import { createHmac, randomUUID, timingSafeEqual } from "node:crypto";

// Every message in both directions is an envelope {p, s}: p is the JSON payload as a
// string and s is HMAC-SHA256(secret, p) in hex. Signing the exact string avoids any
// mismatch from re-serializing JSON on the other side.

export const MAX_SKEW_MS = 120_000;

export interface Message {
  type: string;
  id: string;
  ts: number;
  [key: string]: unknown;
}

export function hmacHex(secret: string, data: string): string {
  return createHmac("sha256", secret).update(data, "utf8").digest("hex");
}

export function seal(secret: string, payload: Record<string, unknown>): string {
  const full = { ...payload, id: typeof payload.id === "string" ? payload.id : randomUUID(), ts: Date.now() };
  const p = JSON.stringify(full);
  return JSON.stringify({ p, s: hmacHex(secret, p) });
}

// Rejects stale messages and any message id seen before.
export class ReplayGuard {
  private seen = new Map<string, number>();

  check(id: string, ts: number): boolean {
    const now = Date.now();
    if (Math.abs(now - ts) > MAX_SKEW_MS) return false;
    if (this.seen.has(id)) return false;
    this.seen.set(id, ts);
    if (this.seen.size > 5000) {
      for (const [key, value] of this.seen) {
        if (now - value > MAX_SKEW_MS) this.seen.delete(key);
      }
    }
    return true;
  }
}

export function unseal(secret: string, raw: string, guard: ReplayGuard): Message | null {
  let envelope: unknown;
  try {
    envelope = JSON.parse(raw);
  } catch {
    return null;
  }
  const env = envelope as { p?: unknown; s?: unknown };
  if (!env || typeof env.p !== "string" || typeof env.s !== "string") return null;
  if (!/^[0-9a-f]{64}$/i.test(env.s)) return null;
  const expected = Buffer.from(hmacHex(secret, env.p), "hex");
  const got = Buffer.from(env.s, "hex");
  if (expected.length !== got.length || !timingSafeEqual(expected, got)) return null;
  let msg: unknown;
  try {
    msg = JSON.parse(env.p);
  } catch {
    return null;
  }
  const m = msg as Partial<Message>;
  if (!m || typeof m.id !== "string" || typeof m.ts !== "number" || typeof m.type !== "string") return null;
  if (!guard.check(m.id, m.ts)) return null;
  return m as Message;
}

import { createHmac, randomUUID, timingSafeEqual } from "node:crypto";

// Every message in both directions is an envelope {p, s}: p is the JSON payload as a
// string and s is HMAC-SHA256(secret, p) in hex. Signing the exact string avoids any
// mismatch from re-serializing JSON on the other side.

export const MAX_SKEW_MS = 120_000;

export interface Message {
  type: string;
  id: string;
  ts: number;
  [key: string]: unknown;
}

export function hmacHex(secret: string, data: string): string {
  return createHmac("sha256", secret).update(data, "utf8").digest("hex");
}

export function seal(secret: string, payload: Record<string, unknown>): string {
  const full = { ...payload, id: typeof payload.id === "string" ? payload.id : randomUUID(), ts: Date.now() };
  const p = JSON.stringify(full);
  return JSON.stringify({ p, s: hmacHex(secret, p) });
}

// Rejects stale messages and any message id seen before.
export class ReplayGuard {
  private seen = new Map<string, number>();

  check(id: string, ts: number): boolean {
    const now = Date.now();
    if (Math.abs(now - ts) > MAX_SKEW_MS) return false;
    if (this.seen.has(id)) return false;
    this.seen.set(id, ts);
    if (this.seen.size > 5000) {
      for (const [key, value] of this.seen) {
        if (now - value > MAX_SKEW_MS) this.seen.delete(key);
      }
    }
    return true;
  }
}

export function unseal(secret: string, raw: string, guard: ReplayGuard): Message | null {
  let envelope: unknown;
  try {
    envelope = JSON.parse(raw);
  } catch {
    return null;
  }
  const env = envelope as { p?: unknown; s?: unknown };
  if (!env || typeof env.p !== "string" || typeof env.s !== "string") return null;
  if (!/^[0-9a-f]{64}$/i.test(env.s)) return null;
  const expected = Buffer.from(hmacHex(secret, env.p), "hex");
  const got = Buffer.from(env.s, "hex");
  if (expected.length !== got.length || !timingSafeEqual(expected, got)) return null;
  let msg: unknown;
  try {
    msg = JSON.parse(env.p);
  } catch {
    return null;
  }
  const m = msg as Partial<Message>;
  if (!m || typeof m.id !== "string" || typeof m.ts !== "number" || typeof m.type !== "string") return null;
  if (!guard.check(m.id, m.ts)) return null;
  return m as Message;
}