<?php

namespace App\Services\Chain;

use Elliptic\EC;
use RuntimeException;

final class TronSigner
{
    /**
     * Sign a Tron txID (sha256 hex of raw_data) → 65-byte hex signature (r||s||v).
     */
    public static function signTxId(string $privateKeyHex, string $txIdHex): string
    {
        $txIdHex = strtolower(ltrim($txIdHex, '0x'));
        if (strlen($txIdHex) !== 64) {
            throw new RuntimeException('Invalid txID');
        }

        $ec = new EC('secp256k1');
        $key = $ec->keyFromPrivate($privateKeyHex);
        $sig = $key->sign($txIdHex, ['canonical' => true]);

        $r = str_pad($sig->r->toString(16), 64, '0', STR_PAD_LEFT);
        $s = str_pad($sig->s->toString(16), 64, '0', STR_PAD_LEFT);
        $v = dechex($sig->recoveryParam & 0xff);
        if (strlen($v) === 1) {
            $v = '0'.$v;
        }

        return $r.$s.$v;
    }
}