/*
 *
 *    Copyright (c) 2020 Project CHIP Authors
 *    All rights reserved.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */

/**
 *    @file
 *      This file defines object for a CHIP IM Invoke Command Handler
 *
 */

#include "CommandHandler.h"
#include "InteractionModelEngine.h"
#include "RequiredPrivilege.h"
#include "messaging/ExchangeContext.h"

#include <access/AccessControl.h>
#include <app-common/zap-generated/cluster-objects.h>
#include <app/RequiredPrivilege.h>
#include <app/util/MatterCallbacks.h>
#include <credentials/GroupDataProvider.h>
#include <lib/core/TLVData.h>
#include <lib/core/TLVUtilities.h>
#include <lib/support/TypeTraits.h>
#include <platform/LockTracker.h>
#include <protocols/secure_channel/Constants.h>

namespace chip {
namespace app {
using Status = Protocols::InteractionModel::Status;

CommandHandler::CommandHandler(Callback * apCallback) : mExchangeCtx(*this), mpCallback(apCallback), mSuppressResponse(false) {}

CHIP_ERROR CommandHandler::AllocateBuffer()
{
    if (!mBufferAllocated)
    {
        mCommandMessageWriter.Reset();

        System::PacketBufferHandle commandPacket = System::PacketBufferHandle::New(chip::app::kMaxSecureSduLengthBytes);
        VerifyOrReturnError(!commandPacket.IsNull(), CHIP_ERROR_NO_MEMORY);

        mCommandMessageWriter.Init(std::move(commandPacket));
        ReturnErrorOnFailure(mInvokeResponseBuilder.Init(&mCommandMessageWriter));

        mInvokeResponseBuilder.SuppressResponse(mSuppressResponse);
        ReturnErrorOnFailure(mInvokeResponseBuilder.GetError());

        mInvokeResponseBuilder.CreateInvokeResponses();
        ReturnErrorOnFailure(mInvokeResponseBuilder.GetError());
        mBufferAllocated = true;
    }

    return CHIP_NO_ERROR;
}

void CommandHandler::OnInvokeCommandRequest(Messaging::ExchangeContext * ec, const PayloadHeader & payloadHeader,
                                            System::PacketBufferHandle && payload, bool isTimedInvoke)
{
    System::PacketBufferHandle response;
    Status status = Status::Failure;
    VerifyOrDieWithMsg(ec != nullptr, DataManagement, "Incoming exchange context should not be null");
    VerifyOrDieWithMsg(mState == State::Idle, DataManagement, "state should be Idle");

    // NOTE: we already know this is an InvokeCommand Request message because we explicitly registered with the
    // Exchange Manager for unsolicited InvokeCommand Requests.
    mExchangeCtx.Grab(ec);

    // Use the RAII feature, if this is the only Handle when this function returns, DecrementHoldOff will trigger sending response.
    // TODO: This is broken!  If something under here returns error, we will try
    // to SendCommandResponse(), and then our caller will try to send a status
    // response too.  Figure out at what point it's our responsibility to
    // handler errors vs our caller's.
    Handle workHandle(this);

    mExchangeCtx->WillSendMessage();
    status = ProcessInvokeRequest(std::move(payload), isTimedInvoke);
    if (status != Status::Success)
    {
        StatusResponse::Send(status, mExchangeCtx.Get(), false /*aExpectResponse*/);
        mSentStatusResponse = true;
    }

    mGoneAsync = true;
}

Status CommandHandler::ProcessInvokeRequest(System::PacketBufferHandle && payload, bool isTimedInvoke)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    System::PacketBufferTLVReader reader;
    TLV::TLVReader invokeRequestsReader;
    InvokeRequestMessage::Parser invokeRequestMessage;
    InvokeRequests::Parser invokeRequests;
    reader.Init(std::move(payload));
    VerifyOrReturnError(invokeRequestMessage.Init(reader) == CHIP_NO_ERROR, Status::InvalidAction);
#if CHIP_CONFIG_IM_PRETTY_PRINT
    invokeRequestMessage.PrettyPrint();
#endif

    VerifyOrReturnError(invokeRequestMessage.GetSuppressResponse(&mSuppressResponse) == CHIP_NO_ERROR, Status::InvalidAction);
    VerifyOrReturnError(invokeRequestMessage.GetTimedRequest(&mTimedRequest) == CHIP_NO_ERROR, Status::InvalidAction);
    VerifyOrReturnError(invokeRequestMessage.GetInvokeRequests(&invokeRequests) == CHIP_NO_ERROR, Status::InvalidAction);
    VerifyOrReturnError(mTimedRequest == isTimedInvoke, Status::UnsupportedAccess);
    invokeRequests.GetReader(&invokeRequestsReader);

    {
        // We don't support handling multiple commands but the protocol is ready to support it in the future, reject all of them and
        // IM Engine will send a status response.
        size_t commandCount = 0;
        TLV::Utilities::Count(invokeRequestsReader, commandCount, false /* recurse */);
        VerifyOrReturnError(commandCount == 1, Status::InvalidAction);
    }

    while (CHIP_NO_ERROR == (err = invokeRequestsReader.Next()))
    {
        VerifyOrReturnError(TLV::AnonymousTag() == invokeRequestsReader.GetTag(), Status::InvalidAction);
        CommandDataIB::Parser commandData;
        VerifyOrReturnError(commandData.Init(invokeRequestsReader) == CHIP_NO_ERROR, Status::InvalidAction);
        Status status = Status::Success;
        if (mExchangeCtx->IsGroupExchangeContext())
        {
            status = ProcessGroupCommandDataIB(commandData);
        }
        else
        {
            status = ProcessCommandDataIB(commandData);
        }
        if (status != Status::Success)
        {
            return status;
        }
    }

    // if we have exhausted this container
    if (CHIP_END_OF_TLV == err)
    {
        err = CHIP_NO_ERROR;
    }
    VerifyOrReturnError(err == CHIP_NO_ERROR, Status::InvalidAction);
    VerifyOrReturnError(invokeRequestMessage.ExitContainer() == CHIP_NO_ERROR, Status::InvalidAction);
    return Status::Success;
}

CHIP_ERROR CommandHandler::OnMessageReceived(Messaging::ExchangeContext * apExchangeContext, const PayloadHeader & aPayloadHeader,
                                             System::PacketBufferHandle && aPayload)
{
    ChipLogDetail(DataManagement, "CommandHandler: Unexpected message type %d", aPayloadHeader.GetMessageType());
    StatusResponse::Send(Status::InvalidAction, mExchangeCtx.Get(), false /*aExpectResponse*/);
    return CHIP_ERROR_INVALID_MESSAGE_TYPE;
}

void CommandHandler::Close()
{
    mSuppressResponse = false;
    MoveToState(State::AwaitingDestruction);

    // We must finish all async work before we can shut down a CommandHandler. The actual CommandHandler MUST finish their work
    // in reasonable time or there is a bug. The only case for releasing CommandHandler without CommandHandler::Handle releasing its
    // reference is the stack shutting down, in which case Close() is not called. So the below check should always pass.
    VerifyOrDieWithMsg(mPendingWork == 0, DataManagement, "CommandHandler::Close() called with %u unfinished async work items",
                       static_cast<unsigned int>(mPendingWork));

    if (mpCallback)
    {
        mpCallback->OnDone(*this);
    }
}

void CommandHandler::IncrementHoldOff()
{
    mPendingWork++;
}

void CommandHandler::DecrementHoldOff()
{
    mPendingWork--;
    ChipLogDetail(DataManagement, "Decreasing reference count for CommandHandler, remaining %u",
                  static_cast<unsigned int>(mPendingWork));
    if (mPendingWork != 0)
    {
        return;
    }

    if (!mSentStatusResponse)
    {
        if (!mExchangeCtx)
        {
            ChipLogProgress(DataManagement, "Skipping command response: exchange context is null");
        }
        else if (!mExchangeCtx->IsGroupExchangeContext())
        {
            CHIP_ERROR err = SendCommandResponse();
            if (err != CHIP_NO_ERROR)
            {
                ChipLogError(DataManagement, "Failed to send command response: %" CHIP_ERROR_FORMAT, err.Format());
            }
        }
    }

    Close();
}

CHIP_ERROR CommandHandler::SendCommandResponse()
{
    System::PacketBufferHandle commandPacket;

    VerifyOrReturnError(mPendingWork == 0, CHIP_ERROR_INCORRECT_STATE);
    VerifyOrReturnError(mState == State::AddedCommand, CHIP_ERROR_INCORRECT_STATE);
    VerifyOrReturnError(mExchangeCtx, CHIP_ERROR_INCORRECT_STATE);

    ReturnErrorOnFailure(Finalize(commandPacket));
    ReturnErrorOnFailure(
        mExchangeCtx->SendMessage(Protocols::InteractionModel::MsgType::InvokeCommandResponse, std::move(commandPacket)));
    // The ExchangeContext is automatically freed here, and it makes mpExchangeCtx be temporarily dangling, but in
    // all cases, we are going to call Close immediately after this function, which nulls out mpExchangeCtx.

    MoveToState(State::CommandSent);

    return CHIP_NO_ERROR;
}

namespace {
// We use this when the sender did not actually provide a CommandFields struct,
// to avoid downstream consumers having to worry about cases when there is or is
// not a struct available.  We use an empty struct with anonymous tag, since we
// can't use a context tag at top level, and consumers should not care about the
// tag here).
constexpr uint8_t sNoFields[] = {
    CHIP_TLV_STRUCTURE(CHIP_TLV_TAG_ANONYMOUS),
    CHIP_TLV_END_OF_CONTAINER,
};
} // anonymous namespace

Status CommandHandler::ProcessCommandDataIB(CommandDataIB::Parser & aCommandElement)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    CommandPathIB::Parser commandPath;
    ConcreteCommandPath concretePath(0, 0, 0);
    TLV::TLVReader commandDataReader;

    // NOTE: errors may occur before the concrete command path is even fully decoded.

    err = aCommandElement.GetPath(&commandPath);
    VerifyOrReturnError(err == CHIP_NO_ERROR, Status::InvalidAction);

    err = commandPath.GetConcreteCommandPath(concretePath);
    VerifyOrReturnError(err == CHIP_NO_ERROR, Status::InvalidAction);

    {
        Status commandExists = mpCallback->CommandExists(concretePath);
        if (commandExists != Status::Success)
        {
            ChipLogDetail(DataManagement, "No command " ChipLogFormatMEI " in Cluster " ChipLogFormatMEI " on Endpoint 0x%x",
                          ChipLogValueMEI(concretePath.mCommandId), ChipLogValueMEI(concretePath.mClusterId),
                          concretePath.mEndpointId);
            return FallibleAddStatus(concretePath, commandExists) != CHIP_NO_ERROR ? Status::Failure : Status::Success;
        }
    }

    VerifyOrExit(mExchangeCtx && mExchangeCtx->HasSessionHandle(), err = CHIP_ERROR_INCORRECT_STATE);

    {
        Access::SubjectDescriptor subjectDescriptor = GetSubjectDescriptor();
        Access::RequestPath requestPath{ .cluster = concretePath.mClusterId, .endpoint = concretePath.mEndpointId };
        Access::Privilege requestPrivilege = RequiredPrivilege::ForInvokeCommand(concretePath);
        err                                = Access::GetAccessControl().Check(subjectDescriptor, requestPath, requestPrivilege);
        if (err != CHIP_NO_ERROR)
        {
            if (err != CHIP_ERROR_ACCESS_DENIED)
            {
                return FallibleAddStatus(concretePath, Status::Failure) != CHIP_NO_ERROR ? Status::Failure : Status::Success;
            }
            // TODO: when wildcard invokes are supported, handle them to discard rather than fail with status
            return FallibleAddStatus(concretePath, Status::UnsupportedAccess) != CHIP_NO_ERROR ? Status::Failure : Status::Success;
        }
    }

    if (CommandNeedsTimedInvoke(concretePath.mClusterId, concretePath.mCommandId) && !IsTimedInvoke())
    {
        // TODO: when wildcard invokes are supported, discard a
        // wildcard-expanded path instead of returning a status.
        return FallibleAddStatus(concretePath, Status::NeedsTimedInteraction) != CHIP_NO_ERROR ? Status::Failure : Status::Success;
    }

    if (CommandIsFabricScoped(concretePath.mClusterId, concretePath.mCommandId))
    {
        // SPEC: Else if the command in the path is fabric-scoped and there is no accessing fabric,
        // a CommandStatusIB SHALL be generated with the UNSUPPORTED_ACCESS Status Code.

        // Fabric-scoped commands are not allowed before a specific accessing fabric is available.
        // This is mostly just during a PASE session before AddNOC.
        if (GetAccessingFabricIndex() == kUndefinedFabricIndex)
        {
            // TODO: when wildcard invokes are supported, discard a
            // wildcard-expanded path instead of returning a status.
            return FallibleAddStatus(concretePath, Status::UnsupportedAccess) != CHIP_NO_ERROR ? Status::Failure : Status::Success;
        }
    }

    err = aCommandElement.GetFields(&commandDataReader);
    if (CHIP_END_OF_TLV == err)
    {
        ChipLogDetail(DataManagement,
                      "Received command without data for Endpoint=%u Cluster=" ChipLogFormatMEI " Command=" ChipLogFormatMEI,
                      concretePath.mEndpointId, ChipLogValueMEI(concretePath.mClusterId), ChipLogValueMEI(concretePath.mCommandId));
        commandDataReader.Init(sNoFields);
        err = commandDataReader.Next();
    }
    if (CHIP_NO_ERROR == err)
    {
        ChipLogDetail(DataManagement, "Received command for Endpoint=%u Cluster=" ChipLogFormatMEI " Command=" ChipLogFormatMEI,
                      concretePath.mEndpointId, ChipLogValueMEI(concretePath.mClusterId), ChipLogValueMEI(concretePath.mCommandId));
        SuccessOrExit(err = MatterPreCommandReceivedCallback(concretePath, GetSubjectDescriptor()));
        mpCallback->DispatchCommand(*this, concretePath, commandDataReader);
        MatterPostCommandReceivedCallback(concretePath, GetSubjectDescriptor());
    }

exit:
    if (err != CHIP_NO_ERROR)
    {
        return FallibleAddStatus(concretePath, Status::InvalidCommand) != CHIP_NO_ERROR ? Status::Failure : Status::Success;
    }

    // We have handled the error status above and put the error status in response, now return success status so we can process
    // other commands in the invoke request.
    return Status::Success;
}

Status CommandHandler::ProcessGroupCommandDataIB(CommandDataIB::Parser & aCommandElement)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    CommandPathIB::Parser commandPath;
    TLV::TLVReader commandDataReader;
    ClusterId clusterId;
    CommandId commandId;
    GroupId groupId;
    FabricIndex fabric;

    Credentials::GroupDataProvider::GroupEndpoint mapping;
    Credentials::GroupDataProvider * groupDataProvider = Credentials::GetGroupDataProvider();
    Credentials::GroupDataProvider::EndpointIterator * iterator;

    err = aCommandElement.GetPath(&commandPath);
    VerifyOrReturnError(err == CHIP_NO_ERROR, Status::InvalidAction);

    err = commandPath.GetGroupCommandPath(&clusterId, &commandId);
    VerifyOrReturnError(err == CHIP_NO_ERROR, Status::InvalidAction);

    groupId = mExchangeCtx->GetSessionHandle()->AsIncomingGroupSession()->GetGroupId();
    fabric  = GetAccessingFabricIndex();

    ChipLogDetail(DataManagement, "Received group command for Group=%u Cluster=" ChipLogFormatMEI " Command=" ChipLogFormatMEI,
                  groupId, ChipLogValueMEI(clusterId), ChipLogValueMEI(commandId));

    err = aCommandElement.GetFields(&commandDataReader);
    if (CHIP_END_OF_TLV == err)
    {
        ChipLogDetail(DataManagement,
                      "Received command without data for Group=%u Cluster=" ChipLogFormatMEI " Command=" ChipLogFormatMEI, groupId,
                      ChipLogValueMEI(clusterId), ChipLogValueMEI(commandId));
        commandDataReader.Init(sNoFields);
        err = commandDataReader.Next();
        VerifyOrReturnError(err == CHIP_NO_ERROR, Status::InvalidAction);
    }
    VerifyOrReturnError(err == CHIP_NO_ERROR, Status::Failure);

    // Per spec, we do the "is this a timed command?" check for every path, but
    // since all paths that fail it just get silently discarded we can do it
    // once up front and discard all the paths at once.  Ordering with respect
    // to ACL and command presence checks does not matter, because the behavior
    // is the same for all of them: ignore the path.
    if (CommandNeedsTimedInvoke(clusterId, commandId))
    {
        // Group commands are never timed.
        return Status::Success;
    }

    // No check for `CommandIsFabricScoped` unlike in `ProcessCommandDataIB()` since group commands
    // always have an accessing fabric, by definition.

    // Find which endpoints can process the command, and dispatch to them.
    iterator = groupDataProvider->IterateEndpoints(fabric);
    VerifyOrReturnError(iterator != nullptr, Status::Failure);

    while (iterator->Next(mapping))
    {
        if (groupId != mapping.group_id)
        {
            continue;
        }

        ChipLogDetail(DataManagement,
                      "Processing group command for Endpoint=%u Cluster=" ChipLogFormatMEI " Command=" ChipLogFormatMEI,
                      mapping.endpoint_id, ChipLogValueMEI(clusterId), ChipLogValueMEI(commandId));

        const ConcreteCommandPath concretePath(mapping.endpoint_id, clusterId, commandId);

        if (mpCallback->CommandExists(concretePath) != Status::Success)
        {
            ChipLogDetail(DataManagement, "No command " ChipLogFormatMEI " in Cluster " ChipLogFormatMEI " on Endpoint 0x%x",
                          ChipLogValueMEI(commandId), ChipLogValueMEI(clusterId), mapping.endpoint_id);

            continue;
        }

        {
            Access::SubjectDescriptor subjectDescriptor = GetSubjectDescriptor();
            Access::RequestPath requestPath{ .cluster = concretePath.mClusterId, .endpoint = concretePath.mEndpointId };
            Access::Privilege requestPrivilege = RequiredPrivilege::ForInvokeCommand(concretePath);
            err                                = Access::GetAccessControl().Check(subjectDescriptor, requestPath, requestPrivilege);
            if (err != CHIP_NO_ERROR)
            {
                // NOTE: an expected error is CHIP_ERROR_ACCESS_DENIED, but there could be other unexpected errors;
                // therefore, keep processing subsequent commands, and if any errors continue, those subsequent
                // commands will likewise fail.
                continue;
            }
        }
        if ((err = MatterPreCommandReceivedCallback(concretePath, GetSubjectDescriptor())) == CHIP_NO_ERROR)
        {
            TLV::TLVReader dataReader(commandDataReader);
            mpCallback->DispatchCommand(*this, concretePath, dataReader);
            MatterPostCommandReceivedCallback(concretePath, GetSubjectDescriptor());
        }
        else
        {
            ChipLogError(DataManagement,
                         "Error when calling MatterPreCommandReceivedCallback for Endpoint=%u Cluster=" ChipLogFormatMEI
                         " Command=" ChipLogFormatMEI " : %" CHIP_ERROR_FORMAT,
                         mapping.endpoint_id, ChipLogValueMEI(clusterId), ChipLogValueMEI(commandId), err.Format());
            continue;
        }
    }
    iterator->Release();
    return Status::Success;
}

CHIP_ERROR CommandHandler::AddStatusInternal(const ConcreteCommandPath & aCommandPath, const StatusIB & aStatus)
{
    ReturnErrorOnFailure(PrepareStatus(aCommandPath));
    CommandStatusIB::Builder & commandStatus = mInvokeResponseBuilder.GetInvokeResponses().GetInvokeResponse().GetStatus();
    StatusIB::Builder & statusIBBuilder      = commandStatus.CreateErrorStatus();
    ReturnErrorOnFailure(commandStatus.GetError());
    statusIBBuilder.EncodeStatusIB(aStatus);
    ReturnErrorOnFailure(statusIBBuilder.GetError());
    return FinishStatus();
}

void CommandHandler::AddStatus(const ConcreteCommandPath & aCommandPath, const Protocols::InteractionModel::Status aStatus,
                               const char * context)
{

    VerifyOrDie(FallibleAddStatus(aCommandPath, aStatus, context) == CHIP_NO_ERROR);
}

CHIP_ERROR CommandHandler::FallibleAddStatus(const ConcreteCommandPath & path, const Protocols::InteractionModel::Status status,
                                             const char * context)
{

    if (status != Status::Success)
    {
        if (context == nullptr)
        {
            context = "no additional context";
        }

        ChipLogError(DataManagement,
                     "Endpoint=%u Cluster=" ChipLogFormatMEI " Command=" ChipLogFormatMEI " status " ChipLogFormatIMStatus " (%s)",
                     path.mEndpointId, ChipLogValueMEI(path.mClusterId), ChipLogValueMEI(path.mCommandId),
                     ChipLogValueIMStatus(status), context);
    }

    return AddStatusInternal(path, StatusIB(status));
}

CHIP_ERROR CommandHandler::AddClusterSpecificSuccess(const ConcreteCommandPath & aCommandPath, ClusterStatus aClusterStatus)
{
    return AddStatusInternal(aCommandPath, StatusIB(Status::Success, aClusterStatus));
}

CHIP_ERROR CommandHandler::AddClusterSpecificFailure(const ConcreteCommandPath & aCommandPath, ClusterStatus aClusterStatus)
{
    return AddStatusInternal(aCommandPath, StatusIB(Status::Failure, aClusterStatus));
}

CHIP_ERROR CommandHandler::PrepareCommand(const ConcreteCommandPath & aCommandPath, bool aStartDataStruct)
{
    ReturnErrorOnFailure(AllocateBuffer());

    mInvokeResponseBuilder.Checkpoint(mBackupWriter);
    //
    // We must not be in the middle of preparing a command, or having prepared or sent one.
    //
    VerifyOrReturnError(mState == State::Idle, CHIP_ERROR_INCORRECT_STATE);
    MoveToState(State::Preparing);
    InvokeResponseIBs::Builder & invokeResponses = mInvokeResponseBuilder.GetInvokeResponses();
    InvokeResponseIB::Builder & invokeResponse   = invokeResponses.CreateInvokeResponse();
    ReturnErrorOnFailure(invokeResponses.GetError());

    CommandDataIB::Builder & commandData = invokeResponse.CreateCommand();
    ReturnErrorOnFailure(commandData.GetError());
    CommandPathIB::Builder & path = commandData.CreatePath();
    ReturnErrorOnFailure(commandData.GetError());
    ReturnErrorOnFailure(path.Encode(aCommandPath));
    if (aStartDataStruct)
    {
        ReturnErrorOnFailure(commandData.GetWriter()->StartContainer(TLV::ContextTag(CommandDataIB::Tag::kFields),
                                                                     TLV::kTLVType_Structure, mDataElementContainerType));
    }
    MoveToState(State::AddingCommand);
    return CHIP_NO_ERROR;
}

CHIP_ERROR CommandHandler::FinishCommand(bool aStartDataStruct)
{
    VerifyOrReturnError(mState == State::AddingCommand, CHIP_ERROR_INCORRECT_STATE);
    CommandDataIB::Builder & commandData = mInvokeResponseBuilder.GetInvokeResponses().GetInvokeResponse().GetCommand();
    if (aStartDataStruct)
    {
        ReturnErrorOnFailure(commandData.GetWriter()->EndContainer(mDataElementContainerType));
    }
    ReturnErrorOnFailure(commandData.EndOfCommandDataIB());
    ReturnErrorOnFailure(mInvokeResponseBuilder.GetInvokeResponses().GetInvokeResponse().EndOfInvokeResponseIB());
    ReturnErrorOnFailure(mInvokeResponseBuilder.GetInvokeResponses().EndOfInvokeResponses());
    ReturnErrorOnFailure(mInvokeResponseBuilder.EndOfInvokeResponseMessage());
    MoveToState(State::AddedCommand);
    return CHIP_NO_ERROR;
}

CHIP_ERROR CommandHandler::PrepareStatus(const ConcreteCommandPath & aCommandPath)
{
    ReturnErrorOnFailure(AllocateBuffer());
    //
    // We must not be in the middle of preparing a command, or having prepared or sent one.
    //
    VerifyOrReturnError(mState == State::Idle, CHIP_ERROR_INCORRECT_STATE);
    MoveToState(State::Preparing);
    InvokeResponseIBs::Builder & invokeResponses = mInvokeResponseBuilder.GetInvokeResponses();
    InvokeResponseIB::Builder & invokeResponse   = invokeResponses.CreateInvokeResponse();
    ReturnErrorOnFailure(invokeResponses.GetError());
    CommandStatusIB::Builder & commandStatus = invokeResponse.CreateStatus();
    ReturnErrorOnFailure(commandStatus.GetError());
    CommandPathIB::Builder & path = commandStatus.CreatePath();
    ReturnErrorOnFailure(commandStatus.GetError());
    ReturnErrorOnFailure(path.Encode(aCommandPath));
    MoveToState(State::AddingCommand);
    return CHIP_NO_ERROR;
}

CHIP_ERROR CommandHandler::FinishStatus()
{
    VerifyOrReturnError(mState == State::AddingCommand, CHIP_ERROR_INCORRECT_STATE);
    ReturnErrorOnFailure(mInvokeResponseBuilder.GetInvokeResponses().GetInvokeResponse().GetStatus().EndOfCommandStatusIB());
    ReturnErrorOnFailure(mInvokeResponseBuilder.GetInvokeResponses().GetInvokeResponse().EndOfInvokeResponseIB());
    ReturnErrorOnFailure(mInvokeResponseBuilder.GetInvokeResponses().EndOfInvokeResponses());
    ReturnErrorOnFailure(mInvokeResponseBuilder.EndOfInvokeResponseMessage());
    MoveToState(State::AddedCommand);
    return CHIP_NO_ERROR;
}

CHIP_ERROR CommandHandler::RollbackResponse()
{
    VerifyOrReturnError(mState == State::Preparing || mState == State::AddingCommand, CHIP_ERROR_INCORRECT_STATE);
    mInvokeResponseBuilder.Rollback(mBackupWriter);
    // Note: We only support one command per request, so we reset the state to Idle here, need to review the states when adding
    // supports of having multiple requests in the same transaction.
    MoveToState(State::Idle);
    return CHIP_NO_ERROR;
}

TLV::TLVWriter * CommandHandler::GetCommandDataIBTLVWriter()
{
    if (mState != State::AddingCommand)
    {
        return nullptr;
    }

    return mInvokeResponseBuilder.GetInvokeResponses().GetInvokeResponse().GetCommand().GetWriter();
}

FabricIndex CommandHandler::GetAccessingFabricIndex() const
{
    VerifyOrDie(!mGoneAsync);
    return mExchangeCtx->GetSessionHandle()->GetFabricIndex();
}

CommandHandler * CommandHandler::Handle::Get()
{
    // Not safe to work with CommandHandler in parallel with other Matter work.
    assertChipStackLockedByCurrentThread();

    return (mMagic == InteractionModelEngine::GetInstance()->GetMagicNumber()) ? mpHandler : nullptr;
}

void CommandHandler::Handle::Release()
{
    if (mpHandler != nullptr)
    {
        if (mMagic == InteractionModelEngine::GetInstance()->GetMagicNumber())
        {
            mpHandler->DecrementHoldOff();
        }
        mpHandler = nullptr;
        mMagic    = 0;
    }
}

CommandHandler::Handle::Handle(CommandHandler * handle)
{
    if (handle != nullptr)
    {
        handle->IncrementHoldOff();
        mpHandler = handle;
        mMagic    = InteractionModelEngine::GetInstance()->GetMagicNumber();
    }
}

CHIP_ERROR CommandHandler::Finalize(System::PacketBufferHandle & commandPacket)
{
    VerifyOrReturnError(mState == State::AddedCommand, CHIP_ERROR_INCORRECT_STATE);
    return mCommandMessageWriter.Finalize(&commandPacket);
}

const char * CommandHandler::GetStateStr() const
{
#if CHIP_DETAIL_LOGGING
    switch (mState)
    {
    case State::Idle:
        return "Idle";

    case State::Preparing:
        return "Preparing";

    case State::AddingCommand:
        return "AddingCommand";

    case State::AddedCommand:
        return "AddedCommand";

    case State::CommandSent:
        return "CommandSent";

    case State::AwaitingDestruction:
        return "AwaitingDestruction";
    }
#endif // CHIP_DETAIL_LOGGING
    return "N/A";
}

void CommandHandler::MoveToState(const State aTargetState)
{
    mState = aTargetState;
    ChipLogDetail(DataManagement, "Command handler moving to [%10.10s]", GetStateStr());
}

} // namespace app
} // namespace chip

CHIP_ERROR __attribute__((weak)) MatterPreCommandReceivedCallback(const chip::app::ConcreteCommandPath & commandPath,
                                                                  const chip::Access::SubjectDescriptor & subjectDescriptor)
{
    return CHIP_NO_ERROR;
}
void __attribute__((weak)) MatterPostCommandReceivedCallback(const chip::app::ConcreteCommandPath & commandPath,
                                                             const chip::Access::SubjectDescriptor & subjectDescriptor)
{}