Implement friend APIs and target profile support

- Add friend search/list/request/requestCancel/response/expel handlers and schemas
- Store friend relationships in user_friend and backfill default friend links at startup
- Auto-add the default user as a friend for newly created accounts
- Support target user_id in /api profile requests and return target profile data
- Make profile accessory_info optional to avoid zero-value accessory payloads
- Update login topInfo friend counters from friend relationship state

Signed-off-by: Sean Du <do4suki@gmail.com>

internal/model/user/userfriend.go

@@ -0,0 +1,107 @@
+package usermodel
+
+import (
+	"time"
+
+	"xorm.io/xorm"
+)
+
+const (
+	DefaultSystemPhone = "1"
+
+	FriendStatusApproved = iota
+	FriendStatusPending
+	FriendStatusAwaitingApproval
+
+	FriendListPageSize = 40
+)
+
+type UserFriend struct {
+	ID           int   `xorm:"id pk autoincr"`
+	UserID       int   `xorm:"user_id unique(friend_pair) index"`
+	FriendUserID int   `xorm:"friend_user_id unique(friend_pair) index"`
+	Status       int   `xorm:"status index"`
+	IsNew        bool  `xorm:"is_new"`
+	InsertDate   int64 `xorm:"insert_date index"`
+	UpdateDate   int64 `xorm:"update_date"`
+}
+
+func (UserFriend) TableName() string {
+	return "user_friend"
+}
+
+func EnsureFriendLink(dbSession *xorm.Session, userID, friendUserID, status int, isNew bool) error {
+	if dbSession == nil || userID <= 0 || friendUserID <= 0 || userID == friendUserID {
+		return nil
+	}
+
+	now := time.Now().Unix()
+	link := UserFriend{}
+	has, err := dbSession.Table(new(UserFriend)).
+		Where("user_id = ? AND friend_user_id = ?", userID, friendUserID).
+		Get(&link)
+	if err != nil {
+		return err
+	}
+
+	if has {
+		update := UserFriend{
+			Status:     status,
+			IsNew:      isNew,
+			UpdateDate: now,
+		}
+		if link.InsertDate <= 0 {
+			update.InsertDate = now
+		}
+
+		_, err = dbSession.Table(new(UserFriend)).
+			Where("user_id = ? AND friend_user_id = ?", userID, friendUserID).
+			Cols("status", "is_new", "update_date", "insert_date").
+			Update(&update)
+		return err
+	}
+
+	_, err = dbSession.Table(new(UserFriend)).Insert(&UserFriend{
+		UserID:       userID,
+		FriendUserID: friendUserID,
+		Status:       status,
+		IsNew:        isNew,
+		InsertDate:   now,
+		UpdateDate:   now,
+	})
+	return err
+}
+
+func EnsureMutualFriend(dbSession *xorm.Session, userID, friendUserID, status int) error {
+	if err := EnsureFriendLink(dbSession, userID, friendUserID, status, false); err != nil {
+		return err
+	}
+	return EnsureFriendLink(dbSession, friendUserID, userID, status, false)
+}
+
+func EnsureMutualFriendWithIsNew(dbSession *xorm.Session, userID, friendUserID, status int, userIsNew, friendIsNew bool) error {
+	if err := EnsureFriendLink(dbSession, userID, friendUserID, status, userIsNew); err != nil {
+		return err
+	}
+	return EnsureFriendLink(dbSession, friendUserID, userID, status, friendIsNew)
+}
+
+func EnsureDefaultFriendship(dbSession *xorm.Session, userID int) error {
+	if dbSession == nil || userID <= 0 {
+		return nil
+	}
+
+	defaultUser := Users{}
+	has, err := dbSession.Table(new(Users)).
+		Where("phone = ?", DefaultSystemPhone).
+		Cols("user_id").
+		Get(&defaultUser)
+	if err != nil {
+		return err
+	}
+	if !has || defaultUser.UserID <= 0 || defaultUser.UserID == userID {
+		return nil
+	}
+
+	return EnsureMutualFriend(dbSession, userID, defaultUser.UserID, FriendStatusApproved)
+}