基本功能完成，下一步开始美化UI

api/models/userGroup.ts

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+import { v4 as uuidv4 } from 'uuid';
+import { query, run, get } from '../database';
+import { User } from './user';
+
+export interface UserGroup {
+  id: string;
+  name: string;
+  description?: string;
+  isSystem: boolean;
+  createdAt: string;
+  memberCount?: number;
+}
+
+export interface CreateUserGroupData {
+  name: string;
+  description?: string;
+}
+
+export class UserGroupModel {
+  static async create(data: CreateUserGroupData): Promise<UserGroup> {
+    const id = uuidv4();
+    const sql = `
+      INSERT INTO user_groups (id, name, description, is_system) 
+      VALUES (?, ?, ?, 0)
+    `;
+    
+    try {
+      await run(sql, [id, data.name, data.description || '']);
+      return this.findById(id) as Promise<UserGroup>;
+    } catch (error: any) {
+      if (error.code === 'SQLITE_CONSTRAINT_UNIQUE') {
+        throw new Error('用户组名称已存在');
+      }
+      throw error;
+    }
+  }
+
+  static async update(id: string, data: Partial<CreateUserGroupData>): Promise<UserGroup> {
+    const group = await this.findById(id);
+    if (!group) throw new Error('用户组不存在');
+    if (group.isSystem) throw new Error('系统内置用户组无法修改');
+
+    const fields: string[] = [];
+    const values: any[] = [];
+    
+    if (data.name !== undefined) {
+      fields.push('name = ?');
+      values.push(data.name);
+    }
+    
+    if (data.description !== undefined) {
+      fields.push('description = ?');
+      values.push(data.description);
+    }
+    
+    if (fields.length === 0) {
+      return group;
+    }
+    
+    values.push(id);
+    const sql = `UPDATE user_groups SET ${fields.join(', ')} WHERE id = ?`;
+    
+    try {
+      await run(sql, values);
+      return this.findById(id) as Promise<UserGroup>;
+    } catch (error: any) {
+      if (error.code === 'SQLITE_CONSTRAINT_UNIQUE') {
+        throw new Error('用户组名称已存在');
+      }
+      throw error;
+    }
+  }
+
+  static async delete(id: string): Promise<void> {
+    const group = await this.findById(id);
+    if (!group) throw new Error('用户组不存在');
+    if (group.isSystem) throw new Error('系统内置用户组无法删除');
+
+    await run(`DELETE FROM user_groups WHERE id = ?`, [id]);
+  }
+
+  static async findById(id: string): Promise<UserGroup | null> {
+    const sql = `
+      SELECT id, name, description, is_system as isSystem, created_at as createdAt 
+      FROM user_groups WHERE id = ?
+    `;
+    const group = await get(sql, [id]);
+    return group || null;
+  }
+
+  static async findAll(): Promise<UserGroup[]> {
+    const sql = `
+      SELECT 
+        g.id, g.name, g.description, g.is_system as isSystem, g.created_at as createdAt,
+        (SELECT COUNT(*) FROM user_group_members m WHERE m.group_id = g.id) as memberCount
+      FROM user_groups g
+      ORDER BY g.is_system DESC, g.created_at DESC
+    `;
+    return await query(sql);
+  }
+
+  static async addMember(groupId: string, userId: string): Promise<void> {
+    const sql = `INSERT OR IGNORE INTO user_group_members (group_id, user_id) VALUES (?, ?)`;
+    await run(sql, [groupId, userId]);
+  }
+
+  static async removeMember(groupId: string, userId: string): Promise<void> {
+    const group = await this.findById(groupId);
+    if (group?.isSystem) {
+       // Check if user is being deleted? No, this method is for removing member.
+       // Requirement: "User cannot actively exit this group".
+       // Implementation: Cannot remove member from system group via this API.
+       // Only user deletion removes them (cascade).
+       throw new Error('无法从系统内置组中移除成员');
+    }
+    const sql = `DELETE FROM user_group_members WHERE group_id = ? AND user_id = ?`;
+    await run(sql, [groupId, userId]);
+  }
+
+  static async getMembers(groupId: string): Promise<User[]> {
+    const sql = `
+      SELECT u.id, u.name, u.phone, u.created_at as createdAt
+      FROM users u
+      JOIN user_group_members m ON u.id = m.user_id
+      WHERE m.group_id = ?
+      ORDER BY m.created_at DESC
+    `;
+    return await query(sql, [groupId]);
+  }
+  
+  static async getUserGroups(userId: string): Promise<UserGroup[]> {
+    const sql = `
+      SELECT g.id, g.name, g.description, g.is_system as isSystem, g.created_at as createdAt
+      FROM user_groups g
+      JOIN user_group_members m ON g.id = m.group_id
+      WHERE m.user_id = ?
+      ORDER BY g.is_system DESC, g.created_at DESC
+    `;
+    return await query(sql, [userId]);
+  }
+
+  static async getSystemGroup(): Promise<UserGroup | null> {
+    const sql = `
+      SELECT id, name, description, is_system as isSystem, created_at as createdAt 
+      FROM user_groups WHERE is_system = 1
+    `;
+    return await get(sql);
+  }
+
+  static async updateMembers(groupId: string, userIds: string[]): Promise<void> {
+    const group = await this.findById(groupId);
+    if (!group) throw new Error('用户组不存在');
+    if (group.isSystem) throw new Error('无法修改系统内置组成员');
+
+    // Transaction-like behavior needed but SQLite wrapper doesn't expose it easily.
+    // We'll do delete then insert.
+    await run(`DELETE FROM user_group_members WHERE group_id = ?`, [groupId]);
+    
+    if (userIds.length > 0) {
+      // Batch insert
+      // SQLite limit is usually high enough, but safer to loop or construct big query
+      // For simplicity in this helper:
+      for (const userId of userIds) {
+        await run(`INSERT INTO user_group_members (group_id, user_id) VALUES (?, ?)`, [groupId, userId]);
+      }
+    }
+  }
+
+  static async updateUserGroups(userId: string, groupIds: string[]): Promise<void> {
+    // 1. Get current system group(s) the user belongs to
+    const currentGroups = await this.getUserGroups(userId);
+    const systemGroupIds = currentGroups.filter(g => g.isSystem).map(g => g.id);
+
+    // 2. Ensure system groups are in the new list (force keep them)
+    const newGroupSet = new Set(groupIds);
+    for (const sysId of systemGroupIds) {
+      newGroupSet.add(sysId);
+    }
+    
+    // Also ensure the default "All Users" group is there if not already
+    // (In case the user was created before groups existed and somehow not migrated, though migration handles it)
+    // Safe to just ensure "All Users" is present.
+    const allUsersGroup = await this.getSystemGroup();
+    if (allUsersGroup) {
+      newGroupSet.add(allUsersGroup.id);
+    }
+
+    const finalGroupIds = Array.from(newGroupSet);
+
+    // 3. Update
+    await run(`DELETE FROM user_group_members WHERE user_id = ?`, [userId]);
+    
+    for (const gid of finalGroupIds) {
+       await run(`INSERT INTO user_group_members (group_id, user_id) VALUES (?, ?)`, [gid, userId]);
+    }
+  }
+}