You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: metrics.go
    path of file: ./repos/prometheus/discovery
    
    the code of the file until where you have to start completion: // Copyright 2016 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package discovery

import (
	"fmt"

	"github.com/prometheus/client_golang/prometheus"
)

var (
	clientGoRequestMetrics  = &clientGoRequestMetricAdapter{}
	clientGoWorkloadMetrics = &clientGoWorkqueueMetricsProvider{}
)

func init() {
	clientGoRequestMetrics.RegisterWithK8sGoClient()
	clientGoWorkloadMetrics.RegisterWithK8sGoClient()
}

// Metrics to be used with a discovery manager.
type Metrics struct {
	FailedConfigs     prometheus.Gauge
	DiscoveredTargets *prometheus.GaugeVec
	ReceivedUpdates   prometheus.Counter
	DelayedUpdates    prometheus.Counter
	SentUpdates       prometheus.Counter
}

func NewMa
    
func NewManagerMetrics(registerer prometheus.Registerer, sdManagerName string) (*Metrics, error) {
	m := &Metrics{}

	m.FailedConfigs = prometheus.NewGauge(
		prometheus.GaugeOpts{
			Name:        "prometheus_sd_failed_configs",
			Help:        "Current number of service discovery configurations that failed to load.",
			ConstLabels: prometheus.Labels{"name": sdManagerName},
		},
	)

	m.DiscoveredTargets = prometheus.NewGaugeVec(
		prometheus.GaugeOpts{
			Name:        "prometheus_sd_discovered_targets",
			Help:        "Current number of discovered targets.",
			ConstLabels: prometheus.Labels{"name": sdManagerName},
		},
		[]string{"config"},
	)

	m.ReceivedUpdates = prometheus.NewCounter(
		prometheus.CounterOpts{
			Name:        "prometheus_sd_received_updates_total",
			Help:        "Total number of update events received from the SD providers.",
			ConstLabels: prometheus.Labels{"name": sdManagerName},
		},
	)

	m.DelayedUpdates = prometheus.NewCounter(
		prometheus.CounterOpts{
			Name:        "prometheus_sd_updates_delayed_total",
			Help:        "Total number of update events that couldn't be sent immediately.",
			ConstLabels: prometheus.Labels{"name": sdManagerName},
		},
	)

	m.SentUpdates = prometheus.NewCounter(
		prometheus.CounterOpts{
			Name:        "prometheus_sd_updates_total",
			Help:        "Total number of update events sent to the SD consumers.",
			ConstLabels: prometheus.Labels{"name": sdManagerName},
		},
	)

	metrics := []prometheus.Collector{
		m.FailedConfigs,
		m.DiscoveredTargets,
		m.ReceivedUpdates,
		m.DelayedUpdates,
		m.SentUpdates,
	}

	for _, collector := range metrics {
		err := registerer.Register(collector)
		if err != nil {
			return nil, fmt.Errorf("failed to register discovery manager metrics: %w", err)
		}
	}

	return m, nil
}