-- SPDX-FileCopyrightText: 2020 Tocqueville Group
--
-- SPDX-License-Identifier: LicenseRef-MIT-TQ

-- | Executor and typechecker of a contract in Morley language.

module Morley.Michelson.Runtime
  (
    -- * High level interface for end user
    originateContract
  , runContract
  , transfer

  -- * Other helpers
  , parseContract
  , parseExpandContract
  , readAndParseContract
  , prepareContract

  -- * Re-exports
  , ContractState (..)
  , AddressState (..)
  , VotingPowers
  , mkVotingPowers
  , mkVotingPowersFromMap
  , TxData (..)
  , TxParam (..)

  -- * For testing
  , ExecutorOp (..)
  , ExecutorRes (..)
  , ExecutorError' (..)
  , ExecutorError
  , ExecutorM
  , runExecutorM
  , runExecutorMWithDB
  , executeGlobalOperations
  , executeGlobalOrigination
  , executeOrigination
  , executeTransfer

  -- * To avoid warnings (can't generate lenses only for some fields)
  , erInterpretResults
  , erUpdates
  , erGState
  , erRemainingSteps
  , elInterpreterResults
  , elUpdates
  ) where

import Control.Lens (assign, at, makeLenses, (.=), (<>=))
import Control.Monad.Except (Except, liftEither, runExcept, throwError)
import Data.Default (def)
import qualified Data.HashSet as HS
import Data.Semigroup.Generic
import Data.Text.IO (getContents)
import qualified Data.Text.IO.Utf8 as Utf8 (readFile)
import Fmt (Buildable(build), blockListF, fmt, fmtLn, indentF, nameF, pretty, (+|), (|+))
import Text.Megaparsec (parse)

import Morley.Michelson.Interpret
  (ContractEnv(..), InterpretError(..), InterpretResult(..), InterpreterState(..), MorleyLogs(..),
  RemainingSteps(..), assignBigMapIds, handleContractReturn, interpret)
import Morley.Michelson.Macro (ParsedOp, expandContract)
import qualified Morley.Michelson.Parser as P
import Morley.Michelson.Runtime.GState
import Morley.Michelson.Runtime.TxData
import Morley.Michelson.TypeCheck
import Morley.Michelson.Typed
  (CreateContract(..), EntrypointCallT, EpName, Operation'(..), SomeContractAndStorage(..),
  SomeStorage(..), SomeValue(..), TransferTokens(..), untypeValue)
import qualified Morley.Michelson.Typed as T
import Morley.Michelson.Typed.Operation
import Morley.Michelson.Untyped (Contract)
import qualified Morley.Michelson.Untyped as U
import Morley.Tezos.Address (Address(..), GlobalCounter(..), isKeyAddress)
import Morley.Tezos.Core
  (Mutez, Timestamp(..), getCurrentTime, unsafeAddMutez, unsafeSubMutez, zeroMutez)
import Morley.Tezos.Crypto (KeyHash, parseKeyHash)
import Morley.Util.Named

----------------------------------------------------------------------------
-- Auxiliary types
----------------------------------------------------------------------------

-- | Operations executed by interpreter.
-- In our model one Michelson's operation (@operation@ type in Michelson)
-- corresponds to 0 or 1 interpreter operation.
--
-- Note: 'Address' is not part of 'TxData', because 'TxData' is
-- supposed to be provided by the user, while 'Address' can be
-- computed by our code.
data ExecutorOp
  = OriginateOp OriginationOperation
  -- ^ Originate a contract.
  | TransferOp TransferOperation
  -- ^ Transfer tokens to the address.
  | SetDelegateOp SetDelegateOperation
  -- ^ Set the delegate of a contract.
  deriving stock (Show)

instance Buildable ExecutorOp where
  build = \case
    TransferOp (TransferOperation addr TxData{..} _)->
      "Transfer " +| tdAmount |+ " tokens from " +| tdSenderAddress |+ " to " +| addr |+ ""
    OriginateOp OriginationOperation{..} ->
      "Originate a contract with" <>
      " delegate " +| maybe "<nobody>" build ooDelegate |+
      " and balance = " +| ooBalance |+ ""
    SetDelegateOp SetDelegateOperation{..} ->
      "Set delegate of contract " +| sdoContract |+
      " to " +| maybe "<nobody>" build sdoDelegate |+ ""

-- | Result of a single execution of interpreter.
data ExecutorRes = ExecutorRes
  { _erGState :: GState
  -- ^ New 'GState'.
  , _erUpdates :: [GStateUpdate]
  -- ^ Updates applied to 'GState'.
  , _erInterpretResults :: [(Address, InterpretResult)]
  -- ^ During execution a contract can print logs and in the end it returns
  -- a pair. All logs and returned values are kept until all called contracts
  -- are executed. In the end they are printed.
  , _erRemainingSteps :: RemainingSteps
  -- ^ Now much gas all remaining executions can consume.
  } deriving stock (Show)

data ExecutorEnv = ExecutorEnv
  { _eeNow :: Timestamp
  , _eeLevel :: Natural
  }
  deriving stock (Show, Generic)

data ExecutorState = ExecutorState
  { _esGState :: GState
  , _esRemainingSteps :: RemainingSteps
  , _esSourceAddress :: Maybe Address
  , _esLog :: ExecutorLog
  , _esOperationHash :: ~OperationHash
  , _esPrevCounters :: HashSet GlobalCounter
  }
  deriving stock (Show, Generic)

data ExecutorLog = ExecutorLog
  { _elUpdates :: [GStateUpdate]
  , _elInterpreterResults :: [(Address, InterpretResult)]
  }
  deriving stock (Show, Generic)
  deriving (Semigroup, Monoid) via GenericSemigroupMonoid ExecutorLog

makeLenses ''ExecutorRes
makeLenses ''ExecutorEnv
makeLenses ''ExecutorState
makeLenses ''ExecutorLog

-- | Errors that can happen during contract interpreting.
-- Type parameter @a@ determines how contracts will be represented
-- in these errors, e.g. 'Address'.
data ExecutorError' a
  = EEUnknownContract a
  -- ^ The interpreted contract hasn't been originated.
  | EEInterpreterFailed a
                        InterpretError
  -- ^ Interpretation of Michelson contract failed.
  | EEAlreadyOriginated a
                        ContractState
  -- ^ A contract is already originated.
  | EEUnknownSender a
  -- ^ Sender address is unknown.
  | EEUnknownManager a
  -- ^ Manager address is unknown.
  | EENotEnoughFunds a Mutez
  -- ^ Sender doesn't have enough funds.
  | EEZeroTransaction a
  -- ^ Sending 0tz towards an address.
  | EEFailedToApplyUpdates GStateUpdateError
  -- ^ Failed to apply updates to GState.
  | EEIllTypedParameter a TCError
  -- ^ Contract parameter is ill-typed.
  | EEUnexpectedParameterType a T.T T.T
  -- ^ Contract parameter is well-typed, but its type does
  -- not match the entrypoint's type.
  | EEUnknownEntrypoint EpName
  -- ^ Specified entrypoint to run is not found.
  | EETransactionFromContract a Mutez
  -- ^ A transaction from an originated contract was attempted as a global operation.
  | EEWrongParameterType a
  -- ^ Type of parameter in transfer to an implicit account is not Unit.
  | EEOperationReplay ExecutorOp
  -- ^ An attempt to perform the operation duplicated with @DUP@ instruction.
  deriving stock (Show, Functor)

instance (Buildable a) => Buildable (ExecutorError' a) where
  build =
    \case
      EEUnknownContract addr -> "The contract is not originated " +| addr |+ ""
      EEInterpreterFailed addr err ->
        "Michelson interpreter failed for contract " +| addr |+ ": " +| err |+ ""
      EEAlreadyOriginated addr cs ->
        "The following contract is already originated: " +| addr |+
        ", " +| cs |+ ""
      EEUnknownSender addr -> "The sender address is unknown " +| addr |+ ""
      EEUnknownManager addr -> "The manager address is unknown " +| addr |+ ""
      EENotEnoughFunds addr amount ->
        "The sender (" +| addr |+
        ") doesn't have enough funds (has only " +| amount |+ ")"
      EEZeroTransaction addr ->
        "Transaction of 0ꜩ towards a key address " +| addr |+ " which has no code is prohibited"
      EEFailedToApplyUpdates err -> "Failed to update GState: " +| err |+ ""
      EEIllTypedParameter _ err -> "The contract parameter is ill-typed: " +| err |+ ""
      EEUnexpectedParameterType _ actualT expectedT ->
        "The contract parameter is well-typed, but did not match the contract's entrypoint's type.\n" <>
        "Expected: " +| expectedT |+ "\n" <>
        "Got: " +| actualT |+ ""
      EEUnknownEntrypoint epName -> "The contract does not contain entrypoint '" +| epName |+ "'"
      EETransactionFromContract addr amount ->
        "Global transaction of funds (" +| amount |+ ") from an originated contract (" +| addr |+ ") is prohibited."
      EEWrongParameterType addr ->
        "Bad contract parameter for: " +| addr |+ ""
      EEOperationReplay op ->
        "Operation replay attempt:\n" +| indentF 2 (build op) |+ ""

type ExecutorError = ExecutorError' Address

instance (Typeable a, Show a, Buildable a) => Exception (ExecutorError' a) where
  displayException = pretty

----------------------------------------------------------------------------
-- Interface
----------------------------------------------------------------------------

-- | Parse a contract from 'Text'.
parseContract ::
     P.MichelsonSource -> Text -> Either P.ParserException (U.Contract' ParsedOp)
parseContract source =
  first P.ParserException . parse P.program (pretty source)

-- | Parse a contract from 'Text' and expand macros.
parseExpandContract ::
     P.MichelsonSource -> Text -> Either P.ParserException Contract
parseExpandContract = fmap expandContract ... parseContract

-- | Read and parse a contract from give path or `stdin` (if the
-- argument is 'Nothing'). The contract is not expanded.
readAndParseContract :: Maybe FilePath -> IO (U.Contract' ParsedOp)
readAndParseContract mFilename = do
  code <- readCode mFilename
  either throwM pure $ parseContract (toSrc mFilename) code
  where
    readCode :: Maybe FilePath -> IO Text
    readCode = maybe getContents Utf8.readFile

    toSrc :: Maybe FilePath -> P.MichelsonSource
    toSrc = maybe P.MSUnspecified P.MSFile

-- | Read a contract using 'readAndParseContract', expand and
-- flatten. The contract is not type checked.
prepareContract :: Maybe FilePath -> IO Contract
prepareContract mFile = expandContract <$> readAndParseContract mFile

-- | Originate a contract. Returns the address of the originated
-- contract.
originateContract
  :: FilePath
  -> TypeCheckOptions
  -> Address
  -> Maybe KeyHash
  -> Mutez
  -> U.Value
  -> U.Contract
  -> "verbose" :! Bool
  -> IO Address
originateContract dbPath tcOpts originator delegate balance uStorage uContract verbose = do
  origination <- either throwM pure . typeCheckingWith tcOpts $
    mkOrigination <$> typeCheckContractAndStorage uContract uStorage
  -- pass 100500 as maxSteps, because it doesn't matter for origination,
  -- as well as 'now'
  fmap snd $ runExecutorMWithDB Nothing Nothing dbPath 100500 verbose (#dryRun :? Nothing) $ do
    executeGlobalOrigination origination
  where
    mkOrigination (SomeContractAndStorage contract storage) = OriginationOperation
      { ooOriginator = originator
      , ooDelegate = delegate
      , ooBalance = balance
      , ooStorage = storage
      , ooContract = contract
      , ooCounter = 0
      }

-- | Run a contract. The contract is originated first (if it's not
-- already) and then we pretend that we send a transaction to it.
runContract
  :: Maybe Timestamp
  -> Maybe Natural
  -> Word64
  -> Mutez
  -> FilePath
  -> TypeCheckOptions
  -> U.Value
  -> U.Contract
  -> TxData
  -> "verbose" :! Bool
  -> "dryRun" :! Bool
  -> IO SomeStorage
runContract maybeNow maybeLevel maxSteps initBalance dbPath tcOpts uStorage uContract txData
  verbose (N dryRun) = do
  origination <- either throwM pure . typeCheckingWith tcOpts $
    mkOrigination <$> typeCheckContractAndStorage uContract uStorage
  (_, newSt) <- runExecutorMWithDB maybeNow maybeLevel dbPath (RemainingSteps maxSteps) verbose ! #dryRun dryRun $ do
    -- Here we are safe to bypass executeGlobalOperations for origination,
    -- since origination can't generate more operations.
    addr <- executeGlobalOrigination origination
    let transferOp = TransferOp $ TransferOperation addr txData 1
    executeGlobalOperations tcOpts [transferOp]
    getContractStorage addr
  return newSt
  where
    -- We hardcode some random key hash here as delegate to make sure that:
    -- 1. Contract's address won't clash with already originated one (because
    -- it may have different storage value which may be confusing).
    -- 2. If one uses this functionality twice with the same contract and
    -- other data, the contract will have the same address.
    delegate =
      either (error . mappend "runContract can't parse delegate: " . pretty) id $
      parseKeyHash "tz1YCABRTa6H8PLKx2EtDWeCGPaKxUhNgv47"
    mkOrigination (SomeContractAndStorage contract storage) = OriginationOperation
      { ooOriginator = genesisAddress
      , ooDelegate = Just delegate
      , ooBalance = initBalance
      , ooStorage = storage
      , ooContract = contract
      , ooCounter = 0
      }

    getContractStorage :: Address -> ExecutorM SomeStorage
    getContractStorage addr = do
      addrs <- use (esGState . gsAddressesL)
      case addrs ^. at addr of
        Nothing -> error $ pretty addr <> " is unknown"
        Just (ASSimple {}) -> error $ pretty addr <> " is a simple address"
        Just (ASContract (ContractState{..})) -> return $ SomeStorage csStorage

-- | Send a transaction to given address with given parameters.
transfer ::
     Maybe Timestamp
  -> Maybe Natural
  -> Word64
  -> FilePath
  -> TypeCheckOptions
  -> Address
  -> TxData
  -> "verbose" :! Bool
  -> "dryRun" :? Bool
  -> IO ()
transfer maybeNow maybeLevel maxSteps dbPath tcOpts destination txData verbose dryRun = do
  void $ runExecutorMWithDB maybeNow maybeLevel dbPath (RemainingSteps maxSteps) verbose dryRun $
    executeGlobalOperations tcOpts [TransferOp $ TransferOperation destination txData 0]

----------------------------------------------------------------------------
-- Executor
----------------------------------------------------------------------------

-- | A monad in which contract executor runs.
type ExecutorM =
  ReaderT ExecutorEnv
    (StateT ExecutorState
      (Except ExecutorError)
    )

-- | Run some executor action, returning its result and final executor state in 'ExecutorRes'.
--
-- The action has access to the hash of currently executed global operation, in order to construct
-- addresses of originated contracts. It is expected that the action uses @#isGlobalOp :! True@
-- to specify this hash. Otherwise it is initialized with 'error'.
runExecutorM
  :: Timestamp
  -> Natural
  -> RemainingSteps
  -> GState
  -> ExecutorM a
  -> Either ExecutorError (ExecutorRes, a)
runExecutorM now level remainingSteps gState action =
  fmap preResToRes
    $ runExcept
    $ runStateT (runReaderT action $ ExecutorEnv now level)
      initialState
  where
    initialOpHash = error "Initial OperationHash touched"

    initialState = ExecutorState
      { _esGState = gState
      , _esRemainingSteps = remainingSteps
      , _esSourceAddress = Nothing
      , _esLog = mempty
      , _esOperationHash = initialOpHash
      , _esPrevCounters = mempty
      }

    preResToRes :: (a, ExecutorState) -> (ExecutorRes, a)
    preResToRes (r, ExecutorState{..}) =
      ( ExecutorRes
          { _erGState = _esGState
          , _erUpdates = _esLog ^. elUpdates
          , _erInterpretResults = _esLog ^. elInterpreterResults
          , _erRemainingSteps = _esRemainingSteps
          }
      , r
      )

-- | Run some executor action, reading state from the DB on disk.
--
-- Unless @dryRun@ is @False@, the final state is written back to the disk.
--
-- If the executor fails with 'ExecutorError' it will be thrown as an exception.
runExecutorMWithDB
  :: Maybe Timestamp
  -> Maybe Natural
  -> FilePath
  -> RemainingSteps
  -> "verbose" :! Bool
  -> "dryRun" :? Bool
  -> ExecutorM a
  -> IO (ExecutorRes, a)
runExecutorMWithDB maybeNow maybeLevel dbPath remainingSteps
  (N verbose)
  (argDef #dryRun False -> dryRun)
  action = do
  gState <- readGState dbPath
  now <- maybe getCurrentTime pure maybeNow
  let level = fromMaybe 0 maybeLevel
  (res@ExecutorRes{..}, a) <- either throwM pure $ runExecutorM now level remainingSteps gState action

  unless dryRun $
    writeGState dbPath _erGState

  mapM_ printInterpretResult _erInterpretResults
  when (verbose && not (null _erUpdates)) $ do
    fmtLn $ nameF "Updates" (blockListF _erUpdates)
    putTextLn $ "Remaining gas: " <> pretty _erRemainingSteps <> "."

  return (res, a)
  where
    printInterpretResult
      :: (Address, InterpretResult) -> IO ()
    printInterpretResult (addr, InterpretResult {..}) = do
      putTextLn $ "Executed contract " <> pretty addr
      case iurOps of
        [] -> putTextLn "It didn't return any operations."
        _ -> fmt $ nameF "It returned operations" (blockListF iurOps)
      putTextLn $
        "It returned storage: " <> pretty (untypeValue iurNewStorage) <> "."
      let MorleyLogs logs = iurMorleyLogs
      unless (null logs) $ do
        putTextLn "And produced logs:"
        mapM_ putTextLn logs
      putTextLn "" -- extra break line to separate logs from two sequence contracts

-- | Execute a list of global operations, discarding their results.
executeGlobalOperations
  :: TypeCheckOptions
  -> [ExecutorOp]
  -> ExecutorM ()
executeGlobalOperations tcOpts = mapM_ $ \op ->
  executeMany (#isGlobalOp :! True) [op]
  where
    -- | Execute a list of operations and additional operations they return, until there are none.
    executeMany :: "isGlobalOp" :! Bool -> [ExecutorOp] -> ExecutorM ()
    executeMany isGlobalOp = \case
        [] -> pass
        (op:opsTail) -> do
          case op of
            OriginateOp origination -> do
              void $ executeOrigination isGlobalOp origination
              executeMany (#isGlobalOp :! False) opsTail
            SetDelegateOp operation -> do
              executeDelegation isGlobalOp operation
              executeMany (#isGlobalOp :! False) opsTail
            TransferOp transferOperation -> do
              moreOps <- executeTransfer isGlobalOp tcOpts transferOperation
              executeMany (#isGlobalOp :! False) $ moreOps <> opsTail

-- | Execute a global origination operation.
executeGlobalOrigination :: OriginationOperation -> ExecutorM Address
executeGlobalOrigination = executeOrigination ! #isGlobalOp True

-- | Execute an origination operation.
executeOrigination
  :: "isGlobalOp" :! Bool
  -> OriginationOperation
  -> ExecutorM Address
executeOrigination (N isGlobalOp) origination@(OriginationOperation{..}) = do
  when isGlobalOp $ do
    beginGlobalOperation
    assign esOperationHash $ mkOriginationOperationHash origination

  checkOperationReplay $ OriginateOp origination

  opHash <- use esOperationHash

  gs <- use esGState

  -- Add big_map IDS to storage
  let bigMapCounter0 = gs ^. gsBigMapCounterL
  let (storageWithIds, bigMapCounter1) = runState (assignBigMapIds ooStorage) bigMapCounter0

  let contractState = ContractState ooBalance ooContract storageWithIds ooDelegate

  let originatorAddress = ooOriginator
  originatorBalance <- case gsAddresses gs ^. at originatorAddress of
    Nothing -> throwError (EEUnknownManager originatorAddress)
    Just (asBalance -> oldBalance)
      | oldBalance < ooBalance ->
        throwError $ EENotEnoughFunds originatorAddress oldBalance
      | otherwise ->
        -- Subtraction is safe because we have checked its
        -- precondition in guard.
        return $ oldBalance `unsafeSubMutez` ooBalance
  let
    address = mkContractAddress opHash ooCounter
    updates =
      catMaybes
        [ Just $ GSAddAddress address (ASContract contractState)
        , Just $ GSSetBalance originatorAddress originatorBalance
        , Just GSIncrementCounter
        , if bigMapCounter0 == bigMapCounter1
            then Nothing
            else Just $ GSSetBigMapCounter bigMapCounter1
        ]

  case applyUpdates updates gs of
    Left _ ->
      throwError $ EEAlreadyOriginated address contractState
    Right newGS -> do
      esGState .= newGS
      esLog <>= ExecutorLog updates []

      return address

-- | Execute delegation operation.
executeDelegation
  :: "isGlobalOp" :! Bool
  -> SetDelegateOperation
  -> ExecutorM ()
executeDelegation (N isGlobalOp) delegation@(SetDelegateOperation{..}) = do
  when isGlobalOp $ do
    beginGlobalOperation
    assign esOperationHash $ mkDelegationOperationHash delegation

  checkOperationReplay $ SetDelegateOp delegation

  gs <- use esGState

  let updates = [GSSetDelegate sdoContract sdoDelegate]
  case applyUpdates updates gs of
    Left err -> throwError $ EEFailedToApplyUpdates err
    Right newGS -> do
      esGState .= newGS
      esLog <>= ExecutorLog updates []

      return ()

-- | Execute a transfer operation.
executeTransfer
  :: "isGlobalOp" :! Bool
  -> TypeCheckOptions
  -> TransferOperation
  -> ExecutorM [ExecutorOp]
executeTransfer (N isGlobalOp) tcOpts transferOperation@(TransferOperation addr txData _) = do
    when isGlobalOp $
      beginGlobalOperation

    now <- view eeNow
    level <- view eeLevel
    gs <- use esGState
    remainingSteps <- use esRemainingSteps
    mSourceAddr <- use esSourceAddress

    let globalCounter = gsCounter gs
    let addresses = gsAddresses gs
    let senderAddr = tdSenderAddress txData
    let sourceAddr = fromMaybe senderAddr mSourceAddr
    let isZeroTransfer = tdAmount txData == zeroMutez

    checkOperationReplay $ TransferOp transferOperation

    when (badParamToImplicitAccount addr $ tdParameter txData) $
      throwError $ EEWrongParameterType addr

    -- Transferring 0 XTZ to a key address is prohibited.
    when (isZeroTransfer && isKeyAddress addr) $
      throwError $ EEZeroTransaction addr
    mDecreaseSenderBalance <- case (isZeroTransfer, addresses ^. at senderAddr) of
      (True, _) -> pure Nothing
      (False, Nothing) -> throwError $ EEUnknownSender senderAddr
      (False, Just (asBalance -> balance))
        | balance < tdAmount txData ->
          throwError $ EENotEnoughFunds senderAddr balance
        | otherwise ->
          -- Subtraction is safe because we have checked its
          -- precondition in guard.
          return $ Just $ GSSetBalance senderAddr (balance `unsafeSubMutez` tdAmount txData)
    when (not (isKeyAddress senderAddr) && isGlobalOp && not isZeroTransfer) $
      throwError $ EETransactionFromContract senderAddr $ tdAmount txData
    let onlyUpdates updates = return (updates, [], Nothing, remainingSteps)
    (otherUpdates, sideEffects, maybeInterpretRes :: Maybe InterpretResult, newRemSteps)
        <- case (addresses ^. at addr, addr) of
      (Nothing, ContractAddress _) ->
        throwError $ EEUnknownContract addr
      (Nothing, KeyAddress _) -> do
        let
          transferAmount = tdAmount txData
          addrState = ASSimple transferAmount
          upd = GSAddAddress addr addrState
        onlyUpdates [upd]
      (Just (ASSimple oldBalance), _) -> do
        -- can't overflow if global state is correct (because we can't
        -- create money out of nowhere)
        let
          newBalance = oldBalance `unsafeAddMutez` tdAmount txData
          upd = GSSetBalance addr newBalance
        onlyUpdates [upd]
      (Just (ASContract (ContractState {..})), _) -> do
        let
          existingContracts = extractAllContracts gs
          -- can't overflow if global state is correct (because we can't
          -- create money out of nowhere)
          newBalance = csBalance `unsafeAddMutez` tdAmount txData
          epName = tdEntrypoint txData

        T.MkEntrypointCallRes _ (epc :: EntrypointCallT cp epArg)
          <- T.mkEntrypointCall epName (T.cParamNotes csContract)
             & maybe (throwError $ EEUnknownEntrypoint epName) pure

        -- If the parameter has already been typechecked, simply check if
        -- its type matches the contract's entrypoint's type.
        -- Otherwise (e.g. if it was parsed from stdin via the CLI),
        -- we need to typecheck the parameter.
        typedParameter <-
          case tdParameter txData of
            TxTypedParam (typedVal :: T.Value t) -> do
              T.castM @t @epArg typedVal (throwError ... EEUnexpectedParameterType addr)
            TxUntypedParam untypedVal ->
              liftEither $ first (EEIllTypedParameter addr) $ typeCheckingWith tcOpts $
                typeVerifyParameter @epArg existingContracts untypedVal

        let bigMapCounter0 = gs ^. gsBigMapCounterL
        let (typedParameterWithIds, bigMapCounter1) = runState (assignBigMapIds typedParameter) bigMapCounter0

        -- I'm not entirely sure why we need to pattern match on `()` here,
        -- but, if we don't, we get a compiler error that I suspect is somehow related
        -- to the existential types we're matching on a few lines above.
        --
        -- • Couldn't match type ‘a0’
        --                  with ‘(InterpretResult, RemainingSteps, [Operation], [GStateUpdate])’
        --     ‘a0’ is untouchable inside the constraints: StorageScope st1
        () <- when isGlobalOp $
          esOperationHash .= mkTransferOperationHash
            addr
            typedParameterWithIds
            (tdEntrypoint txData)
            (tdAmount txData)

        opHash <- use esOperationHash
        let
          contractEnv = ContractEnv
            { ceNow = now
            , ceMaxSteps = remainingSteps
            , ceBalance = newBalance
            , ceContracts = gsAddresses gs
            , ceSelf = addr
            , ceSource = sourceAddr
            , ceSender = senderAddr
            , ceAmount = tdAmount txData
            , ceVotingPowers = gsVotingPowers gs
            , ceChainId = gsChainId gs
            , ceOperationHash = Just opHash
            , ceLevel = level
            , ceInstrCallStack = def
            }

        iur@InterpretResult
          { iurOps = sideEffects
          , iurNewStorage = newValue
          , iurNewState = InterpreterState newRemainingSteps globalCounter2 bigMapCounter2
          }
          <- liftEither $ first (EEInterpreterFailed addr) $
             handleContractReturn $
                interpret
                  csContract
                  epc
                  typedParameterWithIds
                  csStorage
                  (gsCounter gs)
                  bigMapCounter1
                  contractEnv

        let
          updBalance
            | newBalance == csBalance = Nothing
            | otherwise = Just $ GSSetBalance addr newBalance
          updStorage
            | SomeValue newValue == SomeValue csStorage = Nothing
            | otherwise = Just $ GSSetStorageValue addr newValue
          updBigMapCounter
            | bigMapCounter0 == bigMapCounter2 = Nothing
            | otherwise = Just $ GSSetBigMapCounter bigMapCounter2
          updGlobalCounter
            | globalCounter == globalCounter2 = Nothing
            | otherwise = Just $ GSUpdateCounter globalCounter2
          updates = catMaybes
            [ updBalance
            , updStorage
            , updBigMapCounter
            , updGlobalCounter
            ]
        return (updates, sideEffects, Just iur, newRemainingSteps)

    let
      -- According to the reference implementation, counter is incremented for transfers as well.
      updates = (maybe id (:) mDecreaseSenderBalance otherUpdates) ++ [GSIncrementCounter]

    newGState <- liftEither $ first EEFailedToApplyUpdates $ applyUpdates updates gs

    esGState .= newGState
    esRemainingSteps .= newRemSteps
    esSourceAddress .= Just sourceAddr

    esLog <>= ExecutorLog updates (maybe mempty (one . (addr, )) maybeInterpretRes)

    return $ convertOp addr <$> sideEffects

----------------------------------------------------------------------------
-- Simple helpers
----------------------------------------------------------------------------

checkOperationReplay :: ExecutorOp -> ExecutorM ()
checkOperationReplay op = do
  let
    opCounter = op & \case
      OriginateOp OriginationOperation{..} -> ooCounter
      TransferOp TransferOperation{..} -> toCounter
      SetDelegateOp SetDelegateOperation{..} -> sdoCounter
  prevCounters <- use esPrevCounters
  when (opCounter `HS.member` prevCounters) $
    throwError $ EEOperationReplay op
  esPrevCounters <>= one opCounter

-- The argument is the address of the contract that generated this operation.
convertOp :: Address -> T.Operation -> ExecutorOp
convertOp interpretedAddr =
  \case
    OpTransferTokens tt ->
      case ttContract tt of
        T.VContract destAddress sepc ->
          let txData =
                TxData
                  { tdSenderAddress = interpretedAddr
                  , tdEntrypoint = T.sepcName sepc
                  , tdParameter = TxTypedParam (ttTransferArgument tt)
                  , tdAmount = ttAmount tt
                  }
              transferOperation =
                TransferOperation
                  { toDestination = destAddress
                  , toTxData = txData
                  , toCounter = ttCounter tt
                  }
          in TransferOp transferOperation
    OpSetDelegate T.SetDelegate{..} -> SetDelegateOp SetDelegateOperation
      { sdoContract = interpretedAddr
      , sdoDelegate = sdMbKeyHash
      , sdoCounter = sdCounter
      }
    OpCreateContract cc ->
      let origination = OriginationOperation
            { ooOriginator = ccOriginator cc
            , ooDelegate = ccDelegate cc
            , ooBalance = ccBalance cc
            , ooStorage = ccStorageVal cc
            , ooContract = ccContract cc
            , ooCounter = ccCounter cc
            }
       in OriginateOp origination

-- | Reset source address before executing a global operation.
beginGlobalOperation :: ExecutorM ()
beginGlobalOperation =
  esSourceAddress .= Nothing

-- | Return True if address is an implicit account yet the param is not Unit.
badParamToImplicitAccount :: Address -> TxParam -> Bool
badParamToImplicitAccount (ContractAddress _) _                       = False
badParamToImplicitAccount (KeyAddress _) (TxTypedParam T.VUnit)       = False
badParamToImplicitAccount (KeyAddress _) (TxUntypedParam U.ValueUnit) = False
badParamToImplicitAccount _ _                                         = True