}
	if err := in.normalize(); err != nil {
		return nil, err
	}

	// 判断是否有实际字段变化
	changed := snippet.Title != in.Title ||
		snippet.Language != in.Language ||
		snippet.Description != in.Description ||
		snippet.Code != in.Code ||
		snippet.Visibility != in.Visibility

	if changed {
		ver := model.SnippetVersion{
			SnippetID:      snippet.ID,
			EditorID:       editorID,
			OldTitle:       snippet.Title,
			OldLanguage:    snippet.Language,
			OldDescription: snippet.Description,
			OldCode:        snippet.Code,
		}
		if err := s.db.Create(&ver).Error; err != nil {
			return nil, err
		}
	}

	snippet.Title = in.Title
	snippet.Language = in.Language
	snippet.Description = in.Description
	snippet.Code = in.Code
	oldVisibility := snippet.Visibility
	snippet.Visibility = in.Visibility

	err := s.db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Model(&snippet).Updates(map[string]interface{}{
			"title":       snippet.Title,
			"language":    snippet.Language,
			"description": snippet.Description,
			"code":        snippet.Code,
			"visibility":  snippet.Visibility,
		}).Error; err != nil {
			return err
		}
		// fork 副本在私有/公开之间切换时，同步源片段的公开 fork 计数
		if snippet.ForkedFromID != nil && oldVisibility != snippet.Visibility {
			expr := "GREATEST(fork_count - 1, 0)"
			if snippet.Visibility == model.SnippetVisibilityPublic {
				expr = "fork_count + 1"
			}
			if err := tx.Model(&model.CodeSnippet{}).Where("id = ?", *snippet.ForkedFromID).
				UpdateColumn("fork_count", gorm.Expr(expr)).Error; err != nil {
				return err
			}
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	return &snippet, nil
}

// GetPublic 获取片段详情（public 或 owner/staff 可见）
func (s *SnippetService) GetPublic(id uint, viewerID uint, isStaff bool) (*SnippetDetail, error) {
	var snippet model.CodeSnippet
	if err := s.db.First(&snippet, id).Error; err != nil {
		return nil, ErrSnippetNotFound
	}
	if snippet.Visibility != model.SnippetVisibilityPublic && snippet.UserID != viewerID && !isStaff {
		return nil, ErrSnippetNotFound
	}
	// ViewCount++（失败不影响主流程）
	s.db.Model(&snippet).UpdateColumn("view_count", gorm.Expr("view_count + 1"))

	ownerMap := s.ownerMap([]uint{snippet.UserID})
	detail := &SnippetDetail{
		CodeSnippet: snippet,
		User:        ownerMap[snippet.UserID],
	}
	if snippet.ForkedFromID != nil {
		var src model.CodeSnippet
		if err := s.db.Select("id, title").First(&src, *snippet.ForkedFromID).Error; err == nil {
			detail.ForkedFrom = &SnippetForkedFrom{ID: src.ID, Title: src.Title}
		}
	}
	return detail, nil
}

// ListPublic 公开广场列表（仅 public 未删）
func (s *SnippetService) ListPublic(q, lang, sort string, page, size int) ([]SnippetListItem, int64, error) {
	if page < 1 {
		page = 1
	}
	if size < 1 || size > 50 {
		size = 12
	}
	db := s.db.Model(&model.CodeSnippet{}).Where("visibility = ?", model.SnippetVisibilityPublic)

	if q = strings.TrimSpace(q); q != "" {
		like := "%" + escapeILike(q) + "%"
		db = db.Where("title ILIKE ? OR description ILIKE ? OR code ILIKE ?", like, like, like)
	}
	if lang != "" {
		if _, ok := snippetLanguages[lang]; ok {
			db = db.Where("language = ?", lang)
		}
	}

	var total int64
	if err := db.Count(&total).Error; err != nil {
		return nil, 0, err
	}

	switch sort {
	case "copy":
		db = db.Order("copy_count DESC, id DESC")
	case "comment":
		db = db.Order("comment_count DESC, id DESC")
	case "fork":
		db = db.Order("fork_count DESC, id DESC")
	default:
		db = db.Order("created_at DESC, id DESC")
	}

	var snippets []model.CodeSnippet
	if err := db.Offset((page - 1) * size).Limit(size).Find(&snippets).Error; err != nil {
		return nil, 0, err
	}
	ownerIDs := make([]uint, 0, len(snippets))
	for _, sn := range snippets {
		ownerIDs = append(ownerIDs, sn.UserID)
	}
	owners := s.ownerMap(ownerIDs)
	items := make([]SnippetListItem, 0, len(snippets))
	for _, sn := range snippets {
		items = append(items, toSnippetListItem(sn, owners[sn.UserID]))
	}
	return items, total, nil
}

// ListMine 我的片段列表（含私有）
func (s *SnippetService) ListMine(userID uint, q string, page, size int) ([]SnippetListItem, int64, error) {
	if page < 1 {
		page = 1
	}
	if size < 1 || size > 50 {
		size = 12
	}
	db := s.db.Model(&model.CodeSnippet{}).Where("user_id = ?", userID)
	if q = strings.TrimSpace(q); q != "" {
		like := "%" + escapeILike(q) + "%"
		db = db.Where("title ILIKE ? OR description ILIKE ? OR code ILIKE ?", like, like, like)
	}

	var total int64
	if err := db.Count(&total).Error; err != nil {
		return nil, 0, err
	}

	var snippets []model.CodeSnippet
	if err := db.Order("created_at DESC, id DESC").Offset((page - 1) * size).Limit(size).Find(&snippets).Error; err != nil {
		return nil, 0, err
	}
	ownerIDs := make([]uint, 0, len(snippets))
	for _, sn := range snippets {
		ownerIDs = append(ownerIDs, sn.UserID)
	}
	owners := s.ownerMap(ownerIDs)
	items := make([]SnippetListItem, 0, len(snippets))
	for _, sn := range snippets {
		items = append(items, toSnippetListItem(sn, owners[sn.UserID]))
	}
	return items, total, nil
}

// Fork 复制公开片段为自己的私有片段
func (s *SnippetService) Fork(id uint, userID uint) (*model.CodeSnippet, error) {
	var src model.CodeSnippet
	if err := s.db.First(&src, id).Error; err != nil {
		return nil, ErrSnippetNotFound
	}
	if src.Visibility != model.SnippetVisibilityPublic {
		return nil, ErrSnippetForbidden
	}

	fork := &model.CodeSnippet{
		Title:        src.Title,
		Language:     src.Language,
		Description:  src.Description,
		Code:         src.Code,
		Visibility:   model.SnippetVisibilityPrivate,
		UserID:       userID,
		ForkedFromID: &src.ID,
	}
	// 源标题本身已受限长约束，无需再次截断

	// 副本初始为私有，不计入源片段的公开 fork 数；
	// 作者将其改为公开时（见 Update）再计数。
	if err := s.db.Create(fork).Error; err != nil {
		return nil, err
	}
	return fork, nil
}

// RecordCopy 复制计数（按 key 节流 10s）
func (s *SnippetService) RecordCopy(id uint, key string) error {
	s.copyMu.Lock()
	now := time.Now()
	if t, ok := s.copyRecords[key]; ok && now.Sub(t) < snippetCopyThrottle {
		s.copyMu.Unlock()
		return nil
	}
	s.copyRecords[key] = now
	// 清理过期记录（简单 LRU，防止内存膨胀）
	if len(s.copyRecords) > 10000 {
		for k, v := range s.copyRecords {
			if now.Sub(v) > time.Minute {
				delete(s.copyRecords, k)
			}
		}
	}
	s.copyMu.Unlock()

	var snippet model.CodeSnippet
	if err := s.db.First(&snippet, id).Error; err != nil {
		return ErrSnippetNotFound
	}
	return s.db.Model(&snippet).UpdateColumn("copy_count", gorm.Expr("copy_count + 1")).Error
}

// Delete 软删片段（owner 或 staff）
func (s *SnippetService) Delete(id uint, actorID uint, isStaff bool) error {
	var snippet model.CodeSnippet
	if err := s.db.First(&snippet, id).Error; err != nil {
		return ErrSnippetNotFound
	}
	if snippet.UserID != actorID && !isStaff {
		return ErrSnippetForbidden
	}
	return s.db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Delete(&snippet).Error; err != nil {
			return err
		}
		// 删除公开的 fork 副本时，回溯源片段的公开 fork 计数；
		// 私有副本从未计入，无需回溯。
		if snippet.ForkedFromID != nil && snippet.Visibility == model.SnippetVisibilityPublic {
			if err := tx.Model(&model.CodeSnippet{}).Where("id = ?", *snippet.ForkedFromID).
				UpdateColumn("fork_count", gorm.Expr("GREATEST(fork_count - 1, 0)")).Error; err != nil {
				return err
			}
		}
		return nil
	})
}

// ListHistory 版本历史（倒序分页）
func (s *SnippetService) ListHistory(snippetID uint, page, size int) ([]model.SnippetVersion, int64, error) {
	if page < 1 {
		page = 1
	}
	if size < 1 || size > 50 {
		size = 10
	}
	var total int64
	if err := s.db.Model(&model.SnippetVersion{}).Where("snippet_id = ?", snippetID).Count(&total).Error; err != nil {
		return nil, 0, err
	}
	var versions []model.SnippetVersion
	if err := s.db.Where("snippet_id = ?", snippetID).
		Order("created_at DESC, id DESC").
		Offset((page - 1) * size).Limit(size).
		Find(&versions).Error; err != nil {
		return nil, 0, err
	}
	return versions, total, nil
}

// ListForks 公开 fork 列表（一层）
func (s *SnippetService) ListForks(id uint, page, size int) ([]SnippetListItem, int64, error) {
	if page < 1 {
		page = 1
	}
	if size < 1 || size > 50 {
		size = 12
	}
	db := s.db.Model(&model.CodeSnippet{}).
		Where("forked_from_id = ? AND visibility = ?", id, model.SnippetVisibilityPublic)

	var total int64
	if err := db.Count(&total).Error; err != nil {
		return nil, 0, err
	}

	var snippets []model.CodeSnippet
	if err := db.Order("created_at DESC, id DESC").Offset((page - 1) * size).Limit(size).Find(&snippets).Error; err != nil {
		return nil, 0, err
	}
	ownerIDs := make([]uint, 0, len(snippets))
	for _, sn := range snippets {
		ownerIDs = append(ownerIDs, sn.UserID)
	}
	owners := s.ownerMap(ownerIDs)
	items := make([]SnippetListItem, 0, len(snippets))
	for _, sn := range snippets {
		items = append(items, toSnippetListItem(sn, owners[sn.UserID]))
	}
	return items, total, nil
}

// snippetFloorNumber 主评楼层号（含软删，按 created_at/id 升序）
func (s *SnippetService) snippetFloorNumber(snippetID, commentID uint) int {
	var c model.SnippetComment
	if err := s.db.Unscoped().Select("id", "snippet_id", "parent_id", "root_id", "created_at").
		Where("id = ? AND snippet_id = ?", commentID, snippetID).First(&c).Error; err != nil {
		return 0
	}
	floorID := c.ID
	floorCreated := c.CreatedAt
	if c.ParentID != nil {
		rootID := c.ID
		if c.RootID != nil {
			rootID = *c.RootID
		}
		var root model.SnippetComment
		if err := s.db.Unscoped().Select("id", "created_at").
			Where("id = ? AND snippet_id = ? AND parent_id IS NULL", rootID, snippetID).First(&root).Error; err != nil {
			return 0
		}
		floorID = root.ID
		floorCreated = root.CreatedAt
	}
	var ahead int64
	s.db.Unscoped().Model(&model.SnippetComment{}).
		Where("snippet_id = ? AND parent_id IS NULL AND (created_at < ? OR (created_at = ? AND id < ?))",
			snippetID, floorCreated, floorCreated, floorID).
		Count(&ahead)
	return int(ahead) + 1
}

// toSnippetCommentNode 转评论节点（软删 tombstone 清空正文）
func toSnippetCommentNode(c model.SnippetComment, user *SnippetOwner, replies []SnippetCommentNode, floor int) SnippetCommentNode {
	edited := c.UpdatedAt.Sub(c.CreatedAt) > time.Minute
	if c.DeletedAt.Valid {
		c.Content = ""
		return SnippetCommentNode{
			SnippetComment: c,
			Floor:          floor,
			Deleted:        true,
			Edited:         edited,
			User:           user,
			Replies:        replies,
		}
	}
	return SnippetCommentNode{
		SnippetComment: c,
		Floor:          floor,
		Deleted:        false,
		Edited:         edited,
		User:           user,
		Replies:        replies,
	}
}

// ListComments 片段评论列表（主评分页，含回复）
func (s *SnippetService) ListComments(snippetID uint, page, size int) ([]SnippetCommentNode, int64, error) {
	if page < 1 {
		page = 1
	}
	if size < 1 || size > 100 {
		size = 20
	}
	// tombstone 语义：软删评论保留占位壳（内容清空，前端显示"该评论已删除"），
	// 其子回复仍挂在壳下；因此列表/计数均使用 Unscoped 包含软删行。
	base := s.db.Unscoped().Model(&model.SnippetComment{}).Where("snippet_id = ?", snippetID)

	var total int64
	if err := base.Count(&total).Error; err != nil {
		return nil, 0, err
	}

	var roots []model.SnippetComment
	if err := s.db.Unscoped().Where("snippet_id = ? AND parent_id IS NULL", snippetID).
		Order("created_at ASC, id ASC").
		Offset((page - 1) * size).Limit(size).
		Find(&roots).Error; err != nil {
		return nil, 0, err
	}
	if len(roots) == 0 {
		return []SnippetCommentNode{}, total, nil
	}

	rootIDs := make([]uint, len(roots))
	for i, r := range roots {
		rootIDs[i] = r.ID
	}
	var replies []model.SnippetComment
	if err := s.db.Unscoped().Where("snippet_id = ? AND root_id IN ?", snippetID, rootIDs).
		Order("created_at ASC, id ASC").Find(&replies).Error; err != nil {
		return nil, 0, err
	}

	children := make(map[uint][]model.SnippetComment, len(replies))
	for _, r := range replies {
		if r.ParentID != nil {
			children[*r.ParentID] = append(children[*r.ParentID], r)
		}
	}

	allRows := make([]model.SnippetComment, 0, len(roots)+len(replies))
	allRows = append(allRows, roots...)
	allRows = append(allRows, replies...)
	userIDs := make([]uint, 0, len(allRows))
	for _, c := range allRows {
		userIDs = append(userIDs, c.UserID)
	}
	users := s.ownerMap(userIDs)

	var build func(pid uint) []SnippetCommentNode
	build = func(pid uint) []SnippetCommentNode {
		out := []SnippetCommentNode{}
		for _, c := range children[pid] {
			out = append(out, toSnippetCommentNode(c, users[c.UserID], build(c.ID), 0))
		}
		return out
	}

	result := make([]SnippetCommentNode, 0, len(roots))
	for _, r := range roots {
		floor := s.snippetFloorNumber(snippetID, r.ID)
		result = append(result, toSnippetCommentNode(r, users[r.UserID], build(r.ID), floor))
	}
	return result, total, nil
}

// CreateComment 创建片段评论
func (s *SnippetService) CreateComment(userID, snippetID uint, content string, parentID *uint) (*model.SnippetComment, error) {
	content = strings.TrimSpace(content)
	if content == "" {
		return nil, badInput("评论内容不能为空")
	}
	if utf8.RuneCountInString(content) > snippetCommentMaxLen {
		return nil, badInput("评论不能超过 2000 字")
	}

	var snippet model.CodeSnippet
	if err := s.db.First(&snippet, snippetID).Error; err != nil {
		return nil, ErrSnippetNotFound
	}
	if snippet.Visibility != model.SnippetVisibilityPublic {
		return nil, ErrSnippetNotFound
	}

	comment := &model.SnippetComment{
		SnippetID: snippetID,
		UserID:    userID,
		Content:   content,
	}

	if parentID != nil {
		var parent model.SnippetComment
		if err := s.db.Where("id = ? AND snippet_id = ? AND deleted_at IS NULL", *parentID, snippetID).First(&parent).Error; err != nil {
			return nil, badInput("回复的评论不存在")
		}
		if parent.Depth >= maxReplyDepth {
			return nil, badInput("回复层级过深")
		}
		rootID := parent.ID
		if parent.RootID != nil {
			rootID = *parent.RootID
		}
		comment.ParentID = parentID
		comment.RootID = &rootID
		comment.Depth = parent.Depth + 1
	}

	err := s.db.Transaction(func(tx *gorm.DB) error {
		if err := tx.Create(comment).Error; err != nil {
			return err
		}
		return tx.Model(&snippet).UpdateColumn("comment_count", gorm.Expr("comment_count + 1")).Error
	})
	if err != nil {
		return nil, err
	}
	return comment, nil
}

// UpdateComment 更新评论（仅本人）
func (s *SnippetService) UpdateComment(commentID, userID uint, content string) (*model.SnippetComment, error) {
	content = strings.TrimSpace(content)
	if content == "" {
		return nil, badInput("评论内容不能为空")
	}
	if utf8.RuneCountInString(content) > snippetCommentMaxLen {
		return nil, badInput("评论不能超过 2000 字")
	}
	var comment model.SnippetComment
	if err := s.db.First(&comment, commentID).Error; err != nil {
		return nil, ErrCommentNotFound
	}
	if comment.UserID != userID {
		return nil, ErrCommentForbidden
	}
	if comment.Content == content {
		return nil, ErrCommentNotChanged
	}
	old := comment.Content
	if err := s.db.Transaction(func(tx *gorm.DB) error {
		hist := model.SnippetCommentEditHistory{
			CommentID:  comment.ID,
			EditorID:   userID,
			OldContent: old,
		}
		if err := tx.Create(&hist).Error; err != nil {
			return err
		}
		return tx.Model(&comment).Update("content", content).Error
	}); err != nil {
		return nil, err
	}
	if err := s.db.First(&comment, comment.ID).Error; err != nil {
		return nil, err
	}
	return &comment, nil
}

// DeleteComment 软删评论（本人或 staff；tombstone：DeleteType/DeletedBy）
// 保留占位壳与楼层计数：评论数不减，列表中显示"该评论已删除"，子回复仍挂其下。
func (s *SnippetService) DeleteComment(commentID, userID uint, isStaff bool) error {
	var comment model.SnippetComment
	if err := s.db.First(&comment, commentID).Error; err != nil {
		return ErrCommentNotFound
	}
	if comment.UserID != userID && !isStaff {
		return ErrCommentForbidden
	}
	deleteType := "self"
	if comment.UserID != userID {
		deleteType = "admin"
	}
	if err := s.db.Model(&comment).Updates(map[string]interface{}{
		"delete_type": deleteType,
		"deleted_by":  userID,
	}).Error; err != nil {
		return err
	}
	return s.db.Delete(&comment).Error
}

// SnippetCommentHistoryItem 片段评论历史项
type SnippetCommentHistoryItem struct {
	ID         uint         `json:"id"`
	Editor     *SnippetOwner `json:"editor"`
	OldContent string       `json:"old_content"`
	CreatedAt  time.Time    `json:"created_at"`
}

// ListCommentHistory 片段评论编辑历史（登录即可见；含软删评论；倒序分页）
func (s *SnippetService) ListCommentHistory(actor *Actor, commentID uint, page, size int) ([]SnippetCommentHistoryItem, int64, error) {
	if page < 1 {
		page = 1
	}
	if size < 1 || size > 50 {
		size = 10
	}
	var comment model.SnippetComment
	if err := s.db.Unscoped().Select("id").First(&comment, commentID).Error; err != nil {
		return nil, 0, ErrCommentNotFound
	}
	if actor == nil {
		return nil, 0, ErrCommentForbidden
	}

	q := s.db.Model(&model.SnippetCommentEditHistory{}).Where("comment_id = ?", commentID)
	var total int64
	if err := q.Count(&total).Error; err != nil {
		return nil, 0, err
	}

	var rows []model.SnippetCommentEditHistory
	if err := s.db.Where("comment_id = ?", commentID).
		Order("created_at DESC").
		Offset((page - 1) * size).Limit(size).
		Find(&rows).Error; err != nil {
		return nil, 0, err
	}

	editorIDs := make([]uint, 0, len(rows))
	seen := map[uint]struct{}{}
	for _, r := range rows {
		if _, ok := seen[r.EditorID]; ok {
			continue
		}
		seen[r.EditorID] = struct{}{}
		editorIDs = append(editorIDs, r.EditorID)
	}
	editors := s.ownerMap(editorIDs)

	items := make([]SnippetCommentHistoryItem, 0, len(rows))
	for _, r := range rows {
		ed := editors[r.EditorID]
		if ed == nil {
			ed = &SnippetOwner{ID: r.EditorID, Username: "已注销", Nickname: "已注销"}
		}
		items = append(items, SnippetCommentHistoryItem{
			ID:         r.ID,
			Editor:     ed,
			OldContent: r.OldContent,
			CreatedAt:  r.CreatedAt,
		})
	}
	return items, total, nil
}

// AdminListSnippetItem 管理端片段列表项（含 code）
type AdminListSnippetItem struct {
	model.CodeSnippet
	User *SnippetOwner `json:"user,omitempty"`
}

// AdminList 管理端全量列表（含 code）
func (s *SnippetService) AdminList(q, visibility string, page, size int) ([]AdminListSnippetItem, int64, error) {
	if page < 1 {
		page = 1
	}
	if size < 1 || size > 50 {
		size = 20
	}
	db := s.db.Model(&model.CodeSnippet{})
	if q = strings.TrimSpace(q); q != "" {
		like := "%" + escapeILike(q) + "%"
		db = db.Where("title ILIKE ? OR description ILIKE ? OR code ILIKE ?", like, like, like)
	}
	if visibility != "" {
		db = db.Where("visibility = ?", model.NormalizeSnippetVisibility(visibility))
	}

	var total int64
	if err := db.Count(&total).Error; err != nil {
		return nil, 0, err
	}

	var snippets []model.CodeSnippet
	if err := db.Order("created_at DESC, id DESC").Offset((page - 1) * size).Limit(size).Find(&snippets).Error; err != nil {
		return nil, 0, err
	}
	ownerIDs := make([]uint, 0, len(snippets))
	for _, sn := range snippets {
		ownerIDs = append(ownerIDs, sn.UserID)
	}
	owners := s.ownerMap(ownerIDs)
	items := make([]AdminListSnippetItem, 0, len(snippets))
	for _, sn := range snippets {
		items = append(items, AdminListSnippetItem{CodeSnippet: sn, User: owners[sn.UserID]})
	}
	return items, total, nil
}

// AdminSetVisibility 管理端强制修改可见性
func (s *SnippetService) AdminSetVisibility(id uint, visibility string) error {
	visibility = model.NormalizeSnippetVisibility(visibility)
	result := s.db.Model(&model.CodeSnippet{}).Where("id = ?", id).Update("visibility", visibility)
	if result.Error != nil {
		return result.Error
	}
	if result.RowsAffected == 0 {
		return ErrSnippetNotFound
	}
	return nil
}

// AdminDelete 管理端软删（DeleteType=admin）
func (s *SnippetService) AdminDelete(id uint, adminID uint) error {
	var snippet model.CodeSnippet
	if err := s.db.First(&snippet, id).Error; err != nil {
		return ErrSnippetNotFound
	}
	return s.db.Delete(&snippet).Error
}