import { Injectable, Logger } from '@nestjs/common';
import { DataSource, EntityManager } from 'typeorm';
import { v4 as uuid } from 'uuid';
import { UserEntity, UserRole, UserStatus } from '../../database/entities/user.entity';
import { RefreshTokenEntity } from '../../database/entities/refresh-token.entity';
import { UsersService } from '../users/users.service';
import { ApiError } from '../../common/errors/api-error';
import { ERROR_CODES } from '../../common/errors/error-codes';
import { validatePassword } from '../../common/utils/password-policy';
import { hashPassword } from '../../common/utils/password-hashing';
import { ConfigService } from '@nestjs/config';
import { AdminPlayerView, ListUsersQueryDto } from './dto/admin.dto';

/**
 * Every table that has a `userId` column and must be cleaned up when the
 * parent `user` row is deleted. Iterated by `deleteUserOwnedRows` so future
 * user-owned tables (e.g. comments, notifications) only need to be appended
 * here. The ON DELETE CASCADE migration that backs this list is the
 * deployment-wide safety net; the imperative delete below is what the
 * admin delete path requires.
 */
const USER_OWNED_TABLES: { tableName: string; userIdColumn: string }[] = [
  { tableName: 'solve', userIdColumn: 'user_id' },
  { tableName: 'refresh_token', userIdColumn: 'user_id' },
];

async function deleteUserOwnedRows(manager: EntityManager, userId: string): Promise<Record<string, number>> {
  const counts: Record<string, number> = {};
  for (const { tableName, userIdColumn } of USER_OWNED_TABLES) {
    const res = await manager.query(
      `DELETE FROM "${tableName}" WHERE "${userIdColumn}" = ?`,
      [userId],
    );
    counts[tableName] = Number(res?.changes ?? res?.affected ?? 0);
  }
  return counts;
}

@Injectable()
export class AdminService {
  private readonly logger = new Logger(AdminService.name);

  constructor(
    private readonly usersService: UsersService,
    private readonly dataSource: DataSource,
    private readonly config: ConfigService,
  ) {}

  async listUsers(query: ListUsersQueryDto = {}): Promise<AdminPlayerView[]> {
    return this.listPlayers(query);
  }

  async listPlayers(query: ListUsersQueryDto = {}): Promise<AdminPlayerView[]> {
    const limit = Math.min(Math.max(query.limit ?? 50, 1), 200);
    const repo = this.dataSource.getRepository(UserEntity);
    const qb = repo
      .createQueryBuilder('u')
      .orderBy('u.createdAt', 'ASC')
      .addOrderBy('u.id', 'ASC')
      .limit(limit + 1);
    if (query.role) qb.andWhere('u.role = :role', { role: query.role });
    if (query.cursor) qb.andWhere('u.id > :cursor', { cursor: query.cursor });
    const rows = await qb.getMany();
    return rows.slice(0, limit).map(toPlayerView);
  }

  async updateUserRole(targetId: string, role: UserRole): Promise<AdminPlayerView> {
    return this.updatePlayerRole(targetId, role);
  }

  async updatePlayerRole(targetId: string, role: UserRole): Promise<AdminPlayerView> {
    if (role !== 'admin' && role !== 'player') {
      throw ApiError.validation('Invalid role');
    }
    const updated = await this.usersService.applyLastAdminSafeMutation<AdminPlayerView>(targetId, {
      demotesOrDelete: true,
      updatedRole: role,
      mutate: async (manager, target) => {
        target.role = role;
        await manager.save(target);
        return toPlayerView(target);
      },
    });
    return updated;
  }

  async updatePlayerStatus(targetId: string, enabled: boolean): Promise<AdminPlayerView> {
    const target = await this.usersService.findById(targetId);
    if (!target) throw ApiError.notFound('User not found');
    const newStatus: UserStatus = enabled ? 'enabled' : 'disabled';
    return this.dataSource.transaction(async (manager) => {
      const user = await manager.findOne(UserEntity, { where: { id: targetId } });
      if (!user) throw ApiError.notFound('User not found');
      user.status = newStatus;
      await manager.save(user);
      if (!enabled) {
        await manager
          .createQueryBuilder()
          .update(RefreshTokenEntity)
          .set({ revokedAt: new Date().toISOString() })
          .where('userId = :userId', { userId: user.id })
          .andWhere('revokedAt IS NULL')
          .execute();
      }
      return toPlayerView(user);
    });
  }

  async resetPlayerPassword(targetId: string, newPassword: string): Promise<void> {
    if (!newPassword) {
      throw ApiError.validation('New password is required');
    }
    validatePassword(newPassword, this.config);
    const target = await this.usersService.findById(targetId);
    if (!target) throw ApiError.notFound('User not found');
    const hash = await hashPassword(newPassword, this.config);
    await this.dataSource.transaction(async (manager) => {
      const user = await manager.findOne(UserEntity, { where: { id: targetId } });
      if (!user) throw ApiError.notFound('User not found');
      user.passwordHash = hash;
      await manager.save(user);
      await manager
        .createQueryBuilder()
        .update(RefreshTokenEntity)
        .set({ revokedAt: new Date().toISOString() })
        .where('userId = :userId', { userId: user.id })
        .andWhere('revokedAt IS NULL')
        .execute();
    });
  }

  async deleteUser(targetId: string): Promise<void> {
    return this.deletePlayer(targetId);
  }

  async deletePlayer(targetId: string): Promise<void> {
    await this.usersService.applyLastAdminSafeMutation<null>(targetId, {
      demotesOrDelete: true,
      mutate: async (manager) => {
        // Imperative dependent cleanup in the SAME transaction. The
        // ON DELETE CASCADE migration is a safety net, but the explicit
        // deletes (a) surface the affected row counts to the application,
        // (b) keep deletes observable for future audit logging, and
        // (c) ensure that the post-mutation admin count is the only
        // invariant the caller still needs to verify.
        const cleanedCounts = await deleteUserOwnedRows(manager, targetId);

        const res = await manager.delete(UserEntity, { id: targetId });
        if (!res.affected) {
          throw ApiError.notFound('User not found');
        }

        // Note per-table cleanup counts; never log password hashes, token
        // hashes, or the plaintext password.
        this.logger.log(
          `Deleted user ${targetId}; dependent rows: ${Object.entries(cleanedCounts)
            .map(([t, n]) => `${t}=${n}`)
            .join(', ') || 'none'}`,
        );
        return null;
      },
    });
  }

  async createUser(username: string, password: string, role: UserRole): Promise<AdminPlayerView> {
    validatePassword(password, this.config);
    const created = await this.dataSource.transaction(async (manager) => {
      const existing = await manager.findOne(UserEntity, { where: { username } });
      if (existing) throw ApiError.conflict(ERROR_CODES.CONFLICT, 'Username already taken');
      const hash = await hashPassword(password, this.config);
      const user = manager.create(UserEntity, {
        id: uuid(),
        username,
        passwordHash: hash,
        role,
        status: 'enabled',
      });
      await manager.save(user);
      return toPlayerView(user);
    });
    return created;
  }
}

export function toPlayerView(user: UserEntity): AdminPlayerView {
  return {
    id: user.id,
    username: user.username,
    role: user.role,
    status: user.status,
    createdAt: user.createdAt,
  };
}