/*
Copyright 2018 The Kubernetes 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 metrics

import (
	"fmt"
	"net"

	logf "sigs.k8s.io/controller-runtime/pkg/internal/log"
)

var log = logf.RuntimeLog.WithName("metrics")

// DefaultBindAddress sets the default bind address for the metrics listener
// The metrics is on by default.
var DefaultBindAddress = ":8080"

// NewListener creates a new TCP listener bound to the given address.
func NewListener(addr string) (net.Listener, error) {
	if addr == "" {
		// If the metrics bind address is empty, default to ":8080"
		addr = DefaultBindAddress
	}

	// Add a case to disable metrics altogether
	if addr == "0" {
		return nil, nil
	}

	log.Info("metrics server is starting to listen", "addr", addr)
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		er := fmt.Errorf("error listening on %s: %w", addr, err)
		log.Error(er, "metrics server failed to listen. You may want to disable the metrics server or use another port if it is due to conflicts")
		return nil, er
	}
	return ln, nil
}
