package handler

import (
	"fmt"

	"kefu-sys/server/internal/model"
	"kefu-sys/server/internal/ws"
)

const offlineLeavePrompt = "当前无客服在线，请留言并留下联系方式，我们上线后会尽快回复您。"

// pickLeastLoadedAgent 在在线一线客服中选择当前进行中会话最少的一位。
func pickLeastLoadedAgent(tenantID uint) (*model.User, error) {
	var agents []model.User
	if err := model.DB.Where("tenant_id = ? AND role = ? AND status = ?", tenantID, "agent", "online").
		Order("id asc").Find(&agents).Error; err != nil {
		return nil, err
	}
	if len(agents) == 0 {
		return nil, nil
	}

	best := &agents[0]
	bestCount := int64(-1)
	for i := range agents {
		var count int64
		if err := model.DB.Model(&model.Session{}).
			Where("tenant_id = ? AND agent_id = ? AND status = ?", tenantID, agents[i].ID, "active").
			Count(&count).Error; err != nil {
			return nil, err
		}
		if bestCount < 0 || count < bestCount {
			bestCount = count
			best = &agents[i]
		}
	}
	return best, nil
}

// countOnlineAgents 统计租户当前可接待的在线客服数。
func countOnlineAgents(tenantID uint) (int64, error) {
	var count int64
	err := model.DB.Model(&model.User{}).
		Where("tenant_id = ? AND role = ? AND status = ?", tenantID, "agent", "online").
		Count(&count).Error
	return count, err
}

// tryAutoAssign 将会话自动分配给负载最低的在线客服；无可分配客服时返回 nil。
func tryAutoAssign(session *model.Session) (*model.User, error) {
	if session == nil || session.ID == 0 {
		return nil, nil
	}
	if session.Status != "waiting" || session.AgentID != nil {
		return nil, nil
	}

	agent, err := pickLeastLoadedAgent(session.TenantID)
	if err != nil || agent == nil {
		return nil, err
	}

	result := model.DB.Model(&model.Session{}).
		Where("id = ? AND tenant_id = ? AND status = ? AND agent_id IS NULL", session.ID, session.TenantID, "waiting").
		Updates(map[string]interface{}{
			"agent_id":      agent.ID,
			"status":        "active",
			"last_read_seq": 0,
		})
	if result.Error != nil {
		return nil, result.Error
	}
	if result.RowsAffected == 0 {
		// 并发下可能已被他人领取
		if err := model.DB.First(session, session.ID).Error; err != nil {
			return nil, err
		}
		return nil, nil
	}

	session.AgentID = &agent.ID
	session.Status = "active"
	detail := fmt.Sprintf("系统自动分配给 %s", agent.Nickname)
	model.DB.Create(&model.SessionEvent{
		SessionID:  session.ID,
		OperatorID: 0,
		Action:     "auto_assign",
		Detail:     detail,
	})

	if payload, err := ws.NewEvent("session_updated", session.ID, session); err == nil {
		ws.DefaultHub.BroadcastToTenantStaff(session.TenantID, payload)
		ws.DefaultHub.BroadcastToVisitor(session.TenantID, session.ID, payload)
	}
	return agent, nil
}