package main

import (
    "bytes"
    "encoding/hex"
    "fmt"

    "github.com/bcext/gcash/btcec"
    "github.com/bcext/gcash/txscript"
    "github.com/bcext/gcash/wire"
)

func main() {
    rawPriv, err := hex.DecodeString("3957ae9390a1341738a8fb667e0fb9e0ffd01ce0e4ee4de1b3a6deb162c81b48")
    if err != nil {
        panic(err)
    }
    privKey, pubKey := btcec.PrivKeyFromBytes(btcec.S256(), rawPriv)
    rawTx, err := hex.DecodeString("0200000001ceda94b0beabb9510bc03e803c8aaceef736ea40d5d8a4d943927d1135cd57e40100000000ffffffff0300e1f505000000001976a9140000000000000000000000000000000000376e4388ac00000000000000000a6a080877686300000044e00f9700000000001976a914f9757e1b9caa87ef4377d977754ae95908cc6df188ac00000000")
    if err != nil {
        panic(err)
    }
    
        wif, err := cashutil.DecodeWIF("cSnfjz72jSMQhdxQeQ6uW8eUko9xndFoZ5w5fTvbSCNgeTjaUgQW")
    if err != nil {
        panic(err)
    }
        // use:     wif.PrivKey.PubKey()

    var tx wire.MsgTx
    err = tx.Deserialize(bytes.NewReader(rawTx))
    if err != nil {
        panic(err)
    }

    scriptPubKey, err := hex.DecodeString("76a914f9757e1b9caa87ef4377d977754ae95908cc6df188ac")
    if err != nil {
        panic(err)
    }

    sig, err := txscript.RawTxInSignature(&tx, 0, scriptPubKey, 110000000, txscript.SigHashAll|txscript.SigHashForkID, privKey)
    if err != nil {
        panic(err)
    }
    sig, err = txscript.NewScriptBuilder().AddData(sig).Script()
    if err != nil {
        panic(err)
    }
    pk, err := txscript.NewScriptBuilder().AddData(pubKey.SerializeCompressed()).Script()
    if err != nil {
        panic(err)
    }
    sig = append(sig, pk...)
    tx.TxIn[0].SignatureScript = sig
    fmt.Println("signature", hex.EncodeToString(sig))
    w := bytes.NewBuffer(make([]byte, 0))
    err = tx.Serialize(w)
    if err != nil {
        panic(err)
    }
    fmt.Println("transaction", hex.EncodeToString(w.Bytes()))

    engine, err := txscript.NewEngine(scriptPubKey, &tx, 0, txscript.StandardVerifyFlags, nil, nil, 110000000)
    if err != nil {
        panic(err)
    }
    
    // verify the signature
    err = engine.Execute()
    if err != nil {
        panic(err)
    }
}