//go:build !windows && !nacl && !plan9
// +build !windows,!nacl,!plan9

package logging

import (
	"errors"
	"fmt"
	"log/syslog"
	"strings"
)

var errUnknownFacility = errors.New("unknown facility")

//
// Syslog Backend
//

// SyslogBackend writes the logs to a syslog system.
type SyslogBackend struct {
	w         *syslog.Writer
	formatter Formatter
	level     Level
}

// NewSyslogBackend initializes a new connection to a syslog server with the
// given facility.
// tag can contain an identifier for the log stream. It defaults to os.Arg[0].
func NewSyslogBackend(facilityName, tag string) (*SyslogBackend, error) {
	f, err := facility(facilityName)
	if err != nil {
		return nil, err
	}

	w, err := syslog.New(f, tag)
	if err != nil {
		return nil, fmt.Errorf("cannot initialize syslog: %w", err)
	}

	sb := &SyslogBackend{
		w:         w,
		formatter: basicFormatter,
	}

	return sb, nil
}

// Write sends an entry to the syslog server.
func (sb *SyslogBackend) Write(r *Record) error {
	var err error

	text := sb.formatter(r)

	switch r.Level {
	case Trace, Debug:
		err = sb.w.Debug(text)
	case Info:
		err = sb.w.Info(text)
	case Notice:
		err = sb.w.Notice(text)
	case Warning:
		err = sb.w.Warning(text)
	case Error:
		err = sb.w.Err(text)
	case Critical:
		err = sb.w.Crit(text)
	case Alert:
		err = sb.w.Alert(text)
	case Fatal:
		err = sb.w.Emerg(text)
	}

	return fmt.Errorf("cannot log to syslog: %w", err)
}

// SetFormatter defines the formatter for this backend.
func (sb *SyslogBackend) SetFormatter(f Formatter) {
	sb.formatter = f
}

// SetLevel changes the log level of the backend.
func (sb *SyslogBackend) SetLevel(level Level) {
	sb.level = level
}

// Level returns the log level set for this backend.
func (sb *SyslogBackend) Level() Level {
	return sb.level
}

// Reopen is a no-op.
func (*SyslogBackend) Reopen() error {
	return nil
}

// Close closes the connection to the syslog daemon.
func (sb *SyslogBackend) Close() error {
	if err := sb.w.Close(); err != nil {
		return fmt.Errorf("cannot close syslog: %w", err)
	}

	return nil
}

//nolint:gochecknoglobals // global var is used by design
var facilities = map[string]syslog.Priority{
	"kern":     syslog.LOG_KERN,
	"user":     syslog.LOG_USER,
	"mail":     syslog.LOG_MAIL,
	"daemon":   syslog.LOG_DAEMON,
	"auth":     syslog.LOG_AUTH,
	"syslog":   syslog.LOG_SYSLOG,
	"lpr":      syslog.LOG_LPR,
	"news":     syslog.LOG_NEWS,
	"uucp":     syslog.LOG_UUCP,
	"cron":     syslog.LOG_CRON,
	"authpriv": syslog.LOG_AUTHPRIV,
	"ftp":      syslog.LOG_FTP,
	"local0":   syslog.LOG_LOCAL0,
	"local1":   syslog.LOG_LOCAL1,
	"local2":   syslog.LOG_LOCAL2,
	"local3":   syslog.LOG_LOCAL3,
	"local4":   syslog.LOG_LOCAL4,
	"local5":   syslog.LOG_LOCAL5,
	"local6":   syslog.LOG_LOCAL6,
	"local7":   syslog.LOG_LOCAL7,
}

func facility(name string) (syslog.Priority, error) {
	p, ok := facilities[strings.ToLower(name)]
	if !ok {
		return 0, fmt.Errorf("facility '%s' does not exist: %w", name, errUnknownFacility)
	}

	return p, nil
}