package services

import (
	"errors"
	"fmt"
	"strings"

	"golang.org/x/crypto/bcrypt"
	"gorm.io/gorm"

	"git.beifan.cn/trace-system/backend-go/database"
	"git.beifan.cn/trace-system/backend-go/models"
)

// UsersService 用户管理服务
type UsersService struct{}

func toUserDTO(user models.User) models.UserDTO {
	return models.UserDTO{
		ID:        user.ID,
		Username:  user.Username,
		Name:      user.Name,
		Email:     user.Email,
		Role:      user.Role,
		CreatedAt: user.CreatedAt,
	}
}

// Create 创建用户
func (s *UsersService) Create(dto models.CreateUserDTO) (*models.UserDTO, error) {
	username := strings.TrimSpace(dto.Username)

	var existing models.User
	err := database.DB.Where("username = ?", username).First(&existing).Error
	if err == nil {
		return nil, errors.New("用户名已存在")
	}
	if !errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, fmt.Errorf("查询用户失败: %w", err)
	}

	hashed, err := bcrypt.GenerateFromPassword([]byte(dto.Password), bcrypt.DefaultCost)
	if err != nil {
		return nil, fmt.Errorf("密码加密失败: %w", err)
	}

	user := models.User{
		Username: username,
		Password: string(hashed),
		Name:     dto.Name,
		Email:    dto.Email,
		Role:     dto.Role,
	}

	if err := database.DB.Create(&user).Error; err != nil {
		return nil, fmt.Errorf("创建用户失败: %w", err)
	}

	dtoOut := toUserDTO(user)
	return &dtoOut, nil
}

// FindAll 分页 + 按角色过滤
func (s *UsersService) FindAll(page int, limit int, role string, search string) ([]models.UserDTO, int, int, error) {
	var users []models.User
	var total int64

	db := database.DB.Model(&models.User{})
	if role != "" {
		db = db.Where("role = ?", role)
	}
	if search != "" {
		pattern := "%" + search + "%"
		db = db.Where("username LIKE ? OR name LIKE ? OR email LIKE ?", pattern, pattern, pattern)
	}

	if err := db.Count(&total).Error; err != nil {
		return nil, 0, 0, fmt.Errorf("统计用户数失败: %w", err)
	}

	offset := (page - 1) * limit
	if err := db.Order("created_at DESC").Offset(offset).Limit(limit).Find(&users).Error; err != nil {
		return nil, 0, 0, fmt.Errorf("查询用户列表失败: %w", err)
	}

	result := make([]models.UserDTO, 0, len(users))
	for _, u := range users {
		result = append(result, toUserDTO(u))
	}

	totalPages := (int(total) + limit - 1) / limit
	return result, int(total), totalPages, nil
}

// FindAssignable 获取可分配的用户（admin + technician），用于售后工单分配
func (s *UsersService) FindAssignable() ([]models.UserDTO, error) {
	var users []models.User
	if err := database.DB.Where("role IN ?", []string{"admin", "technician"}).
		Order("role DESC, created_at ASC").Find(&users).Error; err != nil {
		return nil, fmt.Errorf("查询可分配用户失败: %w", err)
	}
	result := make([]models.UserDTO, 0, len(users))
	for _, u := range users {
		result = append(result, toUserDTO(u))
	}
	return result, nil
}

// Update 更新用户信息（不含密码）
func (s *UsersService) Update(userId uint, dto models.UpdateUserDTO, currentUserId uint) (*models.UserDTO, error) {
	var user models.User
	if err := database.DB.First(&user, userId).Error; err != nil {
		return nil, errors.New("用户不存在")
	}

	if dto.Name != "" {
		user.Name = dto.Name
	}
	if dto.Email != "" {
		user.Email = dto.Email
	}
	if dto.Role != "" {
		// 防止管理员把自己降级
		if user.ID == currentUserId && user.Role == "admin" && dto.Role != "admin" {
			return nil, errors.New("不能修改自己的管理员角色")
		}
		user.Role = dto.Role
	}

	if err := database.DB.Save(&user).Error; err != nil {
		return nil, fmt.Errorf("更新用户失败: %w", err)
	}

	dtoOut := toUserDTO(user)
	return &dtoOut, nil
}

// ResetPassword 管理员重置用户密码
func (s *UsersService) ResetPassword(userId uint, newPassword string) error {
	var user models.User
	if err := database.DB.First(&user, userId).Error; err != nil {
		return errors.New("用户不存在")
	}

	hashed, err := bcrypt.GenerateFromPassword([]byte(newPassword), bcrypt.DefaultCost)
	if err != nil {
		return fmt.Errorf("密码加密失败: %w", err)
	}

	user.Password = string(hashed)
	if err := database.DB.Save(&user).Error; err != nil {
		return fmt.Errorf("重置密码失败: %w", err)
	}
	return nil
}

// Delete 删除用户
func (s *UsersService) Delete(userId uint, currentUserId uint) error {
	if userId == currentUserId {
		return errors.New("不能删除自己")
	}

	var user models.User
	if err := database.DB.First(&user, userId).Error; err != nil {
		return errors.New("用户不存在")
	}

	if user.Role == "admin" {
		// 防止删除最后一个 admin
		var adminCount int64
		database.DB.Model(&models.User{}).Where("role = ?", "admin").Count(&adminCount)
		if adminCount <= 1 {
			return errors.New("不能删除最后一个管理员")
		}
	}

	if err := database.DB.Delete(&user).Error; err != nil {
		return fmt.Errorf("删除用户失败: %w", err)
	}
	return nil
}