package transactions

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"

	ethereum "github.com/ethereum/go-ethereum"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/common/hexutil"
)

var (
	// ErrInvalidSendTxArgs is returned when the structure of SendTxArgs is ambigious.
	ErrInvalidSendTxArgs = errors.New("Transaction arguments are invalid (are both 'input' and 'data' fields used?)")
	// ErrUnexpectedArgs returned when args are of unexpected length.
	ErrUnexpectedArgs = errors.New("unexpected args")

	//ErrInvalidCompleteTxSender - error transaction with invalid sender
	ErrInvalidCompleteTxSender = errors.New("transaction can only be completed by its creator")
)

// PendingNonceProvider provides information about nonces.
type PendingNonceProvider interface {
	PendingNonceAt(ctx context.Context, account common.Address) (uint64, error)
}

// GasCalculator provides methods for estimating and pricing gas.
type GasCalculator interface {
	ethereum.GasEstimator
	ethereum.GasPricer
}

// SendTxArgs represents the arguments to submit a new transaction into the transaction pool.
// This struct is based on go-ethereum's type in internal/ethapi/api.go, but we have freedom
// over the exact layout of this struct.
type SendTxArgs struct {
	From     common.Address  `json:"from"`
	To       *common.Address `json:"to"`
	Gas      *hexutil.Uint64 `json:"gas"`
	GasPrice *hexutil.Big    `json:"gasPrice"`
	Value    *hexutil.Big    `json:"value"`
	Nonce    *hexutil.Uint64 `json:"nonce"`
	// We keep both "input" and "data" for backward compatibility.
	// "input" is a preferred field.
	// see `vendor/github.com/ethereum/go-ethereum/internal/ethapi/api.go:1107`
	Input hexutil.Bytes `json:"input"`
	Data  hexutil.Bytes `json:"data"`
}

// Valid checks whether this structure is filled in correctly.
func (args SendTxArgs) Valid() bool {
	// if at least one of the fields is empty, it is a valid struct
	if isNilOrEmpty(args.Input) || isNilOrEmpty(args.Data) {
		return true
	}

	// we only allow both fields to present if they have the same data
	return bytes.Equal(args.Input, args.Data)
}

// GetInput returns either Input or Data field's value dependent on what is filled.
func (args SendTxArgs) GetInput() hexutil.Bytes {
	if !isNilOrEmpty(args.Input) {
		return args.Input
	}

	return args.Data
}

func isNilOrEmpty(bytes hexutil.Bytes) bool {
	return bytes == nil || len(bytes) == 0
}

// RPCCalltoSendTxArgs creates SendTxArgs based on RPC parameters
func RPCCalltoSendTxArgs(args ...interface{}) (SendTxArgs, error) {
	var txArgs SendTxArgs
	if len(args) != 1 {
		return txArgs, ErrUnexpectedArgs
	}
	data, err := json.Marshal(args[0])
	if err != nil {
		return txArgs, err
	}
	if err := json.Unmarshal(data, &txArgs); err != nil {
		return txArgs, err
	}

	return txArgs, nil
}