{ config, lib, pkgs, ... }:

let
  cfg = config.exporters;
in
{
  options.exporters = {
    sqlExporterPort = lib.mkOption {
      type = lib.types.int;
    };
  };

  imports = [
    <top/shared/prometheus-sql-exporter/service.nix>
  ];

  config = {
    services.prometheus-sql-exporter = {
      enable = true;
      port = cfg.sqlExporterPort;
      config = {
        target = {
          # This URL should be postgresql:///postgres?host=/run/postgresql
          # but sql_exporter uses xo/dburl which isn't spec-compliant: https://github.com/xo/dburl/issues/46
          data_source_name = "postgresql:/run/postgresql:/postgres";
          collectors = ["db-sizes"];
        };
        collectors = [
          {
            collector_name = "db-sizes";
            metrics = [
              {
                metric_name = "pg_db_size_bytes";
                help = "disk space used by the database";
                type = "gauge";
                key_labels = ["database_name"];
                values = ["size"];
                query = "SELECT datname AS database_name, pg_database_size(datname) as size from pg_database";
              }
            ];
          }
        ];
      };
    };

    monitoring.prometheusScrapeConfigs = [
      {
        job_name = "sql";
        static_configs = [{
          targets = [ "localhost:${toString cfg.sqlExporterPort}" ];
        }];
      }
    ];
  };
}