package config

import (
	"flag"
	"fmt"
	"net"
)

const ServerVersion = "2026.05.14.1904"

type Config struct {
	HTTPHost         string
	HTTPPort         int
	UDPHost          string
	UDPPort          int
	MaintenanceIP    string
	MaintenanceCIDR  string
	AdminPassword    string
	ServerVersion    string
	DeviceIDFallback string
}

func Load(args []string) Config {
	cfg := Config{
		HTTPHost:         "0.0.0.0",
		HTTPPort:         48888,
		UDPHost:          "0.0.0.0",
		UDPPort:          50000,
		MaintenanceIP:    "",
		MaintenanceCIDR:  "",
		AdminPassword:    "Dieteng2026",
		ServerVersion:    ServerVersion,
		DeviceIDFallback: "networktool-device",
	}

	fs := flag.NewFlagSet("networktool-server", flag.ContinueOnError)
	fs.StringVar(&cfg.MaintenanceIP, "ip", cfg.MaintenanceIP, "maintenance IPv4 address, must be in 169.254.0.0/16 when set")
	fs.IntVar(&cfg.HTTPPort, "port", cfg.HTTPPort, "HTTP listen port")
	fs.StringVar(&cfg.AdminPassword, "password", cfg.AdminPassword, "admin password")
	_ = fs.Parse(args)

	if cfg.MaintenanceIP != "" {
		parsed := net.ParseIP(cfg.MaintenanceIP)
		ipv4 := parsed.To4()
		if parsed == nil || ipv4 == nil || ipv4[0] != 169 || ipv4[1] != 254 {
			panic(fmt.Sprintf("invalid maintenance ip: %s", cfg.MaintenanceIP))
		}
		if isNetworkOrBroadcastAddress(ipv4, 16) {
			panic(fmt.Sprintf("maintenance ip cannot be network or broadcast address: %s", cfg.MaintenanceIP))
		}
		cfg.MaintenanceCIDR = fmt.Sprintf("%s/16", cfg.MaintenanceIP)
	}

	return cfg
}

func isNetworkOrBroadcastAddress(ip net.IP, prefix int) bool {
	if prefix > 30 {
		return false
	}
	ipv4 := ip.To4()
	if ipv4 == nil {
		return false
	}
	mask := net.CIDRMask(prefix, 32)
	network := ipv4.Mask(mask)
	broadcast := make(net.IP, len(network))
	for i := range network {
		broadcast[i] = network[i] | ^mask[i]
	}
	return ipv4.Equal(network) || ipv4.Equal(broadcast)
}