// Package mainchain defines services that interacts with a Geth node via RPC.
// This package is useful for an actor in a sharded system to interact with
// a Sharding Manager Contract.
package mainchain

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"math/big"
	"os"
	"sync"
	"time"

	ethereum "github.com/ethereum/go-ethereum"
	"github.com/ethereum/go-ethereum/accounts"
	"github.com/ethereum/go-ethereum/accounts/abi/bind"
	"github.com/ethereum/go-ethereum/accounts/keystore"
	"github.com/ethereum/go-ethereum/common"
	"github.com/ethereum/go-ethereum/core/types"
	"github.com/ethereum/go-ethereum/ethclient"
	"github.com/ethereum/go-ethereum/log"
	"github.com/ethereum/go-ethereum/node"
	"github.com/ethereum/go-ethereum/rpc"
	"github.com/ethereum/go-ethereum/sharding/contracts"
)

// ClientIdentifier tells us what client the node we interact with over RPC is running.
const ClientIdentifier = "geth"

// Client contains useful methods for a sharding node to interact with
// an Ethereum client running on the mainchain.
type Client interface {
	Account() *accounts.Account
	CreateTXOpts(value *big.Int) (*bind.TransactOpts, error)
	SMCCaller() *contracts.SMCCaller
	SMCTransactor() *contracts.SMCTransactor
	SMCFilterer() *contracts.SMCFilterer
	TransactionReceipt(common.Hash) (*types.Receipt, error)
	ChainReader() ethereum.ChainReader
	DepositFlag() bool
	SetDepositFlag(deposit bool)
	DataDirPath() string
	Sign(hash common.Hash) ([]byte, error)
}

// SMCClient defines a struct that interacts with a
// mainchain node via RPC. Specifically, it aids in SMC bindings that are useful
// to other sharding services.
type SMCClient struct {
	endpoint     string             // Endpoint to JSON RPC.
	dataDirPath  string             // Path to the data directory.
	depositFlag  bool               // Keeps track of the deposit option passed in as via CLI flags.
	passwordFile string             // Path to the account password file.
	client       *ethclient.Client  // Ethereum RPC client.
	keystore     *keystore.KeyStore // Keystore containing the single signer.
	smc          *contracts.SMC     // The deployed sharding management contract.
	rpcClient    *rpc.Client        // The RPC client connection to the main geth node.
	lock         sync.Mutex         // Mutex lock for concurrency management.
}

// NewSMCClient constructs a new instance of an SMCClient.
func NewSMCClient(endpoint string, dataDirPath string, depositFlag bool, passwordFile string) (*SMCClient, error) {
	config := &node.Config{
		DataDir: dataDirPath,
	}

	scryptN, scryptP, keydir, err := config.AccountConfig()
	if err != nil {
		return nil, err
	}

	ks := keystore.NewKeyStore(keydir, scryptN, scryptP)

	// Sets up a connection to a Geth node via RPC.
	rpcClient, err := dialRPC(endpoint)
	if err != nil {
		return nil, fmt.Errorf("cannot start rpc client: %v", err)
	}
	client := ethclient.NewClient(rpcClient)

	// Check account existence and unlock account before starting.
	accounts := ks.Accounts()
	if len(accounts) == 0 {
		return nil, fmt.Errorf("no accounts found")
	}

	smcClient := &SMCClient{
		keystore:     ks,
		endpoint:     endpoint,
		depositFlag:  depositFlag,
		dataDirPath:  dataDirPath,
		passwordFile: passwordFile,
		rpcClient:    rpcClient,
		client:       client,
	}

	if err := smcClient.unlockAccount(accounts[0]); err != nil {
		return nil, fmt.Errorf("cannot unlock account: %v", err)
	}

	// Initializes bindings to SMC.
	smc, err := initSMC(smcClient)
	if err != nil {
		return nil, err
	}
	smcClient.smc = smc

	return smcClient, nil
}

// CreateTXOpts creates a *TransactOpts with a signer using the default account on the keystore.
func (s *SMCClient) CreateTXOpts(value *big.Int) (*bind.TransactOpts, error) {
	account := s.Account()

	return &bind.TransactOpts{
		From:  account.Address,
		Value: value,
		Signer: func(signer types.Signer, addr common.Address, tx *types.Transaction) (*types.Transaction, error) {
			networkID, err := s.client.NetworkID(context.Background())
			if err != nil {
				return nil, fmt.Errorf("unable to fetch networkID: %v", err)
			}
			return s.keystore.SignTx(*account, tx, networkID /* chainID */)
		},
	}, nil
}

// Account to use for sharding transactions.
func (s *SMCClient) Account() *accounts.Account {
	accounts := s.keystore.Accounts()
	return &accounts[0]
}

// ChainReader for interacting with the chain.
func (s *SMCClient) ChainReader() ethereum.ChainReader {
	return ethereum.ChainReader(s.client)
}

// SMCCaller to interact with the sharding manager contract.
func (s *SMCClient) SMCCaller() *contracts.SMCCaller {
	return &s.smc.SMCCaller
}

// SMCTransactor allows us to send tx's to the SMC programmatically.
func (s *SMCClient) SMCTransactor() *contracts.SMCTransactor {
	return &s.smc.SMCTransactor
}

// SMCFilterer allows for easy filtering of events from the Sharding Manager Contract.
func (s *SMCClient) SMCFilterer() *contracts.SMCFilterer {
	return &s.smc.SMCFilterer
}

// TransactionReceipt allows an SMCClient to retrieve transaction receipts on
// the mainchain by hash.
func (s *SMCClient) TransactionReceipt(hash common.Hash) (*types.Receipt, error) {

	for pending, err := true, error(nil); pending; _, pending, err = s.client.TransactionByHash(context.Background(), hash) {
		if err != nil {
			return nil, fmt.Errorf("Unable to retrieve transaction: %v", err)
		}
		time.Sleep(1 * time.Second)
	}
	log.Info(fmt.Sprintf("Transaction: %s has been mined", hash.Hex()))

	receipt, err := s.client.TransactionReceipt(context.Background(), hash)
	if err != nil {
		return nil, err
	}

	return receipt, err
}

// DepositFlag returns true for cli flag --deposit.
func (s *SMCClient) DepositFlag() bool {
	return s.depositFlag
}

// SetDepositFlag updates the deposit flag property of SMCClient.
func (s *SMCClient) SetDepositFlag(deposit bool) {
	s.depositFlag = deposit
}

// DataDirPath returns the datadir flag as a string.
func (s *SMCClient) DataDirPath() string {
	return s.dataDirPath
}

// Client to interact with a geth node via JSON-RPC.
func (s *SMCClient) ethereumClient() *ethclient.Client {
	return s.client
}

// unlockAccount will unlock the specified account using utils.PasswordFileFlag
// or empty string if unset.
func (s *SMCClient) unlockAccount(account accounts.Account) error {
	pass := ""

	if s.passwordFile != "" {
		file, err := os.Open(s.passwordFile)
		if err != nil {
			return fmt.Errorf("unable to open file containing account password %s. %v", s.passwordFile, err)
		}
		scanner := bufio.NewScanner(file)
		scanner.Split(bufio.ScanWords)
		if !scanner.Scan() {
			err = scanner.Err()
			if err != nil {
				return fmt.Errorf("unable to read contents of file %v", err)
			}
			return errors.New("password not found in file")
		}

		pass = scanner.Text()
	}

	return s.keystore.Unlock(account, pass)
}

// Sign signs the hash of collationHeader contents by
// using default account on keystore and returns signed signature.
func (s *SMCClient) Sign(hash common.Hash) ([]byte, error) {
	account := s.Account()
	return s.keystore.SignHash(*account, hash.Bytes())
}