package commands

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

	"github.com/holiman/uint256"

	"github.com/ledgerwatch/turbo-geth/common"
	"github.com/ledgerwatch/turbo-geth/common/hexutil"
	"github.com/ledgerwatch/turbo-geth/core"
	"github.com/ledgerwatch/turbo-geth/core/rawdb"
	"github.com/ledgerwatch/turbo-geth/core/state"
	"github.com/ledgerwatch/turbo-geth/core/types"
	"github.com/ledgerwatch/turbo-geth/core/vm"
	"github.com/ledgerwatch/turbo-geth/internal/ethapi"
	"github.com/ledgerwatch/turbo-geth/log"
	"github.com/ledgerwatch/turbo-geth/params"
	"github.com/ledgerwatch/turbo-geth/rpc"
)

const callTimeout = 5 * time.Second

func (api *APIImpl) Call(ctx context.Context, args ethapi.CallArgs, blockNrOrHash rpc.BlockNumberOrHash, overrides map[common.Address]ethapi.Account) (hexutil.Bytes, error) {
	result, err := api.doCall(ctx, args, blockNrOrHash, overrides)
	if err != nil {
		return nil, err
	}

	// If the result contains a revert reason, try to unpack and return it.
	if len(result.Revert()) > 0 {
		return nil, ethapi.NewRevertError(result)
	}

	return result.Return(), result.Err
}

func (api *APIImpl) doCall(ctx context.Context, args ethapi.CallArgs, blockNrOrHash rpc.BlockNumberOrHash, overrides map[common.Address]ethapi.Account) (*core.ExecutionResult, error) {
	// todo: Pending state is only known by the miner
	/*
		if blockNrOrHash.BlockNumber != nil && *blockNrOrHash.BlockNumber == rpc.PendingBlockNumber {
			block, state, _ := b.eth.miner.Pending()
			return state, block.Header(), nil
		}
	*/

	blockNumber, hash, err := GetBlockNumber(blockNrOrHash, api.dbReader)
	if err != nil {
		return nil, err
	}

	ds := state.NewPlainDBState(api.db, blockNumber)
	state := state.New(ds)
	if state == nil {
		return nil, fmt.Errorf("can't get the state for %d", blockNumber)
	}

	header := rawdb.ReadHeader(api.dbReader, hash, blockNumber)
	if header == nil {
		return nil, fmt.Errorf("block %d(%x) not found", blockNumber, hash)
	}

	// Override the fields of specified contracts before execution.
	for addr, account := range overrides {
		// Override account nonce.
		if account.Nonce != nil {
			state.SetNonce(addr, uint64(*account.Nonce))
		}
		// Override account(contract) code.
		if account.Code != nil {
			state.SetCode(addr, *account.Code)
		}
		// Override account balance.
		if account.Balance != nil {
			balance, _ := uint256.FromBig((*big.Int)(*account.Balance))
			state.SetBalance(addr, balance)
		}
		if account.State != nil && account.StateDiff != nil {
			return nil, fmt.Errorf("account %s has both 'state' and 'stateDiff'", addr.Hex())
		}
		// Replace entire state if caller requires.
		if account.State != nil {
			state.SetStorage(addr, *account.State)
		}
		// Apply state diff into specified accounts.
		if account.StateDiff != nil {
			for key, value := range *account.StateDiff {
				key := key
				state.SetState(addr, &key, value)
			}
		}
	}
	// Setup context so it may be cancelled the call has completed
	// or, in case of unmetered gas, setup a context with a timeout.
	var cancel context.CancelFunc
	if callTimeout > 0 {
		ctx, cancel = context.WithTimeout(ctx, callTimeout)
	} else {
		ctx, cancel = context.WithCancel(ctx)
	}

	// Make sure the context is cancelled when the call has completed
	// this makes sure resources are cleaned up.
	defer cancel()

	// Get a new instance of the EVM.
	msg := args.ToMessage(big.NewInt(0).SetUint64(cfg.gascap))

	evmCtx := GetEvmContext(msg, header, blockNrOrHash.RequireCanonical, api.dbReader)

	evm := vm.NewEVM(evmCtx, state, params.MainnetChainConfig, vm.Config{}, nil)

	// Wait for the context to be done and cancel the evm. Even if the
	// EVM has finished, cancelling may be done (repeatedly)
	go func() {
		<-ctx.Done()
		evm.Cancel()
	}()

	gp := new(core.GasPool).AddGas(msg.Gas())
	result, err := core.ApplyMessage(evm, msg, gp)
	if err != nil {
		return nil, err
	}

	// If the timer caused an abort, return an appropriate error message
	if evm.Cancelled() {
		return nil, fmt.Errorf("execution aborted (timeout = %v)", callTimeout)
	}
	return result, nil
}

func GetEvmContext(msg core.Message, header *types.Header, requireCanonical bool, dbReader rawdb.DatabaseReader) vm.Context {
	return vm.Context{
		CanTransfer: core.CanTransfer,
		Transfer:    core.Transfer,
		GetHash:     getHashGetter(requireCanonical, dbReader),
		Origin:      msg.From(),
		Coinbase:    header.Coinbase,
		BlockNumber: new(big.Int).Set(header.Number),
		Time:        new(big.Int).SetUint64(header.Time),
		Difficulty:  new(big.Int).Set(header.Difficulty),
		GasLimit:    header.GasLimit,
		GasPrice:    msg.GasPrice().ToBig(),
	}
}

func getHashGetter(requireCanonical bool, dbReader rawdb.DatabaseReader) func(uint64) common.Hash {
	return func(n uint64) common.Hash {
		hash, err := GetHashByNumber(n, requireCanonical, dbReader)
		if err != nil {
			log.Debug("can't get block hash by number", "number", n, "only-canonical", requireCanonical)
		}
		return hash
	}
}

// EstimateGas returns an estimate of the amount of gas needed to execute the
// given transaction against the current pending block.
func (api *APIImpl) EstimateGas(ctx context.Context, args ethapi.CallArgs) (hexutil.Uint64, error) {
	//fixme: blockNrOrHash := rpc.BlockNumberOrHashWithNumber(rpc.PendingBlockNumber)
	hash := rawdb.ReadHeadBlockHash(api.dbReader)

	return api.DoEstimateGas(ctx, args, rpc.BlockNumberOrHash{BlockHash: &hash}, big.NewInt(0).SetUint64(cfg.gascap))
}

func (api *APIImpl) DoEstimateGas(ctx context.Context, args ethapi.CallArgs, blockNrOrHash rpc.BlockNumberOrHash, gasCap *big.Int) (hexutil.Uint64, error) {
	// Binary search the gas requirement, as it may be higher than the amount used
	var (
		lo  uint64 = params.TxGas - 1
		hi  uint64
		cap uint64
	)
	// Use zero address if sender unspecified.
	if args.From == nil {
		args.From = new(common.Address)
	}

	blockNumber, hash, err := GetBlockNumber(blockNrOrHash, api.dbReader)
	if err != nil {
		return 0, err
	}

	// Determine the highest gas limit can be used during the estimation.
	if args.Gas != nil && uint64(*args.Gas) >= params.TxGas {
		hi = uint64(*args.Gas)
	} else {
		// Retrieve the block to act as the gas ceiling
		header := rawdb.ReadHeader(api.dbReader, hash, blockNumber)
		hi = header.GasLimit
	}
	// Recap the highest gas limit with account's available balance.
	if args.GasPrice != nil && args.GasPrice.ToInt().Uint64() != 0 {
		ds := state.NewPlainDBState(api.db, blockNumber)
		state := state.New(ds)
		if state == nil {
			return 0, fmt.Errorf("can't get the state for %d", blockNumber)
		}

		balance := state.GetBalance(*args.From) // from can't be nil
		available := balance.ToBig()
		if args.Value != nil {
			if args.Value.ToInt().Cmp(available) >= 0 {
				return 0, errors.New("insufficient funds for transfer")
			}
			available.Sub(available, args.Value.ToInt())
		}
		allowance := new(big.Int).Div(available, args.GasPrice.ToInt())
		if hi > allowance.Uint64() {
			transfer := args.Value
			if transfer == nil {
				transfer = new(hexutil.Big)
			}
			log.Warn("Gas estimation capped by limited funds", "original", hi, "balance", balance,
				"sent", transfer.ToInt(), "gasprice", args.GasPrice.ToInt(), "fundable", allowance)
			hi = allowance.Uint64()
		}
	}
	// Recap the highest gas allowance with specified gascap.
	if gasCap != nil && hi > gasCap.Uint64() {
		log.Warn("Caller gas above allowance, capping", "requested", hi, "cap", gasCap)
		hi = gasCap.Uint64()
	}
	cap = hi

	// Create a helper to check if a gas allowance results in an executable transaction
	executable := func(gas uint64) (bool, *core.ExecutionResult, error) {
		args.Gas = (*hexutil.Uint64)(&gas)

		result, err := api.doCall(ctx, args, blockNrOrHash, nil)
		if err != nil {
			if errors.Is(err, core.ErrIntrinsicGas) {
				// Special case, raise gas limit
				return true, nil, nil
			}

			// Bail out
			return true, nil, err
		}
		return result.Failed(), result, nil
	}
	// Execute the binary search and hone in on an executable gas limit
	for lo+1 < hi {
		mid := (hi + lo) / 2
		failed, _, err := executable(mid)

		// If the error is not nil(consensus error), it means the provided message
		// call or transaction will never be accepted no matter how much gas it is
		// assigened. Return the error directly, don't struggle any more.
		if err != nil {
			return 0, err
		}
		if failed {
			lo = mid
		} else {
			hi = mid
		}
	}
	// Reject the transaction as invalid if it still fails at the highest allowance
	if hi == cap {
		failed, result, err := executable(hi)
		if err != nil {
			return 0, err
		}
		if failed {
			if result != nil && !errors.Is(result.Err, vm.ErrOutOfGas) {
				if len(result.Revert()) > 0 {
					return 0, ethapi.NewRevertError(result)
				}
				return 0, result.Err
			}
			// Otherwise, the specified gas cap is too low
			return 0, fmt.Errorf("gas required exceeds allowance (%d)", cap)
		}
	}
	return hexutil.Uint64(hi), nil
}