/**
 * Internal helpers shared by the public {@link createRootKeys} /
 * {@link createServerKeys} / {@link openVault} surface. These are NOT part of
 * the package's public API — they are an implementation seam that keeps
 * `orchestration.ts` under the file-size budget. Consumers always go through
 * the top-level barrel.
 */

import { aeadDecrypt, aeadEncrypt } from "@suaveplan/crypto";
import {
    encodePublicKeychain,
    extractPublicKeys,
    type Keychain,
    type PublicKeychain,
} from "@suaveplan/crypto/keychain";
import { ed25519 } from "@suaveplan/crypto-curve";
import {
    DEFAULT_ARGON2ID_PARAMS,
    deriveKeyWithArgon2id,
} from "../argon2id/argon2id.js";
import { CRYPTO_VAULT_CODES } from "../errors/codes.js";
import { CryptoVaultError } from "../errors/crypto-vault-error.js";
import type { Argon2idParams } from "../types/types.js";
import type { LayoutV1Fields } from "./orchestration.types.js";

/** Length of the Argon2id salt embedded in the vault header. */
export const SALT_BYTES = 16;
/** Length of the XChaCha20-Poly1305 nonce embedded in the vault header. */
export const NONCE_BYTES = 24;
/** Length of an Ed25519 signature appended to the public-key file. */
export const SIGNATURE_BYTES = 64;
/** Combined header size: salt (16) + nonce (24). */
export const VAULT_HEADER_BYTES = SALT_BYTES + NONCE_BYTES;

const PASSWORD_ENCODER = new TextEncoder();

function randomBytes(length: number): Uint8Array {
    const out = new Uint8Array(length);
    crypto.getRandomValues(out);
    return out;
}

/**
 * Encrypt `plaintext` under a password-derived KEK. Layout:
 * `salt(16) || nonce(24) || ciphertext`. Both header values are drawn fresh
 * so two encryptions of the same plaintext under the same password share no
 * bytes.
 */
export async function sealVault(
    plaintext: Uint8Array,
    password: string,
    params: Argon2idParams
): Promise<Uint8Array> {
    const salt = randomBytes(SALT_BYTES);
    const nonce = randomBytes(NONCE_BYTES);
    const kek = await deriveKeyWithArgon2id(
        PASSWORD_ENCODER.encode(password),
        salt,
        params
    );
    const ciphertext = aeadEncrypt("XChaCha20-Poly1305", kek, plaintext, {
        nonce,
    });
    const out = new Uint8Array(VAULT_HEADER_BYTES + ciphertext.length);
    out.set(salt, 0);
    out.set(nonce, SALT_BYTES);
    out.set(ciphertext, VAULT_HEADER_BYTES);
    return out;
}

/**
 * Inverse of {@link sealVault}. Any failure — short input, wrong password, or
 * tampered ciphertext — surfaces as a single
 * `CryptoVaultError(CRYPTOVAULT.ORCHESTRATION.DECRYPT_FAILED)` so callers do
 * not learn whether the password or the integrity tag was the failure.
 */
export async function openVaultBytes(
    vaultBytes: Uint8Array,
    password: string
): Promise<Uint8Array> {
    if (vaultBytes.length <= VAULT_HEADER_BYTES) {
        throw new CryptoVaultError(
            CRYPTO_VAULT_CODES["ORCHESTRATION.DECRYPT_FAILED"],
            "error.crypto-vault.orchestration.decrypt-failed",
            { context: { reason: "short-input", length: vaultBytes.length } }
        );
    }
    const salt = vaultBytes.slice(0, SALT_BYTES);
    const nonce = vaultBytes.slice(SALT_BYTES, VAULT_HEADER_BYTES);
    const ciphertext = vaultBytes.slice(VAULT_HEADER_BYTES);
    const kek = await deriveKeyWithArgon2id(
        PASSWORD_ENCODER.encode(password),
        salt,
        DEFAULT_ARGON2ID_PARAMS
    );
    try {
        return aeadDecrypt("XChaCha20-Poly1305", kek, ciphertext, { nonce });
    } catch {
        throw new CryptoVaultError(
            CRYPTO_VAULT_CODES["ORCHESTRATION.DECRYPT_FAILED"],
            "error.crypto-vault.orchestration.decrypt-failed",
            { context: { reason: "aead-verify-failed" } }
        );
    }
}

/**
 * Sign `data` with the supplied Ed25519 secret key and append the 64-byte
 * signature, producing the canonical signed public-key file layout
 * `data || signature`.
 */
function signAndAppend(
    data: Uint8Array,
    ed25519SecretKey: Uint8Array
): Uint8Array {
    const signature = ed25519.sign(data, ed25519SecretKey);
    const out = new Uint8Array(data.length + signature.length);
    out.set(data, 0);
    out.set(signature, data.length);
    return out;
}

/**
 * Project `keychain` to its public-only counterpart, encode, sign, and
 * package both forms for callers.
 */
export function buildPublicKeyFile(
    keychain: Keychain<LayoutV1Fields>,
    signingSlotSecretKey: Uint8Array
): {
    publicKeyBytes: Uint8Array;
    publicKeys: PublicKeychain<LayoutV1Fields>;
} {
    const publicKeys = extractPublicKeys(keychain);
    const encoded = encodePublicKeychain(publicKeys);
    return {
        publicKeyBytes: signAndAppend(encoded, signingSlotSecretKey),
        publicKeys,
    };
}