import { beforeEach, describe, expect, it, vi } from "vitest";
import { generateKeyPairFromSeed } from "@stablelib/x25519";

// PCH-01-002: the Noise handshakes derive `h` (protocol-name init hash) and the
// HKDF in MixKey/Split over BLAKE2s, matching the declared pattern name. These
// are KNOWN-ANSWER tests over a fully deterministic handshake (fixed statics +
// seeded ephemerals): a revert to SHA-256 changes every derived byte, so the
// pinned handshakeHash below stops matching and the test fails. That failure is
// the intended signal of an accidental hash-algorithm change.

// Mock ONLY ephemeral generation so the handshake is deterministic; sharedKey
// and the seeded keygen stay real. File-scoped, so other noise tests are
// unaffected. The counter lives on globalThis and is reset per test.
vi.mock("@stablelib/x25519", async (importOriginal) => {
  const actual = await importOriginal<typeof import("@stablelib/x25519")>();
  return {
    ...actual,
    generateKeyPair: () => {
      const g = globalThis as { __kpCounter?: number };
      g.__kpCounter = (g.__kpCounter ?? 0) + 1;
      return actual.generateKeyPairFromSeed(new Uint8Array(32).fill(g.__kpCounter));
    },
  };
});

function memoryPair() {
  const a: Uint8Array[] = [];
  const b: Uint8Array[] = [];
  const aR: Array<(v: Uint8Array) => void> = [];
  const bR: Array<(v: Uint8Array) => void> = [];
  const tA = {
    async send(m: Uint8Array) { const r = bR.shift(); if (r) r(m); else b.push(m); },
    receive(): Promise<Uint8Array> {
      const v = a.shift();
      if (v) return Promise.resolve(v);
      return new Promise<Uint8Array>((resolve) => aR.push(resolve));
    },
  };
  const tB = {
    async send(m: Uint8Array) { const r = aR.shift(); if (r) r(m); else a.push(m); },
    receive(): Promise<Uint8Array> {
      const v = b.shift();
      if (v) return Promise.resolve(v);
      return new Promise<Uint8Array>((resolve) => bR.push(resolve));
    },
  };
  return [tA, tB] as const;
}

function hex(b: Uint8Array): string {
  return Array.from(b, (x) => x.toString(16).padStart(2, "0")).join("");
}

describe("PCH-01-002 — Noise handshakes derive over BLAKE2s", () => {
  beforeEach(() => {
    (globalThis as { __kpCounter?: number }).__kpCounter = 0;
  });

  it("noise_xx_handshake_hash_is_blake2s_derived", async () => {
    const { noiseXXInitiator, noiseXXResponder } = await import("./noise-xx");
    const alice = generateKeyPairFromSeed(new Uint8Array(32).fill(0xa1));
    const bob = generateKeyPairFromSeed(new Uint8Array(32).fill(0xb2));
    const [tA, tB] = memoryPair();

    const [a, b] = await Promise.all([
      noiseXXInitiator(alice.secretKey, alice.publicKey, tA.send, tA.receive),
      noiseXXResponder(bob.secretKey, bob.publicKey, tB.send, tB.receive),
    ]);

    // Both directions agree (consistency) ...
    expect(hex(a.handshakeHash)).toBe(hex(b.handshakeHash));
    // ... and equal the pinned BLAKE2s vector (a SHA-256 revert changes this).
    expect(hex(a.handshakeHash)).toBe(
      "11c8bf7fcefad1f00ff8573c7bca66891626d053addae6d2b78b2f195a9ffd8a",
    );

    // Transport keys are also BLAKE2s-derived; a frame must still round-trip.
    const ct = a.encrypt(new TextEncoder().encode("hello"));
    expect(new TextDecoder().decode(b.decrypt(ct))).toBe("hello");
  });

  it("noise_nk_handshake_hash_is_blake2s_derived", async () => {
    const { noiseNKInitiator, noiseNKResponder } = await import("./noise-js");
    const responder = generateKeyPairFromSeed(new Uint8Array(32).fill(0xc3));
    const [tA, tB] = memoryPair();

    const [a, b] = await Promise.all([
      noiseNKInitiator(responder.publicKey, tA.send, tA.receive),
      noiseNKResponder(responder.secretKey, responder.publicKey, tB.send, tB.receive),
    ]);

    expect(hex(a.handshakeHash)).toBe(hex(b.handshakeHash));
    expect(hex(a.handshakeHash)).toBe(
      "0fbab8cd1782bf4b17d69beb69f5b80b0bf24d93da4924959c76ee701c32e655",
    );

    const ct = a.encrypt(new TextEncoder().encode("ping"));
    expect(new TextDecoder().decode(b.decrypt(ct))).toBe("ping");
  });
});