/*
 *  Copyright (c) 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
 *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *  POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * @file
 *   This file includes definitions for the Received RA Tracker.
 */

#ifndef OT_CORE_BORDER_ROUTER_RX_RA_TRACKER_HPP_
#define OT_CORE_BORDER_ROUTER_RX_RA_TRACKER_HPP_

#include "openthread-core-config.h"

#if OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE

#include <openthread/border_routing.h>

#include "border_router/br_types.hpp"
#include "border_router/infra_if.hpp"
#include "common/callback.hpp"
#include "common/clearable.hpp"
#include "common/equatable.hpp"
#include "common/error.hpp"
#include "common/heap_allocatable.hpp"
#include "common/linked_list.hpp"
#include "common/locator.hpp"
#include "common/message.hpp"
#include "common/notifier.hpp"
#include "common/owning_list.hpp"
#include "common/pool.hpp"
#include "common/string.hpp"
#include "common/tasklet.hpp"
#include "common/timer.hpp"
#include "net/ip6.hpp"
#include "net/nd6.hpp"

namespace ot {
namespace BorderRouter {

class NetDataBrTracker;

/**
 * Implements processing and tracking of received Router Advertisement (RA) and Neighbor Advertisement (NA) messages.
 *
 * This class processes received RA and NA messages, tracking a table of active routers on the infrastructure link and
 * their advertised on-link and route prefixes and other information. It also manages prefix lifetimes and router
 * reachability (sending Neighbor Solicitation probes as needed).
 */
class RxRaTracker : public InstanceLocator
{
    friend class NetDataBrTracker;
    friend class ot::Notifier;
    friend class InfraIf;

public:
    /**
     * Represents an entity requesting to enable/disable the `RxRaTracker`.
     */
    enum Requester : uint8_t
    {
        kRequesterRoutingManager,   ///< Requested by `RoutingManager`.
        kRequesterMultiAilDetector, ///< Requested by `MultiAilDetector`.
    };

    /**
     * Represents different events that can occur within the `RxRaTracker`.
     *
     * Used in callbacks `HandleRxRaTrackerEvents()` to notify other BR components of changes/events by `RxRaTracker`.
     */
    struct Events : public Clearable<Events>
    {
        bool mInitialDiscoveryFinished : 1; ///< Indicates that the initial router discovery process is finished.
        bool mDecisionFactorChanged : 1;    ///< Indicates that a decision factor (e.g., on-link prefix) was changed.
        bool mLocalRaHeaderChanged : 1;     ///< Indicates that the tracked local RA header was changed.
    };

    /**
     * Initializes the `RxRaTracker` object.
     *
     * @param[in] aInstance  The OpenThread instance.
     */
    explicit RxRaTracker(Instance &aInstance);

    /**
     * Enables or disables the `RxRaTracker`.
     *
     * The `RxRaTracker` can be enabled by multiple requesters (see `Requester`). It remains enabled as long as
     * at least one requester has it enabled. It is disabled only when all requesters have disabled it.
     *
     * @param[in] aEnable      A boolean to enable/disable the  Tracker.
     * @param[in] aRequester   The entity requesting to enable/disable.
     */
    void SetEnabled(bool aEnable, Requester aRequester);

    /**
     * Indicates whether the initial router discovery process (sending Router Solicitation (RS) message) is finished.
     *
     * When `RxRaTracker` is started, it sends multiple RS messages to discover routers on the infrastructure interface.
     * It sends three RS messages every four seconds, starting with a random delay of up to one second for the first
     * RS transmission. After sending the final RS message, it waits one second before concluding discovery process.
     *
     * @retval TRUE   If the initial router discovery process is finished.
     * @retval FALSE  If the initial router discovery process is not finished.
     */
    bool IsInitialRouterDiscoveryFinished(void) const { return mInitialDiscoveryFinished; }

    /**
     * Initializes a `PrefixTableIterator`.
     *
     * An iterator can be initialized again to start from the beginning of the table.
     *
     * When iterating over entries in the table, to ensure the entry update times are consistent, they are given
     * relative to the time the iterator was initialized.
     *
     * @param[out] aIterator  The iterator to initialize.
     */
    void InitIterator(PrefixTableIterator &aIterator) const;

    /**
     * Iterates over entries in the discovered prefix table.
     *
     * @param[in,out] aIterator  An iterator.
     * @param[out]    aEntry     A reference to the entry to populate.
     *
     * @retval kErrorNone        Got the next entry, @p aEntry is updated and @p aIterator is advanced.
     * @retval kErrorNotFound    No more entries in the table.
     */
    Error GetNextPrefixTableEntry(PrefixTableIterator &aIterator, PrefixTableEntry &aEntry) const;

    /**
     * Iterates over discovered router entries on infrastructure link.
     *
     * @param[in,out] aIterator  An iterator.
     * @param[out]    aEntry     A reference to the entry to populate.
     *
     * @retval kErrorNone        Got the next router info, @p aEntry is updated and @p aIterator is advanced.
     * @retval kErrorNotFound    No more routers.
     */
    Error GetNextRouterEntry(PrefixTableIterator &aIterator, RouterEntry &aEntry) const;

#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
    /**
     * Iterates over the discovered NAT64 prefix entries.
     *
     * @param[in,out] aIterator    An iterator.
     * @param[out]    aEntry       A reference to the entry to populate.
     *
     * @retval kErrorNone         Iterated to the next address entry, @p aEntry and @p aIterator are updated.
     * @retval kErrorNotFound     No more entries in the table.
     * @retval kErrorInvalidArgs  The @p aIterator is not valid (e.g. used to iterate over other entry types).
     */
    Error GetNextNat64PrefixEntry(PrefixTableIterator &aIterator, Nat64PrefixEntry &aEntry) const;
#endif

    /**
     * Iterates over the discovered Recursive DNS Server (RDNSS) address entries.
     *
     * @param[in,out] aIterator    An iterator.
     * @param[out]    aEntry       A reference to the entry to populate.
     *
     * @retval kErrorNone         Iterated to the next address entry, @p aEntry and @p aIterator are updated.
     * @retval kErrorNotFound     No more entries in the table.
     * @retval kErrorInvalidArgs  The @p aIterator is not valid (e.g. used to iterate over other entry types).
     */
    Error GetNextRdnssAddrEntry(PrefixTableIterator &aIterator, RdnssAddrEntry &aEntry) const;

    /**
     * Sets the callback to be notified of changes to discovered Recursive DNS Server (RDNSS) address entries.
     *
     * A subsequent call to this method, replaces a previously set callback.
     *
     * @param[in] aCallback   The callback function pointer. Can be `nullptr` if no callback is required.
     * @param[in] aConext     An arbitrary context information (used when invoking the callback).
     */
    void SetRdnssAddrCallback(RdnssAddrCallback aCallback, void *aContext) { mRdnssCallback.Set(aCallback, aContext); }

    /**
     * Iterates over the infrastructure interface address entries.
     *
     * These are addresses used by the BR itself, for example, when sending Router Advertisements.
     *
     * @param[in,out] aIterator    An iterator.
     * @param[out]    aEntry       A reference to the entry to populate.
     *
     * @retval kErrorNone         Iterated to the next address entry, @p aEntry and @p aIterator are updated.
     * @retval kErrorNotFound     No more entries in the table.
     * @retval kErrorInvalidArgs  The @p aIterator is not valid (e.g. used to iterate over other entry types).
     */
    Error GetNextIfAddrEntry(PrefixTableIterator &aIterator, IfAddrEntry &aEntry) const;

    /**
     * Indicates whether a discovered route prefix is a default route or a non-ULA prefix.
     *
     * @retval TRUE   A default route or a non-ULA route prefix is discovered.
     * @retval FALSE  No default route or non-ULA route prefix is discovered.
     */
    bool ContainsDefaultOrNonUlaRoutePrefix(void) const { return mDecisionFactors.mHasNonUlaRoute; }

    /**
     * Indicates whether a discovered on-link prefix is a non-ULA prefix.
     *
     * @retval TRUE   A non-ULA on-link prefix is discovered.
     * @retval FALSE  No non-ULA on-link prefix is discovered.
     */
    bool ContainsNonUlaOnLinkPrefix(void) const { return mDecisionFactors.mHasNonUlaOnLink; }

    /**
     * Indicates whether a discovered on-link prefix is a ULA prefix.
     *
     * @retval TRUE   A ULA on-link prefix is discovered.
     * @retval FALSE  No ULA on-link prefix is discovered.
     */
    bool ContainsUlaOnLinkPrefix(void) const { return mDecisionFactors.mHasUlaOnLink; }

#if OPENTHREAD_CONFIG_BORDER_ROUTING_MULTI_AIL_DETECTION_ENABLE
    /**
     * Gets the number of reachable peer Border Routers.
     *
     * A peer BR is a BR on the same Thread mesh that is also connected to the same infrastructure link.
     *
     * @returns The number of reachable peer BRs.
     */
    uint16_t GetReachablePeerBrCount(void) const { return mDecisionFactors.mReachablePeerBrCount; }
#endif

    /**
     * Gets the favored on-link prefix among all discovered on-link prefixes.
     *
     * @returns The favored on-link prefix.
     */
    const Ip6::Prefix &GetFavoredOnLinkPrefix(void) const { return mDecisionFactors.mFavoredOnLinkPrefix; }

#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
    /**
     * Gets the favored NAT64 prefix among all discovered NAT64 prefixes.
     *
     * @returns The favored NAT64 prefix.
     */
    const Ip6::Prefix &GetFavoredNat64Prefix(void) const { return mDecisionFactors.mFavoredNat64Prefix; }
#endif

    /**
     * Sets the Managed Address Configuration (M) and Other Configuration (O) flags on a Router Advertisement header.
     *
     * The flags are set based on the currently discovered information from other routers on the infrastructure link.
     *
     * @param[out] aHeader  The RA header to update.
     */
    void SetHeaderFlagsOn(RouterAdvert::Header &aHeader) const;

    /**
     * Gets the last received Router Advertisement header from a local software entity.
     *
     * This can be used to mirror the RA flags in the RA messages sent by the Border Router.
     *
     * @returns The last received RA header from a local software entity.
     */
    const RouterAdvert::Header &GetLocalRaHeaderToMirror(void) const { return mLocalRaHeader; }

    /**
     * Indicates whether an address is considered on-link on the infrastructure link.
     *
     * An address is considered on-link if it matches the local on-link prefix or any of the discovered on-link
     * prefixes advertised by other routers.
     *
     * @param[in] aAddress  The IPv6 address to check.
     *
     * @retval TRUE   The address is on-link.
     * @retval FALSE  The address is not on-link.
     */
    bool IsAddressOnLink(const Ip6::Address &aAddress) const;

    /**
     * Indicates whether an address is reachable through an explicit route on the infrastructure link.
     *
     * This method checks if the given address matches any discovered route prefix, excluding the default route.
     *
     * @param[in] aAddress  The IPv6 address to check.
     *
     * @retval TRUE   The address is reachable through an explicit route.
     * @retval FALSE  The address is not reachable through an explicit route.
     */
    bool IsAddressReachableThroughExplicitRoute(const Ip6::Address &aAddress) const;

    /**
     * Indicates whether a given prefix is seen as an on-link prefix in any tracked RA.
     *
     * @param[in] aPrefix  The IPv6 prefix to check.
     *
     * @retval TRUE   The prefix is on-link.
     * @retval FALSE  The prefix is not on-link.
     */
    bool IsPrefixOnLink(const Ip6::Prefix &aPrefix) const;

    /**
     * Indicates whether a given prefix is seen as a route prefix advertised by any router.
     *
     * @param[in] aPrefix  The IPv6 prefix to check.
     *
     * @retval TRUE   The prefix is seen as a route prefix.
     * @retval FALSE  The prefix is not seen as a route prefix.
     */
    bool ContainsRoutePrefix(const Ip6::Prefix &aPrefix) const;

    // Callbacks notifying of changes
    void HandleLocalOnLinkPrefixChanged(void);

private:
    static constexpr uint32_t kStaleTime = 600; // 10 minutes.

    typedef Ip6::Nd::Option    Option;
    typedef Ip6::Nd::TxMessage TxMessage;

    //-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

    enum RouterAdvOrigin : uint8_t
    {
        kAnotherRouter,        // From another router on the infrastructure interface.
        kThisBrRoutingManager, // From this Border Router, generated by `RoutingManager` itself.
        kThisBrOtherEntity,    // From this Border Router, generated by another software entity.
    };

    //-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

    template <class Type>
    struct Entry : public Type,
                   public LinkedListEntry<Entry<Type>>,
#if OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE
                   public Heap::Allocatable<Entry<Type>>
#else
                   public InstanceLocatorInit
#endif
    {
#if !OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE
        void Init(Instance &aInstance) { InstanceLocatorInit::Init(aInstance); }
        void Free(void);
#endif

        Entry<Type> *mNext;
    };

    //-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

    struct Router : public Clearable<Router>
    {
        // Reachability timeout intervals before starting Neighbor
        // Solicitation (NS) probes. Generally 60 seconds (± 2
        // seconds jitter) is used. For peer BRs a longer timeout
        // of 200 seconds (3 min and 20 seconds) is used. This is
        // selected to be longer than regular RA beacon interval
        // of 3 minutes (± 15 seconds jitter).

        static constexpr uint32_t kReachableInterval = OPENTHREAD_CONFIG_BORDER_ROUTING_ROUTER_ACTIVE_CHECK_TIMEOUT;
        static constexpr uint32_t kPeerBrReachableInterval = Time::kOneSecondInMsec * 200;

        static constexpr uint8_t  kMaxNsProbes          = 5;    // Max number of NS probe attempts.
        static constexpr uint32_t kNsProbeRetryInterval = 1000; // In msec. Time between NS probe attempts.
        static constexpr uint32_t kNsProbeTimeout       = 2000; // In msec. Max Wait time after last NS probe.
        static constexpr uint32_t kJitter               = 2000; // In msec. Jitter to randomize probe starts.

        static_assert(kMaxNsProbes < 255, "kMaxNsProbes MUST not be 255");

        struct EmptyChecker
        {
        };

#if OPENTHREAD_CONFIG_HISTORY_TRACKER_ENABLE
        struct HistoryInfo : public Equatable<HistoryInfo>, public Clearable<HistoryInfo>
        {
            void DetermineFrom(const Router &aRouter);

            bool            mHistoryRecorded : 1;
            bool            mManagedAddressConfigFlag : 1;
            bool            mOtherConfigFlag : 1;
            bool            mSnacRouterFlag : 1;
            bool            mIsLocalDevice : 1;
            bool            mIsReachable : 1;
            bool            mIsPeerBr : 1;
            bool            mProvidesDefaultRoute : 1;
            RoutePreference mDefRoutePreference;
            Ip6::Prefix     mFavoredOnLinkPrefix;
        };
#endif

        bool IsReachable(void) const { return mNsProbeCount <= kMaxNsProbes; }
        bool ShouldCheckReachability(void) const;
        void ResetReachabilityState(void);
        void DetermineReachabilityTimeout(void);
        bool Matches(const Ip6::Address &aAddress) const { return aAddress == mAddress; }
        bool Matches(const EmptyChecker &aChecker);
        bool IsPeerBr(void) const;
        void CopyInfoTo(RouterEntry &aEntry, TimeMilli aNow, uint32_t aUptime) const;

        using OnLinkPrefixList = OwningList<Entry<OnLinkPrefix>>;
        using RoutePrefixList  = OwningList<Entry<RoutePrefix>>;
#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
        using Nat64PrefixList = OwningList<Entry<Nat64Prefix>>;
#endif
        using RdnssAddressList = OwningList<Entry<RdnssAddress>>;

        // `mDiscoverTime` tracks the initial discovery time of
        // this router. To accommodate longer durations, the
        // `Uptime` is used, as `TimeMilli` (which uses `uint32_t`
        // intervals) would be limited to tracking ~ 49 days.
        //
        // `mLastUpdateTime` tracks the most recent time an RA or
        // NA was received from this router. It is bounded due to
        // the frequency of reachability checks, so we can safely
        // use `TimeMilli` for it.

        Ip6::Address     mAddress;
        OnLinkPrefixList mOnLinkPrefixes;
        RoutePrefixList  mRoutePrefixes;
#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
        Nat64PrefixList mNat64Prefixes;
#endif
        RdnssAddressList mRdnssAddresses;
        UptimeSec        mDiscoverTime;
        TimeMilli        mLastUpdateTime;
        TimeMilli        mTimeoutTime;
        uint8_t          mNsProbeCount;
        bool             mManagedAddressConfigFlag : 1;
        bool             mOtherConfigFlag : 1;
        bool             mSnacRouterFlag : 1;
        bool             mIsLocalDevice : 1;
        bool             mAllEntriesDisregarded : 1;
#if OPENTHREAD_CONFIG_HISTORY_TRACKER_ENABLE
        HistoryInfo mHistoryInfo;
#endif
    };

    //-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

    struct Iterator : public PrefixTableIterator
    {
        enum Type : uint8_t
        {
            kUnspecified,
            kRouterIterator,
            kPrefixIterator,
            kNat64PrefixIterator,
            kRdnssAddrIterator,
            kIfAddrIterator,
            kNetDataBrIterator, // Used by `NetDataPeerBrTracker`
        };

        enum PrefixType : uint8_t
        {
            kOnLinkPrefix,
            kRoutePrefix,
        };

        void  Init(const Entry<Router> *aRoutersHead, UptimeSec aUptime);
        Error AdvanceToNextRouter(Type aType);
        Error AdvanceToNextPrefixEntry(void);
#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
        Error AdvanceToNextNat64PrefixEntry(void);
#endif
        Error                AdvanceToNextRdnssAddrEntry(void);
        Error                AdvanceToNextIfAddrEntry(const Entry<IfAddress> *aListHead);
        UptimeSec            GetInitUptime(void) const { return mData0; }
        void                 SetInitUptime(UptimeSec aUptime) { mData0 = aUptime; }
        TimeMilli            GetInitTime(void) const { return TimeMilli(mData1); }
        void                 SetInitTime(void) { mData1 = TimerMilli::GetNow().GetValue(); }
        const Entry<Router> *GetRouter(void) const { return static_cast<const Entry<Router> *>(mPtr1); }
        void                 SetRouter(const Entry<Router> *aRouter) { mPtr1 = aRouter; }
        Type                 GetType(void) const { return static_cast<Type>(mData2); }
        void                 SetType(Type aType) { mData2 = aType; }
        const void          *GetEntry(void) const { return mPtr2; }
        void                 SetEntry(const void *aEntry) { mPtr2 = aEntry; }
        bool                 HasEntry(void) const { return mPtr2 != nullptr; }
        PrefixType           GetPrefixType(void) const { return static_cast<PrefixType>(mData3); }
        void                 SetPrefixType(PrefixType aType) { mData3 = aType; }

        template <typename ObjectType> const Entry<ObjectType> *GetEntry(void) const
        {
            return static_cast<const Entry<ObjectType> *>(mPtr2);
        }
    };

    //-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

#if !OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE
    static constexpr uint16_t kMaxRouters = OPENTHREAD_CONFIG_BORDER_ROUTING_MAX_DISCOVERED_ROUTERS;
    static constexpr uint16_t kMaxEntries = OPENTHREAD_CONFIG_BORDER_ROUTING_MAX_DISCOVERED_PREFIXES;

    union SharedEntry
    {
        SharedEntry(void) { mNext = nullptr; }
        void               SetNext(SharedEntry *aNext) { mNext = aNext; }
        SharedEntry       *GetNext(void) { return mNext; }
        const SharedEntry *GetNext(void) const { return mNext; }

        template <class Type> Entry<Type> &GetEntry(void);

        SharedEntry        *mNext;
        Entry<OnLinkPrefix> mOnLinkEntry;
        Entry<RoutePrefix>  mRouteEntry;
#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
        Entry<Nat64Prefix> mNat64PrefixEntry;
#endif
        Entry<RdnssAddress> mRdnssAddrEntry;
        Entry<IfAddress>    mIfAddrEntry;
    };
#endif

    //-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

    struct DecisionFactors : public Clearable<DecisionFactors>, public Equatable<DecisionFactors>
    {
        DecisionFactors(void) { Clear(); }

        bool HasFavoredOnLink(void) const { return (mFavoredOnLinkPrefix.GetLength() != 0); }
        void UpdateFlagsFrom(const Router &aRouter);
        void UpdateFrom(const OnLinkPrefix &aOnLinkPrefix);
        void UpdateFrom(const RoutePrefix &aRoutePrefix);
#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
        void UpdateFrom(const Nat64Prefix &aNat64Prefix);
#endif

        Ip6::Prefix mFavoredOnLinkPrefix;
#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
        Ip6::Prefix mFavoredNat64Prefix;
#endif
        bool mHasNonUlaRoute : 1;
        bool mHasNonUlaOnLink : 1;
        bool mHasUlaOnLink : 1;
        bool mHeaderManagedAddressConfigFlag : 1;
        bool mHeaderOtherConfigFlag : 1;

#if OPENTHREAD_CONFIG_BORDER_ROUTING_MULTI_AIL_DETECTION_ENABLE
        uint16_t mReachablePeerBrCount;
#endif
    };

    //-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

    void HandleRsSenderTimer(void) { mRsSender.HandleTimer(); }

    class RsSender : public InstanceLocator
    {
    public:
        // This class implements tx of Router Solicitation (RS)
        // messages to discover other routers. `Start()` schedules
        // a cycle of RS transmissions of `kMaxTxCount` separated
        // by `kTxInterval`. At the end of cycle the callback
        // `HandleRsSenderFinished()` is invoked to inform end of
        // the cycle to `RxRaTracker`.

        explicit RsSender(Instance &aInstance);

        bool IsInProgress(void) const { return mTimer.IsRunning(); }
        void Start(void);
        void Stop(void);
        void HandleTimer(void);

    private:
        // All time intervals are in msec.
        static constexpr uint32_t kMaxStartDelay     = 1000;        // Max random delay to send the first RS.
        static constexpr uint32_t kTxInterval        = 4000;        // Interval between RS tx.
        static constexpr uint32_t kRetryDelay        = kTxInterval; // Interval to wait to retry a failed RS tx.
        static constexpr uint32_t kWaitOnLastAttempt = 1000;        // Wait interval after last RS tx.
        static constexpr uint8_t  kMaxTxCount        = 3;           // Number of RS tx in one cycle.

        Error SendRs(void);

        using RsTimer = TimerMilliIn<RxRaTracker, &RxRaTracker::HandleRsSenderTimer>;

        uint8_t   mTxCount;
        RsTimer   mTimer;
        TimeMilli mStartTime;
    };

    //-  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -  -

    void UpdateState(void);
    void Start(void);
    void Stop(void);
    void HandleRsSenderFinished(TimeMilli aStartTime);
    void ProcessRaHeader(const RouterAdvert::Header &aRaHeader, Router &aRouter, RouterAdvOrigin aRaOrigin);
    void ProcessPrefixInfoOption(const PrefixInfoOption &aPio, Router &aRouter);
    void ProcessRouteInfoOption(const RouteInfoOption &aRio, Router &aRouter);
#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
    void ProcessNat64PrefixOption(const Nat64PrefixOption &aNat64Prefix, Router &aRouter);
#endif
    void ProcessRecursiveDnsServerOption(const RecursiveDnsServerOption &aRdnss, Router &aRouter);
    void UpdateIfAddresses(const Ip6::Address &aAddress);
    void RemoveOrDeprecateOldEntries(TimeMilli aTimeThreshold);
    void Evaluate(void);
    void DetermineStaleTimeFor(const OnLinkPrefix &aPrefix, NextFireTime &aStaleTime);
    void DetermineStaleTimeFor(const RoutePrefix &aPrefix, NextFireTime &aStaleTime);
    void SendNeighborSolicitToRouter(const Router &aRouter);
#if OPENTHREAD_CONFIG_BORDER_ROUTING_MULTI_AIL_DETECTION_ENABLE
    uint16_t CountReachablePeerBrs(void) const;
#endif
#if OPENTHREAD_CONFIG_HISTORY_TRACKER_ENABLE
    void ReportChangesToHistoryTracker(Router &aRouter, bool aRemoved);
#endif
    void HandleNotifierEvents(ot::Events aEvents);
    void HandleNetDataChange(void);

    // Callbacks from `InfraIf`
    void HandleInfraIfStateChanged(void) { UpdateState(); }
    void HandleRouterAdvertisement(const InfraIf::Icmp6Packet &aPacket, const Ip6::Address &aSrcAddress);
    void HandleNeighborAdvertisement(const InfraIf::Icmp6Packet &aPacket);

    // Tasklet or timer callbacks
    void HandleEventTask(void);
    void HandleRdnssAddrTask(void);
    void HandleExpirationTimer(void);
    void HandleStaleTimer(void);
    void HandleRouterTimer(void);
    void HandleRdnssAddrTimer(void);

#if OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE
    template <class Type> Entry<Type> *AllocateEntry(void) { return Entry<Type>::Allocate(); }
#else
    template <class Type> Entry<Type> *AllocateEntry(void);
#endif

    static const char *RouterAdvOriginToString(RouterAdvOrigin aRaOrigin);

    using EventTask       = TaskletIn<RxRaTracker, &RxRaTracker::HandleEventTask>;
    using RdnssAddrTask   = TaskletIn<RxRaTracker, &RxRaTracker::HandleRdnssAddrTask>;
    using ExpirationTimer = TimerMilliIn<RxRaTracker, &RxRaTracker::HandleExpirationTimer>;
    using StaleTimer      = TimerMilliIn<RxRaTracker, &RxRaTracker::HandleStaleTimer>;
    using RouterTimer     = TimerMilliIn<RxRaTracker, &RxRaTracker::HandleRouterTimer>;
    using RdnssAddrTimer  = TimerMilliIn<RxRaTracker, &RxRaTracker::HandleRdnssAddrTimer>;
    using RouterList      = OwningList<Entry<Router>>;
    using IfAddressList   = OwningList<Entry<IfAddress>>;
    using RdnssCallback   = Callback<RdnssAddrCallback>;

    bool                 mRoutingManagerEnabled : 1;
    bool                 mMultiAilDetectorEnabled : 1;
    bool                 mIsRunning : 1;
    bool                 mInitialDiscoveryFinished : 1;
    Events               mPendingEvents;
    RsSender             mRsSender;
    DecisionFactors      mDecisionFactors;
    RouterList           mRouters;
    IfAddressList        mIfAddresses;
    ExpirationTimer      mExpirationTimer;
    StaleTimer           mStaleTimer;
    RouterTimer          mRouterTimer;
    RdnssAddrTimer       mRdnssAddrTimer;
    EventTask            mEventTask;
    RdnssAddrTask        mRdnssAddrTask;
    RdnssCallback        mRdnssCallback;
    RouterAdvert::Header mLocalRaHeader;
    TimeMilli            mLocalRaHeaderUpdateTime;

#if !OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE
    Pool<SharedEntry, kMaxEntries>   mEntryPool;
    Pool<Entry<Router>, kMaxRouters> mRouterPool;
#endif
};

#if !OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE

//----------------------------------------------------------------------------------------------------------------------
// Template specializations and declarations

template <> inline RxRaTracker::Entry<OnLinkPrefix> &RxRaTracker::SharedEntry::GetEntry(void) { return mOnLinkEntry; }

template <> inline RxRaTracker::Entry<RoutePrefix> &RxRaTracker::SharedEntry::GetEntry(void) { return mRouteEntry; }

#if OPENTHREAD_CONFIG_NAT64_BORDER_ROUTING_ENABLE
template <> inline RxRaTracker::Entry<Nat64Prefix> &RxRaTracker::SharedEntry::GetEntry(void)
{
    return mNat64PrefixEntry;
}
#endif

template <> inline RxRaTracker::Entry<RdnssAddress> &RxRaTracker::SharedEntry::GetEntry(void)
{
    return mRdnssAddrEntry;
}

template <> inline RxRaTracker::Entry<IfAddress> &RxRaTracker::SharedEntry::GetEntry(void) { return mIfAddrEntry; }

// Declare template (full) specializations for `Router` type.

template <> RxRaTracker::Entry<RxRaTracker::Router> *RxRaTracker::AllocateEntry(void);

template <> void RxRaTracker::Entry<RxRaTracker::Router>::Free(void);

#endif // #if !OPENTHREAD_CONFIG_BORDER_ROUTING_USE_HEAP_ENABLE

} // namespace BorderRouter
} // namespace ot

#endif // OPENTHREAD_CONFIG_BORDER_ROUTING_ENABLE

#endif // OT_CORE_BORDER_ROUTER_RX_RA_TRACKER_HPP_
