// Sealing to a public key, against vectors/contra-v1.json ("handoff").
//
// The device handoff is the one place a secret travels through the server, so
// the JS half of it is pinned to the same bytes the Go half is — generated by
// neither, in vectors/gen/gen.c against OpenSSL, itself checked against
// RFC 5903 before it may emit anything.

import { test } from "node:test";
import assert from "node:assert/strict";
import { readFileSync } from "node:fs";
import { fileURLToPath } from "node:url";
import { dirname, join } from "node:path";

const here = dirname(fileURLToPath(import.meta.url));
const mod = (name) => join(here, "..", "internal", "contra", "static", "crypto", name);

const { toHex, fromHex } = await import(mod("bytes.js"));
const { deriveP256 } = await import(mod("p256.js"));
const { aad, OBJECT_HANDOFF } = await import(mod("sealed.js"));
const ecies = await import(mod("ecies.js"));

const V = JSON.parse(readFileSync(join(here, "..", "vectors", "contra-v1.json"), "utf8"));
const H = V.handoff;

test("handoff: both keypairs derive from their published seeds", async () => {
  for (const [name, seed, scalar, pub] of [
    ["recipient", H.recipient_seed_hex, H.recipient_scalar_hex, H.recipient_public_hex],
    ["ephemeral", H.ephemeral_seed_hex, H.ephemeral_scalar_hex, H.ephemeral_public_hex],
  ]) {
    const key = await deriveP256(fromHex(seed));
    assert.equal(toHex(key.scalar), scalar, `${name} scalar`);
    assert.equal(toHex(key.publicKey), pub, `${name} public key`);
  }
});

// Both directions. A one-sided check would pass on something that is not
// actually Diffie-Hellman.
test("handoff: ECDH agrees from both sides", async () => {
  const fwd = await ecies.ecdh(fromHex(H.ephemeral_scalar_hex), fromHex(H.recipient_public_hex));
  assert.equal(toHex(fwd), H.shared_secret_hex, "sender side");

  const back = await ecies.ecdh(fromHex(H.recipient_scalar_hex), fromHex(H.ephemeral_public_hex));
  assert.equal(toHex(back), H.shared_secret_hex, "recipient side");
});

test("handoff: the derived key, the AAD and the sealed bytes", async () => {
  const key = await ecies.eciesKey(
    fromHex(H.ephemeral_public_hex),
    fromHex(H.recipient_public_hex),
    fromHex(H.shared_secret_hex));
  assert.equal(toHex(key), H.key_hex, "handoff key");

  const a = aad(fromHex(H.account_id_hex), H.object_type,
    fromHex(H.recipient_public_hex), H.version);
  assert.equal(toHex(a), H.aad_hex, "handoff AAD");

  const { seal } = await import(mod("sealed.js"));
  const sealed = await seal(key, fromHex(H.nonce_hex), a, fromHex(H.plaintext_hex));
  assert.equal(toHex(sealed.slice(0, -16)), H.ciphertext_hex, "ciphertext");
  assert.equal(toHex(sealed.slice(-16)), H.tag_hex, "tag");
});

// sealTo mints its own ephemeral key and nonce, so it cannot be checked
// against fixed bytes. What can be checked is the property that matters.
test("handoff: an envelope opens for its device and for nobody else", async () => {
  const recipientPublic = fromHex(H.recipient_public_hex);
  const recipientScalar = fromHex(H.recipient_scalar_hex);
  const accountKey = fromHex(H.plaintext_hex);
  const a = aad(fromHex(H.account_id_hex), OBJECT_HANDOFF, recipientPublic, 1);

  const envelope = await ecies.sealTo(recipientPublic, a, accountKey);
  assert.equal(envelope.length, 65 + 12 + accountKey.length + 16, "envelope length");

  const got = await ecies.openFrom(recipientScalar, recipientPublic, a, envelope);
  assert.equal(toHex(got), H.plaintext_hex, "round trip");

  const other = await deriveP256(fromHex(H.ephemeral_seed_hex));
  await assert.rejects(
    () => ecies.openFrom(other.scalar, other.publicKey, a, envelope),
    "a different device must not open an envelope sealed to another");

  // The AAD names the recipient, so the server cannot relay one envelope on.
  const wrong = aad(fromHex(H.account_id_hex), OBJECT_HANDOFF, other.publicKey, 1);
  await assert.rejects(
    () => ecies.openFrom(recipientScalar, recipientPublic, wrong, envelope),
    "an envelope must not open under an AAD naming a different device");
});

test("handoff: the Go and JS halves seal for each other", async () => {
  // A fresh ephemeral pair from the browser side, opened with the scalar it
  // kept — the exact shape the fresh device runs.
  const device = await ecies.newEphemeral();
  assert.equal(device.publicKey.length, 65);
  assert.equal(device.publicKey[0], 0x04);

  const a = aad(fromHex(H.account_id_hex), OBJECT_HANDOFF, device.publicKey, 1);
  const envelope = await ecies.sealTo(device.publicKey, a, fromHex(H.plaintext_hex));
  const got = await ecies.openFrom(device.scalar, device.publicKey, a, envelope);
  assert.equal(toHex(got), H.plaintext_hex);
});

test("handoff: a truncated envelope is refused before any key work", async () => {
  const recipientPublic = fromHex(H.recipient_public_hex);
  const a = aad(fromHex(H.account_id_hex), OBJECT_HANDOFF, recipientPublic, 1);
  await assert.rejects(
    () => ecies.openFrom(fromHex(H.recipient_scalar_hex), recipientPublic, a,
      new Uint8Array(40)),
    /too short/);
});