package main

// Reality target scanner (round-3 item 16, modeled on the 3x-ui
// scanner): the panel itself performs a real TLS handshake against
// each candidate and reports whether it can serve as a Reality dest —
// handshake success plus an X25519-family key exchange. Results are
// the PANEL's point of view (the router reaches the internet through
// its own egress; a node's view can differ), and the UI says so.
//
// Bounds: at most scanMaxTargets probes per request, scanConcurrency
// in flight, scanProbeTimeout per probe — a scan can never wedge the
// panel.

import (
	"crypto/tls"
	"encoding/binary"
	"fmt"
	"net"
	"strconv"
	"strings"
	"sync"
	"time"
)

const (
	scanMaxTargets   = 32
	scanConcurrency  = 8
	scanProbeTimeout = 4 * time.Second
	scanCIDRMaxHosts = 32
)

// scanPool is the built-in candidate pool: the form's Reality presets
// (same source) plus the usual scanner extras.
func scanPool() []string {
	seen := map[string]bool{}
	pool := []string{}
	add := func(host string) {
		if !seen[host] {
			seen[host] = true
			pool = append(pool, host)
		}
	}
	for _, preset := range RealityPresets {
		add(preset.ServerName)
	}
	for _, host := range []string{
		"www.microsoft.com", "www.google.com", "www.nvidia.com",
		"www.samsung.com", "www.cloudflare.com", "www.bing.com",
		"www.github.com", "www.yahoo.com", "www.mozilla.org",
	} {
		add(host)
	}
	return pool
}

type scanTarget struct {
	Host string
	Port int
}

// parseScanTargets expands operator input (comma/space separated
// domains, IPs, host:port pairs and CIDRs) into probe targets. Empty
// input means the built-in pool.
func parseScanTargets(input string) ([]scanTarget, error) {
	input = strings.TrimSpace(input)
	if input == "" {
		pool := scanPool()
		out := make([]scanTarget, 0, len(pool))
		for _, host := range pool {
			out = append(out, scanTarget{Host: host, Port: 443})
		}
		return out, nil
	}
	out := []scanTarget{}
	for _, part := range strings.FieldsFunc(input, func(r rune) bool {
		return r == ',' || r == ' ' || r == '\t' || r == '\n' || r == ';'
	}) {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		if strings.Contains(part, "/") {
			hosts, err := expandCIDR(part)
			if err != nil {
				return nil, httpErr(400, "CIDR 无效: %s", part)
			}
			for _, host := range hosts {
				out = append(out, scanTarget{Host: host, Port: 443})
			}
			continue
		}
		host, port := part, 443
		if h, p, err := net.SplitHostPort(part); err == nil {
			n, err := strconv.Atoi(p)
			if err != nil || n < 1 || n > 65535 {
				return nil, httpErr(400, "端口无效: %s", part)
			}
			host, port = h, n
		}
		host = strings.Trim(host, "[]")
		if host == "" || strings.ContainsAny(host, " \t") {
			return nil, httpErr(400, "目标无效: %s", part)
		}
		out = append(out, scanTarget{Host: host, Port: port})
		if len(out) > scanMaxTargets {
			return nil, httpErr(400, "一次最多扫描 %d 个目标", scanMaxTargets)
		}
	}
	if len(out) == 0 {
		return nil, httpErr(400, "没有可扫描的目标")
	}
	if len(out) > scanMaxTargets {
		out = out[:scanMaxTargets]
	}
	return out, nil
}

func expandCIDR(cidr string) ([]string, error) {
	ip, network, err := net.ParseCIDR(cidr)
	if err != nil {
		return nil, err
	}
	if ip.To4() == nil {
		return nil, fmt.Errorf("only IPv4 CIDR supported")
	}
	base := network.IP.To4()
	mask := binary.BigEndian.Uint32(network.Mask)
	start := binary.BigEndian.Uint32(base) & mask
	count := uint32(1) << (32 - onesCount(network.Mask))
	hosts := []string{}
	for i := uint32(0); i < count && len(hosts) < scanCIDRMaxHosts; i++ {
		addr := make(net.IP, 4)
		binary.BigEndian.PutUint32(addr, start+i)
		hosts = append(hosts, addr.String())
	}
	return hosts, nil
}

func onesCount(mask net.IPMask) int {
	ones, _ := mask.Size()
	return ones
}

type scanResult struct {
	Target        string `json:"target"`
	Host          string `json:"host"`
	Port          int    `json:"port"`
	OK            bool   `json:"ok"`
	Reason        string `json:"reason,omitempty"`
	TLSVersion    string `json:"tlsVersion,omitempty"`
	ALPN          string `json:"alpn,omitempty"`
	KeyExchange   string `json:"keyExchange,omitempty"`
	KeyExchangeOK bool   `json:"keyExchangeOk"`
	CertName      string `json:"certName,omitempty"`
	LatencyMs     int64  `json:"latencyMs"`
}

func tlsVersionName(v uint16) string {
	switch v {
	case tls.VersionTLS13:
		return "TLS 1.3"
	case tls.VersionTLS12:
		return "TLS 1.2"
	case tls.VersionTLS11:
		return "TLS 1.1"
	case tls.VersionTLS10:
		return "TLS 1.0"
	}
	return ""
}

// dialScanTLS performs one bounded TLS handshake. curves, when
// non-nil, restricts the offered key-exchange groups — the only way a
// Go TLS client can learn which groups a server accepts (the negotiated
// group is not exposed on ConnectionState in this Go version).
func dialScanTLS(target scanTarget, curves []tls.CurveID) (*tls.Conn, error) {
	dialer := &net.Dialer{Timeout: scanProbeTimeout}
	conf := &tls.Config{
		ServerName: target.Host,
		NextProtos: []string{"h2", "http/1.1"},
		MinVersion: tls.VersionTLS12,
		// The probe judges reachability and key exchange, not trust:
		// Reality dests are public sites whose cert the panel has no
		// business pinning. The SAN is still reported for the operator.
		InsecureSkipVerify: true, //nolint:gosec -- probe only, see above
	}
	if curves != nil {
		conf.CurvePreferences = curves
	}
	return tls.DialWithDialer(dialer, "tcp", net.JoinHostPort(target.Host, strconv.Itoa(target.Port)), conf)
}

func curveSupported(target scanTarget, curves ...tls.CurveID) bool {
	conn, err := dialScanTLS(target, curves)
	if err != nil {
		return false
	}
	_ = conn.Close()
	return true
}

// probeRealityTarget judges a target by the Reality dest criteria: a
// TLS handshake completes and the key exchange can be X25519 or
// X25519MLKEM768 (probed strongest first; a combined-offer handshake
// is the fallback so a server that refuses single-group offers is not
// misjudged).
func probeRealityTarget(target scanTarget) scanResult {
	result := scanResult{Target: target.Host, Host: target.Host, Port: target.Port}
	start := time.Now()
	conn, err := dialScanTLS(target, nil)
	result.LatencyMs = time.Since(start).Milliseconds()
	if err != nil {
		result.Reason = "连接或握手失败: " + truncateRunes(err.Error(), 120)
		return result
	}
	state := conn.ConnectionState()
	_ = conn.Close()
	result.TLSVersion = tlsVersionName(state.Version)
	result.ALPN = state.NegotiatedProtocol
	if len(state.PeerCertificates) > 0 {
		cert := state.PeerCertificates[0]
		if len(cert.DNSNames) > 0 {
			result.CertName = cert.DNSNames[0]
		} else {
			result.CertName = cert.Subject.CommonName
		}
	}
	switch {
	case curveSupported(target, tls.X25519MLKEM768):
		result.KeyExchange = "X25519MLKEM768"
	case curveSupported(target, tls.X25519):
		result.KeyExchange = "X25519"
	case curveSupported(target, tls.X25519MLKEM768, tls.X25519):
		result.KeyExchange = "X25519 / X25519MLKEM768"
	}
	result.KeyExchangeOK = result.KeyExchange != ""
	if !result.KeyExchangeOK {
		result.Reason = "密钥交换不支持 X25519"
		return result
	}
	result.OK = true
	return result
}

// scanRealityTargets probes all targets with bounded concurrency and
// returns results in input order.
func scanRealityTargets(targets []scanTarget) []scanResult {
	results := make([]scanResult, len(targets))
	sem := make(chan struct{}, scanConcurrency)
	var wg sync.WaitGroup
	for i, target := range targets {
		wg.Add(1)
		go func(i int, target scanTarget) {
			defer wg.Done()
			sem <- struct{}{}
			defer func() { <-sem }()
			results[i] = probeRealityTarget(target)
		}(i, target)
	}
	wg.Wait()
	return results
}