import { getIV } from "encryption/low-level/util";

export interface EncryptedData {
    iv: Uint8Array;
    data: ArrayBuffer;
}

export interface AESEncryptorI {
    encryptBinary(data: Uint8Array | ArrayBuffer): Promise<EncryptedData>;
    decryptBinary(
        iv: Uint8Array | ArrayBuffer,
        data: Uint8Array | ArrayBuffer
    ): Promise<ArrayBuffer>;
    getAlgorithm(): AesKeyAlgorithm;
}

/**
 * Creates an instance of an AES.
 *
 * This is meant to be fairly low level, and is not intended to be used directly.
 * You're probably instead interested in the DataEncryptor.
 *
 * @constructor {CryptoKey} The key used to encrypt and decrypt data.
 */
export function AESEncryptor(key: CryptoKey): AESEncryptorI {
    const algorithm = AESEncryptor.getDefaultAlgorithm();

    // For AES-GCM we will use 12 bytes
    // https://crypto.stackexchange.com/questions/41601/aes-gcm-recommended-iv-size-why-12-bytes/41610
    const IVLength = 12;

    const getAlgorithm = (iv: Uint8Array | ArrayBuffer): AesKeyAlgorithm =>
        Object.assign({}, algorithm, { iv: iv });

    return {
        async encryptBinary(
            data: Uint8Array | ArrayBuffer
        ): Promise<EncryptedData> {
            const iv = getIV(IVLength);
            const cipherText = await crypto.subtle.encrypt(
                getAlgorithm(iv),
                key,
                data
            );

            return {
                iv: iv,
                data: cipherText
            };
        },
        async decryptBinary(
            iv: Uint8Array | ArrayBuffer,
            data: Uint8Array | ArrayBuffer
        ): Promise<ArrayBuffer> {
            const rawResult = await crypto.subtle.decrypt(
                getAlgorithm(iv),
                key,
                data
            );
            return rawResult;
        },
        getAlgorithm(): AesKeyAlgorithm {
            return algorithm;
        }
    };
}

AESEncryptor.getDefaultAlgorithm = function(): AesKeyAlgorithm {
    return Object.freeze({
        name: "AES-GCM",
        length: 256
    });
};

AESEncryptor.generateKey = async function(): Promise<CryptoKey> {
    return (await crypto.subtle.generateKey(
        AESEncryptor.getDefaultAlgorithm(),
        // We need to be able to encrypt this key, so it needs to be extractable
        true,
        ["encrypt", "decrypt"]
    )) as CryptoKey;
};