/**
 * Usage metering service for SentryAgent.ai AgentIdP.
 * Provides daily usage summaries and active agent counts per tenant.
 */

import { Pool } from 'pg';

/**
 * Daily usage summary for a tenant.
 */
export interface IUsageSummary {
  /** The tenant (organization) UUID. */
  tenantId: string;
  /** Date string in YYYY-MM-DD format. */
  date: string;
  /** Number of API calls made on the given date. */
  apiCalls: number;
  /** Number of active (non-decommissioned) agents for the tenant. */
  agentCount: number;
}

/**
 * Service for retrieving per-tenant usage data.
 * Reads from the `usage_events` and `agents` tables.
 */
export class UsageService {
  /**
   * @param pool - PostgreSQL connection pool.
   */
  constructor(private readonly pool: Pool) {}

  /**
   * Returns the daily usage summary for a tenant on a given date.
   * If no usage row exists for the date, apiCalls defaults to 0.
   *
   * @param tenantId - The tenant UUID.
   * @param date - Date string in 'YYYY-MM-DD' format.
   * @returns A resolved IUsageSummary with api_calls and agent count.
   */
  async getDailyUsage(tenantId: string, date: string): Promise<IUsageSummary> {
    const usageResult = await this.pool.query<{ count: string }>(
      `SELECT COALESCE(SUM(count), 0) AS count
       FROM usage_events
       WHERE tenant_id = $1
         AND date = $2
         AND metric_type = 'api_calls'`,
      [tenantId, date],
    );

    const agentCount = await this.getActiveAgentCount(tenantId);
    const apiCalls = parseInt(usageResult.rows[0]?.count ?? '0', 10);

    return { tenantId, date, apiCalls, agentCount };
  }

  /**
   * Returns the number of non-decommissioned agents for a tenant.
   *
   * @param tenantId - The tenant UUID.
   * @returns The count of active agents (status != 'decommissioned').
   */
  async getActiveAgentCount(tenantId: string): Promise<number> {
    const result = await this.pool.query<{ count: string }>(
      `SELECT COUNT(*) AS count
       FROM agents
       WHERE organization_id = $1
         AND status != 'decommissioned'`,
      [tenantId],
    );

    return parseInt(result.rows[0]?.count ?? '0', 10);
  }
}