/*
 *  Copyright (c) 2019, The OpenThread Authors.
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 *  1. Redistributions of source code must retain the above copyright
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 *  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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 */

/**
 * @file
 *   This file includes definitions for Thread Radio Encapsulation Link (TREL).
 */

#ifndef TREL_LINK_HPP_
#define TREL_LINK_HPP_

#include "openthread-core-config.h"

#if OPENTHREAD_CONFIG_RADIO_LINK_TREL_ENABLE

#include "common/encoding.hpp"
#include "common/locator.hpp"
#include "common/notifier.hpp"
#include "common/tasklet.hpp"
#include "common/timer.hpp"
#include "mac/mac_frame.hpp"
#include "mac/mac_types.hpp"
#include "radio/trel_interface.hpp"
#include "radio/trel_packet.hpp"

namespace ot {

class Neighbor;

namespace Trel {

/**
 * @addtogroup core-trel
 *
 * @brief
 *   This module includes definitions for Thread Radio Encapsulation Link (TREL)
 *
 * @{
 */

/**
 * Represents a Thread Radio Encapsulation Link (TREL).
 */
class Link : public InstanceLocator
{
    friend class ot::Instance;
    friend class ot::Notifier;
    friend class Interface;

public:
    static constexpr uint16_t kMtuSize = 1280 - 48 - sizeof(Header); ///< MTU size for TREL frame.
    static constexpr uint8_t  kFcsSize = 0;                          ///< FCS size for TREL frame.

    /**
     * Used as input by `CheckPeerAddrOnRxSuccess()` to determine whether the peer socket address can be updated based
     * on a received TREL packet from the peer if there is a discrepancy.
     */
    enum PeerSockAddrUpdateMode : uint8_t
    {
        kAllowPeerSockAddrUpdate,    ///< Peer socket address can be updated.
        kDisallowPeerSockAddrUpdate, ///< Peer socket address cannot be updated.
    };

    /**
     * Initializes the `Link` object.
     *
     * @param[in]  aInstance  A reference to the OpenThread instance.
     */
    explicit Link(Instance &aInstance);

    /**
     * Sets the PAN Identifier.
     *
     * @param[in] aPanId   A PAN Identifier.
     */
    void SetPanId(Mac::PanId aPanId) { mPanId = aPanId; }

    /**
     * Notifies TREL radio link that device's extended MAC address has changed for it to update any
     * internal address/state.
     */
    void HandleExtAddressChange(void) { mInterface.HandleExtAddressChange(); }

    /**
     * Enables the TREL radio link.
     */
    void Enable(void);

    /**
     * Disables the TREL radio link.
     */
    void Disable(void);

    /**
     * Requests TREL radio link to transition to Sleep mode
     */
    void Sleep(void);

    /**
     * Requests TREL radio link to transition to Receive mode on a given channel.
     *
     * `Mac::HandleReceivedFrame()` is used to notify MAC layer upon receiving a frame.
     *
     * @param[in] aChannel   The channel to receive on.
     */
    void Receive(uint8_t aChannel);

    /**
     * Gets the radio transmit frame for TREL radio link.
     *
     * @returns The transmit frame.
     */
    Mac::TxFrame &GetTransmitFrame(void) { return mTxFrame; }

    /**
     * Requests a frame to be sent over TREL radio link.
     *
     * The frame should be already placed in `GetTransmitFrame()` frame.
     *
     * `Mac::RecordFrameTransmitStatus()` and `Mac::HandleTransmitDone()` are used to notify the success or error status
     * of frame transmission upon completion of send.
     */
    void Send(void);

    /**
     * Checks the address/port from the last received TREL packet against the ones recorded in the corresponding `Peer`
     * entry and acts if there is a discrepancy.
     *
     * This method signals to the platform about the discrepancy. Based on @p aMode, it may also update the `Peer`
     * entry information directly to match the new address/port information.
     *
     * @param[in] aMode   Determines whether to update the `Peer` entry if there is a discrepancy.
     */
    void CheckPeerAddrOnRxSuccess(PeerSockAddrUpdateMode aMode);

private:
    static constexpr uint16_t kMaxHeaderSize   = sizeof(Header);
    static constexpr uint16_t k154AckFrameSize = 3 + kFcsSize;
    static constexpr int8_t   kRxRssi          = -20; // The RSSI value used for received frames on TREL radio link.
    static constexpr uint32_t kAckWaitWindow   = 750; // (in msec)
    static constexpr uint16_t kFcfFramePending = 1 << 4;

    typedef Interface::Peer Peer;

    enum State : uint8_t
    {
        kStateDisabled,
        kStateSleep,
        kStateReceive,
        kStateTransmit,
    };

    void AfterInit(void);
    void SetState(State aState);
    void BeginTransmit(void);
    void InvokeSendDone(Error aError) { InvokeSendDone(aError, nullptr); }
    void InvokeSendDone(Error aError, Mac::RxFrame *aAckFrame);
    void ProcessReceivedPacket(Packet &aPacket, const Ip6::SockAddr &aSockAddr);
    void HandleAck(Packet &aAckPacket);
    void SendAck(Packet &aRxPacket);
    void ReportDeferredAckStatus(Neighbor &aNeighbor, Error aError);
    void HandleTimer(Neighbor &aNeighbor);
    void HandleNotifierEvents(Events aEvents);
    void HandleTxTasklet(void);
    void HandleTimer(void);

    static const char *StateToString(State aState);

    using TxTasklet    = TaskletIn<Link, &Link::HandleTxTasklet>;
    using TimeoutTimer = TimerMilliIn<Link, &Link::HandleTimer>;

    State         mState;
    uint8_t       mRxChannel;
    Mac::PanId    mPanId;
    uint32_t      mTxPacketNumber;
    TxTasklet     mTxTasklet;
    TimeoutTimer  mTimer;
    Interface     mInterface;
    Ip6::SockAddr mRxPacketSenderAddr;
    Peer         *mRxPacketPeer;
    Mac::RxFrame  mRxFrame;
    Mac::TxFrame  mTxFrame;
    uint8_t       mTxPacketBuffer[kMaxHeaderSize + kMtuSize];
    uint8_t       mAckPacketBuffer[kMaxHeaderSize];
    uint8_t       mAckFrameBuffer[k154AckFrameSize];
};

/**
 * Defines all the neighbor info required for TREL link.
 *
 * `Neighbor` class publicly inherits from this class.
 */
class NeighborInfo
{
    friend class Link;

private:
    uint32_t GetPendingTrelAckCount(void) const { return (mTrelPreviousPendingAcks + mTrelCurrentPendingAcks); }

    void DecrementPendingTrelAckCount(void)
    {
        if (mTrelPreviousPendingAcks != 0)
        {
            mTrelPreviousPendingAcks--;
        }
        else if (mTrelCurrentPendingAcks != 0)
        {
            mTrelCurrentPendingAcks--;
        }
    }

    uint32_t GetExpectedTrelAckNumber(void) const { return mTrelTxPacketNumber - GetPendingTrelAckCount(); }

    bool IsRxAckNumberValid(uint32_t aAckNumber) const
    {
        // Note that calculating the difference between `aAckNumber`
        // and `GetExpectedTrelAckNumber` will correctly handle the
        // roll-over of packet number value.

        return (GetPendingTrelAckCount() != 0) && (aAckNumber - GetExpectedTrelAckNumber() < GetPendingTrelAckCount());
    }

    uint32_t mTrelTxPacketNumber;      // Next packet number to use for tx
    uint16_t mTrelCurrentPendingAcks;  // Number of pending acks for current interval.
    uint16_t mTrelPreviousPendingAcks; // Number of pending acks for previous interval.
};

/**
 * @}
 */

} // namespace Trel
} // namespace ot

#endif // #if OPENTHREAD_CONFIG_RADIO_LINK_TREL_ENABLE

#endif // TREL_LINK_HPP_