import {
    SERVER_KEYS_CODES,
    ServerKeysError,
} from "../../error-codes/error-codes.js";

/** Encode a byte array as a lowercase hex string (no separators). */
export function bytesToHex(bytes: Uint8Array): string {
    let out = "";
    for (const byte of bytes) out += byte.toString(16).padStart(2, "0");
    return out;
}

/**
 * Decode a lowercase or uppercase hex string into a `Uint8Array`. Throws
 * `ServerKeysError(SERVER_KEYS_INVALID_INPUT)` on odd length or non-hex
 * characters. Used by the license sub-commands to deserialise the
 * `signingKey` / `publicKey` fields of the `LicenseKeypairFile` JSON
 * envelope.
 */
export function hexToBytes(hex: string): Uint8Array {
    if (hex.length % 2 !== 0) {
        throw new ServerKeysError(
            SERVER_KEYS_CODES.INVALID_INPUT,
            "Hex string length must be even"
        );
    }
    const out = new Uint8Array(hex.length / 2);
    for (let i = 0; i < out.length; i++) {
        const start = i * 2;
        const slice = hex.slice(start, start + 2);
        if (!/^[0-9a-fA-F]{2}$/.test(slice)) {
            throw new ServerKeysError(
                SERVER_KEYS_CODES.INVALID_INPUT,
                `Invalid hex byte "${slice}" at offset ${start}`
            );
        }
        out[i] = Number.parseInt(slice, 16);
    }
    return out;
}