import crypto from "crypto";
import sodium from "libsodium-wrappers";
import { type Ed25519Keypair, type Ed25519PublicKey } from "./ed25519.js";
import { type PreHash, prehashFn } from "./prehash.js";
import { SignatureWithKey } from "./signature.js";

export const sign = async (
	data: Uint8Array,
	keypair: Ed25519Keypair,
	prehash: PreHash,
) => {
	const hashedData = await prehashFn(data, prehash);

	if (!keypair.privateKey.keyObject) {
		keypair.privateKey.keyObject = crypto.createPrivateKey({
			format: "der",
			type: "pkcs8",
			key: toDER(keypair.privateKeyPublicKey, true),
		});
	}
	return new SignatureWithKey({
		prehash,
		publicKey: keypair.publicKey,
		signature: crypto.sign(null, hashedData, keypair.privateKey.keyObject),
	});
};

export const verifySignatureEd25519 = async (
	signature: SignatureWithKey,
	data: Uint8Array,
) => {
	let res = false;
	try {
		const hashedData = await prehashFn(data, signature.prehash);
		res = verifySignatureEd25519Prepared(signature, hashedData);
	} catch (error) {
		return false;
	}
	return res;
};

export const verifySignatureEd25519Prepared = (
	signature: SignatureWithKey,
	preparedData: Uint8Array,
) =>
	sodium.crypto_sign_verify_detached(
		signature.signature,
		preparedData,
		(signature.publicKey as Ed25519PublicKey).publicKey,
	);

const DER_PREFIX = Buffer.from([
	48, 46, 2, 1, 0, 48, 5, 6, 3, 43, 101, 112, 4, 34, 4, 32,
]);
const ED25519_OID = Buffer.from([0x06, 0x03, 0x2b, 0x65, 0x70]);
const SEQUENCE_TAG = Buffer.from([0x30]); // Sequence tag
const BIT_TAG = Buffer.from([0x03]); // Bit tag
const ZERO_BIT_TAG = Buffer.from([0x00]); // Zero bit
function toDER(key: Uint8Array, p = false) {
	if (p) {
		return Buffer.concat([DER_PREFIX, key]);
	}

	// Ed25519's OID
	const oid = ED25519_OID;

	// Create a byte sequence containing the OID and key
	const elements = Buffer.concat([
		SEQUENCE_TAG,
		Buffer.from([oid.length]),
		oid,
		BIT_TAG,
		Buffer.from([key.length + 1]),
		ZERO_BIT_TAG,
		key,
	]);

	// Wrap up by creating a sequence of elements
	const der = Buffer.concat([
		SEQUENCE_TAG,
		Buffer.from([elements.length]),
		elements,
	]);

	return der;
}