package service

import (
	"sort"
	"strings"
	"time"
	"unicode/utf8"

	"gorm.io/gorm"
	"kefu-cloud/server/internal/model"
)

// Actor 请求发起者（由 handler 从鉴权中间件结果构造），service 层据此做数据范围判断。
type Actor struct {
	UserID     uint
	SessionAll bool // 对 session 模块具有全量数据范围（主管/管理员）
	HistoryAll bool // 对 chat_history 模块具有全量数据范围
}

// SessionListItem 会话列表项（含批量补全的关联信息）。
type SessionListItem struct {
	model.Session
	UnreadCount   int        `json:"unread_count"`
	LastMessage   string     `json:"last_message"`
	LastMessageAt *time.Time `json:"last_message_at,omitempty"`
	MessageCount  int        `json:"message_count"`
	CustomerName  string     `json:"customer_name"`
	AgentName     string     `json:"agent_name"`
	ChannelName   string     `json:"channel_name"`
	ChannelType   string     `json:"channel_type"`
}

// AgentItem 可转接/筛选坐席项。
type AgentItem struct {
	ID       uint   `json:"id"`
	Nickname string `json:"nickname"`
	Status   string `json:"status"` // online | busy | offline | disabled
	Role     string `json:"role,omitempty"`
}

// SessionFilter 会话列表筛选。
type SessionFilter struct {
	Status    string
	Priority  string
	AgentID   string
	ChannelID string
	Search    string
	From      string
	To        string
	Page      int
	PageSize  int
}

// LoadTenantSession 加载本租户会话；跨租户访问返回 403。
func LoadTenantSession(id string, tenantID uint) (*model.Session, error) {
	var session model.Session
	if err := model.DB.First(&session, id).Error; err != nil {
		return nil, NotFound("会话不存在")
	}
	if session.TenantID != tenantID {
		return nil, Forbidden("无权访问其他租户会话")
	}
	return &session, nil
}

// CanReadSession 按会话状态区分数据范围（进行中走 session，已结束走 chat_history）。
func CanReadSession(actor Actor, session *model.Session) bool {
	all := actor.SessionAll
	if session.Status == "ended" || session.Status == "archived" {
		all = actor.HistoryAll
	}
	if all {
		return true
	}
	return session.Status == "waiting" || (session.AgentID != nil && *session.AgentID == actor.UserID)
}

// CanOperateSession 是否可操作（转接/结束/备注/发消息）该会话。
func CanOperateSession(actor Actor, session *model.Session) bool {
	if actor.SessionAll {
		return true
	}
	return session.AgentID != nil && *session.AgentID == actor.UserID
}

// loadAssignableAgent 校验目标坐席属于本租户、未停用，且具备接待能力。
func loadAssignableAgent(tenantID, agentID uint) error {
	var agent model.User
	if err := model.DB.First(&agent, agentID).Error; err != nil {
		return err
	}
	if agent.TenantID != tenantID || agent.Status == "disabled" {
		return gorm.ErrRecordNotFound
	}
	if agent.Role == "agent" {
		return nil
	}
	var count int64
	if err := model.DB.Table("roles r").
		Joins("JOIN role_permissions rp ON rp.role_id = r.id").
		Joins("JOIN permissions p ON p.id = rp.permission_id").
		Where("r.tenant_id = ? AND r.code = ? AND r.type = ? AND p.code = ?", tenantID, agent.Role, "custom", "session.reply").
		Count(&count).Error; err != nil || count == 0 {
		return gorm.ErrRecordNotFound
	}
	return nil
}

// assignableRoleCodes 可被分配/转接的角色（内置 agent + 拥有 session.reply 的自定义角色）。
func assignableRoleCodes(tenantID uint) []string {
	codes := []string{"agent"}
	var customCodes []string
	model.DB.Table("roles r").
		Joins("JOIN role_permissions rp ON rp.role_id = r.id").
		Joins("JOIN permissions p ON p.id = rp.permission_id").
		Where("r.tenant_id = ? AND r.type = ? AND p.code = ?", tenantID, "custom", "session.reply").
		Distinct().Pluck("r.code", &customCodes)
	return append(codes, customCodes...)
}

func unreadCount(session model.Session) int {
	var count int64
	model.DB.Model(&model.Message{}).
		Where("session_id = ? AND sender_type = ? AND seq > ?", session.ID, "visitor", session.LastReadSeq).
		Count(&count)
	return int(count)
}

// ListSessions 会话列表：筛选、分页并批量补全客户/坐席/渠道/消息数。
func ListSessions(actor Actor, tenantID uint, f SessionFilter) ([]SessionListItem, int64, error) {
	var sessions []model.Session
	var total int64

	query := model.DB.Model(&model.Session{}).Where("sessions.tenant_id = ?", tenantID)
	if !actor.SessionAll || !actor.HistoryAll {
		query = query.Where("sessions.agent_id = ? OR sessions.status = ?", actor.UserID, "waiting")
	}
	if f.Status != "" {
		query = query.Where("sessions.status = ?", f.Status)
	}
	if f.Priority != "" {
		query = query.Where("sessions.priority = ?", f.Priority)
	}
	if f.AgentID != "" {
		query = query.Where("sessions.agent_id = ?", f.AgentID)
	}
	if f.ChannelID != "" {
		query = query.Where("sessions.channel_id = ?", f.ChannelID)
	}
	if f.From != "" {
		if t, err := time.ParseInLocation("2006-01-02", f.From, time.Local); err == nil {
			query = query.Where("sessions.created_at >= ?", t)
		}
	}
	if f.To != "" {
		if t, err := time.ParseInLocation("2006-01-02", f.To, time.Local); err == nil {
			query = query.Where("sessions.created_at < ?", t.Add(24*time.Hour))
		}
	}
	if f.Search != "" {
		like := "%" + f.Search + "%"
		query = query.Joins("LEFT JOIN customers ON customers.id = sessions.customer_id").
			Where("customers.name LIKE ? OR CAST(sessions.id AS TEXT) LIKE ? OR COALESCE(sessions.end_reason, '') LIKE ?", like, like, like)
	}

	query.Count(&total)
	if err := query.Order("sessions.created_at desc").Offset((f.Page - 1) * f.PageSize).Limit(f.PageSize).Find(&sessions).Error; err != nil {
		return nil, 0, Internal("查询会话失败")
	}

	// 批量补全客户 / 客服 / 渠道 / 消息数
	customerIDs := make([]uint, 0)
	agentIDs := make([]uint, 0)
	channelIDs := make([]uint, 0)
	sessionIDs := make([]uint, 0, len(sessions))
	for _, s := range sessions {
		sessionIDs = append(sessionIDs, s.ID)
		customerIDs = append(customerIDs, s.CustomerID)
		channelIDs = append(channelIDs, s.ChannelID)
		if s.AgentID != nil {
			agentIDs = append(agentIDs, *s.AgentID)
		}
	}
	customerMap := map[uint]model.Customer{}
	if len(customerIDs) > 0 {
		var customers []model.Customer
		model.DB.Where("id IN ?", UniqueUint(customerIDs)).Find(&customers)
		for _, cu := range customers {
			customerMap[cu.ID] = cu
		}
	}
	agentMap := map[uint]model.User{}
	if len(agentIDs) > 0 {
		var users []model.User
		model.DB.Where("id IN ?", UniqueUint(agentIDs)).Find(&users)
		for _, u := range users {
			agentMap[u.ID] = u
		}
	}
	channelMap := map[uint]model.Channel{}
	if len(channelIDs) > 0 {
		var channels []model.Channel
		model.DB.Where("id IN ?", UniqueUint(channelIDs)).Find(&channels)
		for _, ch := range channels {
			channelMap[ch.ID] = ch
		}
	}
	msgCountMap := map[uint]int{}
	if len(sessionIDs) > 0 {
		type row struct {
			SessionID uint
			Cnt       int
		}
		var rows []row
		model.DB.Model(&model.Message{}).
			Select("session_id, COUNT(*) as cnt").
			Where("session_id IN ?", sessionIDs).
			Group("session_id").
			Scan(&rows)
		for _, r := range rows {
			msgCountMap[r.SessionID] = r.Cnt
		}
	}

	items := make([]SessionListItem, 0, len(sessions))
	for _, session := range sessions {
		item := SessionListItem{Session: session, MessageCount: msgCountMap[session.ID]}
		if !actor.SessionAll && session.AgentID != nil && *session.AgentID == actor.UserID {
			item.UnreadCount = unreadCount(session)
		}
		if cu, ok := customerMap[session.CustomerID]; ok {
			item.CustomerName = cu.Name
		}
		if session.AgentID != nil {
			if u, ok := agentMap[*session.AgentID]; ok {
				item.AgentName = u.Nickname
			}
		}
		if ch, ok := channelMap[session.ChannelID]; ok {
			item.ChannelName = ch.Name
			item.ChannelType = ch.Type
		}
		var lastMsg model.Message
		if err := model.DB.Where("session_id = ?", session.ID).Order("seq desc").First(&lastMsg).Error; err == nil {
			if lastMsg.Type == "image" {
				item.LastMessage = "[图片]"
			} else {
				item.LastMessage = lastMsg.Content
				if utf8.RuneCountInString(item.LastMessage) > 40 {
					runes := []rune(item.LastMessage)
					item.LastMessage = string(runes[:40]) + "…"
				}
			}
			t := lastMsg.SentAt
			item.LastMessageAt = &t
		}
		items = append(items, item)
	}

	return items, total, nil
}

// SessionDetailResult 会话详情聚合结果。
type SessionDetailResult struct {
	Messages     []model.Message
	Events       []model.SessionEvent
	PageViews    []model.VisitorPageView
	PendingCount int64
	MaxSeq       int
}

// SessionDetail 会话详情：消息、事件、浏览轨迹与同客户排队数。
func SessionDetail(session *model.Session) (*SessionDetailResult, error) {
	var messages []model.Message
	if err := model.DB.Where("session_id = ?", session.ID).Order("seq asc").Find(&messages).Error; err != nil {
		return nil, Internal("查询消息失败")
	}
	var events []model.SessionEvent
	model.DB.Where("session_id = ?", session.ID).Order("created_at asc").Find(&events)
	var pageViews []model.VisitorPageView
	// 最新在前，坐席侧无需滚到底
	model.DB.Where("session_id = ?", session.ID).Order("entered_at desc").Limit(MaxPageViewsPerSession).Find(&pageViews)
	var pendingCount int64
	model.DB.Model(&model.Session{}).Where("customer_id = ? AND tenant_id = ? AND status = ?", session.CustomerID, session.TenantID, "waiting").Count(&pendingCount)

	maxSeq := 0
	for _, m := range messages {
		if m.Seq > maxSeq {
			maxSeq = m.Seq
		}
	}
	return &SessionDetailResult{
		Messages:     messages,
		Events:       events,
		PageViews:    pageViews,
		PendingCount: pendingCount,
		MaxSeq:       maxSeq,
	}, nil
}

// MessagePage 按 seq 增量拉取的消息页。
type MessagePage struct {
	Messages []model.Message
	AfterSeq int
	MaxSeq   int
	HasMore  bool
}

// SessionMessagePage 按 seq 增量拉取消息（重连 catch-up）。
func SessionMessagePage(sessionID uint, afterSeq, limit int) (*MessagePage, error) {
	query := model.DB.Where("session_id = ?", sessionID)
	if afterSeq > 0 {
		query = query.Where("seq > ?", afterSeq)
	}

	var messages []model.Message
	if err := query.Order("seq asc").Limit(limit).Find(&messages).Error; err != nil {
		return nil, Internal("查询消息失败")
	}

	var maxSeq int
	if err := model.DB.Model(&model.Message{}).
		Where("session_id = ?", sessionID).
		Select("COALESCE(MAX(seq), 0)").
		Scan(&maxSeq).Error; err != nil {
		return nil, Internal("查询消息失败")
	}

	return &MessagePage{
		Messages: messages,
		AfterSeq: afterSeq,
		MaxSeq:   maxSeq,
		HasMore:  len(messages) >= limit && (len(messages) == 0 || messages[len(messages)-1].Seq < maxSeq),
	}, nil
}

// MarkSessionRead 坐席标记已读；仅会话归属坐席生效，其余原样返回当前进度。
func MarkSessionRead(session *model.Session, actor Actor) (int, error) {
	if session.AgentID == nil || actor.SessionAll || *session.AgentID != actor.UserID {
		return session.LastReadSeq, nil
	}
	var maxSeq int
	if err := model.DB.Model(&model.Message{}).Where("session_id = ?", session.ID).Select("COALESCE(MAX(seq), 0)").Scan(&maxSeq).Error; err != nil {
		return 0, Internal("标记已读失败")
	}
	if err := model.DB.Model(&model.Session{}).Where("id = ?", session.ID).Update("last_read_seq", maxSeq).Error; err != nil {
		return 0, Internal("标记已读失败")
	}
	return maxSeq, nil
}

// AddSessionNote 添加内部备注（1-500 字）。
func AddSessionNote(session *model.Session, operatorID uint, content string) (model.SessionEvent, error) {
	content = strings.TrimSpace(content)
	if content == "" || utf8.RuneCountInString(content) > 500 {
		return model.SessionEvent{}, BadRequest("内部备注需为 1 至 500 字")
	}
	event := model.SessionEvent{SessionID: session.ID, OperatorID: operatorID, Action: "note", Detail: content}
	if err := model.DB.Create(&event).Error; err != nil {
		return model.SessionEvent{}, Internal("保存内部备注失败")
	}
	return event, nil
}

// ListAvailableAgents 可转接/筛选坐席列表；includeOffline 用于对话记录筛选。
func ListAvailableAgents(tenantID uint, includeOffline bool) ([]AgentItem, error) {
	q := model.DB.Where("tenant_id = ? AND role IN ?", tenantID, assignableRoleCodes(tenantID))
	if !includeOffline {
		q = q.Where("status IN ?", []string{"online", "busy"})
	}
	var users []model.User
	if err := q.Order("nickname asc").Find(&users).Error; err != nil {
		return nil, Internal("查询客服失败")
	}
	// 在线优先，其次忙碌，再按昵称（Order 已按昵称，稳定排序保持次序）
	statusRank := map[string]int{"online": 0, "busy": 1, "offline": 2, "disabled": 3}
	sort.SliceStable(users, func(i, j int) bool {
		return statusRank[users[i].Status] < statusRank[users[j].Status]
	})
	items := make([]AgentItem, 0, len(users))
	for _, user := range users {
		items = append(items, AgentItem{
			ID: user.ID, Nickname: user.Nickname, Status: user.Status, Role: user.Role,
		})
	}
	return items, nil
}

// CreateSession 主管/管理员代客建会话。
func CreateSession(tenantID, channelID, customerID uint, priority string) (model.Session, error) {
	var channel model.Channel
	if err := model.DB.Where("id = ? AND tenant_id = ? AND status = ?", channelID, tenantID, "enabled").First(&channel).Error; err != nil {
		return model.Session{}, BadRequest("渠道不存在或未启用")
	}
	var customer model.Customer
	if err := model.DB.Where("id = ? AND tenant_id = ?", customerID, tenantID).First(&customer).Error; err != nil {
		return model.Session{}, BadRequest("客户不存在")
	}

	session := model.Session{
		TenantID:   tenantID,
		ChannelID:  channelID,
		CustomerID: customerID,
		Priority:   priority,
		Status:     "waiting",
	}

	if session.Priority == "" {
		session.Priority = "normal"
	}

	if err := model.DB.Create(&session).Error; err != nil {
		return model.Session{}, Internal("创建会话失败")
	}
	model.DB.Model(&model.Customer{}).Where("id = ? AND tenant_id = ?", customer.ID, tenantID).
		Updates(map[string]interface{}{"conversation_count": gorm.Expr("conversation_count + 1"), "last_contact_at": time.Now()})

	return session, nil
}

// AssignSession 分配/领取会话（仅 waiting）。
// 无转接权限时强制分配给本人；有权限的非管理员只能领取给自己。
func AssignSession(session *model.Session, actor Actor, canTransfer bool, agentID uint) (string, error) {
	if session.Status != "waiting" {
		return "", Conflict("会话已被分配")
	}
	if !canTransfer {
		agentID = actor.UserID
	} else if !actor.SessionAll && agentID != actor.UserID {
		return "", Forbidden("无权分配会话")
	}
	if agentID == 0 {
		return "", BadRequest("请选择目标客服")
	}
	if err := loadAssignableAgent(session.TenantID, agentID); err != nil {
		return "", BadRequest("目标客服不存在或不可用")
	}

	result := model.DB.Model(&model.Session{}).
		Where("id = ? AND tenant_id = ? AND status = ?", session.ID, session.TenantID, "waiting").
		Updates(map[string]interface{}{"agent_id": agentID, "status": "active", "last_read_seq": 0})

	if result.Error != nil {
		return "", Internal("分配失败")
	}
	if result.RowsAffected == 0 {
		return "", Conflict("会话已被分配")
	}

	operatorID := actor.UserID
	operatorName := UserDisplayName(operatorID)
	targetName := UserDisplayName(agentID)
	detail := "会话分配给 " + targetName
	if operatorID == agentID {
		detail = operatorName + " 领取了会话"
	} else {
		detail = operatorName + " 将会话分配给 " + targetName
	}
	model.DB.Create(&model.SessionEvent{
		SessionID:  session.ID,
		OperatorID: operatorID,
		Action:     "assign",
		Detail:     detail,
	})
	session.AgentID = &agentID
	session.Status = "active"
	BroadcastSessionUpdate(session)
	return detail, nil
}

// TransferSession 转接进行中的会话。
func TransferSession(session *model.Session, actor Actor, agentID uint) (string, error) {
	if err := loadAssignableAgent(session.TenantID, agentID); err != nil {
		return "", BadRequest("目标客服不存在或不可用")
	}
	if session.AgentID != nil && *session.AgentID == agentID {
		return "", BadRequest("不能转接给当前接待坐席")
	}

	operatorID := actor.UserID
	operatorName := UserDisplayName(operatorID)
	targetName := UserDisplayName(agentID)
	fromName := ""
	if session.AgentID != nil {
		fromName = UserDisplayName(*session.AgentID)
	}

	result := model.DB.Model(&model.Session{}).
		Where("id = ? AND tenant_id = ? AND status = ?", session.ID, session.TenantID, "active").
		Updates(map[string]interface{}{"agent_id": agentID, "last_read_seq": 0})
	if result.Error != nil {
		return "", Internal("转接失败")
	}
	if result.RowsAffected == 0 {
		return "", Conflict("会话不可转接")
	}

	// 详情写明「谁 → 谁」，便于接手坐席在备注/时间线中一眼看清
	detail := operatorName + " 转接给 " + targetName
	if fromName != "" && fromName != operatorName {
		detail = operatorName + " 将会话由 " + fromName + " 转接给 " + targetName
	}

	model.DB.Create(&model.SessionEvent{
		SessionID:  session.ID,
		OperatorID: operatorID,
		Action:     "transfer",
		Detail:     detail,
	})
	session.AgentID = &agentID
	BroadcastSessionUpdate(session)

	return detail, nil
}

var endReasons = map[string]bool{
	"resolved": true, "no_response": true, "visitor_left": true, "transferred": true, "other": true,
}

// EndSession 结束会话（记录原因）。
func EndSession(session *model.Session, operatorID uint, reason string) error {
	if reason == "" {
		return BadRequest("请填写结束原因")
	}
	if !endReasons[reason] {
		return BadRequest("结束原因无效")
	}
	now := time.Now()

	result := model.DB.Model(&model.Session{}).
		Where("id = ? AND tenant_id = ? AND status <> ?", session.ID, session.TenantID, "ended").
		Updates(map[string]interface{}{"status": "ended", "end_reason": reason, "ended_at": now})

	if result.RowsAffected == 0 {
		return NotFound("会话不存在")
	}

	model.DB.Create(&model.SessionEvent{
		SessionID:  session.ID,
		OperatorID: operatorID,
		Action:     "end",
		Detail:     "结束会话: " + reason,
	})
	session.Status = "ended"
	session.EndedAt = &now
	BroadcastSessionUpdate(session)

	return nil
}

// UpdateSessionPriority 调整会话优先级（urgent / normal）。
func UpdateSessionPriority(session *model.Session, actor Actor, priority string) error {
	if priority != "urgent" && priority != "normal" {
		return BadRequest("优先级无效")
	}

	result := model.DB.Model(&model.Session{}).
		Where("id = ? AND tenant_id = ?", session.ID, session.TenantID).
		Update("priority", priority)
	if result.Error != nil || result.RowsAffected == 0 {
		return Internal("更新失败")
	}
	session.Priority = priority
	BroadcastSessionUpdate(session)

	return nil
}

// ArchiveSession 将已结束会话归档。
func ArchiveSession(session *model.Session, operatorID uint) (*model.Session, error) {
	if session.Status != "ended" {
		return nil, BadRequest("仅已结束的会话可归档")
	}
	result := model.DB.Model(&model.Session{}).
		Where("id = ? AND tenant_id = ? AND status = ?", session.ID, session.TenantID, "ended").
		Update("status", "archived")
	if result.Error != nil || result.RowsAffected == 0 {
		return nil, Internal("归档失败")
	}
	model.DB.Create(&model.SessionEvent{
		SessionID:  session.ID,
		OperatorID: operatorID,
		Action:     "archive",
		Detail:     "会话已归档",
	})
	session.Status = "archived"
	BroadcastSessionUpdate(session)
	return session, nil
}

// BatchArchiveSessions 批量归档已结束会话，返回归档条数。
func BatchArchiveSessions(tenantID, operatorID uint, ids []uint) (int64, error) {
	if len(ids) == 0 {
		return 0, BadRequest("请选择要归档的会话")
	}
	if len(ids) > 100 {
		return 0, BadRequest("单次最多归档 100 条")
	}
	result := model.DB.Model(&model.Session{}).
		Where("tenant_id = ? AND status = ? AND id IN ?", tenantID, "ended", ids).
		Update("status", "archived")
	if result.Error != nil {
		return 0, Internal("批量归档失败")
	}
	for _, id := range ids {
		model.DB.Create(&model.SessionEvent{
			SessionID:  id,
			OperatorID: operatorID,
			Action:     "archive",
			Detail:     "会话已归档",
		})
	}
	return result.RowsAffected, nil
}

// AgentSendMessage 坐席向会话发送消息并广播。
func AgentSendMessage(session *model.Session, actor Actor, msgType, content string) (*model.Message, error) {
	validated, err := ValidateMessageContent(msgType, content)
	if err != nil {
		return nil, BadRequest(err.Error())
	}

	if !CanOperateSession(actor, session) {
		return nil, Forbidden("无权向该会话发送消息")
	}
	if session.Status == "ended" || session.Status == "archived" {
		return nil, Conflict("会话已结束")
	}

	senderID := actor.UserID
	msg := model.Message{
		SessionID:  session.ID,
		SenderType: "agent",
		SenderID:   &senderID,
		Content:    validated,
		Type:       msgType,
		SentAt:     time.Now(),
	}

	if err := model.CreateMessage(&msg); err != nil {
		return nil, Internal("发送失败")
	}
	// 一线坐席发送后同步自己的已读进度；管理员/主管非会话归属，不推进
	if !actor.SessionAll {
		model.DB.Model(&model.Session{}).Where("id = ?", session.ID).Update("last_read_seq", msg.Seq)
		session.LastReadSeq = msg.Seq
	}
	BroadcastSessionMessage(session, msg)

	return &msg, nil
}