///===--- DistributedActor.cpp - Distributed actor implementation ----------===///
///
/// This source file is part of the Swift.org open source project
///
/// Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
/// Licensed under Apache License v2.0 with Runtime Library Exception
///
/// See https:///swift.org/LICENSE.txt for license information
/// See https:///swift.org/CONTRIBUTORS.txt for the list of Swift project authors
///
///===----------------------------------------------------------------------===///
///
/// The implementation of Swift distributed actors.
///
///===----------------------------------------------------------------------===///

#include "swift/ABI/Task.h"
#include "swift/ABI/Actor.h"
#include "swift/ABI/Metadata.h"
#include "swift/Runtime/AccessibleFunction.h"
#include "swift/Runtime/Concurrency.h"

using namespace swift;

static const AccessibleFunctionRecord *
findDistributedAccessor(const char *targetNameStart, size_t targetNameLength) {
  if (auto *func = runtime::swift_findAccessibleFunction(targetNameStart,
                                                         targetNameLength)) {
    assert(func->Flags.isDistributed());
    return func;
  }
  return nullptr;
}

/// Find an accessible function record given a concrete actor type we're
/// attempting to make the call on, and the remote call method identifier.
static const AccessibleFunctionRecord *findDistributedProtocolMethodAccessor(
    bool findConcreteWitness, const char *targetActorTypeNameStart,
    size_t targetActorTypeNameLength, const char *targetNameStart,
    size_t targetNameLength) {
  // Find using just the method identifier;
  // This will work if the call is a concrete method identifier
  if (auto *func = runtime::swift_findAccessibleFunctionForConcreteType(
          findConcreteWitness, targetActorTypeNameStart,
          targetActorTypeNameLength, targetNameStart, targetNameLength)) {
    assert(func->Flags.isDistributed());
    return func;
  }

  return nullptr;
}

/// Given the presence of protocol witness distributed invocation targets,
/// obtain a concrete target name.
///
/// A distributed target can be identified by a protocol method name:
/// ```
/// protocol WorkerProtocol {
///   associatedtype Ret
///   distributed func func test() -> Ret
/// }
/// ```
///
/// So the remote call identifier may be "WorkerProtocol.test", however in order
/// to perform the invocation on a concrete target actor, we need to obtain
/// the concrete function we are about to invoke -- not least because of
/// its generic context details.
///
/// A concrete type on the server may be:
///
/// ```
/// distributed actor WorkerImpl: WorkerProtocol {
///   distributed func func test() -> String { "Hello" }
/// }
/// ```
///
/// Thus this method allows mapping the "protocol method identifier" and
/// concrete actor name, into the target witness name.
///
/// This way the generic context and other concrete information may be obtained
/// in order to perform the call on the concrete `WorkerImpl` type.
SWIFT_CC(swift)
SWIFT_EXPORT_FROM(swiftDistributed)
TypeNamePair swift_distributed_getConcreteAccessibleWitnessName(
    DefaultActor *actor, const char *targetNameStart, size_t targetNameLength) {

  // TODO(distributed): Avoid mangling twice; we do it here and in `execute_`
  auto actorTy = swift_getObjectType(actor);
  auto actorTyNamePair = swift_getMangledTypeName(actorTy);
  std::string actorTyName = actorTyNamePair.data;

  auto accessor = findDistributedProtocolMethodAccessor(
      /*findConcreteWitness=*/true, actorTyNamePair.data,
      actorTyNamePair.length, targetNameStart, targetNameLength);

  if (!accessor) {
    return {"", 0};
  }

  auto concreteNameData = accessor->Name.get();
  auto concreteNameLength = strlen(accessor->Name.get());
  return {concreteNameData, concreteNameLength};
}

SWIFT_CC(swift)
SWIFT_EXPORT_FROM(swiftDistributed)
void *swift_distributed_getGenericEnvironmentForConcreteActor(
    DefaultActor *actor, const char *targetNameStart, size_t targetNameLength) {

  // TODO(distributed): Avoid mangling  twice; we do it here and in `execute_`
  auto actorTy = swift_getObjectType(actor);
  auto actorTyNamePair = swift_getMangledTypeName(actorTy);

  auto *accessor = findDistributedProtocolMethodAccessor(
      /*findConcreteWitness=*/true, actorTyNamePair.data,
      actorTyNamePair.length, targetNameStart, targetNameLength);
  if (!accessor) {
    return nullptr;
  }

  return accessor->GenericEnvironment.get();
}

SWIFT_CC(swift)
SWIFT_EXPORT_FROM(swiftDistributed)
void *swift_distributed_getGenericEnvironment(const char *targetNameStart,
                                              size_t targetNameLength) {
  auto *accessor = findDistributedAccessor(targetNameStart, targetNameLength);
  return accessor ? accessor->GenericEnvironment.get() : nullptr;
}

/// func _executeDistributedTarget<D: DistributedTargetInvocationDecoder>(
///    on: AnyObject,
///    _ targetName: UnsafePointer<UInt8>,
///    _ targetNameLength: UInt,
///    argumentDecoder: inout D,
///    argumentTypes: UnsafeBufferPointer<Any.Type>,
///    resultBuffer: Builtin.RawPointer,
///    substitutions: UnsafeRawPointer?,
///    witnessTables: UnsafeRawPointer?,
///    numWitnessTables: UInt
/// ) async throws
using TargetExecutorSignature =
    AsyncSignature<void(/*on=*/DefaultActor *, // FIXME(distributed): Make this
                                               // accept AnyObject and not
                                               // witness tables
                        /*targetName=*/const char *, /*targetNameSize=*/size_t,
                        /*argumentDecoder=*/HeapObject *,
                        /*argumentTypes=*/const Metadata *const *,
                        /*resultBuffer=*/void *,
                        /*substitutions=*/void *,
                        /*witnessTables=*/void **,
                        /*numWitnessTables=*/size_t,
                        /*decoderType=*/Metadata *,
                        /*actorType=*/Metadata *,
                        /*decoderWitnessTable=*/void **,
                        /*distributedActorWitnessTable=*/void **),
                   /*throws=*/true>;

SWIFT_CC(swiftasync)
SWIFT_EXPORT_FROM(swiftDistributed)
TargetExecutorSignature::FunctionType swift_distributed_execute_target;

/// Accessor takes:
///   - an async context
///   - an argument decoder as an instance of type conforming to `InvocationDecoder`
///   - a list of all argument types (with substitutions applied)
///   - a result buffer as a raw pointer
///   - a list of substitutions
///   - a list of witness tables
///   - a number of witness tables in the buffer
///   - a reference to an actor to execute method on.
///   - a type of the argument decoder
///   - a witness table associated with argument decoder value
using DistributedAccessorSignature =
    AsyncSignature<void(/*argumentDecoder=*/HeapObject *,
                        /*argumentTypes=*/const Metadata *const *,
                        /*resultBuffer=*/void *,
                        /*substitutions=*/void *,
                        /*witnessTables=*/void **,
                        /*numWitnessTables=*/size_t,
                        /*actor=*/HeapObject *,
                        /*decoderType=*/Metadata *,
                        /*actorType=*/Metadata *,
                        /*decoderWitnessTable=*/void **,
                        /*actorWitnessTable=*/void **),
                   /*throws=*/true>;

SWIFT_CC(swiftasync)
static DistributedAccessorSignature::ContinuationType
    swift_distributed_execute_target_resume;

SWIFT_CC(swiftasync)
static void swift_distributed_execute_target_resume(
    SWIFT_ASYNC_CONTEXT AsyncContext *context,
    SWIFT_CONTEXT SwiftError *error) {
  auto parentCtx = context->Parent;
  auto resumeInParent =
      reinterpret_cast<TargetExecutorSignature::ContinuationType *>(
          parentCtx->ResumeParent);
  swift_task_dealloc(context);
  // See `swift_distributed_execute_target` - `parentCtx` in this case
  // is `callContext` which should be completely transparent on resume.
  return resumeInParent(parentCtx, error);
}

SWIFT_CC(swift) SWIFT_RUNTIME_STDLIB_INTERNAL
SwiftError* swift_distributed_makeDistributedTargetAccessorNotFoundError();

SWIFT_CC(swiftasync)
void swift_distributed_execute_target(
    SWIFT_ASYNC_CONTEXT AsyncContext *callerContext, DefaultActor *actor,
    const char *targetNameStart, size_t targetNameLength,
    HeapObject *argumentDecoder, const Metadata *const *argumentTypes,
    void *resultBuffer, void *substitutions, void **witnessTables,
    size_t numWitnessTables, Metadata *decoderType, Metadata *actorType,
    void **decoderWitnessTable, void **actorWitnessTable) {
  std::string targetName(targetNameStart, targetNameLength);

  auto actorTy = swift_getObjectType(actor);
  auto actorTyNamePair = swift_getMangledTypeName(actorTy);

  auto *accessor = findDistributedProtocolMethodAccessor(
      /*findConcreteWitness=*/false,
      actorTyNamePair.data, actorTyNamePair.length,
      targetNameStart, targetNameLength);

  if (!accessor) {
    SwiftError *error =
        swift_distributed_makeDistributedTargetAccessorNotFoundError();
    auto resumeInParent =
        reinterpret_cast<TargetExecutorSignature::ContinuationType *>(
            callerContext->ResumeParent);
    resumeInParent(callerContext, error);
    return;
  }

  auto *asyncFnPtr = reinterpret_cast<
      const AsyncFunctionPointer<DistributedAccessorSignature> *>(
      accessor->Function.get());
  assert(asyncFnPtr && "no function pointer for distributed_execute_target");

  DistributedAccessorSignature::FunctionType *accessorEntry =
      asyncFnPtr->Function.get();

  AsyncContext *calleeContext = reinterpret_cast<AsyncContext *>(
      swift_task_alloc(asyncFnPtr->ExpectedContextSize));

  calleeContext->Parent = callerContext;
  calleeContext->ResumeParent = reinterpret_cast<TaskContinuationFunction *>(
      swift_distributed_execute_target_resume);

  accessorEntry(calleeContext,
                argumentDecoder,
                argumentTypes,
                resultBuffer,
                substitutions,
                witnessTables,
                numWitnessTables,
                actor,
                decoderType,
                actorType,
                decoderWitnessTable,
                actorWitnessTable);
}