AI Implementation feature(857): Authenticated Shell: Header, Quick Tabs and Change Password (#14)

backend/src/modules/users/users-rank.service.ts

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+import { Injectable } from '@nestjs/common';
+import { EntityManager } from 'typeorm';
+import { SolveEntity } from '../../database/entities/solve.entity';
+
+export interface RankInfo {
+  rank: number | null;
+  points: number;
+}
+
+@Injectable()
+export class UsersRankService {
+  async rankOfUser(manager: EntityManager, userId: string): Promise<RankInfo> {
+    const solveRepo = manager.getRepository(SolveEntity);
+    const pointsRow = await solveRepo
+      .createQueryBuilder('s')
+      .select('COALESCE(SUM(s.pointsAwarded), 0)', 'total')
+      .where('s.userId = :userId', { userId })
+      .getRawOne<{ total: string | number | null }>();
+    const points = Number(pointsRow?.total ?? 0);
+
+    if (points <= 0) {
+      return { rank: null, points: 0 };
+    }
+
+    const ahead = await solveRepo
+      .createQueryBuilder('s')
+      .select('s.userId', 'userId')
+      .addSelect('SUM(s.pointsAwarded)', 'total')
+      .groupBy('s.userId')
+      .having('SUM(s.pointsAwarded) > :points', { points })
+      .getRawMany<{ userId: string }>();
+    return { rank: ahead.length + 1, points };
+  }
+}