/*
 *  Copyright (c) 2019-2025, The OpenThread Authors.
 *  All rights reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  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
 *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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 */

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

#ifndef TREL_PEER_DISCOVERER_HPP_
#define TREL_PEER_DISCOVERER_HPP_

#include "openthread-core-config.h"

#if OPENTHREAD_CONFIG_RADIO_LINK_TREL_ENABLE

#include <openthread/platform/trel.h>

#include "common/clearable.hpp"
#include "common/locator.hpp"
#include "common/tasklet.hpp"
#include "radio/trel_peer.hpp"

namespace ot {
namespace Trel {

class Link;

extern "C" void otPlatTrelHandleDiscoveredPeerInfo(otInstance *aInstance, const otPlatTrelPeerInfo *aInfo);

/**
 * Represents a TREL module responsible for peer discovery and mDNS service registration.
 */
class PeerDiscoverer : public InstanceLocator
{
    friend class Link;
    friend void otPlatTrelHandleDiscoveredPeerInfo(otInstance *aInstance, const otPlatTrelPeerInfo *aInfo);

public:
    /**
     * Starts the peer discovery.
     */
    void Start(void);

    /**
     * Stops the peer discovery and clears the peer table.
     */
    void Stop(void);

    /**
     * Notifies that device's Extended MAC Address has changed.
     */
    void HandleExtAddressChange(void) { PostRegisterServiceTask(); }

    /**
     * Notifies that device's Extended PAN Identifier has changed.
     */
    void HandleExtPanIdChange(void) { PostRegisterServiceTask(); }

    /**
     * Notifies that a TREL packet is received from a peer using a different socket address than the one reported
     * earlier.
     *
     * @param[in] aPeerSockAddr   The previously reported peer sock address.
     * @param[in] aRxSockAddr     The address of received packet from the same peer.
     */
    void NotifyPeerSocketAddressDifference(const Ip6::SockAddr &aPeerSockAddr, const Ip6::SockAddr &aRxSockAddr);

private:
    static constexpr uint32_t kRemoveDelay = 7 * Time::kOneSecondInMsec;

    class TxtData
    {
    public:
        struct Info : public Clearable<Info>
        {
            Mac::ExtAddress        mExtAddress;
            MeshCoP::ExtendedPanId mExtPanId;
        };

        void           Init(const uint8_t *aData, uint16_t aLength);
        const uint8_t *GetBytes(void) const { return mData; }
        uint16_t       GetLength(void) const { return mLength; }
        Error          Decode(Info &aInfo);

    protected:
        static const char kExtAddressKey[]; // "xa"
        static const char kExtPanIdKey[];   // "xp"

        const uint8_t *mData;
        uint16_t       mLength;
    };

    class TxtDataEncoder : public InstanceLocator, public TxtData
    {
    public:
        explicit TxtDataEncoder(Instance &aInstance);
        void Encode(void);

    private:
        // TXT data consists of two entries: `xa` for extended address
        // and `xp` for extended PAN ID. Each entry starts with one
        // byte for length, then the two-character key, followed by
        // an `=` character, and then the value. This adds up to
        // (4 + 8 [value]) = 12 bytes total per entry. The value of
        // 32 accommodates these two entries and more.
        static constexpr uint8_t kMaxSize = 32;

        uint8_t mBuffer[kMaxSize];
    };

    struct PeerInfo : public otPlatTrelPeerInfo
    {
        bool                 IsRemoved(void) const { return mRemoved; }
        const Ip6::SockAddr &GetSockAddr(void) const { return AsCoreType(&mSockAddr); }
    };

    explicit PeerDiscoverer(Instance &aInstance);

    void HandleDiscoveredPeerInfo(const PeerInfo &aInfo);
    void PostRegisterServiceTask(void);
    void RegisterService(void);

    using RegisterServiceTask = TaskletIn<PeerDiscoverer, &PeerDiscoverer::RegisterService>;

    bool                mIsRunning;
    RegisterServiceTask mRegisterServiceTask;
};

} // namespace Trel
} // namespace ot

#endif // #if OPENTHREAD_CONFIG_RADIO_LINK_TREL_ENABLE

#endif // TREL_PEER_DISCOVERER_HPP_