feat(contact): Contact 模型、DAO、常量与 DTO

- model/friendship.go: 好友关系模型（双向存储，4 种状态）
- model/friend_group.go: 好友分组模型
- constants/contact.go: 好友关系状态常量
- dto/contact_dto.go: 联系人请求/响应 DTO
- dao/friendship_dao.go: 好友关系 CRUD + 搜索 + 共同好友
- dao/friend_group_dao.go: 好友分组 CRUD + 移动好友

Made-with: Cursor

backend/go-service/app/contact/dao/friend_group_dao.go

@@ -0,0 +1,116 @@
+package dao
+
+import (
+	"context"
+
+	"github.com/echochat/backend/app/contact/model"
+	"github.com/echochat/backend/pkg/logs"
+	"go.uber.org/zap"
+	"gorm.io/gorm"
+)
+
+// FriendGroupDAO 好友分组数据访问对象
+type FriendGroupDAO struct {
+	db *gorm.DB
+}
+
+// NewFriendGroupDAO 创建 FriendGroupDAO 实例
+func NewFriendGroupDAO(db *gorm.DB) *FriendGroupDAO {
+	return &FriendGroupDAO{db: db}
+}
+
+// CreateGroup 创建好友分组
+func (d *FriendGroupDAO) CreateGroup(ctx context.Context, userID int64, name string) (*model.FriendGroup, error) {
+	funcName := "dao.friend_group_dao.CreateGroup"
+	logs.Info(ctx, funcName, "创建好友分组",
+		zap.Int64("user_id", userID), zap.String("name", name))
+
+	group := &model.FriendGroup{
+		UserID: userID,
+		Name:   name,
+	}
+	err := d.db.WithContext(ctx).Create(group).Error
+	if err != nil {
+		logs.Error(ctx, funcName, "创建分组失败", zap.Error(err))
+	}
+	return group, err
+}
+
+// GetGroups 获取用户的所有好友分组
+func (d *FriendGroupDAO) GetGroups(ctx context.Context, userID int64) ([]model.FriendGroup, error) {
+	funcName := "dao.friend_group_dao.GetGroups"
+	logs.Debug(ctx, funcName, "查询好友分组", zap.Int64("user_id", userID))
+
+	var groups []model.FriendGroup
+	err := d.db.WithContext(ctx).
+		Where("user_id = ?", userID).
+		Order("sort_order ASC, id ASC").
+		Find(&groups).Error
+	return groups, err
+}
+
+// UpdateGroup 更新分组信息
+func (d *FriendGroupDAO) UpdateGroup(ctx context.Context, groupID int64, userID int64, name string, sortOrder *int) error {
+	funcName := "dao.friend_group_dao.UpdateGroup"
+	logs.Info(ctx, funcName, "更新好友分组",
+		zap.Int64("group_id", groupID), zap.String("name", name))
+
+	updates := map[string]interface{}{"name": name}
+	if sortOrder != nil {
+		updates["sort_order"] = *sortOrder
+	}
+
+	result := d.db.WithContext(ctx).
+		Model(&model.FriendGroup{}).
+		Where("id = ? AND user_id = ?", groupID, userID).
+		Updates(updates)
+
+	if result.Error != nil {
+		return result.Error
+	}
+	if result.RowsAffected == 0 {
+		return gorm.ErrRecordNotFound
+	}
+	return nil
+}
+
+// DeleteGroup 删除分组（同时将该分组下的好友移出分组）
+func (d *FriendGroupDAO) DeleteGroup(ctx context.Context, groupID int64, userID int64) error {
+	funcName := "dao.friend_group_dao.DeleteGroup"
+	logs.Info(ctx, funcName, "删除好友分组",
+		zap.Int64("group_id", groupID), zap.Int64("user_id", userID))
+
+	return d.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
+		tx.Model(&model.Friendship{}).
+			Where("user_id = ? AND group_id = ?", userID, groupID).
+			Update("group_id", nil)
+
+		result := tx.Where("id = ? AND user_id = ?", groupID, userID).
+			Delete(&model.FriendGroup{})
+		if result.RowsAffected == 0 {
+			return gorm.ErrRecordNotFound
+		}
+		return result.Error
+	})
+}
+
+// MoveToGroup 移动好友到指定分组
+func (d *FriendGroupDAO) MoveToGroup(ctx context.Context, userID, friendID int64, groupID *int64) error {
+	funcName := "dao.friend_group_dao.MoveToGroup"
+	logs.Info(ctx, funcName, "移动好友到分组",
+		zap.Int64("user_id", userID), zap.Int64("friend_id", friendID))
+
+	return d.db.WithContext(ctx).
+		Model(&model.Friendship{}).
+		Where("user_id = ? AND friend_id = ? AND status = 1", userID, friendID).
+		Update("group_id", groupID).Error
+}
+
+// GetGroupByID 根据 ID 获取分组
+func (d *FriendGroupDAO) GetGroupByID(ctx context.Context, groupID, userID int64) (*model.FriendGroup, error) {
+	var group model.FriendGroup
+	err := d.db.WithContext(ctx).
+		Where("id = ? AND user_id = ?", groupID, userID).
+		First(&group).Error
+	return &group, err
+}