# Nimbus
# Copyright (c) 2018-2023 Status Research & Development GmbH
# Licensed under either of
#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
#    http://www.apache.org/licenses/LICENSE-2.0)
#  * MIT license ([LICENSE-MIT](LICENSE-MIT) or
#    http://opensource.org/licenses/MIT)
# at your option. This file may not be copied, modified, or distributed except
# according to those terms.

const
  # help with low memory when compiling selectVM() function
  lowmem {.intdefine.}: int = 0
  lowMemoryCompileTime {.used.} = lowmem > 0

import
  std/[macros, strformat],
  pkg/[chronicles, chronos, stew/byteutils],
  ".."/[constants, db/accounts_cache],
  "."/[code_stream, computation],
  "."/[message, precompiles, state, types],
  ./async/operations,
  ./interpreter/[op_dispatcher, gas_costs]

{.push raises: [].}

logScope:
  topics = "vm opcode"

# ------------------------------------------------------------------------------
# Private functions
# ------------------------------------------------------------------------------

const
  supportedOS = defined(windows) or defined(linux) or defined(macosx)
  optimizationCondition = not lowMemoryCompileTime and defined(release) and supportedOS

when optimizationCondition:
  # this is a top level pragma since nim 1.6.16
  {.optimization: speed.}

proc selectVM(c: Computation, fork: EVMFork, shouldPrepareTracer: bool)
    {.gcsafe, raises: [CatchableError].} =
  ## Op code execution handler main loop.
  var desc: Vm2Ctx
  desc.cpt = c

  # It's important not to re-prepare the tracer after
  # an async operation, only after a call/create.
  #
  # That is, tracingEnabled is checked in many places, and
  # indicates something like, "Do we want tracing to be
  # enabled?", whereas shouldPrepareTracer is more like,
  # "Are we at a spot right now where we want to re-initialize
  # the tracer?"
  if c.tracingEnabled and shouldPrepareTracer:
    c.prepareTracer()

  while true:
    c.instr = c.code.next()

    # Note Mamy's observation in opTableToCaseStmt() from original VM
    # regarding computed goto
    #
    # ackn:
    #   #{.computedGoto.}
    #   # computed goto causing stack overflow, it consumes a lot of space
    #   # we could use manual jump table instead
    #   # TODO lots of macro magic here to unravel, with chronicles...
    #   # `c`.logger.log($`c`.stack & "\n\n", fgGreen)
    when not lowMemoryCompileTime:
      when defined(release):
        #
        # FIXME: OS case list below needs to be adjusted
        #
        when defined(windows):
          when defined(cpu64):
            {.warning: "*** Win64/VM2 handler switch => computedGoto".}
            {.computedGoto.}
          else:
            # computedGoto not compiling on github/ci (out of memory) -- jordan
            {.warning: "*** Win32/VM2 handler switch => optimisation disabled".}
            # {.computedGoto.}

        elif defined(linux):
          when defined(cpu64):
            {.warning: "*** Linux64/VM2 handler switch => computedGoto".}
            {.computedGoto.}
          else:
            {.warning: "*** Linux32/VM2 handler switch => computedGoto".}
            {.computedGoto.}

        elif defined(macosx):
          when defined(cpu64):
            {.warning: "*** MacOs64/VM2 handler switch => computedGoto".}
            {.computedGoto.}
          else:
            {.warning: "*** MacOs32/VM2 handler switch => computedGoto".}
            {.computedGoto.}

        else:
          {.warning: "*** Unsupported OS => no handler switch optimisation".}

      genOptimisedDispatcher(fork, c.instr, desc)

    else:
      {.warning: "*** low memory compiler mode => program will be slow".}

      genLowMemDispatcher(fork, c.instr, desc)

proc beforeExecCall(c: Computation) =
  c.snapshot()
  if c.msg.kind == EVMC_CALL:
    c.vmState.mutateStateDB:
      db.subBalance(c.msg.sender, c.msg.value)
      db.addBalance(c.msg.contractAddress, c.msg.value)

proc afterExecCall(c: Computation) =
  ## Collect all of the accounts that *may* need to be deleted based on EIP161
  ## https://github.com/ethereum/EIPs/blob/master/EIPS/eip-161.md
  ## also see: https://github.com/ethereum/EIPs/issues/716

  if c.isError or c.fork >= FkByzantium:
    if c.msg.contractAddress == ripemdAddr:
      # Special case to account for geth+parity bug
      c.vmState.stateDB.ripemdSpecial()

  if c.isSuccess:
    c.commit()
  else:
    c.rollback()

proc beforeExecCreate(c: Computation): bool
    {.gcsafe, raises: [ValueError].} =
  c.vmState.mutateStateDB:
    let nonce = db.getNonce(c.msg.sender)
    if nonce+1 < nonce:
      c.setError(&"Nonce overflow when sender={c.msg.sender.toHex} wants to create contract", false)
      return true
    db.setNonce(c.msg.sender, nonce+1)

    # We add this to the access list _before_ taking a snapshot.
    # Even if the creation fails, the access-list change should not be rolled
    # back EIP2929
    if c.fork >= FkBerlin:
      db.accessList(c.msg.contractAddress)

  c.snapshot()

  if c.vmState.readOnlyStateDB().hasCodeOrNonce(c.msg.contractAddress):
    # let blurb = c.msg.contractAddress.toHex -- notused
    c.setError("Address collision when creating contract address={blurb}", true)
    c.rollback()
    return true

  c.vmState.mutateStateDB:
    db.subBalance(c.msg.sender, c.msg.value)
    db.addBalance(c.msg.contractAddress, c.msg.value)
    db.clearStorage(c.msg.contractAddress)
    if c.fork >= FkSpurious:
      # EIP161 nonce incrementation
      db.incNonce(c.msg.contractAddress)

  return false

proc afterExecCreate(c: Computation)
    {.gcsafe, raises: [CatchableError].} =
  if c.isSuccess:
    # This can change `c.isSuccess`.
    c.writeContract()
    # Contract code should never be returned to the caller.  Only data from
    # `REVERT` is returned after a create.  Clearing in this branch covers the
    # right cases, particularly important with EVMC where it must be cleared.
    if c.output.len > 0:
      c.output = @[]

  if c.isSuccess:
    c.commit()
  else:
    c.rollback()


const
  MsgKindToOp: array[CallKind, Op] = [
    CALL,
    DELEGATECALL,
    CALLCODE,
    CREATE,
    CREATE2
  ]

func msgToOp(msg: Message): Op =
  if EVMC_STATIC in msg.flags:
    return STATICCALL
  MsgKindToOp[msg.kind]

proc beforeExec(c: Computation): bool
    {.gcsafe, raises: [ValueError].} =

  if c.msg.depth > 0:
    c.vmState.captureEnter(c,
        msgToOp(c.msg),
        c.msg.sender, c.msg.contractAddress,
        c.msg.data, c.msg.gas,
        c.msg.value)

  if not c.msg.isCreate:
    c.beforeExecCall()
    false
  else:
    c.beforeExecCreate()

proc afterExec(c: Computation)
    {.gcsafe, raises: [CatchableError].} =

  if not c.msg.isCreate:
    c.afterExecCall()
  else:
    c.afterExecCreate()

  if c.msg.depth > 0:
    let gasUsed = c.msg.gas - c.gasMeter.gasRemaining
    c.vmState.captureExit(c, c.output, gasUsed, c.errorOpt)

# ------------------------------------------------------------------------------
# Public functions
# ------------------------------------------------------------------------------

proc executeOpcodes*(c: Computation, shouldPrepareTracer: bool = true)
    {.gcsafe, raises: [].} =
  let fork = c.fork

  block:
    if c.continuation.isNil and c.execPrecompiles(fork):
      break

    try:
      let cont = c.continuation
      if not cont.isNil:
        c.continuation = nil
        cont()
      let nextCont = c.continuation
      if nextCont.isNil:
        # FIXME-Adam: I hate how convoluted this is. See also the comment in
        # op_dispatcher.nim. The idea here is that we need to call
        # traceOpCodeEnded at the end of the opcode (and only if there
        # hasn't been an exception thrown); otherwise we run into problems
        # if an exception (e.g. out of gas) is thrown during a continuation.
        # So this code says, "If we've just run a continuation, but there's
        # no *subsequent* continuation, then the opcode is done."
        if c.tracingEnabled and not(cont.isNil) and nextCont.isNil:
          c.traceOpCodeEnded(c.instr, c.opIndex)
        case c.instr
        of Return, Revert, SelfDestruct: # FIXME-Adam: HACK, fix this in a clean way; I think the idea is that these are the ones from the "always break" case in op_dispatcher
          discard
        else:
          c.selectVM(fork, shouldPrepareTracer)
      else:
        # Return up to the caller, which will run the async operation or child
        # and then call this proc again.
        discard
    except CatchableError as e:
      let
        msg = e.msg
        depth = $(c.msg.depth + 1) # plus one to match tracer depth, and avoid confusion
      c.setError("Opcode Dispatch Error: " & msg & ", depth=" & depth, true)

  if c.isError() and c.continuation.isNil:
    if c.tracingEnabled: c.traceError()

when vm_use_recursion:
  # Recursion with tiny stack frame per level.
  proc execCallOrCreate*(c: Computation)
      {.gcsafe, raises: [CatchableError].} =
    defer: c.dispose()
    if c.beforeExec():
      return
    c.executeOpcodes()
    while not c.continuation.isNil:
      # If there's a continuation, then it's because there's either
      # a child (i.e. call or create) or a pendingAsyncOperation.
      if not c.pendingAsyncOperation.isNil:
        let p = c.pendingAsyncOperation
        c.pendingAsyncOperation = nil
        doAssert(p.finished(), "In synchronous mode, every async operation should be an already-resolved Future.")
        c.executeOpcodes(false)
      else:
        when evmc_enabled:
          c.res = c.host.call(c.child[])
        else:
          execCallOrCreate(c.child)
        c.child = nil
        c.executeOpcodes()
    c.afterExec()

else:
  proc execCallOrCreate*(cParam: Computation)
      {.gcsafe, raises: [CatchableError].} =
    var (c, before, shouldPrepareTracer) = (cParam, true, true)
    defer:
      while not c.isNil:
        c.dispose()
        c = c.parent

    # No actual recursion, but simulate recursion including before/after/dispose.
    while true:
      while true:
        if before and c.beforeExec():
          break
        c.executeOpcodes(shouldPrepareTracer)
        if c.continuation.isNil:
          c.afterExec()
          break
        if not c.pendingAsyncOperation.isNil:
          before = false
          shouldPrepareTracer = false
          let p = c.pendingAsyncOperation
          c.pendingAsyncOperation = nil
          doAssert(p.finished(), "In synchronous mode, every async operation should be an already-resolved Future.")
        else:
          (before, shouldPrepareTracer, c.child, c, c.parent) = (true, true, nil.Computation, c.child, c)
      if c.parent.isNil:
        break
      c.dispose()
      (before, shouldPrepareTracer, c.parent, c) = (false, true, nil.Computation, c.parent)

# FIXME-duplicatedForAsync
#
# In the long run I'd like to make some clever macro/template to
# eliminate the duplication between the synchronous and
# asynchronous versions. But for now let's stick with this for
# simplicity.
#
# Also, I've based this on the recursive one (above), which I think
# is okay because the "async" pragma is going to rewrite this whole
# thing to use callbacks anyway. But maybe I'm wrong? It isn't hard
# to write the async version of the iterative one, but this one is
# a bit shorter and feels cleaner, so if it works just as well I'd
# rather use this one. --Adam
proc asyncExecCallOrCreate*(c: Computation): Future[void] {.async.} =
  defer: c.dispose()

  await ifNecessaryGetCode(c.vmState, c.msg.contractAddress)

  if c.beforeExec():
    return
  c.executeOpcodes()
  while not c.continuation.isNil:
    # If there's a continuation, then it's because there's either
    # a child (i.e. call or create) or a pendingAsyncOperation.
    if not c.pendingAsyncOperation.isNil:
      let p = c.pendingAsyncOperation
      c.pendingAsyncOperation = nil
      await p
      c.executeOpcodes(false)
    else:
      when evmc_enabled:
        # FIXME-asyncAndEvmc
        # Note that this is NOT async. I'm not sure how/whether I
        # can do EVMC asynchronously.
        c.res = c.host.call(c.child[])
      else:
        await asyncExecCallOrCreate(c.child)
      c.child = nil
      c.executeOpcodes()
  c.afterExec()

# ------------------------------------------------------------------------------
# End
# ------------------------------------------------------------------------------