import { Pool } from 'pg';
import { Gauge, Metric } from 'prom-client';
import { DbLogger } from '../common';

const createTimeout = (timeoutInMilliSeconds: number): Promise<void> =>
  new Promise<void>((_, reject) =>
    setTimeout(
      () => reject(new Error('METRIC_COLLECTION_TIMEOUT')),
      timeoutInMilliSeconds,
    ),
  );

/**
 * Creates a `Gauge` metric with the name `ax_postgres_<pgPoolType>_connectivity` which can be added to a metric Registry.
 * This metric will have a value of `1` if the Database can be reached via the corresponding Pool (within the given timeout),
 * or a value of `0` otherwise.
 *
 * @param pgPool The Postgres Pool to use for checking the connectivity. The connectivity test will be done at the point of metric collection.
 * @param pgPoolType The Postgres Pool to check connectivity for.
 * @param timeoutInMilliSeconds The maximum time the connectivity check will run during metric collection. Defaults to `10000ms`.
 * @returns A `Gauge` metric with a name `ax_postgres_<pgPoolType>_connectivity`.
 */
export const createPostgresPoolConnectivityMetric = (
  logger: DbLogger,
  pgPool: Pool,
  pgPoolType: 'dbOwnerPool' | 'envOwnerPool' | 'loginPool',
  timeoutInMilliSeconds = 10000,
): Metric<string> => {
  return new Gauge({
    name: `ax_postgres_${pgPoolType}_connectivity`,
    help: `Connection time from the service to the database via the ${pgPoolType} in milliseconds`,

    async collect() {
      try {
        const startTime = process.hrtime();
        await Promise.race([
          pgPool.query(`SELECT NOW() AS PostgresPoolConnectivityMetric`),
          createTimeout(timeoutInMilliSeconds),
        ]);
        const duration = process.hrtime(startTime);
        this.set(duration[1] / 1e6);
      } catch (error) {
        if ((<Error>error).message === 'METRIC_COLLECTION_TIMEOUT') {
          logger.error(
            `A METRIC_COLLECTION_TIMEOUT error occurred while checking connectivity to the database via the ${pgPoolType} with a timeout of ${timeoutInMilliSeconds}ms.`,
          );
        } else {
          logger.error(<Error>error, `METRIC_COLLECTION_ERROR`);
        }

        this.set(0);
      }
    },
  });
};