import { Injectable } from "@nestjs/common";
import { type Prisma } from "@prisma/client";

/**
 * Transaction-scoped serialization protocol for policy subjects.
 *
 * Every transaction that reads or writes block, sanction, or account-status
 * policy MUST call this method first for every affected account. IDs are
 * de-duplicated and sorted so overlapping multi-account operations cannot
 * deadlock. The lock is released by PostgreSQL only when the transaction ends;
 * callers must therefore pass the transaction client, never PrismaService.
 */
@Injectable()
export class SafetyLockService {
  async lockAccounts(
    tx: Prisma.TransactionClient,
    accountIds: readonly string[],
  ): Promise<void> {
    const canonicalIds = Array.from(new Set(accountIds)).sort();
    for (const accountId of canonicalIds) {
      await tx.$executeRaw`
        SELECT pg_advisory_xact_lock(
          hashtextextended(${`safety:${accountId}`}, 0)
        )
      `;
    }
  }
}