package contracts

import (
	"context"
	"math/big"

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

type RPCClient interface {
	CallContext(ctx context.Context, result interface{}, method string, args ...interface{}) error
}

type ContractCaller struct {
	c RPCClient
}

func NewContractCaller(c RPCClient) *ContractCaller {
	return &ContractCaller{
		c: c,
	}
}

// CodeAt returns the contract code of the given account.
// The block number can be nil, in which case the code is taken from the latest known block.
func (cc *ContractCaller) CodeAt(ctx context.Context, account common.Address, blockNumber *big.Int) ([]byte, error) {
	var result hexutil.Bytes
	err := cc.c.CallContext(ctx, &result, "eth_getCode", account, "latest")
	return result, err
}

// CallContract executes a message call transaction, which is directly executed in the VM
// of the node, but never mined into the blockchain.
//
// blockNumber selects the block height at which the call runs. It can be nil, in which
// case the code is taken from the latest known block. Note that state from very old
// blocks might not be available.
func (cc *ContractCaller) CallContract(ctx context.Context, msg ethereum.CallMsg, blockNumber *big.Int) ([]byte, error) {
	var hex hexutil.Bytes
	err := cc.c.CallContext(ctx, &hex, "eth_call", toCallArg(msg), "latest")
	if err != nil {
		return nil, err
	}
	return hex, nil
}

func toCallArg(msg ethereum.CallMsg) interface{} {
	arg := map[string]interface{}{
		"from": msg.From,
		"to":   msg.To,
	}
	if len(msg.Data) > 0 {
		arg["data"] = hexutil.Bytes(msg.Data)
	}
	if msg.Value != nil {
		arg["value"] = (*hexutil.Big)(msg.Value)
	}
	if msg.Gas != 0 {
		arg["gas"] = hexutil.Uint64(msg.Gas)
	}
	if msg.GasPrice != nil {
		arg["gasPrice"] = (*hexutil.Big)(msg.GasPrice)
	}
	return arg
}