package validator

import (
	"fmt"
	"net"
	"strings"

	"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{}}
	addresses := normalizedAddresses(input)
	routes := normalizedRoutes(input)

	if input.Interface == "" {
		resp.Errors = append(resp.Errors, "目标接口不能为空。")
	}
	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 input.Dhcp4 {
		resp.Valid = len(resp.Errors) == 0
		return resp
	}
	if len(addresses) == 0 {
		resp.Errors = append(resp.Errors, "至少需要填写一个 IP 地址。")
	}
	seenAddresses := make(map[string]struct{})
	validNetworks := make([]*net.IPNet, 0, len(addresses))
	for _, address := range addresses {
		ip := net.ParseIP(address.IP)
		if ip == nil || ip.To4() == nil {
			resp.Errors = append(resp.Errors, fmt.Sprintf("IP 地址格式不正确：%s", address.IP))
			continue
		}
		if address.Prefix < 0 || address.Prefix > 32 {
			resp.Errors = append(resp.Errors, fmt.Sprintf("前缀长度不正确：%s/%d", address.IP, address.Prefix))
			continue
		}
		key := fmt.Sprintf("%s/%d", ip.String(), address.Prefix)
		if _, ok := seenAddresses[key]; ok {
			resp.Errors = append(resp.Errors, fmt.Sprintf("IP 地址重复：%s", key))
			continue
		}
		seenAddresses[key] = struct{}{}
		mask := net.CIDRMask(address.Prefix, 32)
		validNetworks = append(validNetworks, &net.IPNet{IP: ip.Mask(mask), Mask: mask})
		ipv4 := ip.To4()
		if ipv4[0] == 169 && ipv4[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。")
		}
	}
	seenRoutes := make(map[string]struct{})
	for _, route := range routes {
		to := strings.TrimSpace(route.To)
		via := strings.TrimSpace(route.Via)
		if to == "" {
			resp.Errors = append(resp.Errors, "路由目标不能为空。")
			continue
		}
		if via == "" {
			resp.Errors = append(resp.Errors, fmt.Sprintf("路由 %s 的下一跳不能为空。", to))
			continue
		}
		if to != "default" {
			ip, ipNet, err := net.ParseCIDR(to)
			if err != nil || ip == nil || ip.To4() == nil || ipNet == nil {
				resp.Errors = append(resp.Errors, fmt.Sprintf("路由目标格式不正确：%s", to))
			}
		}
		gateway := net.ParseIP(via)
		if gateway == nil || gateway.To4() == nil {
			resp.Errors = append(resp.Errors, fmt.Sprintf("路由下一跳格式不正确：%s", via))
			continue
		}
		key := to + " via " + gateway.String()
		if _, ok := seenRoutes[key]; ok {
			resp.Errors = append(resp.Errors, fmt.Sprintf("路由重复：%s", key))
			continue
		}
		seenRoutes[key] = struct{}{}
		if len(validNetworks) > 0 && !containsGateway(validNetworks, gateway) {
			resp.Errors = append(resp.Errors, fmt.Sprintf("路由下一跳与任一目标接口 IP 都不在同一子网：%s", via))
		}
	}
	resp.Valid = len(resp.Errors) == 0
	return resp
}

func normalizedAddresses(input model.InterfaceConfig) []model.InterfaceAddressConfig {
	if len(input.Addresses) > 0 {
		return input.Addresses
	}
	if strings.TrimSpace(input.IP) == "" {
		return nil
	}
	return []model.InterfaceAddressConfig{{IP: strings.TrimSpace(input.IP), Prefix: input.Prefix}}
}

func normalizedRoutes(input model.InterfaceConfig) []model.InterfaceRouteConfig {
	if len(input.Routes) > 0 {
		return input.Routes
	}
	if strings.TrimSpace(input.Gateway) == "" {
		return nil
	}
	return []model.InterfaceRouteConfig{{To: "default", Via: strings.TrimSpace(input.Gateway)}}
}

func containsGateway(networks []*net.IPNet, gateway net.IP) bool {
	for _, network := range networks {
		if network.Contains(gateway) {
			return true
		}
	}
	return false
}