/**
 *
 *    Copyright (c) 2021 Project CHIP Authors
 *    Copyright (c) 2015-2017 Nest Labs, Inc.
 *
 *    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.
 */

#include <app/CriticalSection.h>
#include <app/EventManagement.h>
#include <app/InteractionModelEngine.h>
#include <core/CHIPEventLoggingConfig.h>
#include <core/CHIPTLVUtilities.hpp>
#include <inttypes.h>
#include <support/CodeUtils.h>
#include <support/ErrorStr.h>
#include <support/logging/CHIPLogging.h>
#include <system/SystemTimer.h>

using namespace chip::TLV;

namespace chip {
namespace app {
static EventManagement sInstance;

/**
 * @brief
 *   A TLVReader backed by CircularEventBuffer
 */
class CircularEventReader : public TLV::TLVReader
{
public:
    /**
     * @brief
     *   Initializes a TLVReader object backed by CircularEventBuffer
     *
     * Reading begins in the CircularTLVBuffer belonging to this
     * CircularEventBuffer.  When the reader runs out of data, it begins
     * to read from the previous CircularEventBuffer.
     *
     * @param[in] apBuf A pointer to a fully initialized CircularEventBuffer
     *
     */
    void Init(CircularEventBufferWrapper * apBuf);

    virtual ~CircularEventReader() = default;
};

EventManagement & EventManagement::GetInstance(void)
{
    return sInstance;
}

struct ReclaimEventCtx
{
    CircularEventBuffer * mpEventBuffer = nullptr;
    size_t mSpaceNeededForMovedEvent    = 0;
};

/**
 * @brief
 *  Internal structure for traversing event list.
 */
struct CopyAndAdjustDeltaTimeContext
{
    CopyAndAdjustDeltaTimeContext(TLVWriter * aWriter, EventLoadOutContext * inContext) : mpWriter(aWriter), mpContext(inContext) {}

    TLV::TLVWriter * mpWriter       = nullptr;
    EventLoadOutContext * mpContext = nullptr;
};

/**
 * @brief
 *  Internal structure for traversing events.
 */
struct EventEnvelopeContext
{
    EventEnvelopeContext() {}

    uint16_t mFieldsToRead = 0;
    /* PriorityLevel and DeltaSystemTimestamp are there if that is not first event when putting events in report*/
    Timestamp mDeltaSystemTime = Timestamp::System(0);
    Timestamp mDeltaUtc        = Timestamp::UTC(0);
    PriorityLevel mPriority    = PriorityLevel::First;
    NodeId mNodeId             = 0;
    ClusterId mClusterId       = 0;
    EndpointId mEndpointId     = 0;
    EventId mEventId           = 0;
};

EventManagement::EventManagement(Messaging::ExchangeManager * apExchangeMgr, int aNumBuffers,
                                 CircularEventBuffer * apCircularEventBuffer,
                                 const LogStorageResources * const apLogStorageResources)
{
    Init(apExchangeMgr, aNumBuffers, apCircularEventBuffer, apLogStorageResources);
}

void EventManagement::Init(Messaging::ExchangeManager * apExchangeManager, int aNumBuffers,
                           CircularEventBuffer * apCircularEventBuffer, const LogStorageResources * const apLogStorageResources)
{
    CircularEventBuffer * current = nullptr;
    CircularEventBuffer * prev    = nullptr;
    CircularEventBuffer * next    = nullptr;

    VerifyOrDie(aNumBuffers > 0);

    mpExchangeMgr = apExchangeManager;

    for (int bufferIndex = 0; bufferIndex < aNumBuffers; bufferIndex++)
    {
        next = (bufferIndex < aNumBuffers - 1) ? &apCircularEventBuffer[bufferIndex + 1] : nullptr;

        current = &apCircularEventBuffer[bufferIndex];
        current->Init(apLogStorageResources[bufferIndex].mpBuffer, apLogStorageResources[bufferIndex].mBufferSize, prev, next,
                      apLogStorageResources[bufferIndex].mPriority);

        prev = current;

        current->mProcessEvictedElement = AlwaysFail;
        current->mAppData               = nullptr;
        current->InitCounter(apLogStorageResources[bufferIndex].InitializeCounter());
    }

    mpEventBuffer = apCircularEventBuffer;
    mState        = EventManagementStates::Idle;
    mBytesWritten = 0;
}

CHIP_ERROR EventManagement::CopyToNextBuffer(CircularEventBuffer * apEventBuffer)
{
    CircularTLVWriter writer;
    CircularTLVReader reader;
    CHIP_ERROR err                   = CHIP_NO_ERROR;
    CircularEventBuffer * nextBuffer = apEventBuffer->GetNextCircularEventBuffer();
    if (nextBuffer == nullptr)
    {
        return CHIP_ERROR_INVALID_ARGUMENT;
    }
    CircularEventBuffer backup = *nextBuffer;

    // Set up the next buffer s.t. it fails if needs to evict an element
    nextBuffer->mProcessEvictedElement = AlwaysFail;

    writer.Init(*nextBuffer);

    // Set up the reader s.t. it is positioned to read the head event
    reader.Init(*apEventBuffer);

    err = reader.Next();
    SuccessOrExit(err);

    err = writer.CopyElement(reader);
    SuccessOrExit(err);

    err = writer.Finalize();
    SuccessOrExit(err);

    ChipLogProgress(EventLogging, "Copy Event to next buffer with priority %d", nextBuffer->GetPriorityLevel());
exit:
    if (err != CHIP_NO_ERROR)
    {
        *nextBuffer = backup;
    }
    return err;
}

CHIP_ERROR EventManagement::EnsureSpaceInCircularBuffer(size_t aRequiredSpace)
{
    CHIP_ERROR err                    = CHIP_NO_ERROR;
    size_t requiredSpace              = aRequiredSpace;
    CircularEventBuffer * eventBuffer = mpEventBuffer;
    ReclaimEventCtx ctx;

    // check whether we actually need to do anything, exit if we don't
    VerifyOrExit(requiredSpace > eventBuffer->AvailableDataLength(), err = CHIP_NO_ERROR);

    while (true)
    {
        // check that the request can ultimately be satisfied.
        VerifyOrExit(requiredSpace <= eventBuffer->GetTotalDataLength(), err = CHIP_ERROR_BUFFER_TOO_SMALL);

        if (requiredSpace > eventBuffer->AvailableDataLength())
        {
            ctx.mpEventBuffer             = eventBuffer;
            ctx.mSpaceNeededForMovedEvent = 0;

            eventBuffer->mProcessEvictedElement = EvictEvent;
            eventBuffer->mAppData               = &ctx;
            err                                 = eventBuffer->EvictHead();

            // one of two things happened: either the element was evicted immediately if the head's priority is same as current
            // buffer(final one), or we figured out how much space we need to evict it into the next buffer, the check happens in
            // EvictEvent function

            if (err != CHIP_NO_ERROR)
            {
                VerifyOrExit(ctx.mSpaceNeededForMovedEvent != 0, /* no-op, return err */);
                VerifyOrExit(eventBuffer->GetNextCircularEventBuffer() != nullptr, err = CHIP_ERROR_INCORRECT_STATE);
                if (ctx.mSpaceNeededForMovedEvent <= eventBuffer->GetNextCircularEventBuffer()->AvailableDataLength())
                {
                    // we can copy the event outright.  copy event and
                    // subsequently evict head s.t. evicting the head
                    // element always succeeds.
                    // Since we're calling CopyElement and we've checked
                    // that there is space in the next buffer, we don't expect
                    // this to fail.
                    err = CopyToNextBuffer(eventBuffer);
                    SuccessOrExit(err);
                    // success; evict head unconditionally
                    eventBuffer->mProcessEvictedElement = nullptr;
                    err                                 = eventBuffer->EvictHead();
                    // if unconditional eviction failed, this
                    // means that we have no way of further
                    // clearing the buffer.  fail out and let the
                    // caller know that we could not honor the
                    // request
                    SuccessOrExit(err);
                    continue;
                }
                // we cannot copy event outright. We remember the
                // current required space in mRequiredSpaceForEvicted, we note the
                // space requirements for the event in the current
                // buffer and make that space in the next buffer.
                eventBuffer->SetRequiredSpaceforEvicted(requiredSpace);
                eventBuffer = eventBuffer->GetNextCircularEventBuffer();

                // Sanity check: return error  here on null event buffer.  If
                // eventBuffer->mpNext were null, then the `EvictBuffer`
                // would have succeeded -- the event was
                // already in the final buffer.
                VerifyOrExit(eventBuffer != nullptr, err = CHIP_ERROR_INCORRECT_STATE);
                requiredSpace = ctx.mSpaceNeededForMovedEvent;
            }
        }
        else
        {
            // this branch is only taken when we go back in the buffer chain since we have free/spare enough space in next buffer,
            // and need to retry to copy event from current buffer to next buffer, and free space for current buffer
            if (eventBuffer == mpEventBuffer)
                break;
            eventBuffer   = eventBuffer->GetPreviousCircularEventBuffer();
            requiredSpace = eventBuffer->GetRequiredSpaceforEvicted();
            err           = CHIP_NO_ERROR;
        }
    }

    // On exit, configure the top-level s.t. it will always fail to evict an element
    mpEventBuffer->mProcessEvictedElement = AlwaysFail;
    mpEventBuffer->mAppData               = nullptr;

exit:
    ChipLogFunctError(err);
    return err;
}

CHIP_ERROR EventManagement::CalculateEventSize(EventLoggingDelegate * apDelegate, const EventOptions * apOptions,
                                               uint32_t & requiredSize)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    System::PacketBufferTLVWriter writer;
    EventLoadOutContext ctxt       = EventLoadOutContext(writer, apOptions->mpEventSchema->mPriority,
                                                   GetPriorityBuffer(apOptions->mpEventSchema->mPriority)->GetLastEventNumber());
    System::PacketBufferHandle buf = System::PacketBufferHandle::New(kMaxEventSizeReserve);
    if (buf.IsNull())
    {
        return CHIP_ERROR_NO_MEMORY;
    }
    writer.Init(std::move(buf));

    ctxt.mCurrentEventNumber       = GetPriorityBuffer(apOptions->mpEventSchema->mPriority)->GetLastEventNumber();
    ctxt.mCurrentSystemTime.mValue = GetPriorityBuffer(apOptions->mpEventSchema->mPriority)->GetLastEventSystemTimestamp();
    err                            = ConstructEvent(&ctxt, apDelegate, apOptions);
    if (CHIP_NO_ERROR == err)
    {
        requiredSize = writer.GetLengthWritten();
    }
    return err;
}

CHIP_ERROR EventManagement::ConstructEvent(EventLoadOutContext * apContext, EventLoggingDelegate * apDelegate,
                                           const EventOptions * apOptions)
{

    CHIP_ERROR err       = CHIP_NO_ERROR;
    TLVWriter checkpoint = apContext->mWriter;
    TLV::TLVType dataContainerType;
    EventDataElement::Builder eventDataElementBuilder;
    EventPath::Builder eventPathBuilder;
    uint64_t deltatime = 0;

    VerifyOrExit(apContext->mCurrentEventNumber >= apContext->mStartingEventNumber,
                 /* no-op: don't write event, but advance current event Number */);

    VerifyOrExit(apOptions != nullptr, err = CHIP_ERROR_INVALID_ARGUMENT);
    VerifyOrExit(apOptions->mTimestamp.mType != Timestamp::Type::kInvalid, err = CHIP_ERROR_INVALID_ARGUMENT);

    eventDataElementBuilder.Init(&(apContext->mWriter));
    eventPathBuilder = eventDataElementBuilder.CreateEventPathBuilder();
    err              = eventPathBuilder.GetError();
    SuccessOrExit(err);

    // TODO: Revisit NodeId since the the encoding spec and the IM seem to disagree on how this stuff works
    eventPathBuilder.NodeId(apOptions->mpEventSchema->mNodeId)
        .EndpointId(apOptions->mpEventSchema->mEndpointId)
        .ClusterId(apOptions->mpEventSchema->mClusterId)
        .EventId(apOptions->mpEventSchema->mEventId)
        .EndOfEventPath();
    err = eventPathBuilder.GetError();
    SuccessOrExit(err);

    eventDataElementBuilder.PriorityLevel(static_cast<uint8_t>(apContext->mPriority));

    // TODO: need to add utc and systen system check here
    deltatime = apOptions->mTimestamp.mValue - apContext->mCurrentSystemTime.mValue;
    eventDataElementBuilder.DeltaSystemTimestamp(deltatime);
    err = eventDataElementBuilder.GetError();
    SuccessOrExit(err);

    err = apContext->mWriter.StartContainer(ContextTag(EventDataElement::kCsTag_Data), TLV::kTLVType_Structure, dataContainerType);
    SuccessOrExit(err);
    // Callback to write the EventData
    err = apDelegate->WriteEvent(apContext->mWriter);
    SuccessOrExit(err);

    err = apContext->mWriter.EndContainer(dataContainerType);
    SuccessOrExit(err);

    eventDataElementBuilder.EndOfEventDataElement();
    SuccessOrExit(err = eventDataElementBuilder.GetError());

    err = apContext->mWriter.Finalize();
    SuccessOrExit(err);

    apContext->mFirst = false;

exit:
    if (err != CHIP_NO_ERROR)
    {
        apContext->mWriter = checkpoint;
    }
    else
    {
        // update these variables since ConstructEvent can be used to track the
        // state of a set of events over multiple calls.
        apContext->mCurrentEventNumber++;
        if (apContext->mCurrentSystemTime.mType == Timestamp::Type::kSystem)
        {
            apContext->mCurrentSystemTime = apOptions->mTimestamp;
        }
    }
    return err;
}

void EventManagement::CreateEventManagement(Messaging::ExchangeManager * apExchangeManager, int aNumBuffers,
                                            CircularEventBuffer * apCircularEventBuffer,
                                            const LogStorageResources * const apLogStorageResources)
{

    sInstance.Init(apExchangeManager, aNumBuffers, apCircularEventBuffer, apLogStorageResources);
    static_assert(std::is_trivially_destructible<EventManagement>::value, "EventManagement must be trivially destructible");
}

/**
 * @brief Perform any actions we need to on shutdown.
 */
void EventManagement::DestroyEventManagement()
{
    CriticalSectionEnter();
    sInstance.mState        = EventManagementStates::Shutdown;
    sInstance.mpEventBuffer = nullptr;
    sInstance.mpExchangeMgr = nullptr;
    CriticalSectionExit();
}

EventNumber CircularEventBuffer::VendEventNumber()
{
    CHIP_ERROR err = CHIP_NO_ERROR;

    // Assign event Number to the buffer's counter's value.
    mLastEventNumber = static_cast<EventNumber>(mpEventNumberCounter->GetValue());

    // Now advance the counter.
    err = mpEventNumberCounter->Advance();
    if (err != CHIP_NO_ERROR)
    {
        ChipLogError(EventLogging, "%s Advance() for priority %d failed with %d", __FUNCTION__, mPriority, err);
    }

    return mLastEventNumber;
}

EventNumber EventManagement::GetLastEventNumber(PriorityLevel aPriority)
{
    return GetPriorityBuffer(aPriority)->GetLastEventNumber();
}

EventNumber EventManagement::GetFirstEventNumber(PriorityLevel aPriority)
{
    return GetPriorityBuffer(aPriority)->GetFirstEventNumber();
}

CircularEventBuffer * EventManagement::GetPriorityBuffer(PriorityLevel aPriority) const
{
    CircularEventBuffer * buf = mpEventBuffer;
    while (!buf->IsFinalDestinationForPriority(aPriority))
    {
        buf = buf->GetNextCircularEventBuffer();
        assert(buf != nullptr);
        // code guarantees that every PriorityLevel has a buffer destination.
    }
    return buf;
}

CHIP_ERROR EventManagement::CopyAndAdjustDeltaTime(const TLVReader & aReader, size_t aDepth, void * apContext)
{
    CHIP_ERROR err;
    CopyAndAdjustDeltaTimeContext * ctx = static_cast<CopyAndAdjustDeltaTimeContext *>(apContext);
    TLVReader reader(aReader);

    // TODO: Add UTC timestamp support
    if (aReader.GetTag() == TLV::ContextTag(EventDataElement::kCsTag_DeltaSystemTimestamp))
    {
        if (ctx->mpContext->mFirst) // First event gets a timestamp, subsequent ones get a delta T
        {
            err = ctx->mpWriter->Put(TLV::ContextTag(EventDataElement::kCsTag_SystemTimestamp),
                                     ctx->mpContext->mCurrentSystemTime.mValue);
        }
        else
        {
            err = ctx->mpWriter->Put(TLV::ContextTag(EventDataElement::kCsTag_DeltaSystemTimestamp),
                                     ctx->mpContext->mCurrentSystemTime.mValue - ctx->mpContext->mPreviousSystemTime.mValue);
        }
    }
    else
    {
        err = ctx->mpWriter->CopyElement(reader);
    }

    // First event in the sequence gets a event number neatly packaged
    // right after the priority to keep tags ordered
    if (aReader.GetTag() == TLV::ContextTag(EventDataElement::kCsTag_PriorityLevel))
    {
        if (ctx->mpContext->mFirst)
        {
            err = ctx->mpWriter->Put(TLV::ContextTag(EventDataElement::kCsTag_Number), ctx->mpContext->mCurrentEventNumber);
        }
    }

    return err;
}

CHIP_ERROR EventManagement::LogEvent(EventLoggingDelegate * apDelegate, EventOptions & aEventOptions, EventNumber & aEventNumber)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    CriticalSectionEnter();

    VerifyOrExit(mState != EventManagementStates::Shutdown, err = CHIP_ERROR_INCORRECT_STATE);
    VerifyOrExit(aEventOptions.mpEventSchema != nullptr, err = CHIP_ERROR_INCORRECT_STATE);

    err = LogEventPrivate(apDelegate, aEventOptions, aEventNumber);

exit:
    CriticalSectionExit();
    ChipLogFunctError(err);
    return err;
}

CHIP_ERROR EventManagement::LogEventPrivate(EventLoggingDelegate * apDelegate, EventOptions & aEventOptions,
                                            EventNumber & aEventNumber)
{
    CircularTLVWriter writer;
    CHIP_ERROR err                 = CHIP_NO_ERROR;
    uint32_t requestSize           = 0;
    aEventNumber                   = 0;
    CircularEventBuffer checkpoint = *mpEventBuffer;
    CircularEventBuffer * buffer   = nullptr;
    EventLoadOutContext ctxt       = EventLoadOutContext(writer, aEventOptions.mpEventSchema->mPriority,
                                                   GetPriorityBuffer(aEventOptions.mpEventSchema->mPriority)->GetLastEventNumber());
    Timestamp timestamp(Timestamp::Type::kSystem, System::Timer::GetCurrentEpoch());
    EventOptions opts = EventOptions(timestamp);
    // Start the event container (anonymous structure) in the circular buffer
    writer.Init(*mpEventBuffer);

    // check whether the entry is to be logged or discarded silently
    VerifyOrExit(aEventOptions.mpEventSchema->mPriority >= CHIP_CONFIG_EVENT_GLOBAL_PRIORITY, /* no-op */);

    // Create all event specific data
    // Timestamp; encoded as a delta time
    if (aEventOptions.mTimestamp.mType == Timestamp::Type::kSystem)
    {
        opts.mTimestamp = aEventOptions.mTimestamp;
    }

    if (GetPriorityBuffer(aEventOptions.mpEventSchema->mPriority)->GetFirstEventSystemTimestamp() == 0)
    {
        GetPriorityBuffer(aEventOptions.mpEventSchema->mPriority)->UpdateFirstLastEventTime(opts.mTimestamp);
    }

    opts.mUrgent       = aEventOptions.mUrgent;
    opts.mpEventSchema = aEventOptions.mpEventSchema;

    ctxt.mCurrentEventNumber       = GetPriorityBuffer(opts.mpEventSchema->mPriority)->GetLastEventNumber();
    ctxt.mCurrentSystemTime.mValue = GetPriorityBuffer(opts.mpEventSchema->mPriority)->GetLastEventSystemTimestamp();

    err = CalculateEventSize(apDelegate, &opts, requestSize);
    SuccessOrExit(err);

    // Ensure we have space in the in-memory logging queues
    err = EnsureSpaceInCircularBuffer(requestSize);
    SuccessOrExit(err);

    err = ConstructEvent(&ctxt, apDelegate, &opts);
    SuccessOrExit(err);

    // Check the number of bytes written.  If the event is too large
    // to be evicted from subsequent buffers, drop it now.
    buffer = mpEventBuffer;
    while (true)
    {
        VerifyOrExit(buffer->GetTotalDataLength() >= writer.GetLengthWritten(), err = CHIP_ERROR_BUFFER_TOO_SMALL);
        if (buffer->IsFinalDestinationForPriority(opts.mpEventSchema->mPriority))
        {
            break;
        }
        else
        {
            buffer = buffer->GetNextCircularEventBuffer();
            assert(buffer != nullptr);
            // code guarantees that every PriorityLevel has a buffer destination.
        }
    }

    mBytesWritten += writer.GetLengthWritten();

exit:
    ChipLogFunctError(err);
    if (err != CHIP_NO_ERROR)
    {
        *mpEventBuffer = checkpoint;
    }
    else if (opts.mpEventSchema->mPriority >= CHIP_CONFIG_EVENT_GLOBAL_PRIORITY)
    {
        CircularEventBuffer * currentBuffer = GetPriorityBuffer(opts.mpEventSchema->mPriority);
        aEventNumber                        = currentBuffer->VendEventNumber();
        currentBuffer->UpdateFirstLastEventTime(opts.mTimestamp);

#if CHIP_CONFIG_EVENT_LOGGING_VERBOSE_DEBUG_LOGS
        ChipLogDetail(
            EventLogging,
            "LogEvent event number: %u schema priority: %u cluster id: 0x%x event id: 0x%x sys timestamp: 0x" ChipLogFormatX64,
            aEventNumber, opts.mpEventSchema->mPriority, opts.mpEventSchema->mClusterId, opts.mpEventSchema->mEventId,
            ChipLogValueX64(opts.mTimestamp.mValue));
#endif // CHIP_CONFIG_EVENT_LOGGING_VERBOSE_DEBUG_LOGS

        ScheduleFlushIfNeeded(opts.mUrgent);
    }

    return err;
}

CHIP_ERROR EventManagement::CopyEvent(const TLVReader & aReader, TLVWriter & aWriter, EventLoadOutContext * apContext)
{
    TLVReader reader;
    TLVType containerType;
    CopyAndAdjustDeltaTimeContext context(&aWriter, apContext);
    CHIP_ERROR err = CHIP_NO_ERROR;

    reader.Init(aReader);
    err = reader.EnterContainer(containerType);
    SuccessOrExit(err);

    err = aWriter.StartContainer(AnonymousTag, kTLVType_Structure, containerType);
    SuccessOrExit(err);

    err = TLV::Utilities::Iterate(reader, CopyAndAdjustDeltaTime, &context, false /*recurse*/);
    if (err == CHIP_END_OF_TLV)
    {
        err = CHIP_NO_ERROR;
    }
    SuccessOrExit(err);

    err = aWriter.EndContainer(containerType);
    SuccessOrExit(err);

    err = aWriter.Finalize();
    SuccessOrExit(err);

exit:
    ChipLogFunctError(err);
    return err;
}

static bool IsInterestedEventPaths(EventLoadOutContext * eventLoadOutContext, const EventEnvelopeContext & event)
{
    ClusterInfo * interestedEventPaths = eventLoadOutContext->mpInterestedEventPaths;
    if (eventLoadOutContext->mCurrentEventNumber < eventLoadOutContext->mStartingEventNumber)
    {
        return false;
    }
    while (interestedEventPaths != nullptr)
    {
        if (interestedEventPaths->mNodeId == event.mNodeId && interestedEventPaths->mEndpointId == event.mEndpointId &&
            interestedEventPaths->mClusterId == event.mClusterId && interestedEventPaths->mEventId == event.mEventId)
        {
            return true;
        }
        interestedEventPaths = interestedEventPaths->mpNext;
    }
    return false;
}

CHIP_ERROR EventManagement::EventIterator(const TLVReader & aReader, size_t aDepth, EventLoadOutContext * apEventLoadOutContext)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    TLVReader innerReader;
    TLVType tlvType;
    EventEnvelopeContext event;

    innerReader.Init(aReader);
    ReturnErrorOnFailure(innerReader.EnterContainer(tlvType));

    err = TLV::Utilities::Iterate(innerReader, FetchEventParameters, &event, false /*recurse*/);
    if (event.mFieldsToRead != kRequiredEventField)
    {
        return CHIP_ERROR_INVALID_ARGUMENT;
    }

    if (err == CHIP_END_OF_TLV)
    {
        err = CHIP_NO_ERROR;
    }
    ReturnErrorOnFailure(err);

    if (event.mPriority == apEventLoadOutContext->mPriority)
    {
        apEventLoadOutContext->mCurrentSystemTime.mValue += event.mDeltaSystemTime.mValue;
        if (IsInterestedEventPaths(apEventLoadOutContext, event))
        {
            return CHIP_EVENT_ID_FOUND;
        }
    }

    return CHIP_NO_ERROR;
}

CHIP_ERROR EventManagement::CopyEventsSince(const TLVReader & aReader, size_t aDepth, void * apContext)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    TLV::TLVWriter checkpoint;
    EventLoadOutContext * loadOutContext = static_cast<EventLoadOutContext *>(apContext);
    err                                  = EventIterator(aReader, aDepth, loadOutContext);
    loadOutContext->mCurrentEventNumber++;
    if (err == CHIP_EVENT_ID_FOUND)
    {
        // checkpoint the writer
        checkpoint = loadOutContext->mWriter;

        err = CopyEvent(aReader, loadOutContext->mWriter, loadOutContext);

        // CHIP_NO_ERROR and CHIP_END_OF_TLV signify a
        // successful copy.  In all other cases, roll back the
        // writer state back to the checkpoint, i.e., the state
        // before we began the copy operation.
        VerifyOrExit((err == CHIP_NO_ERROR) || (err == CHIP_END_OF_TLV), loadOutContext->mWriter = checkpoint);

        loadOutContext->mPreviousSystemTime.mValue = loadOutContext->mCurrentSystemTime.mValue;
        loadOutContext->mFirst                     = false;
    }

exit:
    return err;
}

CHIP_ERROR EventManagement::FetchEventsSince(TLVWriter & aWriter, ClusterInfo * apClusterInfolist, PriorityLevel aPriority,
                                             EventNumber & aEventNumber)
{
    // TODO: Add particular set of event Paths in FetchEventsSince so that we can filter the interested paths
    CHIP_ERROR err     = CHIP_NO_ERROR;
    const bool recurse = false;
    TLVReader reader;
    CircularEventBufferWrapper bufWrapper;
    EventLoadOutContext context(aWriter, aPriority, aEventNumber);

    CircularEventBuffer * buf = mpEventBuffer;
    CriticalSectionEnter();

    while (!buf->IsFinalDestinationForPriority(aPriority))
    {
        buf = buf->GetNextCircularEventBuffer();
    }

    context.mpInterestedEventPaths    = apClusterInfolist;
    context.mCurrentSystemTime.mValue = buf->GetFirstEventSystemTimestamp();
    context.mCurrentEventNumber       = buf->GetFirstEventNumber();
    err                               = GetEventReader(reader, aPriority, &bufWrapper);
    SuccessOrExit(err);

    err = TLV::Utilities::Iterate(reader, CopyEventsSince, &context, recurse);
    if (err == CHIP_END_OF_TLV)
    {
        err = CHIP_NO_ERROR;
    }

exit:
    aEventNumber = context.mCurrentEventNumber;
    CriticalSectionExit();

    return err;
}

CHIP_ERROR EventManagement::GetEventReader(TLVReader & aReader, PriorityLevel aPriority, CircularEventBufferWrapper * apBufWrapper)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    CircularEventReader reader;
    CircularEventBuffer * buffer = GetPriorityBuffer(aPriority);
    VerifyOrExit(buffer != nullptr, err = CHIP_ERROR_INVALID_ARGUMENT);
    apBufWrapper->mpCurrent = buffer;
    reader.Init(apBufWrapper);
    aReader.Init(reader);
exit:
    return err;
}

CHIP_ERROR EventManagement::FetchEventParameters(const TLVReader & aReader, size_t aDepth, void * apContext)
{
    CHIP_ERROR err                  = CHIP_NO_ERROR;
    EventEnvelopeContext * envelope = static_cast<EventEnvelopeContext *>(apContext);
    TLVReader reader;
    uint16_t extPriority; // Note: the type here matches the type case in EventManagement::LogEvent, priority section
    reader.Init(aReader);

    if (reader.GetTag() == TLV::ContextTag(EventDataElement::kCsTag_EventPath))
    {
        EventPath::Parser path;
        SuccessOrExit(err = path.Init(aReader));
        SuccessOrExit(err = path.GetNodeId(&(envelope->mNodeId)));
        SuccessOrExit(err = path.GetEndpointId(&(envelope->mEndpointId)));
        SuccessOrExit(err = path.GetClusterId(&(envelope->mClusterId)));
        SuccessOrExit(err = path.GetEventId(&(envelope->mEventId)));
        envelope->mFieldsToRead |= 1 << EventDataElement::kCsTag_EventPath;
    }

    if (reader.GetTag() == TLV::ContextTag(EventDataElement::kCsTag_PriorityLevel))
    {
        err = reader.Get(extPriority);
        SuccessOrExit(err);
        envelope->mPriority = static_cast<PriorityLevel>(extPriority);
        envelope->mFieldsToRead |= 1 << EventDataElement::kCsTag_PriorityLevel;
    }

    if (reader.GetTag() == TLV::ContextTag(EventDataElement::kCsTag_DeltaSystemTimestamp))
    {
        err = reader.Get(envelope->mDeltaSystemTime.mValue);
        SuccessOrExit(err);

        envelope->mFieldsToRead |= 1 << EventDataElement::kCsTag_DeltaSystemTimestamp;
    }

exit:
    return err;
}

CHIP_ERROR EventManagement::EvictEvent(CHIPCircularTLVBuffer & apBuffer, void * apAppData, TLVReader & aReader)
{
    ReclaimEventCtx * ctx             = static_cast<ReclaimEventCtx *>(apAppData);
    CircularEventBuffer * eventBuffer = ctx->mpEventBuffer;
    TLVType containerType;
    EventEnvelopeContext context;
    const bool recurse = false;
    CHIP_ERROR err;
    PriorityLevel imp = PriorityLevel::Invalid;

    // pull out the delta time, pull out the priority
    err = aReader.Next();
    SuccessOrExit(err);

    err = aReader.EnterContainer(containerType);
    SuccessOrExit(err);

    err = TLV::Utilities::Iterate(aReader, FetchEventParameters, &context, recurse);
    if (err == CHIP_END_OF_TLV)
    {
        err = CHIP_NO_ERROR;
    }
    SuccessOrExit(err);

    err = aReader.ExitContainer(containerType);

    SuccessOrExit(err);

    imp = static_cast<PriorityLevel>(context.mPriority);

    if (eventBuffer->IsFinalDestinationForPriority(imp))
    {
        // event is getting dropped.  Increase the event number and first timestamp.
        EventNumber numEventsToDrop = 1;
        eventBuffer->RemoveEvent(numEventsToDrop);
        eventBuffer->SetFirstEventSystemTimestamp(eventBuffer->GetFirstEventSystemTimestamp() + context.mDeltaSystemTime.mValue);
        ChipLogProgress(EventLogging,
                        "Dropped events from buffer with priority %d due to overflow: { event priority_level: %d, count: %d };",
                        eventBuffer->GetPriorityLevel(), imp, numEventsToDrop);
        ctx->mSpaceNeededForMovedEvent = 0;
    }
    else
    {
        // event is not getting dropped. Note how much space it requires, and return.
        ctx->mSpaceNeededForMovedEvent = aReader.GetLengthRead();
        err                            = CHIP_END_OF_TLV;
    }

exit:
    return err;
}

CHIP_ERROR EventManagement::ScheduleFlushIfNeeded(EventOptions::Type aUrgent)
{
    // TODO: Implement ScheduleFlushIfNeeded
    return CHIP_NO_ERROR;
}

void EventManagement::SetScheduledEventEndpoint(EventNumber * apEventEndpoints)
{
    CircularEventBuffer * eventBuffer = mpEventBuffer;

    CriticalSectionEnter();

    while (eventBuffer != nullptr)
    {
        if (eventBuffer->GetPriorityLevel() >= PriorityLevel::First && (eventBuffer->GetPriorityLevel() <= PriorityLevel::Last))
        {
            apEventEndpoints[static_cast<uint8_t>(eventBuffer->GetPriorityLevel())] = eventBuffer->GetLastEventNumber();
        }
        eventBuffer = eventBuffer->GetNextCircularEventBuffer();
    }

    CriticalSectionExit();
}

void CircularEventBuffer::Init(uint8_t * apBuffer, uint32_t aBufferLength, CircularEventBuffer * apPrev,
                               CircularEventBuffer * apNext, PriorityLevel aPriorityLevel)
{
    CHIPCircularTLVBuffer::Init(apBuffer, aBufferLength);
    mpPrev                     = apPrev;
    mpNext                     = apNext;
    mPriority                  = aPriorityLevel;
    mFirstEventNumber          = 1;
    mLastEventNumber           = 0;
    mFirstEventSystemTimestamp = Timestamp::System(0);
    mLastEventSystemTimestamp  = Timestamp::System(0);
    mpEventNumberCounter       = nullptr;
}

bool CircularEventBuffer::IsFinalDestinationForPriority(PriorityLevel aPriority) const
{
    return !((mpNext != nullptr) && (mpNext->mPriority <= aPriority));
}

void CircularEventBuffer::UpdateFirstLastEventTime(Timestamp aEventTimestamp)
{
    if (mFirstEventSystemTimestamp.mValue == 0)
    {
        mFirstEventSystemTimestamp = aEventTimestamp;
        mLastEventSystemTimestamp  = aEventTimestamp;
    }
    mLastEventSystemTimestamp = aEventTimestamp;
}

void CircularEventBuffer::RemoveEvent(EventNumber aNumEvents)
{
    mFirstEventNumber = mFirstEventNumber + aNumEvents;
}

void CircularEventReader::Init(CircularEventBufferWrapper * apBufWrapper)
{
    CircularEventBuffer * prev;

    if (apBufWrapper->mpCurrent == nullptr)
        return;

    TLVReader::Init(*apBufWrapper, apBufWrapper->mpCurrent->DataLength());
    mMaxLen = apBufWrapper->mpCurrent->DataLength();
    for (prev = apBufWrapper->mpCurrent->GetPreviousCircularEventBuffer(); prev != nullptr;
         prev = prev->GetPreviousCircularEventBuffer())
    {
        CircularEventBufferWrapper bufWrapper;
        bufWrapper.mpCurrent = prev;
        mMaxLen += prev->DataLength();
    }
}

CHIP_ERROR CircularEventBufferWrapper::GetNextBuffer(TLVReader & aReader, const uint8_t *& aBufStart, uint32_t & aBufLen)
{
    CHIP_ERROR err = CHIP_NO_ERROR;
    mpCurrent->GetNextBuffer(aReader, aBufStart, aBufLen);
    SuccessOrExit(err);

    if ((aBufLen == 0) && (mpCurrent->GetPreviousCircularEventBuffer() != nullptr))
    {
        mpCurrent = mpCurrent->GetPreviousCircularEventBuffer();
        aBufStart = nullptr;
        err       = GetNextBuffer(aReader, aBufStart, aBufLen);
    }

exit:
    ChipLogFunctError(err);
    return err;
}
} // namespace app
} // namespace chip