# Nimbus - Binary compatibility on the host side of the EVMC API interface
#
# Copyright (c) 2019-2024 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.

{.push raises: [].}

when not declaredInScope(included_from_host_services):
  {.error: "Do not import this file directly, import host_services instead".}

import evmc/evmc, ./evmc_dynamic_loader

template toHost(p: evmc_host_context): TransactionHost =
  cast[TransactionHost](p)

proc accountExists(p: evmc_host_context, address: var evmc_address): c99bool {.cdecl.} =
  toHost(p).accountExists(address.fromEvmc)

proc getStorage(p: evmc_host_context, address: var evmc_address,
                key: var evmc_bytes32): evmc_bytes32
    {.cdecl.} =
  toHost(p).getStorage(address.fromEvmc, key.flip256.fromEvmc).toEvmc.flip256

proc setStorage(p: evmc_host_context, address: var evmc_address,
                key, value: var evmc_bytes32): evmc_storage_status
    {.cdecl.} =
  toHost(p).setStorage(address.fromEvmc, key.flip256.fromEvmc, value.flip256.fromEvmc)

proc getBalance(p: evmc_host_context,
                address: var evmc_address): evmc_uint256be {.cdecl.} =
    toHost(p).getBalance(address.fromEvmc).toEvmc.flip256

proc getCodeSize(p: evmc_host_context,
                 address: var evmc_address): csize_t {.cdecl.} =
    toHost(p).getCodeSize(address.fromEvmc)

proc getCodeHash(p: evmc_host_context,
                 address: var evmc_address): evmc_bytes32 {.cdecl.} =
    toHost(p).getCodeHash(address.fromEvmc).toEvmc

proc copyCode(p: evmc_host_context, address: var evmc_address, code_offset: csize_t,
              buffer_data: ptr byte, buffer_size: csize_t): csize_t {.cdecl.} =
    toHost(p).copyCode(address.fromEvmc, code_offset, buffer_data, buffer_size)

proc selfDestruct(p: evmc_host_context, address,
                  beneficiary: var evmc_address) {.cdecl.} =
  toHost(p).selfDestruct(address.fromEvmc, beneficiary.fromEvmc)

proc call(p: evmc_host_context, msg: var evmc_message): evmc_result
    {.cdecl.} =
  # This would contain `flip256`, but `call` is special.  The C stack usage
  # must be kept small for deeply nested EVM calls.  To ensure small stack,
  # `flip256` must be handled at `host_call_nested`, not here.
  toHost(p).call(msg)

proc getTxContext(p: evmc_host_context): evmc_tx_context {.cdecl.} =
  # This would contain `flip256`, but due to this result being cached in
  # `getTxContext`, it's better to do `flip256` when filling the cache.
  toHost(p).getTxContext()

proc getBlockHash(p: evmc_host_context, number: int64): evmc_bytes32
    {.cdecl.} =
  # TODO: `HostBlockNumber` is 256-bit unsigned.  It should be changed to match
  # EVMC which is more sensible.
  toHost(p).getBlockHash(number.uint64).toEvmc

proc emitLog(p: evmc_host_context, address: var evmc_address,
             data: ptr byte, data_size: csize_t,
             topics: ptr evmc_bytes32, topics_count: csize_t) {.cdecl.} =
  toHost(p).emitLog(address.fromEvmc, data, data_size,
                    cast[ptr HostTopic](topics), topics_count)

proc accessAccount(p: evmc_host_context,
                   address: var evmc_address): evmc_access_status {.cdecl.} =
  toHost(p).accessAccount(address.fromEvmc)

proc accessStorage(p: evmc_host_context, address: var evmc_address,
                   key: var evmc_bytes32): evmc_access_status {.cdecl.} =
  toHost(p).accessStorage(address.fromEvmc, key.flip256.fromEvmc)

proc getTransientStorage(p: evmc_host_context, address: var evmc_address,
                key: var evmc_bytes32): evmc_bytes32
    {.cdecl.} =
  toHost(p).getTransientStorage(address.fromEvmc, key.flip256.fromEvmc).toEvmc.flip256

proc setTransientStorage(p: evmc_host_context, address: var evmc_address,
                key, value: var evmc_bytes32) {.cdecl.} =
  toHost(p).setTransientStorage(address.fromEvmc, key.flip256.fromEvmc, value.flip256.fromEvmc)

let hostInterface = evmc_host_interface(
  account_exists: accountExists,
  get_storage:    getStorage,
  set_storage:    setStorage,
  get_balance:    getBalance,
  get_code_size:  getCodeSize,
  get_code_hash:  getCodeHash,
  copy_code:      copyCode,
  selfdestruct:   selfDestruct,
  call:           call,
  get_tx_context: getTxContext,
  get_block_hash: getBlockHash,
  emit_log:       emitLog,
  access_account: accessAccount,
  access_storage: accessStorage,
  get_transient_storage: getTransientStorage,
  set_transient_storage: setTransientStorage,
)

proc evmcExecComputation*(host: TransactionHost): EvmcResult =
  host.showCallEntry(host.msg)

  let vm = evmcLoadVMCached()
  if vm.isNil:
    warn "No EVM"
    # Nim defaults are fine for all other fields in the result object.
    result = EvmcResult(status_code: EVMC_INTERNAL_ERROR)
    host.showCallReturn(result)
    return

  let hostContext = cast[evmc_host_context](host)
  host.hostInterface = hostInterface.unsafeAddr

  # Without `{.gcsafe.}:` here, the call via `vm.execute` results in a Nim
  # compile-time error in a far away function.  Starting here, a cascade of
  # warnings takes place: "Warning: '...' is not GC-safe as it performs an
  # indirect call here [GCUnsafe2]", then a list of "Warning: '...' is not
  # GC-safe as it calls '...'" at each function up the call stack, to a high
  # level function `persistBlocks` where it terminates compilation as an error
  # instead of a warning.
  #
  # It is tempting to annotate all EVMC API functions with `{.cdecl, gcsafe.}`,
  # overriding the function signatures from the Nim EVMC module.  Perhaps we
  # will do that, though it's conceptually dubious, as the two sides of the
  # EVMC ABI live in different GC worlds (when loaded as a shared library with
  # its own Nim runtime), very similar to calling between threads.
  #
  # TODO: But wait: Why does the Nim EVMC test program compile fine without
  # any `gcsafe`, even with `--threads:on`?
  {.gcsafe.}:
    result = vm.execute(vm, hostInterface.unsafeAddr, hostContext,
                          evmc_revision(host.vmState.fork.ord), host.msg,
                          if host.code.len > 0: host.code[0].unsafeAddr
                          else: nil,
                          host.code.len.csize_t)

  host.showCallReturn(result)

# This code assumes fields, methods and types of ABI version 12, and must be
# checked for compatibility if the `import evmc/evmc` major version is updated.
when EVMC_ABI_VERSION != 12:
  {.error: ("This code assumes EVMC_ABI_VERSION 12;" &
            " update the code to use EVMC_ABI_VERSION " & $EVMC_ABI_VERSION).}