package onvif

import (
	"context"
	"encoding/xml"
	"errors"
	"io"
	"net"
	"sort"
	"strings"
	"time"
)

var (
	ErrDiscoveryNotConfigured = errors.New("未配置获准的发现网卡")
	ErrDiscoveryInterface     = errors.New("配置的发现地址不是本机网卡")
)

const discoveryProbe = `<?xml version="1.0"?><e:Envelope xmlns:e="http://www.w3.org/2003/05/soap-envelope" xmlns:w="http://schemas.xmlsoap.org/ws/2004/08/addressing" xmlns:d="http://schemas.xmlsoap.org/ws/2005/04/discovery" xmlns:dn="http://www.onvif.org/ver10/network/wsdl"><e:Header><w:MessageID>uuid:sense-controlled-discovery</w:MessageID><w:To e:mustUnderstand="true">urn:schemas-xmlsoap-org:ws:2005:04:discovery</w:To><w:Action e:mustUnderstand="true">http://schemas.xmlsoap.org/ws/2005/04/discovery/Probe</w:Action></e:Header><e:Body><d:Probe><d:Types>dn:NetworkVideoTransmitter</d:Types></d:Probe></e:Body></e:Envelope>`

func Discover(ctx context.Context, localIP string, timeout time.Duration, policy Policy) ([]string, error) {
	ip := net.ParseIP(strings.TrimSpace(localIP))
	if ip == nil {
		return nil, ErrDiscoveryNotConfigured
	}
	approved := false
	interfaces, _ := net.Interfaces()
	for _, iface := range interfaces {
		addresses, _ := iface.Addrs()
		for _, address := range addresses {
			host, _, _ := net.ParseCIDR(address.String())
			if host != nil && host.Equal(ip) {
				approved = true
			}
		}
	}
	if !approved {
		return nil, ErrDiscoveryInterface
	}
	connection, err := net.ListenUDP("udp4", &net.UDPAddr{IP: ip})
	if err != nil {
		return nil, err
	}
	defer connection.Close()
	if timeout <= 0 {
		timeout = 3 * time.Second
	}
	_ = connection.SetDeadline(time.Now().Add(timeout))
	if _, err = connection.WriteToUDP([]byte(discoveryProbe), &net.UDPAddr{IP: net.ParseIP("239.255.255.250"), Port: 3702}); err != nil {
		return nil, err
	}
	found := map[string]bool{}
	buffer := make([]byte, 65535)
	for {
		n, _, readErr := connection.ReadFromUDP(buffer)
		if readErr != nil {
			if e, ok := readErr.(net.Error); ok && e.Timeout() {
				break
			}
			return nil, readErr
		}
		for _, candidate := range extractXAddrs(string(buffer[:n])) {
			if _, _, validErr := policy.ValidateURL(ctx, candidate, "http", "https"); validErr == nil {
				found[candidate] = true
			}
		}
	}
	result := make([]string, 0, len(found))
	for value := range found {
		result = append(result, value)
	}
	sort.Strings(result)
	return result, nil
}

func extractXAddrs(value string) []string {
	decoder := xml.NewDecoder(strings.NewReader(value))
	for {
		token, err := decoder.Token()
		if errors.Is(err, io.EOF) {
			break
		}
		if err != nil {
			return nil
		}
		start, ok := token.(xml.StartElement)
		if !ok || start.Name.Local != "XAddrs" {
			continue
		}
		var addresses string
		if decoder.DecodeElement(&addresses, &start) == nil {
			return strings.Fields(addresses)
		}
	}
	return nil
}