// Copyright 2016 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package bind

import (
	"errors"
	"fmt"
	"math/big"

	"github.com/ethereum/go-ethereum/accounts/abi"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/types"
)

// SignerFn is a signer function callback when a contract requires a method to
// sign the transaction before submission.
type SignerFn func(common.Address, *types.Transaction) (*types.Transaction, error)

// AuthOpts is the authorization data required to create a valid Ethereum transaction.
type AuthOpts struct {
	Account common.Address // Ethereum account to send the transaction from
	Nonce   *big.Int       // Nonce to use for the transaction execution (nil = use pending state)
	Signer  SignerFn       // Method to use for signing the transaction (mandatory)

	Value    *big.Int // Funds to transfer along along the transaction (nil = 0 = no funds)
	GasPrice *big.Int // Gas price to use for the transaction execution (nil = gas price oracle)
	GasLimit *big.Int // Gas limit to set for the transaction execution (nil = estimate + 10%)
}

// BoundContract is the base wrapper object that reflects a contract on the
// Ethereum network. It contains a collection of methods that are used by the
// higher level contract bindings to operate.
type BoundContract struct {
	address    common.Address     // Deployment address of the contract on the Ethereum blockchain
	abi        abi.ABI            // Reflect based ABI to access the correct Ethereum methods
	caller     ContractCaller     // Read interface to interact with the blockchain
	transactor ContractTransactor // Write interface to interact with the blockchain
}

// NewBoundContract creates a low level contract interface through which calls
// and transactions may be made through.
func NewBoundContract(address common.Address, abi abi.ABI, caller ContractCaller, transactor ContractTransactor) *BoundContract {
	return &BoundContract{
		address:    address,
		abi:        abi,
		caller:     caller,
		transactor: transactor,
	}
}

// Call invokes the (constant) contract method with params as input values and
// sets the output to result. The result type might be a single field for simple
// returns, a slice of interfaces for anonymous returns and a struct for named
// returns.
func (c *BoundContract) Call(result interface{}, method string, params ...interface{}) error {
	input, err := c.abi.Pack(method, params...)
	if err != nil {
		return err
	}
	output, err := c.caller.ContractCall(c.address, input)
	if err != nil {
		return err
	}
	return c.abi.Unpack(result, method, output)
}

// Transact invokes the (paid) contract method with params as input values and
// value as the fund transfer to the contract.
func (c *BoundContract) Transact(opts *AuthOpts, method string, params ...interface{}) (*types.Transaction, error) {
	input, err := c.abi.Pack(method, params...)
	if err != nil {
		return nil, err
	}
	// Ensure a valid value field and resolve the account nonce
	value := opts.Value
	if value == nil {
		value = new(big.Int)
	}
	nonce := uint64(0)
	if opts.Nonce == nil {
		nonce, err = c.transactor.AccountNonce(opts.Account)
		if err != nil {
			return nil, fmt.Errorf("failed to retrieve account nonce: %v", err)
		}
	} else {
		nonce = opts.Nonce.Uint64()
	}
	// Figure out the gas allowance and gas price values
	gasPrice := opts.GasPrice
	if gasPrice == nil {
		gasPrice, err = c.transactor.GasPrice()
		if err != nil {
			return nil, fmt.Errorf("failed to suggest gas price: %v", err)
		}
	}
	gasLimit := opts.GasLimit
	if gasLimit == nil {
		gasLimit, err = c.transactor.GasLimit(opts.Account, c.address, value, input)
		if err != nil {
			return nil, fmt.Errorf("failed to exstimate gas needed: %v", err)
		}
	}
	// Create the transaction, sign it and schedule it for execution
	rawTx := types.NewTransaction(nonce, c.address, value, gasLimit, gasPrice, input)
	if opts.Signer == nil {
		return nil, errors.New("no signer to authorize the transaction with")
	}
	signedTx, err := opts.Signer(opts.Account, rawTx)
	if err != nil {
		return nil, err
	}
	if err := c.transactor.SendTransaction(signedTx); err != nil {
		return nil, err
	}
	return signedTx, nil
}