// Copyright (c) 2024-present The Bitcoin Core developers

// Distributed under the MIT software license, see the accompanying

// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_NODE_TXDOWNLOADMAN_IMPL_H

#define BITCOIN_NODE_TXDOWNLOADMAN_IMPL_H

#include <node/txdownloadman.h>

#include <common/bloom.h>

#include <consensus/validation.h>

#include <kernel/chain.h>

#include <net.h>

#include <node/txorphanage.h>

#include <primitives/transaction.h>

#include <policy/packages.h>

#include <random.h>

#include <txrequest.h>

class CTxMemPool;

namespace node {

class TxDownloadManagerImpl {

public:

    const CTxMemPool& m_mempool;

    FastRandomContext m_rng;

    /** Manages unvalidated tx data (orphan transactions for which we are downloading ancestors). */

    std::unique_ptr<TxOrphanage> m_orphanage;

    /** Tracks candidates for requesting and downloading transaction data. */

    TxRequestTracker m_txrequest;

    /**

     * Filter for transactions that were recently rejected by the mempool.

     * These are not rerequested until the chain tip changes, at which point

     * the entire filter is reset.

     *

     * Without this filter we'd be re-requesting txs from each of our peers,

     * increasing bandwidth consumption considerably. For instance, with 100

     * peers, half of which relay a tx we don't accept, that might be a 50x

     * bandwidth increase. A flooding attacker attempting to roll-over the

     * filter using minimum-sized, 60byte, transactions might manage to send

     * 1000/sec if we have fast peers, so we pick 120,000 to give our peers a

     * two minute window to send invs to us.

     *

     * Decreasing the false positive rate is fairly cheap, so we pick one in a

     * million to make it highly unlikely for users to have issues with this

     * filter.

     *

     * We typically only add wtxids to this filter. For non-segwit

     * transactions, the txid == wtxid, so this only prevents us from

     * re-downloading non-segwit transactions when communicating with

     * non-wtxidrelay peers -- which is important for avoiding malleation

     * attacks that could otherwise interfere with transaction relay from

     * non-wtxidrelay peers. For communicating with wtxidrelay peers, having

     * the reject filter store wtxids is exactly what we want to avoid

     * redownload of a rejected transaction.

     *

     * In cases where we can tell that a segwit transaction will fail

     * validation no matter the witness, we may add the txid of such

     * transaction to the filter as well. This can be helpful when

     * communicating with txid-relay peers or if we were to otherwise fetch a

     * transaction via txid (eg in our orphan handling).

     *

     * Memory used: 1.3 MB

     */

    std::unique_ptr<CRollingBloomFilter> m_lazy_recent_rejects{nullptr};

    CRollingBloomFilter& RecentRejectsFilter()

    {

        if (!m_lazy_recent_rejects) {

            m_lazy_recent_rejects = std::make_unique<CRollingBloomFilter>(120'000, 0.000'001);

        }

        return *m_lazy_recent_rejects;

    }

    /**

     * Filter for:

     * (1) wtxids of transactions that were recently rejected by the mempool but are

     * eligible for reconsideration if submitted with other transactions.

     * (2) packages (see GetPackageHash) we have already rejected before and should not retry.

     *

     * Similar to m_lazy_recent_rejects, this filter is used to save bandwidth when e.g. all of our peers

     * have larger mempools and thus lower minimum feerates than us.

     *

     * When a transaction's error is TxValidationResult::TX_RECONSIDERABLE (in a package or by

     * itself), add its wtxid to this filter. When a package fails for any reason, add the combined

     * hash to this filter.

     *

     * Upon receiving an announcement for a transaction, if it exists in this filter, do not

     * download the txdata. When considering packages, if it exists in this filter, drop it.

     *

     * Reset this filter when the chain tip changes.

     *

     * Parameters are picked to be the same as m_lazy_recent_rejects, with the same rationale.

     */

    std::unique_ptr<CRollingBloomFilter> m_lazy_recent_rejects_reconsiderable{nullptr};

    CRollingBloomFilter& RecentRejectsReconsiderableFilter()

    {

        if (!m_lazy_recent_rejects_reconsiderable) {

            m_lazy_recent_rejects_reconsiderable = std::make_unique<CRollingBloomFilter>(120'000, 0.000'001);

        }

        return *m_lazy_recent_rejects_reconsiderable;

    }

    /*

     * Filter for transactions that have been recently confirmed.

     * We use this to avoid requesting transactions that have already been

     * confirmed.

     *

     * Blocks don't typically have more than 4000 transactions, so this should

     * be at least six blocks (~1 hr) worth of transactions that we can store,

     * inserting both a txid and wtxid for every observed transaction.

     * If the number of transactions appearing in a block goes up, or if we are

     * seeing getdata requests more than an hour after initial announcement, we

     * can increase this number.

     * The false positive rate of 1/1M should come out to less than 1

     * transaction per day that would be inadvertently ignored (which is the

     * same probability that we have in the reject filter).

     */

    std::unique_ptr<CRollingBloomFilter> m_lazy_recent_confirmed_transactions{nullptr};

    CRollingBloomFilter& RecentConfirmedTransactionsFilter()

    {

        if (!m_lazy_recent_confirmed_transactions) {

            m_lazy_recent_confirmed_transactions = std::make_unique<CRollingBloomFilter>(48'000, 0.000'001);

        }

        return *m_lazy_recent_confirmed_transactions;

    }

    TxDownloadManagerImpl(const TxDownloadOptions& options)

        : m_mempool{options.m_mempool},

          m_rng{options.m_deterministic_txrequest},

          m_orphanage{MakeTxOrphanage()},

          m_txrequest{options.m_deterministic_txrequest}

    {}

    struct PeerInfo {

        /** Information relevant to scheduling tx requests. */

        const TxDownloadConnectionInfo m_connection_info;

        PeerInfo(const TxDownloadConnectionInfo& info) : m_connection_info{info} {}

    };

    /** Information for all of the peers we may download transactions from. This is not necessarily

     * all peers we are connected to (no block-relay-only and temporary connections). */

    std::map<NodeId, PeerInfo> m_peer_info;

    /** Number of wtxid relay peers we have in m_peer_info. */

    uint32_t m_num_wtxid_peers{0};

    void ActiveTipChange();

    void BlockConnected(const std::shared_ptr<const CBlock>& pblock);

    void BlockDisconnected();

    /** Check whether we already have this gtxid in:

     *  - mempool

     *  - orphanage

     *  - m_recent_rejects

     *  - m_recent_rejects_reconsiderable (if include_reconsiderable = true)

     *  - m_recent_confirmed_transactions

     *  */

    bool AlreadyHaveTx(const GenTxid& gtxid, bool include_reconsiderable);

    void ConnectedPeer(NodeId nodeid, const TxDownloadConnectionInfo& info);

    void DisconnectedPeer(NodeId nodeid);

    /** Consider adding this tx hash to txrequest. Should be called whenever a new inv has been received.

     * Also called internally when a transaction is missing parents so that we can request them.

     */

    bool AddTxAnnouncement(NodeId peer, const GenTxid& gtxid, std::chrono::microseconds now);

    /** Get getdata requests to send. */

    std::vector<GenTxid> GetRequestsToSend(NodeId nodeid, std::chrono::microseconds current_time);

    /** Marks a tx as ReceivedResponse in txrequest. */

    void ReceivedNotFound(NodeId nodeid, const std::vector<GenTxid>& gtxids);

    /** Look for a child of this transaction in the orphanage to form a 1-parent-1-child package,

     * skipping any combinations that have already been tried. Return the resulting package along with

     * the senders of its respective transactions, or std::nullopt if no package is found. */

    std::optional<PackageToValidate> Find1P1CPackage(const CTransactionRef& ptx, NodeId nodeid);

    void MempoolAcceptedTx(const CTransactionRef& tx);

    RejectedTxTodo MempoolRejectedTx(const CTransactionRef& ptx, const TxValidationState& state, NodeId nodeid, bool first_time_failure);

    void MempoolRejectedPackage(const Package& package);

    std::pair<bool, std::optional<PackageToValidate>> ReceivedTx(NodeId nodeid, const CTransactionRef& ptx);

    bool HaveMoreWork(NodeId nodeid);

    CTransactionRef GetTxToReconsider(NodeId nodeid);

    void CheckIsEmpty();

    void CheckIsEmpty(NodeId nodeid);

    std::vector<TxOrphanage::OrphanInfo> GetOrphanTransactions() const;

protected:

    /** Helper for getting deduplicated vector of Txids in vin. */

    std::vector<Txid> GetUniqueParents(const CTransaction& tx);

    /** If this peer is an orphan resolution candidate for this transaction, treat the unique_parents as announced by

     * this peer; add them as new invs to m_txrequest.

     * @returns whether this transaction was a valid orphan resolution candidate.

     * */

    bool MaybeAddOrphanResolutionCandidate(const std::vector<Txid>& unique_parents, const Wtxid& wtxid, NodeId nodeid, std::chrono::microseconds now);

};

} // namespace node

#endif // BITCOIN_NODE_TXDOWNLOADMAN_IMPL_H