// Unless explicitly stated otherwise all files in this repository are licensed
// under the Apache License Version 2.0.
// This product includes software developed at Datadog (https://www.datadoghq.com/).
// Copyright 2016-present Datadog, Inc.

// This file is exactly pulled from datadog-agent/pkg/util/hostname/validate only changing the logger

// Package validate provides hostname validation helpers
package validate

import (
	"fmt"
	"regexp"
	"slices"
	"strings"

	"github.com/DataDog/dd-trace-go/v2/internal/log"
)

const maxLength = 255

var (
	validHostnameRfc1123 = regexp.MustCompile(`^(([a-zA-Z0-9]|[a-zA-Z0-9][a-zA-Z0-9\-]*[a-zA-Z0-9])\.)*([A-Za-z0-9]|[A-Za-z0-9][A-Za-z0-9\-]*[A-Za-z0-9])$`)
	localhostIdentifiers = []string{
		"localhost",
		"localhost.localdomain",
		"localhost6.localdomain6",
		"ip6-localhost",
	}
)

// ValidHostname determines whether the passed string is a valid hostname.
// In case it's not, the returned error contains the details of the failure.
func ValidHostname(hostname string) error {
	if hostname == "" {
		return fmt.Errorf("hostname is empty")
	} else if isLocal(hostname) {
		return fmt.Errorf("%s is a local hostname", hostname)
	} else if len(hostname) > maxLength {
		log.Error("ValidHostname: name exceeded the maximum length of %d characters", maxLength)
		return fmt.Errorf("name exceeded the maximum length of %d characters", maxLength)
	} else if !validHostnameRfc1123.MatchString(hostname) {
		log.Error("ValidHostname: %s is not RFC1123 compliant", hostname)
		return fmt.Errorf("%s is not RFC1123 compliant", hostname)
	}
	return nil
}

// check whether the name is in the list of local hostnames
func isLocal(name string) bool {
	name = strings.ToLower(name)
	return slices.Contains(localhostIdentifiers, name)
}
