package service

import (
	"context"
	"crypto/ed25519"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"net/url"
	"os"
	"strconv"
	"strings"
	"time"

	"github.com/gofrs/uuid/v5"
	"go.uber.org/zap"
	"wails-app/internal/dao"
	"wails-app/internal/global"
	"wails-app/internal/modules/deviceprovisioning/model/request"
	responseModel "wails-app/internal/modules/deviceprovisioning/model/response"
)

const (
	discoveryPort      = 31001
	discoveryPacketMax = 4 * 1024
	discoveryWindow    = 3 * time.Second
)

type discoveryRequestPacket struct {
	Schema    string `json:"schema"`
	RequestID string `json:"request_id"`
	IssuedAt  int64  `json:"issued_at"`
	ExpiresAt int64  `json:"expires_at"`
	SystemID  string `json:"system_id"`
	Nonce     string `json:"nonce"`
}

// discoveryResponsePacket intentionally remains an untrusted transport envelope.
// HTTPS certificate pinning and administrator confirmation establish the device trust.
type discoveryResponsePacket struct {
	Schema               string `json:"schema"`
	RequestID            string `json:"request_id"`
	DeviceID             string `json:"device_id"`
	DeviceCode           string `json:"device_code"`
	DeviceType           string `json:"device_type"`
	DeviceModel          string `json:"device_model"`
	FirmwareVersion      string `json:"firmware_version"`
	IP                   string `json:"ip"`
	ConfigURL            string `json:"config_url"`
	PublicKeyFingerprint string `json:"public_key_fingerprint"`
	SigningPublicKey     string `json:"signing_public_key"`
	Nonce                string `json:"nonce"`
	Signature            string `json:"signature"`
}

// Discover broadcasts discovery.request.v1 and stores deduplicated candidates for ten minutes.
func (s *Service) Discover(req request.DiscoverRequest) ([]responseModel.DiscoveryResponse, error) {
	targets, err := discoveryBroadcastTargets(req.BroadcastAddress)
	if err != nil {
		return nil, err
	}
	requestID := uuid.Must(uuid.NewV4()).String()
	nonceBytes := make([]byte, 32)
	if _, err := rand.Read(nonceBytes); err != nil {
		return nil, fmt.Errorf("生成发现随机数失败: %w", err)
	}
	now := time.Now()
	packet := discoveryRequestPacket{
		Schema: "discovery.request.v1", RequestID: requestID, IssuedAt: now.Unix(),
		ExpiresAt: now.Add(30 * time.Second).Unix(), SystemID: discoverySystemID(),
		Nonce: base64.StdEncoding.EncodeToString(nonceBytes),
	}
	body, err := json.Marshal(packet)
	if err != nil {
		return nil, err
	}
	packetConn, err := (&net.ListenConfig{Control: enableBroadcastSocketOption}).ListenPacket(context.Background(), "udp4", ":0")
	if err != nil {
		return nil, fmt.Errorf("创建 UDP 发现监听失败: %w", err)
	}
	conn, ok := packetConn.(*net.UDPConn)
	if !ok {
		_ = packetConn.Close()
		return nil, errors.New("创建 UDP 发现监听失败: 套接字类型异常")
	}
	defer conn.Close()

	send := func() error {
		for _, target := range targets {
			if _, err := conn.WriteToUDP(body, &net.UDPAddr{IP: target, Port: discoveryPort}); err != nil {
				return fmt.Errorf("发送 UDP 发现请求失败: %w", err)
			}
		}
		return nil
	}
	if err := send(); err != nil {
		return nil, err
	}
	deadline := now.Add(discoveryWindow)
	nextSend := now.Add(500 * time.Millisecond)
	sendCount := 1
	results := make(map[string]responseModel.DiscoveryResponse)
	buffer := make([]byte, discoveryPacketMax+1)
	for time.Now().Before(deadline) {
		readUntil := deadline
		if sendCount < 3 && nextSend.Before(readUntil) {
			readUntil = nextSend
		}
		_ = conn.SetReadDeadline(readUntil)
		n, source, readErr := conn.ReadFromUDP(buffer)
		if readErr != nil {
			if netErr, ok := readErr.(net.Error); !ok || !netErr.Timeout() {
				return nil, fmt.Errorf("读取 UDP 发现响应失败: %w", readErr)
			}
			if sendCount < 3 && !time.Now().Before(nextSend) {
				if err := send(); err != nil {
					return nil, err
				}
				nextSend = nextSend.Add(500 * time.Millisecond)
				sendCount++
			}
			continue
		}
		if n > discoveryPacketMax {
			discoveryLogWarn("丢弃过大的 UDP 发现响应", zap.String("source_ip", source.IP.String()), zap.Int("packet_bytes", n))
			continue
		}
		discoveryLogInfo("收到 UDP 发现响应", zap.String("request_id", requestID), zap.String("source_ip", source.IP.String()), zap.Int("packet_bytes", n))
		candidate, err := validateDiscoveryResponse(buffer[:n], source.IP, packet)
		if err != nil {
			discoveryLogWarn("丢弃 UDP 发现响应", zap.String("request_id", requestID), zap.String("source_ip", source.IP.String()), zap.String("reason", err.Error()))
			continue
		}
		expiresAt := time.Now().Add(10 * time.Minute)
		payload := string(buffer[:n])
		if _, exists := results[candidate.DeviceID]; exists {
			discoveryLogInfo("忽略重复 UDP 发现响应", zap.String("request_id", requestID), zap.String("source_ip", source.IP.String()), zap.String("device_id", candidate.DeviceID))
			continue
		}
		record := &dao.DeviceDiscovery{
			RequestID: requestID,
			DeviceID:  candidate.DeviceID, DeviceCode: candidate.DeviceCode, DeviceType: candidate.DeviceType,
			DeviceModel: candidate.DeviceModel, FirmwareVersion: candidate.FirmwareVersion,
			SourceIP: candidate.IP, ConfigPort: candidate.ConfigPort, Payload: payload,
			PublicKeyFingerprint: candidate.PublicKeyFingerprint, Signature: candidateSignature(buffer[:n]),
			SignatureVerified: candidate.SignatureVerified,
			ProvisionMethod:   "auto_udp", ProvisionStatus: "unprovisioned", ExpiredAt: expiresAt,
		}
		if err := s.repo.CreateDiscovery(record); err != nil {
			discoveryLogWarn("保存 UDP 发现结果失败", zap.String("request_id", requestID), zap.String("source_ip", source.IP.String()), zap.String("device_id", candidate.DeviceID), zap.Error(err))
			return nil, err
		}
		discoveryLogInfo("UDP 发现响应校验并保存成功", zap.String("request_id", requestID), zap.String("source_ip", source.IP.String()), zap.String("device_id", candidate.DeviceID), zap.String("device_code", candidate.DeviceCode), zap.Int("config_port", candidate.ConfigPort))
		candidate.RequestID = requestID
		candidate.ExpiredAt = expiresAt
		results[candidate.DeviceID] = candidate
	}
	output := make([]responseModel.DiscoveryResponse, 0, len(results))
	for _, result := range results {
		output = append(output, result)
	}
	return output, nil
}

func (s *Service) Discoveries() ([]responseModel.DiscoveryResponse, error) {
	records, err := s.repo.ActiveDiscoveries()
	if err != nil {
		return nil, err
	}
	items := make([]responseModel.DiscoveryResponse, 0, len(records))
	seen := map[string]bool{}
	for _, record := range records {
		if seen[record.DeviceID] {
			continue
		}
		seen[record.DeviceID] = true
		items = append(items, responseModel.DiscoveryResponse{
			RequestID: record.RequestID, DeviceID: record.DeviceID, DeviceCode: record.DeviceCode,
			DeviceType: record.DeviceType, DeviceModel: record.DeviceModel, FirmwareVersion: record.FirmwareVersion,
			IP: record.SourceIP, ConfigPort: record.ConfigPort, PublicKeyFingerprint: record.PublicKeyFingerprint,
			SignatureVerified: record.SignatureVerified, ProvisionMethod: record.ProvisionMethod,
			ProvisionStatus: record.ProvisionStatus, ExpiredAt: record.ExpiredAt,
		})
	}
	return items, nil
}

// ReadDiscoveredIdentity establishes the HTTPS certificate identity for a UDP candidate.
func (s *Service) ReadDiscoveredIdentity(deviceID string) (*responseModel.IdentityResponse, error) {
	record, err := s.repo.LatestDiscoveryByMethod(deviceID, "auto_udp")
	if err != nil {
		return nil, err
	}
	if record.ProvisionMethod != "auto_udp" {
		return nil, errors.New("该设备不是自动发现记录")
	}
	return s.ReadIdentity(request.ManualIdentityRequest{IP: record.SourceIP, Port: record.ConfigPort, ProvisionMethod: "auto_udp"})
}

func validateDiscoveryResponse(raw []byte, sourceIP net.IP, request discoveryRequestPacket) (responseModel.DiscoveryResponse, error) {
	var packet discoveryResponsePacket
	if err := json.Unmarshal(raw, &packet); err != nil {
		return responseModel.DiscoveryResponse{}, err
	}
	if packet.Schema != "discovery.response.v1" || packet.RequestID != request.RequestID || packet.Nonce != request.Nonce || strings.TrimSpace(packet.DeviceID) == "" {
		return responseModel.DiscoveryResponse{}, errors.New("UDP 响应关联信息无效")
	}
	if strings.TrimSpace(packet.Signature) == "" || strings.TrimSpace(packet.SigningPublicKey) == "" {
		return responseModel.DiscoveryResponse{}, errors.New("UDP 响应缺少签名")
	}
	publicKey, err := base64.StdEncoding.DecodeString(packet.SigningPublicKey)
	if err != nil || len(publicKey) != ed25519.PublicKeySize {
		return responseModel.DiscoveryResponse{}, errors.New("UDP 响应签名公钥无效")
	}
	publicKeyHash := sha256.Sum256(publicKey)
	expectedFingerprint := fmt.Sprintf("%x", publicKeyHash)
	if normalizeFingerprint(packet.PublicKeyFingerprint) != expectedFingerprint {
		return responseModel.DiscoveryResponse{}, fmt.Errorf("UDP 响应公钥指纹不匹配: received=%q expected=SHA256:%s", packet.PublicKeyFingerprint, expectedFingerprint)
	}
	signature, err := base64.StdEncoding.DecodeString(packet.Signature)
	if err != nil || !ed25519.Verify(ed25519.PublicKey(publicKey), discoverySigningPayload(packet), signature) {
		return responseModel.DiscoveryResponse{}, errors.New("UDP 响应签名校验失败")
	}
	claimedIP := net.ParseIP(packet.IP)
	if claimedIP == nil || !claimedIP.Equal(sourceIP) {
		return responseModel.DiscoveryResponse{}, fmt.Errorf("UDP 响应 IP 与报文来源不一致: claimed_ip=%q source_ip=%q", packet.IP, sourceIP.String())
	}
	configURL, err := url.Parse(packet.ConfigURL)
	if err != nil || configURL.Scheme != "https" || configURL.Hostname() != sourceIP.String() {
		return responseModel.DiscoveryResponse{}, errors.New("UDP 响应配置地址无效")
	}
	port := defaultConfigPort
	if configURL.Port() != "" {
		port, err = strconv.Atoi(configURL.Port())
		if err != nil {
			return responseModel.DiscoveryResponse{}, errors.New("UDP 响应配置端口无效")
		}
	}
	if _, err := ValidateAddress(sourceIP.String(), port); err != nil {
		return responseModel.DiscoveryResponse{}, err
	}
	return responseModel.DiscoveryResponse{
		DeviceID: packet.DeviceID, DeviceCode: packet.DeviceCode, DeviceType: packet.DeviceType,
		DeviceModel: packet.DeviceModel, FirmwareVersion: packet.FirmwareVersion, IP: sourceIP.String(),
		ConfigPort: port, PublicKeyFingerprint: packet.PublicKeyFingerprint, SignatureVerified: true, ProvisionMethod: "auto_udp",
		ProvisionStatus: "unprovisioned",
	}, nil
}

// Discovery operates without the full backend bootstrap in unit tests, so logging is optional there.
func discoveryLogInfo(message string, fields ...zap.Field) {
	if global.GVA_LOG != nil {
		global.GVA_LOG.Info(message, fields...)
	}
}

func discoveryLogWarn(message string, fields ...zap.Field) {
	if global.GVA_LOG != nil {
		global.GVA_LOG.Warn(message, fields...)
	}
}

func discoverySigningPayload(packet discoveryResponsePacket) []byte {
	return []byte(strings.Join([]string{
		packet.Schema, packet.RequestID, packet.DeviceID, packet.IP, packet.ConfigURL, packet.Nonce,
	}, "\n"))
}

func candidateSignature(raw []byte) string {
	var packet discoveryResponsePacket
	if json.Unmarshal(raw, &packet) != nil {
		return ""
	}
	return packet.Signature
}

func discoveryBroadcastTargets(rawAddress string) ([]net.IP, error) {
	if value := strings.TrimSpace(rawAddress); value != "" {
		ip := net.ParseIP(value)
		if ip == nil || ip.To4() == nil || ip.IsLoopback() || ip.IsUnspecified() || ip.IsMulticast() {
			return nil, errors.New("广播地址必须是合法 IPv4 定向广播地址")
		}
		return []net.IP{ip.To4()}, nil
	}
	interfaces, err := net.Interfaces()
	if err != nil {
		return nil, fmt.Errorf("枚举网卡失败: %w", err)
	}
	seen := map[string]bool{}
	var targets []net.IP
	for _, iface := range interfaces {
		if iface.Flags&net.FlagUp == 0 || iface.Flags&net.FlagLoopback != 0 {
			continue
		}
		addrs, _ := iface.Addrs()
		for _, address := range addrs {
			ipNet, ok := address.(*net.IPNet)
			if !ok || ipNet.IP.To4() == nil || len(ipNet.Mask) != net.IPv4len {
				continue
			}
			broadcast := make(net.IP, net.IPv4len)
			ip := ipNet.IP.To4()
			for i := range broadcast {
				broadcast[i] = ip[i] | ^ipNet.Mask[i]
			}
			if broadcast.Equal(ip) || seen[broadcast.String()] {
				continue
			}
			seen[broadcast.String()] = true
			targets = append(targets, broadcast)
		}
	}
	if len(targets) == 0 {
		return nil, errors.New("未找到可用 IPv4 网卡，请指定广播地址或使用手工 IP 接入")
	}
	return targets, nil
}

func discoverySystemID() string {
	name, err := os.Hostname()
	if err != nil || strings.TrimSpace(name) == "" {
		return "smart-parking"
	}
	return "smart-parking-" + name
}