Update contract utility GetL2Output (#18)

* Update output of GetL2Output function

* 👌 Applied suggestions

pkg/chain/contracts.go

@@ -5,13 +5,23 @@ import (
 	"fmt"
 	"math/big"
 
+	"github.com/LiskHQ/op-fault-detector/pkg/encoding"
 	"github.com/ethereum/go-ethereum/accounts/abi/bind"
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/ethclient"
 
 	"github.com/ethereum-optimism/optimism/op-bindings/bindings"
 )
 
+// L2Output is the output of GetL2Output.
+type L2Output struct {
+	OutputRoot    string
+	L1Timestamp   uint64
+	L2BlockNumber uint64
+	L2OutputIndex uint64
+}
+
 // OracleAccessor binds oracle contract to an instance for querying data.
 type OracleAccessor struct {
 	contractInstance *bindings.L2OutputOracle
@@ -68,6 +78,16 @@ func (oc *OracleAccessor) GetNextOutputIndex() (*big.Int, error) {
 }
 
 // GetL2Output returns L2 output at given index.
-func (oc *OracleAccessor) GetL2Output(index *big.Int) (bindings.TypesOutputProposal, error) {
-	return oc.contractInstance.GetL2Output(&bind.CallOpts{}, index)
+func (oc *OracleAccessor) GetL2Output(index *big.Int) (L2Output, error) {
+	l2Output, err := oc.contractInstance.GetL2Output(&bind.CallOpts{}, index)
+	if err != nil {
+		return L2Output{}, err
+	}
+
+	return L2Output{
+		OutputRoot:    hexutil.Encode(l2Output.OutputRoot[:]),
+		L1Timestamp:   encoding.MustConvertBigIntToUint64(l2Output.Timestamp),
+		L2BlockNumber: encoding.MustConvertBigIntToUint64(l2Output.L2BlockNumber),
+		L2OutputIndex: encoding.MustConvertBigIntToUint64(index),
+	}, nil
 }

pkg/encoding/encoding.go

@@ -1,2 +1,18 @@
 // Package encoding implements all the utils/helpers for encoding incoming/outgoing RPC requests
 package encoding
+
+import "math/big"
+
+// MustConvertBigIntToUint64 converts big integer to integer.
+func MustConvertBigIntToUint64(value *big.Int) uint64 {
+	valueToString, ok := new(big.Int).SetString(value.String(), 10)
+	if !ok {
+		panic("error while converting big integer to integer")
+	}
+	return valueToString.Uint64()
+}
+
+// MustConvertUint64ToBigInt converts integer to big integer.
+func MustConvertUint64ToBigInt(value uint64) *big.Int {
+	return new(big.Int).SetUint64(value)
+}

pkg/encoding/encoding_test.go

@@ -0,0 +1,26 @@
+package encoding
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMustConvertBigIntToUint64(t *testing.T) {
+	assert := assert.New(t)
+
+	bigIntInput := big.NewInt(1000)
+	const expectedOutput uint64 = 1000
+	result := MustConvertBigIntToUint64(bigIntInput)
+	assert.Equal(expectedOutput, result)
+}
+
+func TestMustConvertUint64ToBigInt(t *testing.T) {
+	assert := assert.New(t)
+
+	const uint64Output uint64 = 1000
+	expectedOutput := big.NewInt(1000)
+	result := MustConvertUint64ToBigInt(uint64Output)
+	assert.Equal(expectedOutput, result)
+}