//
//  Hex.swift
//  OS Vault
//
//  Author: Simon-Pierre Boucher
//  Mail: contact@spboucher.ai
//

import Foundation
import BigInt

/// Minimal hex helpers for JSON-RPC quantities and calldata.
public enum Hex {

    public static func quantity(_ value: BigUInt) -> String {
        "0x" + String(value, radix: 16)
    }

    public static func toBigUInt(_ hex: String) -> BigUInt? {
        let stripped = hex.hasPrefix("0x") ? String(hex.dropFirst(2)) : hex
        if stripped.isEmpty { return 0 }
        return BigUInt(stripped, radix: 16)
    }

    public static func data(_ hex: String) -> Data? {
        var stripped = hex.hasPrefix("0x") ? String(hex.dropFirst(2)) : hex
        if stripped.count % 2 != 0 { stripped = "0" + stripped }
        var out = Data(capacity: stripped.count / 2)
        var index = stripped.startIndex
        while index < stripped.endIndex {
            let next = stripped.index(index, offsetBy: 2)
            guard let byte = UInt8(stripped[index..<next], radix: 16) else { return nil }
            out.append(byte)
            index = next
        }
        return out
    }

    public static func string(_ data: Data) -> String {
        "0x" + data.map { String(format: "%02x", $0) }.joined()
    }

    /// Left-pads to a 32-byte ABI word.
    public static func abiWord(_ data: Data) -> Data {
        if data.count >= 32 { return data.suffix(32) }
        return Data(repeating: 0, count: 32 - data.count) + data
    }

    public static func abiWord(_ value: BigUInt) -> Data {
        abiWord(value.serialize())
    }

    /// ERC-20 `transfer(address,uint256)` calldata.
    public static func erc20TransferData(to recipient: String, amount: BigUInt) -> Data? {
        guard let addressData = data(recipient), addressData.count == 20 else { return nil }
        var calldata = Data([0xa9, 0x05, 0x9c, 0xbb])
        calldata.append(abiWord(addressData))
        calldata.append(abiWord(amount))
        return calldata
    }

    /// ERC-20 `balanceOf(address)` calldata.
    public static func erc20BalanceOfData(owner: String) -> Data? {
        guard let addressData = data(owner), addressData.count == 20 else { return nil }
        var calldata = Data([0x70, 0xa0, 0x82, 0x31])
        calldata.append(abiWord(addressData))
        return calldata
    }
}