/**
 * Experimental KDF for AES.
 * @module
 */
import { hkdf } from "./hkdf.js";
import { pbkdf2 as _pbkdf2 } from "./pbkdf2.js";
import { scrypt as _scrypt } from "./scrypt.js";
import { sha256 } from "./sha2.js";
import { abytes, bytesToHex, clean, createView, hexToBytes, kdfInputToBytes, } from "./utils.js";
// A tiny KDF for various applications like AES key-gen.
// Uses HKDF in a non-standard way, so it's not "KDF-secure", only "PRF-secure".
// Which is good enough: assume sha2-256 retained preimage resistance.
// Fixed ESKDF scrypt work factor: interactive-latency target with about 512 MiB RAM per derivation.
const SCRYPT_FACTOR = /* @__PURE__ */ (() => 2 ** 19)();
// Fixed ESKDF PBKDF2 work factor: CPU-only companion branch in the same rough
// interactive-latency range.
const PBKDF2_FACTOR = /* @__PURE__ */ (() => 2 ** 17)();
/**
 * Scrypt KDF with the fixed ESKDF policy tuple `{ N: 2^19, r: 8, p: 1, dkLen: 32 }`.
 * @param password - user password string, UTF-8 encoded before entering RFC 7914
 * @param salt - unique salt string, UTF-8 encoded before entering RFC 7914
 * @returns Derived 32-byte key.
 * @example
 * Derive the 32-byte scrypt key used by ESKDF.
 * ```ts
 * scrypt('password123', 'user@example.com');
 * ```
 */
export function scrypt(password, salt) {
    return _scrypt(password, salt, { N: SCRYPT_FACTOR, r: 8, p: 1, dkLen: 32 });
}
/**
 * PBKDF2-HMAC-SHA256 with the fixed ESKDF policy tuple `{ sha256, c: 2^17, dkLen: 32 }`.
 * @param password - user password string, UTF-8 encoded before entering PBKDF2-HMAC-SHA-256
 * @param salt - unique salt string, UTF-8 encoded before entering PBKDF2-HMAC-SHA-256
 * @returns Derived 32-byte key.
 * @example
 * Derive the 32-byte PBKDF2 key used by ESKDF.
 * ```ts
 * pbkdf2('password123', 'user@example.com');
 * ```
 */
export function pbkdf2(password, salt) {
    return _pbkdf2(sha256, password, salt, { c: PBKDF2_FACTOR, dkLen: 32 });
}
// Combines two 32-byte byte arrays into a fresh 32-byte result without aliasing either input.
function xor32(a, b) {
    abytes(a, 32);
    abytes(b, 32);
    const arr = new Uint8Array(32);
    for (let i = 0; i < 32; i++) {
        arr[i] = a[i] ^ b[i];
    }
    return arr;
}
// All local string length checks are in JS UTF-16 code units, not UTF-8 bytes.
function strHasLength(str, min, max) {
    return typeof str === 'string' && str.length >= min && str.length <= max;
}
/**
 * Derives main seed. Takes a lot of time; prefer the higher-level `eskdf(...)`
 * flow unless you specifically need the raw main seed.
 * Derives the main seed by xor'ing two branches:
 * the scrypt branch uses a `0x01` separator byte on username/password,
 * and the PBKDF2 branch uses `0x02`.
 * Username and password strings are encoded by the underlying KDFs after the
 * local separator bytes are appended.
 * @param username - account identifier used as public salt
 * @param password - user password string
 * @returns Main 32-byte seed for the account.
 * @throws If the username or password length is invalid. {@link Error}
 * @example
 * Derive the main ESKDF seed from username and password.
 * ```ts
 * deriveMainSeed('example-user', 'example-password');
 * ```
 */
export function deriveMainSeed(username, password) {
    if (!strHasLength(username, 8, 255))
        throw new Error('invalid username');
    if (!strHasLength(password, 8, 255))
        throw new Error('invalid password');
    // Keep the protocol separators as the literal bytes 0x01 / 0x02 even after minification.
    // Embedding them as non-printable characters directly can be awkward across
    // JS tooling and environments.
    const codes = { _1: 1, _2: 2 };
    const sep = { s: String.fromCharCode(codes._1), p: String.fromCharCode(codes._2) };
    const scr = scrypt(password + sep.s, username + sep.s);
    const pbk = pbkdf2(password + sep.p, username + sep.p);
    const res = xor32(scr, pbk);
    clean(scr, pbk);
    return res;
}
/**
 * Converts protocol & accountId pair to HKDF params:
 * `info` is UTF-8 protocol bytes, numeric ids become 4-byte BE `salt`,
 * and string ids become UTF-8 `salt` bytes.
 */
function getSaltInfo(protocol, accountId = 0) {
    // Note that length here also repeats two lines below
    // We do an additional length check here to reduce the scope of DoS attacks
    if (!(strHasLength(protocol, 3, 15) && /^[a-z0-9]{3,15}$/.test(protocol))) {
        throw new Error('invalid protocol');
    }
    // Exact-match only: substring matches like `assh` / `mentor` must not widen the public whitelist.
    const allowsStr = /^(password\d{0,3}|ssh|tor|file)$/.test(protocol);
    let salt; // Assigned below: either 4-byte BE account bytes or UTF-8 account bytes.
    if (typeof accountId === 'string') {
        if (!allowsStr)
            throw new Error('accountId must be a number');
        if (!strHasLength(accountId, 1, 255))
            throw new Error('accountId must be string of length 1..255');
        salt = kdfInputToBytes(accountId);
    }
    else if (Number.isSafeInteger(accountId)) {
        if (accountId < 0 || accountId > Math.pow(2, 32) - 1)
            throw new Error('invalid accountId');
        // Convert to Big Endian Uint32
        salt = new Uint8Array(4);
        createView(salt).setUint32(0, accountId, false);
    }
    else {
        throw new Error('accountId must be a number' + (allowsStr ? ' or string' : ''));
    }
    const info = kdfInputToBytes(protocol);
    return { salt, info };
}
// Local modulus-size helper, not a general bigint-byte-length primitive:
// `<= 128n` is rejected by ESKDF policy.
function countBytes(num) {
    if (typeof num !== 'bigint' || num <= BigInt(128))
        throw new Error('invalid number');
    return Math.ceil(num.toString(2).length / 8);
}
/**
 * Parses keyLength and modulus options to extract length of result key.
 * If modulus is used, adds 64 bits to it per the FIPS 186-5 Appendix A.3.1 /
 * A.4.1 extra-bits guidance.
 */
function getKeyLength(options) {
    if (!options || typeof options !== 'object')
        return 32;
    const hasLen = 'keyLength' in options;
    const hasMod = 'modulus' in options;
    if (hasLen && hasMod)
        throw new Error('cannot combine keyLength and modulus options');
    if (!hasLen && !hasMod)
        throw new Error('must have either keyLength or modulus option');
    // FIPS 186-5 Appendix A.3.1 / A.4.1 calls for at least 64 extra bits.
    const l = hasMod ? countBytes(options.modulus) + 8 : options.keyLength;
    if (!(typeof l === 'number' && l >= 16 && l <= 8192))
        throw new Error('invalid keyLength');
    return l;
}
/**
 * Converts key to bigint and divides it by modulus. Big Endian.
 * Adapts FIPS 186-5 Appendix A.4.1: `getKeyLength()` already requested the
 * extra 64-bit margin, and this step maps the result into `1..modulus-1`.
 */
function modReduceKey(key, modulus) {
    const _1 = BigInt(1);
    const num = BigInt('0x' + bytesToHex(key)); // check for ui8a, then bytesToNumber()
    const res = (num % (modulus - _1)) + _1; // Remove 0 from output
    if (res < _1)
        throw new Error('expected positive number'); // Guard against bad values
    // Strip the extra 64-bit margin that `getKeyLength()` requested
    // for bias reduction.
    const len = key.length - 8;
    const hex = res.toString(16).padStart(len * 2, '0'); // numberToHex()
    const bytes = hexToBytes(hex);
    if (bytes.length !== len)
        throw new Error('invalid length of result key');
    return bytes;
}
/**
 * ESKDF
 * @param username - username, email, or identifier, min: 8 characters, should have enough entropy
 * @param password - password, min: 8 characters, should have enough entropy
 * @returns Frozen API that derives child keys and exposes the account fingerprint.
 * @throws If the username or password length is invalid. {@link Error}
 * @example
 * Derive account-specific child keys from the main ESKDF seed.
 * ```ts
 * const kdf = await eskdf('example-university', 'beginning-new-example');
 * const key = kdf.deriveChildKey('aes', 0);
 * const fingerprint = kdf.fingerprint;
 * kdf.expire();
 * ```
 */
export async function eskdf(username, password) {
    // We are using closure + object instead of class because
    // we want to make `seed` non-accessible for any external function.
    let seed = deriveMainSeed(username, password);
    function deriveCK(protocol, accountId = 0, options) {
        // Reject expired instances before deriving any HKDF inputs from the closure-held seed.
        abytes(seed, 32);
        const { salt, info } = getSaltInfo(protocol, accountId); // validate protocol & accountId
        // Validate option shape and coarse length bounds;
        // `hkdf()` still rejects non-integer lengths.
        const keyLength = getKeyLength(options);
        const key = hkdf(sha256, seed, salt, info, keyLength);
        // Modulus has already been validated
        return options && 'modulus' in options ? modReduceKey(key, options.modulus) : key;
    }
    function expire() {
        // Overwrite the closure-held seed before dropping the reference.
        if (seed)
            seed.fill(1);
        seed = undefined;
    }
    // prettier-ignore
    const fingerprint = Array.from(deriveCK('fingerprint', 0))
        .slice(0, 6)
        .map((char) => char.toString(16).padStart(2, '0').toUpperCase())
        .join(':');
    return Object.freeze({ deriveChildKey: deriveCK, expire, fingerprint });
}
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