package tron

import (
	"encoding/hex"
	"fmt"
	"math/big"

	"github.com/wangjia/pangolin/pay/internal/wallet"
	"golang.org/x/crypto/sha3"
)

// TransferSelector is the TRC20 transfer(address,uint256) function selector
// string that TronGrid's triggersmartcontract expects.
const TransferSelector = "transfer(address,uint256)"

// ABIEncodeTransferParams builds the 64-byte ABI parameter for
// transfer(address,uint256): the recipient (20-byte body, left-padded to 32) and
// the amount (uint256, left-padded to 32). Returns hex (no 0x, no 4-byte
// selector — TronGrid derives the selector from TransferSelector).
func ABIEncodeTransferParams(toAddr string, amount int64) (string, error) {
	if amount <= 0 {
		return "", fmt.Errorf("tron: transfer amount must be positive")
	}
	payload, err := wallet.DecodeTronAddress(toAddr)
	if err != nil {
		return "", err
	}
	out := make([]byte, 64)
	copy(out[12:32], payload[1:]) // 20-byte body, right-aligned in first word
	new(big.Int).SetInt64(amount).FillBytes(out[32:64])
	return hex.EncodeToString(out), nil
}

// keccakAddressBody derives the 20-byte address body from a 65-byte uncompressed
// secp256k1 public key: keccak256(X||Y)[12:].
func keccakAddressBody(uncompressed []byte) []byte {
	h := sha3.NewLegacyKeccak256()
	h.Write(uncompressed[1:])
	sum := h.Sum(nil)
	return sum[12:]
}