/*
 *  Copyright (c) 2018, The OpenThread Authors.
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 *  modification, are permitted provided that the following conditions are met:
 *  1. Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 *  2. Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 *  3. Neither the name of the copyright holder nor the
 *     names of its contributors may be used to endorse or promote products
 *     derived from this software without specific prior written permission.
 *
 *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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 *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 */

/**
 * @file
 *   This file implements OpenThread Time Synchronization Service.
 */

#include "openthread-core-config.h"

#if OPENTHREAD_CONFIG_TIME_SYNC_ENABLE

#include "time_sync_service.hpp"

#include <openthread/platform/alarm-micro.h>
#include <openthread/platform/alarm-milli.h>
#include <openthread/platform/time.h>

#include "common/locator_getters.hpp"
#include "common/log.hpp"
#include "instance/instance.hpp"

#define ABS(value) (((value) >= 0) ? (value) : -(value))

namespace ot {

RegisterLogModule("TimeSync");

TimeSync::TimeSync(Instance &aInstance)
    : InstanceLocator(aInstance)
    , mTimeSyncRequired(false)
    , mTimeSyncSeq(OT_TIME_SYNC_INVALID_SEQ)
    , mTimeSyncPeriod(OPENTHREAD_CONFIG_TIME_SYNC_PERIOD)
    , mXtalThreshold(OPENTHREAD_CONFIG_TIME_SYNC_XTAL_THRESHOLD)
#if OPENTHREAD_FTD
    , mLastTimeSyncSent(0)
#endif
    , mLastTimeSyncReceived(0)
    , mNetworkTimeOffset(0)
    , mTimer(aInstance)
    , mCurrentStatus(kUnsynchronized)
{
    CheckAndHandleChanges(false);
}

TimeSync::Status TimeSync::GetTime(uint64_t &aNetworkTime) const
{
    aNetworkTime = static_cast<uint64_t>(static_cast<int64_t>(otPlatTimeGet()) + mNetworkTimeOffset);

    return mCurrentStatus;
}

void TimeSync::HandleTimeSyncMessage(const Message &aMessage)
{
    const int64_t origNetworkTimeOffset = mNetworkTimeOffset;
    int8_t        timeSyncSeqDelta;

    VerifyOrExit(aMessage.GetTimeSyncSeq() != OT_TIME_SYNC_INVALID_SEQ);

    timeSyncSeqDelta = static_cast<int8_t>(aMessage.GetTimeSyncSeq() - mTimeSyncSeq);

    if (mTimeSyncSeq != OT_TIME_SYNC_INVALID_SEQ && timeSyncSeqDelta < 0)
    {
        // An older time sync sequence was received. This indicates that there is a device that still needs to be
        // synchronized with the current sequence, so forward it.
        mTimeSyncRequired = true;

        LogInfo("Older time sync seq received:%u. Forwarding current seq:%u", aMessage.GetTimeSyncSeq(), mTimeSyncSeq);
    }
    else if (Get<Mle::MleRouter>().IsLeader() && timeSyncSeqDelta > 0)
    {
        // Another device is forwarding a later time sync sequence, perhaps because it merged from a different
        // partition. The leader is authoritative, so ensure all devices synchronize to the time being seeded by this
        // leader instead.
        mTimeSyncSeq      = aMessage.GetTimeSyncSeq() + 1;
        mTimeSyncRequired = true;

        LogInfo("Newer time sync seq:%u received by leader. Setting current seq to:%u and forwarding",
                aMessage.GetTimeSyncSeq(), mTimeSyncSeq);
    }
    else if (!Get<Mle::MleRouter>().IsLeader())
    {
        // For all devices aside from the leader, update network time in following three cases:
        //  1. During first attach.
        //  2. Already attached, and a newer time sync sequence was received.
        //  3. During reattach or migration process.
        if (mTimeSyncSeq == OT_TIME_SYNC_INVALID_SEQ || timeSyncSeqDelta > 0 || Get<Mle::MleRouter>().IsDetached())
        {
            // Update network time and forward it.
            mLastTimeSyncReceived = TimerMilli::GetNow();
            mTimeSyncSeq          = aMessage.GetTimeSyncSeq();
            mNetworkTimeOffset    = aMessage.GetNetworkTimeOffset();
            mTimeSyncRequired     = true;

            LogInfo("Newer time sync seq:%u received. Forwarding", mTimeSyncSeq);

            // Only notify listeners of an update for network time offset jumps of more than
            // OPENTHREAD_CONFIG_TIME_SYNC_JUMP_NOTIF_MIN_US but notify listeners regardless if the status changes.
            CheckAndHandleChanges(ABS(mNetworkTimeOffset - origNetworkTimeOffset) >=
                                  OPENTHREAD_CONFIG_TIME_SYNC_JUMP_NOTIF_MIN_US);
        }
    }

exit:
    return;
}

void TimeSync::IncrementTimeSyncSeq(void)
{
    if (++mTimeSyncSeq == OT_TIME_SYNC_INVALID_SEQ)
    {
        ++mTimeSyncSeq;
    }
}

void TimeSync::NotifyTimeSyncCallback(void) { mTimeSyncCallback.InvokeIfSet(); }

#if OPENTHREAD_FTD
void TimeSync::ProcessTimeSync(void)
{
    if (Get<Mle::MleRouter>().IsLeader() &&
        (TimerMilli::GetNow() - mLastTimeSyncSent > Time::SecToMsec(mTimeSyncPeriod)))
    {
        IncrementTimeSyncSeq();
        mTimeSyncRequired = true;

        LogInfo("Leader seeding new time sync seq:%u", mTimeSyncSeq);
    }

    if (mTimeSyncRequired)
    {
        VerifyOrExit(Get<Mle::MleRouter>().SendTimeSync() == kErrorNone);

        mLastTimeSyncSent = TimerMilli::GetNow();
        mTimeSyncRequired = false;
    }

exit:
    return;
}
#endif // OPENTHREAD_FTD

void TimeSync::HandleNotifierEvents(Events aEvents)
{
    bool stateChanged = false;

    if (aEvents.Contains(kEventThreadRoleChanged))
    {
        stateChanged = true;
    }

    if (aEvents.Contains(kEventThreadPartitionIdChanged) && !Get<Mle::MleRouter>().IsLeader())
    {
        // Partition has changed. Accept any network time currently being seeded on the new partition
        // and don't attempt to forward the currently held network time from the previous partition.
        mTimeSyncSeq      = OT_TIME_SYNC_INVALID_SEQ;
        mTimeSyncRequired = false;

        // Network time status will become kUnsychronized because no network time has yet been received
        // on the new partition.
        mLastTimeSyncReceived.SetValue(0);

        stateChanged = true;

        LogInfo("Resetting time sync seq, partition changed");
    }

    if (stateChanged)
    {
        CheckAndHandleChanges(false);
    }
}

void TimeSync::HandleTimeout(void) { CheckAndHandleChanges(false); }

void TimeSync::CheckAndHandleChanges(bool aTimeUpdated)
{
    Status         networkTimeStatus       = kSynchronized;
    const uint32_t resyncNeededThresholdMs = 2 * Time::SecToMsec(mTimeSyncPeriod);
    const uint32_t timeSyncLastSyncMs      = TimerMilli::GetNow() - mLastTimeSyncReceived;

    mTimer.Stop();

    switch (Get<Mle::MleRouter>().GetRole())
    {
    case Mle::kRoleDisabled:
    case Mle::kRoleDetached:
        networkTimeStatus = kUnsynchronized;
        LogInfo("Time sync status UNSYNCHRONIZED as role:DISABLED/DETACHED");
        break;

    case Mle::kRoleChild:
    case Mle::kRoleRouter:
        if (mLastTimeSyncReceived.GetValue() == 0)
        {
            // Haven't yet received any time sync
            networkTimeStatus = kUnsynchronized;
            LogInfo("Time sync status UNSYNCHRONIZED as mLastTimeSyncReceived:0");
        }
        else if (timeSyncLastSyncMs > resyncNeededThresholdMs)
        {
            // The device hasn’t received time sync for more than two periods time.
            networkTimeStatus = kResyncNeeded;
            LogInfo("Time sync status RESYNC_NEEDED as timeSyncLastSyncMs:%lu > resyncNeededThresholdMs:%lu",
                    ToUlong(timeSyncLastSyncMs), ToUlong(resyncNeededThresholdMs));
        }
        else
        {
            // Schedule a check 1 millisecond after two periods of time
            OT_ASSERT(resyncNeededThresholdMs >= timeSyncLastSyncMs);
            mTimer.Start(resyncNeededThresholdMs - timeSyncLastSyncMs + 1);
            LogInfo("Time sync status SYNCHRONIZED");
        }
        break;

    case Mle::kRoleLeader:
        LogInfo("Time sync status SYNCHRONIZED as role:LEADER");
        break;
    }

    if (networkTimeStatus != mCurrentStatus || aTimeUpdated)
    {
        mCurrentStatus = networkTimeStatus;

        NotifyTimeSyncCallback();
    }
}

} // namespace ot

#endif // OPENTHREAD_CONFIG_TIME_SYNC_ENABLE