```
hydra-notify's Prometheus service
---------------------------------
hydra-notify supports running a Prometheus webserver for metrics. The
exporter does not run unless a listen address and port are specified
in the hydra configuration file, as below:
```conf
<hydra_notify>
  <prometheus>
    listen_address = 127.0.0.1
    port = 9199
  </prometheus>
</hydra_notify>

## Notification Daemon
The `hydra-notify` process can expose Prometheus metrics for plugin execution. See
[hydra-notify's Prometheus service](../configuration.md#hydra-notifys-prometheus-service)
for details on enabling and configuring the exporter.

The notification exporter exposes metrics on a per-plugin, per-event-type basis: execution
durations, frequency, successes, and failures.

sub getHydraNotifyPrometheusConfig {
    my ($config) = @_;
    my $cfg = $config->{hydra_notify};
    if (!defined($cfg) || ref $cfg ne "HASH") {
        return undef;
    }

    my $cfg = $cfg->{prometheus};
    if (!defined($cfg) || ref $cfg ne "HASH") {
        return undef;
    }

    if (defined($cfg->{"listen_address"}) && defined($cfg->{"port"})) {
        return {
            "listen_address" => $cfg->{'listen_address'},
            "port" => $cfg->{'port'},
        };
    }
    return undef;
}

my $prom = Prometheus::Tiny::Shared->new;
my $fork_manager = Parallel::ForkManager->new(1 );
$fork_manager->start_child("metrics_exporter", sub {
    my $server = HTTP::Server::PSGI->new(
        host => "127.0.0.1",
        port => 9091,
        timeout => 5,
    );
    $server->run($prom->psgi);
});

my $config = getHydraConfig();
my $prom = Prometheus::Tiny::Shared->new;
my $promCfg = Hydra::Helper::Nix::getHydraNotifyPrometheusConfig($config);
if (defined($promCfg)) {
    my $fork_manager = Parallel::ForkManager->new(1);
    $fork_manager->start_child("metrics_exporter", sub {
        my $server = HTTP::Server::PSGI->new(
            host => $promCfg->{"listen_address"},
            port => $promCfg->{"port"},
            timeout => 1,
        );
        $server->run($prom->psgi);
    });
}

my $config = getHydraConfig();

use strict;
use Setup;
my %ctx = test_init(hydra_config => q|
<hydra_notify>
  <prometheus>
    listen_address = 127.0.0.1
    port = 9199
  </prometheus>
</hydra_notify>
|);
require Hydra::Helper::Nix;
use Test2::V0;
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig(Hydra::Helper::Nix::getHydraConfig()), {
    'listen_address' => "127.0.0.1",
    'port' => 9199
}, "Reading specific configuration from the hydra.conf works");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => ":)"
}), undef, "Invalid (hydra_notify is a string) configuration options are undef");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => []
}), undef, "Invalid (hydra_notify is a list) configuration options are undef");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => {}
}), undef, "Invalid (hydra_notify is an empty hash) configuration options are undef");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => {
        "prometheus" => ":)"
    }
}), undef, "Invalid (hydra_notify.prometheus is a string) configuration options are undef");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => {
        "prometheus" => {}
    }
}), undef, "Invalid (hydra_notify.prometheus is an empty hash) configuration options are undef");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => {
        "prometheus" => {
            "listen_address" => "0.0.0.0"
        }
    }
}), undef, "Invalid (hydra_notify.prometheus.port is missing) configuration options are undef");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => {
        "prometheus" => {
            "port" => 1234
        }
    }
}), undef, "Invalid (hydra_notify.prometheus.listen_address is missing) configuration options are undef");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => {
        "prometheus" => {
            "listen_address" => "127.0.0.1",
            "port" => 1234
        }
    }
}), {
    "listen_address" => "127.0.0.1",
    "port" => 1234
}, "Fully specified hydra_notify.prometheus config is valid and returned");
is(Hydra::Helper::Nix::getHydraNotifyPrometheusConfig({
    "hydra_notify" => {
        "prometheus" => {
            "listen_address" => "127.0.0.1",
            "port" => 1234,
            "extra_keys" => "meh",
        }
    }
}), {
    "listen_address" => "127.0.0.1",
    "port" => 1234
}, "extra configuration in hydra_notify.prometheus is not returned");
done_testing;