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// Self-contained SilentShield agent-policy enforcer — stdlib only, no SDK.
// Drop this in, wrap your handler with New(cfg).Middleware, and blocked bots
// get a 403 (throttled ones a 429). Fail-open by design: any error, an
// unverifiable bundle, or monitor mode lets the request through — enforcement
// can never take your site down.
package ssenforce

import (
	"bytes"
	"crypto/ed25519"
	"encoding/base64"
	"encoding/json"
	"io"
	"net"
	"net/http"
	"strconv"
	"strings"
	"sync"
	"time"
)

// Config for the enforcer. PolicyURL + APIKey + at least one trusted key are
// required; with any missing the enforcer is a no-op (always allow).
type Config struct {
	PolicyURL string // https://api.silentshield.io/api/v1/agent/policy
	KeysURL   string // https://api.silentshield.io/.well-known/silentshield-agent-keys
	APIKey    string // your publishable site key (x-api-key)
}

type signedBundle struct {
	Payload string `json:"payload"`
	Alg     string `json:"alg"`
	Kid     string `json:"kid"`
	Sig     string `json:"sig"`
}

type bundle struct {
	FormatVersion int     `json:"format_version"`
	Mode          string  `json:"mode"`
	QuotaEnabled  bool    `json:"quota_enabled"`
	Rules         []rule  `json:"rules"`
	Agents        []agent `json:"agents"`
}

type agent struct {
	Slug     string   `json:"slug"`
	Category string   `json:"category"`
	UATokens []string `json:"ua_tokens"`
	CIDRs    []string `json:"cidrs"`
}

type rule struct {
	Match       match      `json:"match"`
	PathPattern string     `json:"path_pattern"`
	Methods     []string   `json:"methods"`
	Action      string     `json:"action"`
	RateLimit   *rateLimit `json:"rate_limit"`
}

type match struct {
	Type  string `json:"type"`
	Value string `json:"value"`
}

type rateLimit struct {
	Requests  int `json:"requests"`
	WindowSec int `json:"window_sec"`
}

// Enforcer fetches, verifies and caches the signed policy, refreshing every
// 5 minutes in the background, and decides per request.
type Enforcer struct {
	cfg     Config
	enabled bool

	mu    sync.RWMutex
	b     *bundle
	cidrs map[string][]*net.IPNet

	countersMu sync.Mutex
	counters   map[string]*window
}

type window struct {
	bucket int64
	count  int
}

// New builds an enforcer and starts background refresh. Call once at startup.
func New(cfg Config) *Enforcer {
	e := &Enforcer{cfg: cfg, counters: map[string]*window{}}
	e.enabled = cfg.PolicyURL != "" && cfg.KeysURL != "" && cfg.APIKey != ""
	if !e.enabled {
		return e
	}
	_ = e.refresh() // best-effort initial load
	go func() {
		t := time.NewTicker(5 * time.Minute)
		defer t.Stop()
		for range t.C {
			_ = e.refresh()
		}
	}()
	return e
}

// Middleware wraps next, blocking disallowed bots. Monitor mode / fail-open
// never block.
func (e *Enforcer) Middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Optional: exempt your own trusted traffic (e.g. logged-in users) from
		// enforcement. Plug in your own check — it runs first, so a matching
		// request is never blocked. Keep it cheap (inspect your session cookie /
		// JWT), no I/O.
		// if isLoggedIn(r) {
		// 	next.ServeHTTP(w, r)
		// 	return
		// }
		if block, status, retry := e.decide(r); block {
			if retry > 0 {
				w.Header().Set("Retry-After", strconv.Itoa(retry))
			}
			w.WriteHeader(status)
			reportBlock(e.cfg.APIKey, r, status) // feed the dashboard's blocked-bots report
			return
		}
		next.ServeHTTP(w, r)
	})
}

// reportBlock fire-and-forgets a report that this request was blocked, so the
// SilentShield dashboard's "blocked bots" report has data. Best-effort: its own
// goroutine + timeout, all errors ignored — it never delays the response.
func reportBlock(apiKey string, r *http.Request, status int) {
	outcome := "deny"
	if status == http.StatusTooManyRequests {
		outcome = "throttle"
	}
	s := map[string]any{"ua": r.UserAgent(), "ip": remoteIP(r), "path": r.URL.Path, "method": r.Method, "outcome": outcome}
	body, _ := json.Marshal(map[string]any{"sightings": []any{s}})
	go func() {
		req, err := http.NewRequest("POST", "https://api.silentshield.io/api/v1/agent/telemetry", bytes.NewReader(body))
		if err != nil {
			return
		}
		req.Header.Set("Content-Type", "application/json")
		req.Header.Set("x-api-key", apiKey)
		if resp, err := (&http.Client{Timeout: 3 * time.Second}).Do(req); err == nil {
			resp.Body.Close()
		}
	}()
}

func (e *Enforcer) decide(r *http.Request) (block bool, status, retry int) {
	if !e.enabled {
		return false, 0, 0
	}
	e.mu.RLock()
	b, cidrs := e.b, e.cidrs
	e.mu.RUnlock()
	if b == nil || b.Mode != "enforce" {
		return false, 0, 0 // no bundle or monitor → never block
	}

	slug, category := "", ""
	best := 0
	ua := strings.ToLower(r.UserAgent())
	for _, a := range b.Agents {
		for _, tok := range a.UATokens {
			tl := strings.ToLower(tok)
			if tl != "" && strings.Contains(ua, tl) && len(tl) > best {
				best, slug, category = len(tl), a.Slug, a.Category
			}
		}
	}
	verified := false
	if slug != "" {
		ip := net.ParseIP(remoteIP(r))
		for _, n := range cidrs[slug] {
			if ip != nil && n.Contains(ip) {
				verified = true
				break
			}
		}
	}

	ru := evaluate(b.Rules, slug, category, verified, r.URL.Path, r.Method)
	if ru == nil {
		return false, 0, 0
	}
	switch ru.Action {
	case "deny":
		return true, http.StatusForbidden, 0
	case "throttle":
		if b.QuotaEnabled && ru.RateLimit != nil {
			key := slug
			if key == "" {
				key = "cat:" + category
			}
			if ok, ra := e.allowThrottle(key, ru.RateLimit); !ok {
				return true, http.StatusTooManyRequests, ra
			}
		}
	}
	return false, 0, 0
}

// evaluate walks the rules in order, first match wins (nil → allow).
func evaluate(rules []rule, slug, category string, verified bool, path, method string) *rule {
	for i := range rules {
		ru := &rules[i]
		if !matchApplies(ru.Match, slug, category, verified) {
			continue
		}
		if !pathMatches(ru.PathPattern, path) {
			continue
		}
		if !methodMatches(ru.Methods, method) {
			continue
		}
		return ru
	}
	return nil
}

func matchApplies(m match, slug, category string, verified bool) bool {
	switch m.Type {
	case "any":
		return true
	case "agent_slug":
		return slug != "" && slug == m.Value
	case "agent_category":
		return category != "" && category == m.Value
	case "unsigned":
		return !verified
	}
	return false
}

func pathMatches(pattern, path string) bool {
	if pattern == "" || pattern == "*" {
		return true
	}
	if strings.HasSuffix(pattern, "*") {
		return strings.HasPrefix(path, strings.TrimSuffix(pattern, "*"))
	}
	return path == pattern
}

func methodMatches(methods []string, method string) bool {
	if len(methods) == 0 {
		return true
	}
	for _, m := range methods {
		if strings.EqualFold(strings.TrimSpace(m), method) {
			return true
		}
	}
	return false
}

func (e *Enforcer) allowThrottle(key string, rl *rateLimit) (bool, int) {
	if rl.Requests <= 0 || rl.WindowSec <= 0 {
		return true, 0
	}
	now := time.Now().Unix()
	bucket := now / int64(rl.WindowSec)
	e.countersMu.Lock()
	defer e.countersMu.Unlock()
	c := e.counters[key]
	if c == nil || c.bucket != bucket {
		c = &window{bucket: bucket}
		e.counters[key] = c
	}
	c.count++
	if c.count > rl.Requests {
		retry := int((bucket+1)*int64(rl.WindowSec) - now)
		if retry < 1 {
			retry = 1
		}
		return false, retry
	}
	return true, 0
}

// refresh fetches + verifies the bundle and swaps it in. On any error the
// previous bundle is kept (fail-open).
func (e *Enforcer) refresh() error {
	keys, err := e.fetchKeys()
	if err != nil {
		return err
	}
	req, _ := http.NewRequest(http.MethodGet, e.cfg.PolicyURL, nil)
	req.Header.Set("x-api-key", e.cfg.APIKey)
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()
	if resp.StatusCode != http.StatusOK {
		return nil // 304/anything else → keep last good bundle
	}
	raw, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return err
	}
	b, err := verifyBundle(raw, keys)
	if err != nil {
		return err
	}
	cidrs := map[string][]*net.IPNet{}
	for _, a := range b.Agents {
		for _, c := range a.CIDRs {
			if _, n, err := net.ParseCIDR(c); err == nil {
				cidrs[a.Slug] = append(cidrs[a.Slug], n)
			}
		}
	}
	e.mu.Lock()
	e.b, e.cidrs = b, cidrs
	e.mu.Unlock()
	return nil
}

func (e *Enforcer) fetchKeys() (map[string]ed25519.PublicKey, error) {
	resp, err := http.Get(e.cfg.KeysURL)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()
	var payload struct {
		Keys []struct {
			Kid string `json:"kid"`
			Key string `json:"key"`
		} `json:"keys"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&payload); err != nil {
		return nil, err
	}
	out := map[string]ed25519.PublicKey{}
	for _, k := range payload.Keys {
		if raw, err := base64.StdEncoding.DecodeString(k.Key); err == nil && len(raw) == ed25519.PublicKeySize {
			out[k.Kid] = ed25519.PublicKey(raw)
		}
	}
	return out, nil
}

// verifyBundle checks the Ed25519 signature over the raw payload and returns the
// decoded bundle. The signed bytes are the payload JSON exactly (no hashing).
func verifyBundle(body []byte, keys map[string]ed25519.PublicKey) (*bundle, error) {
	var sb signedBundle
	if err := json.Unmarshal(body, &sb); err != nil {
		return nil, err
	}
	if sb.Alg != "ed25519" {
		return nil, errInvalid
	}
	pub, ok := keys[sb.Kid]
	if !ok {
		return nil, errInvalid
	}
	payload, err := base64.StdEncoding.DecodeString(sb.Payload)
	if err != nil {
		return nil, err
	}
	sig, err := base64.StdEncoding.DecodeString(sb.Sig)
	if err != nil {
		return nil, err
	}
	if !ed25519.Verify(pub, payload, sig) {
		return nil, errInvalid
	}
	var b bundle
	if err := json.Unmarshal(payload, &b); err != nil {
		return nil, err
	}
	if b.FormatVersion > 1 {
		return nil, errInvalid // a newer wire format we can't be sure we understand
	}
	return &b, nil
}

// remoteIP is the source IP for CIDR verification. Behind a trusted proxy,
// restore the real client IP here (do NOT trust a spoofable header for the
// verification decision).
func remoteIP(r *http.Request) string {
	ip, _, err := net.SplitHostPort(r.RemoteAddr)
	if err != nil {
		return r.RemoteAddr
	}
	return ip
}

type sentinel string

func (s sentinel) Error() string { return string(s) }

const errInvalid = sentinel("invalid bundle")

// Wiring:
//   enf := ssenforce.New(ssenforce.Config{
//       PolicyURL: "https://api.silentshield.io/api/v1/agent/policy",
//       KeysURL:   "https://api.silentshield.io/.well-known/silentshield-agent-keys",
//       APIKey:    "YOUR_API_KEY",
//   })
//   http.ListenAndServe(":8080", enf.Middleware(mux))

// Self-contained SilentShield agent-policy enforcer for Node.js / Express —
// no SDK, only the built-in `crypto`. Wrap your app with enforcer(cfg) and
// blocked bots get a 403 (throttled ones a 429). Fail-open by design: any
// error, an unverifiable bundle, or monitor mode lets the request through.
const crypto = require("crypto");

// Raw 32-byte Ed25519 public key → a verifiable KeyObject (DER SPKI wrap).
const ED25519_SPKI_PREFIX = Buffer.from("302a300506032b6570032100", "hex");
function toPublicKey(rawBase64) {
  const raw = Buffer.from(rawBase64, "base64");
  if (raw.length !== 32) return null;
  return crypto.createPublicKey({
    key: Buffer.concat([ED25519_SPKI_PREFIX, raw]),
    format: "der",
    type: "spki",
  });
}

function ipInCidr(ip, cidr) {
  // Node's net has no CIDR test; do a byte-mask compare on the parsed buffers.
  const [subnet, bitsStr] = cidr.split("/");
  const bits = parseInt(bitsStr, 10);
  const a = ipToBuf(ip);
  const b = ipToBuf(subnet);
  if (!a || !b || a.length !== b.length || bits < 0 || bits > a.length * 8) return false;
  const full = Math.floor(bits / 8);
  for (let i = 0; i < full; i++) if (a[i] !== b[i]) return false;
  const rem = bits % 8;
  if (rem === 0) return true;
  const mask = (0xff << (8 - rem)) & 0xff;
  return (a[full] & mask) === (b[full] & mask);
}
function ipToBuf(ip) {
  if (net_isIPv4(ip)) return Buffer.from(ip.split(".").map((n) => parseInt(n, 10)));
  try {
    // Expand IPv6 to 16 bytes via the built-in parser.
    const parts = require("net").isIPv6(ip) ? ip : null;
    if (!parts) return null;
    return ipv6ToBuf(ip);
  } catch {
    return null;
  }
}
function net_isIPv4(ip) {
  return require("net").isIPv4(ip);
}
function ipv6ToBuf(ip) {
  // Minimal IPv6 → 16-byte buffer (handles "::" compression).
  let [head, tail] = ip.split("::");
  const h = head ? head.split(":") : [];
  const t = tail ? tail.split(":") : [];
  const missing = 8 - (h.length + t.length);
  if (missing < 0) return null;
  const groups = [...h, ...Array(missing).fill("0"), ...t];
  const buf = Buffer.alloc(16);
  for (let i = 0; i < 8; i++) {
    const v = parseInt(groups[i] || "0", 16);
    buf.writeUInt16BE(v, i * 2);
  }
  return buf;
}

function matchApplies(m, slug, category, verified) {
  switch (m && m.type) {
    case "any": return true;
    case "agent_slug": return slug !== "" && slug === m.value;
    case "agent_category": return category !== "" && category === m.value;
    case "unsigned": return !verified;
    default: return false;
  }
}
function pathMatches(pattern, path) {
  if (!pattern || pattern === "*") return true;
  if (pattern.endsWith("*")) return path.startsWith(pattern.slice(0, -1));
  return path === pattern;
}
function methodMatches(methods, method) {
  if (!methods || methods.length === 0) return true;
  return methods.some((m) => String(m).trim().toUpperCase() === method.toUpperCase());
}
function evaluate(rules, slug, category, verified, path, method) {
  for (const r of rules || []) {
    if (!matchApplies(r.match || {}, slug, category, verified)) continue;
    if (!pathMatches(r.path_pattern || "", path)) continue;
    if (!methodMatches(r.methods || [], method)) continue;
    return r;
  }
  return null;
}

function verifyBundle(body, keys) {
  let env;
  try { env = JSON.parse(body); } catch { return null; }
  if (!env || env.alg !== "ed25519") return null;
  const pub = keys[env.kid];
  if (!pub) return null;
  const payload = Buffer.from(env.payload || "", "base64");
  const sig = Buffer.from(env.sig || "", "base64");
  if (sig.length !== 64) return null;
  if (!crypto.verify(null, payload, pub, sig)) return null;
  let bundle;
  try { bundle = JSON.parse(payload.toString("utf8")); } catch { return null; }
  if ((bundle.format_version || 1) > 1) return null;
  return bundle;
}

function enforcer(cfg) {
  const state = { bundle: null };
  const counters = new Map();

  async function refresh() {
    try {
      const keysRes = await fetch(cfg.keysUrl);
      const keysJson = await keysRes.json();
      const keys = {};
      for (const k of keysJson.keys || []) {
        const pk = toPublicKey(k.key);
        if (pk) keys[k.kid] = pk;
      }
      if (Object.keys(keys).length === 0) return;
      const res = await fetch(cfg.policyUrl, { headers: { "x-api-key": cfg.apiKey } });
      if (res.status !== 200) return; // 304/other → keep last good bundle
      const bundle = verifyBundle(await res.text(), keys);
      if (bundle) state.bundle = bundle;
    } catch {
      /* fail-open: keep the last good bundle */
    }
  }
  refresh();
  setInterval(refresh, 5 * 60 * 1000).unref();

  return function (req, res, next) {
    try {
      // Optional: exempt your own trusted traffic (e.g. logged-in users) from
      // enforcement. Plug in your own check — it runs first, so a matching
      // request is never blocked. Keep it cheap (inspect your session cookie /
      // JWT), no I/O.
      // if (isLoggedIn(req)) return next();

      const b = state.bundle;
      if (!b || b.mode !== "enforce") return next();

      const ua = (req.headers["user-agent"] || "").toLowerCase();
      let slug = "", category = "", best = 0, cidrs = [];
      for (const a of b.agents || []) {
        for (const tok of a.ua_tokens || []) {
          const tl = String(tok).toLowerCase();
          if (tl && ua.includes(tl) && tl.length > best) {
            best = tl.length; slug = a.slug; category = a.category; cidrs = a.cidrs || [];
          }
        }
      }
      let verified = false;
      if (slug) {
        const ip = (req.socket && req.socket.remoteAddress) || "";
        verified = cidrs.some((c) => ipInCidr(ip.replace(/^::ffff:/, ""), c));
      }

      const rule = evaluate(b.rules, slug, category, verified, req.path || req.url || "/", req.method);
      if (!rule) return next();

      if (rule.action === "deny") { res.statusCode = 403; reportBlock(cfg.apiKey, req, "deny"); return res.end("Forbidden"); }
      if (rule.action === "throttle" && b.quota_enabled && rule.rate_limit) {
        const key = slug || ("cat:" + category);
        const { ok, retry } = throttleOk(counters, key, rule.rate_limit);
        if (!ok) { res.statusCode = 429; res.setHeader("Retry-After", String(retry)); reportBlock(cfg.apiKey, req, "throttle"); return res.end("Too Many Requests"); }
      }
      return next();
    } catch {
      return next(); // fail-open
    }
  };
}

// reportBlock fire-and-forgets a report that this request was blocked, so the
// SilentShield dashboard's "blocked bots" report has data. Best-effort — errors
// are swallowed and it never delays the response.
function reportBlock(apiKey, req, outcome) {
  try {
    const s = {
      ua: req.headers["user-agent"] || "",
      ip: ((req.socket && req.socket.remoteAddress) || "").replace(/^::ffff:/, ""),
      path: req.path || req.url || "/",
      method: req.method,
      outcome,
    };
    fetch("https://api.silentshield.io/api/v1/agent/telemetry", {
      method: "POST",
      headers: { "Content-Type": "application/json", "x-api-key": apiKey },
      body: JSON.stringify({ sightings: [s] }),
    }).catch(() => {}); // best-effort, fail-open
  } catch {
    /* ignore */
  }
}

function throttleOk(counters, key, rl) {
  const requests = rl.requests | 0, window = rl.window_sec | 0;
  if (requests <= 0 || window <= 0) return { ok: true, retry: 0 };
  const now = Math.floor(Date.now() / 1000);
  const bucket = Math.floor(now / window);
  let c = counters.get(key);
  if (!c || c.bucket !== bucket) { c = { bucket, count: 0 }; counters.set(key, c); }
  c.count++;
  if (c.count > requests) {
    const retry = Math.max(1, (bucket + 1) * window - now);
    return { ok: false, retry };
  }
  return { ok: true, retry: 0 };
}

module.exports = { enforcer };

// Wiring (Express):
//   const { enforcer } = require("./silentshield-enforcer");
//   app.use(enforcer({
//     policyUrl: "https://api.silentshield.io/api/v1/agent/policy",
//     keysUrl:   "https://api.silentshield.io/.well-known/silentshield-agent-keys",
//     apiKey:    "YOUR_API_KEY",
//   }));

AGENT_POLICY_URL="https://api.silentshield.io/api/v1/agent/policy" \
AGENT_SITE_KEY="YOUR_API_KEY" \
AGENT_TRUSTED_KEYS='[{"kid":"…","key":"<base64 ed25519 pubkey>"}]' \
AGENT_SIDECAR_LISTEN=":8127" \
  ./agent-sidecar

location = /_ss_auth {
    internal;
    proxy_pass              http://127.0.0.1:8127/auth;
    proxy_pass_request_body off;
    proxy_set_header        Content-Length "";
    proxy_set_header        X-Forwarded-Method $request_method;
    proxy_set_header        X-Forwarded-Uri    $request_uri;
    proxy_set_header        X-Forwarded-Host   $host;
    proxy_set_header        X-Forwarded-For    $remote_addr;
    proxy_set_header        User-Agent         $http_user_agent;
    proxy_set_header        Signature          $http_signature;
    proxy_set_header        Signature-Input    $http_signature_input;
    proxy_set_header        Signature-Agent    $http_signature_agent;
}
location / {
    auth_request /_ss_auth;
    # ... your normal proxy_pass to the origin ...
}

example.com {
    forward_auth 127.0.0.1:8127 {
        uri /auth
        copy_headers User-Agent Signature Signature-Input Signature-Agent
        # Caddy sends X-Forwarded-Method/-Uri/-Host automatically
    }
    reverse_proxy origin:8080
}

http:
  middlewares:
    silentshield:
      forwardAuth:
        address: "http://agent-sidecar:8127/auth"
        authRequestHeaders:
          - "User-Agent"
          - "Signature"
          - "Signature-Input"
          - "Signature-Agent"

cd enforcers/cloudflare-worker
npx wrangler secret put AGENT_SITE_KEY
# set AGENT_POLICY_URL + AGENT_TRUSTED_KEYS in wrangler.toml [vars]
npx wrangler deploy

npm install @forge12interactive/silentshield-sdk-js

go get github.com/forge12interactive/[email protected]

composer config repositories.silentshield vcs https://github.com/forge12interactive/silentshield-sdk-php
composer require forge12interactive/silentshield-sdk