package dhclient

import (
	"bytes"
	"fmt"
	"html/template"
	"net"
	"os"
	"strings"
)

const (
	resolvConfPath     = "/etc/resolv.conf"
	resolvConfFileMode = 0644
	resolvConfTemplate = `# the resolv.conf file is managed by the jetkvm-dhclient service
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN

{{ if .searchList }}
search {{ join .searchList " " }} # {{ .iface }}
{{- end -}}
{{ if .domain }}
domain {{ .domain }} # {{ .iface }}
{{- end -}}
{{ range .nameservers }}
nameserver {{ printf "%s" . }} # {{ $.iface }}
{{- end }}
`
)

var (
	tplFuncMap = template.FuncMap{
		"join": strings.Join,
	}
)

func toResolvConf(iface string, nameservers []net.IP, searchList []string, domain string) (bytes.Buffer, error) {
	rc := bytes.Buffer{}
	tmpl, err := template.New("resolv.conf").Funcs(tplFuncMap).Parse(resolvConfTemplate)
	if err != nil {
		return rc, fmt.Errorf("failed to parse template: %w", err)
	}

	if err := tmpl.Execute(&rc, map[string]interface{}{
		"iface":       iface,
		"nameservers": nameservers,
		"searchList":  searchList,
		"domain":      domain,
	}); err != nil {
		return rc, fmt.Errorf("failed to execute template: %w", err)
	}

	return rc, nil
}

func updateResolvConf(iface string, nameservers []net.IP, searchList []string, domain string) error {
	rc, err := toResolvConf(iface, nameservers, searchList, domain)
	if err != nil {
		return err
	}

	return os.WriteFile(resolvConfPath, rc.Bytes(), resolvConfFileMode)
}