package validator

import (
	"fmt"
	"net"

	"networktool/internal/model"
)

type Service struct{}

func New() *Service { return &Service{} }

func (s *Service) Validate(input model.InterfaceConfig) model.ValidateResponse {
	resp := model.ValidateResponse{Valid: false, Warnings: []string{}, Errors: []string{}}

	if input.Interface == "" {
		resp.Errors = append(resp.Errors, "目标接口不能为空。")
	}
	if input.Dhcp4 {
		resp.Valid = len(resp.Errors) == 0
		return resp
	}
	ip := net.ParseIP(input.IP)
	if ip == nil || ip.To4() == nil {
		resp.Errors = append(resp.Errors, "IP 地址格式不正确。")
	}
	if input.Prefix < 0 || input.Prefix > 32 {
		resp.Errors = append(resp.Errors, "前缀长度不正确。")
	}
	if input.Gateway != "" {
		gateway := net.ParseIP(input.Gateway)
		if gateway == nil || gateway.To4() == nil {
			resp.Errors = append(resp.Errors, "网关格式不正确。")
		} else if ip != nil && ip.To4() != nil && input.Prefix >= 0 && input.Prefix <= 32 {
			mask := net.CIDRMask(input.Prefix, 32)
			ipNet := &net.IPNet{IP: ip.Mask(mask), Mask: mask}
			if !ipNet.Contains(gateway) {
				resp.Errors = append(resp.Errors, "网关与目标接口 IP 不在同一子网。")
			}
		}
	}
	for _, dns := range input.DNS {
		if dns == "" {
			continue
		}
		parsed := net.ParseIP(dns)
		if parsed == nil || parsed.To4() == nil {
			resp.Errors = append(resp.Errors, fmt.Sprintf("DNS 格式不正确：%s", dns))
		}
	}
	if ip != nil && ip.To4() != nil {
		if ip[0] == 169 && ip[1] == 254 {
			resp.Warnings = append(resp.Warnings, "目标接口使用的是链路本地地址，通常仅适合同链路通信。")
		}
	}

	resp.Valid = len(resp.Errors) == 0
	return resp
}