// tera-snmpd is the minimal privileged Net-SNMP configuration adapter.
package main

import (
	"errors"
	"log"
	"net"
	"os"
	"os/signal"
	"path/filepath"
	"syscall"

	"tera-clone/services/tera-api/internal/snmpagent"
	"tera-clone/services/tera-api/internal/snmpagent/snmpsocket"
)

func main() {
	controller, err := snmpagent.NewOSController(snmpagent.OSOptions{
		ConfigPath:     getenv("TERA_SNMPD_CONFIG", snmpagent.DefaultConfigPath),
		PersistentPath: getenv("TERA_SNMPD_PERSISTENT_CONFIG", snmpagent.DefaultPersistentPath),
		InitScriptPath: getenv("TERA_SNMPD_INIT_SCRIPT", snmpagent.DefaultInitScriptPath),
		ServiceName:    os.Getenv("TERA_SNMPD_SERVICE_NAME"),
	})
	if err != nil {
		log.Fatalf("tera-snmpd setup failed: %v", err)
	}
	socketPath := getenv("TERA_SNMPD_SOCKET", snmpsocket.DefaultSocketPath)
	listener, err := listen(socketPath)
	if err != nil {
		log.Fatalf("tera-snmpd socket setup failed: %v", err)
	}
	defer func() {
		_ = listener.Close()
		_ = os.Remove(socketPath)
	}()
	done := make(chan error, 1)
	go func() { done <- (snmpsocket.Server{Controller: controller}).Serve(listener) }()
	log.Printf("tera-snmpd serving SNMP agent control on %s", socketPath)
	signals := make(chan os.Signal, 1)
	signal.Notify(signals, syscall.SIGINT, syscall.SIGTERM)
	select {
	case signal := <-signals:
		log.Printf("tera-snmpd stopping after %s", signal)
		_ = listener.Close()
		if err := <-done; err != nil {
			log.Printf("tera-snmpd stop error: %v", err)
		}
	case err := <-done:
		if err != nil {
			log.Fatalf("tera-snmpd failed: %v", err)
		}
	}
}

func listen(socketPath string) (net.Listener, error) {
	if socketPath == "" || !filepath.IsAbs(socketPath) {
		return nil, errors.New("TERA_SNMPD_SOCKET must be an absolute path")
	}
	if err := os.MkdirAll(filepath.Dir(socketPath), 0o750); err != nil {
		return nil, err
	}
	if info, err := os.Lstat(socketPath); err == nil {
		if info.Mode()&os.ModeSocket == 0 {
			return nil, errors.New("refusing to replace non-socket SNMP control path")
		}
		if err := os.Remove(socketPath); err != nil {
			return nil, err
		}
	} else if !os.IsNotExist(err) {
		return nil, err
	}
	listener, err := net.Listen("unix", socketPath)
	if err != nil {
		return nil, err
	}
	if err := os.Chmod(socketPath, 0o660); err != nil {
		_ = listener.Close()
		return nil, err
	}
	return listener, nil
}

func getenv(key, fallback string) string {
	if value := os.Getenv(key); value != "" {
		return value
	}
	return fallback
}