// Copyright (c) 2024 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_H

#define BITCOIN_NODE_TXDOWNLOADMAN_H

#include <net.h>

#include <node/txorphanage.h>

#include <policy/packages.h>

#include <cstdint>

#include <memory>

class CBlock;

class CRollingBloomFilter;

class CTxMemPool;

class GenTxid;

class TxRequestTracker;

namespace node {

class TxDownloadManagerImpl;

/** Maximum number of in-flight transaction requests from a peer. It is not a hard limit, but the threshold at which

 *  point the OVERLOADED_PEER_TX_DELAY kicks in. */

static constexpr int32_t MAX_PEER_TX_REQUEST_IN_FLIGHT = 100;

/** Maximum number of transactions to consider for requesting, per peer. It provides a reasonable DoS limit to

 *  per-peer memory usage spent on announcements, while covering peers continuously sending INVs at the maximum

 *  rate (by our own policy, see INVENTORY_BROADCAST_PER_SECOND) for several minutes, while not receiving

 *  the actual transaction (from any peer) in response to requests for them. */

static constexpr int32_t MAX_PEER_TX_ANNOUNCEMENTS = 5000;

/** How long to delay requesting transactions via txids, if we have wtxid-relaying peers */

static constexpr auto TXID_RELAY_DELAY{2s};

/** How long to delay requesting transactions from non-preferred peers */

static constexpr auto NONPREF_PEER_TX_DELAY{2s};

/** How long to delay requesting transactions from overloaded peers (see MAX_PEER_TX_REQUEST_IN_FLIGHT). */

static constexpr auto OVERLOADED_PEER_TX_DELAY{2s};

/** How long to wait before downloading a transaction from an additional peer */

static constexpr auto GETDATA_TX_INTERVAL{60s};

struct TxDownloadOptions {

    /** Read-only reference to mempool. */

    const CTxMemPool& m_mempool;

    /** RNG provided by caller. */

    FastRandomContext& m_rng;

    /** Instantiate TxRequestTracker as deterministic (used for tests). */

    bool m_deterministic_txrequest{false};

};

struct TxDownloadConnectionInfo {

    /** Whether this peer is preferred for transaction download. */

    const bool m_preferred;

    /** Whether this peer has Relay permissions. */

    const bool m_relay_permissions;

    /** Whether this peer supports wtxid relay. */

    const bool m_wtxid_relay;

};

struct PackageToValidate {

    Package m_txns;

    std::vector<NodeId> m_senders;

    /** Construct a 1-parent-1-child package. */

    explicit PackageToValidate(const CTransactionRef& parent,

                               const CTransactionRef& child,

                               NodeId parent_sender,

                               NodeId child_sender) :

        m_txns{parent, child},

        m_senders{parent_sender, child_sender}

    {}

    // Move ctor

    PackageToValidate(PackageToValidate&& other) : m_txns{std::move(other.m_txns)}, m_senders{std::move(other.m_senders)} {}

    // Copy ctor

    PackageToValidate(const PackageToValidate& other) = default;

    // Move assignment

    PackageToValidate& operator=(PackageToValidate&& other) {

        this->m_txns = std::move(other.m_txns);

        this->m_senders = std::move(other.m_senders);

        return *this;

    }

    std::string ToString() const {

        Assume(m_txns.size() == 2);

        return strprintf("parent %s (wtxid=%s, sender=%d) + child %s (wtxid=%s, sender=%d)",

                         m_txns.front()->GetHash().ToString(),

                         m_txns.front()->GetWitnessHash().ToString(),

                         m_senders.front(),

                         m_txns.back()->GetHash().ToString(),

                         m_txns.back()->GetWitnessHash().ToString(),

                         m_senders.back());

    }

};

struct RejectedTxTodo

{

    bool m_should_add_extra_compact_tx;

    std::vector<Txid> m_unique_parents;

    std::optional<PackageToValidate> m_package_to_validate;

};

/**

 * Class responsible for deciding what transactions to request and, once

 * downloaded, whether and how to validate them. It is also responsible for

 * deciding what transaction packages to validate and how to resolve orphan

 * transactions. Its data structures include TxRequestTracker for scheduling

 * requests, rolling bloom filters for remembering transactions that have

 * already been {accepted, rejected, confirmed}, an orphanage, and a registry of

 * each peer's transaction relay-related information.

 *

 * Caller needs to interact with TxDownloadManager:

 * - ValidationInterface callbacks.

 * - When a potential transaction relay peer connects or disconnects.

 * - When a transaction or package is accepted or rejected from mempool

 * - When a inv, notfound, or tx message is received

 * - To get instructions for which getdata messages to send

 *

 * This class is not thread-safe. Access must be synchronized using an

 * external mutex.

 */

class TxDownloadManager {

    const std::unique_ptr<TxDownloadManagerImpl> m_impl;

public:

    explicit TxDownloadManager(const TxDownloadOptions& options);

    ~TxDownloadManager();

    // Responses to chain events. TxDownloadManager is not an actual client of ValidationInterface, these are called through PeerManager.

    void ActiveTipChange();

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

    void BlockDisconnected();

    /** Creates a new PeerInfo. Saves the connection info to calculate tx announcement delays later. */

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

    /** Deletes all txrequest announcements and orphans for a given peer. */

    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.

     * Returns true if this was a dropped inv (p2p_inv=true and we already have the tx), false otherwise. */

    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);

    /** Should be called when a notfound for a tx has been received. */

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

    /** Respond to successful transaction submission to mempool */

    void MempoolAcceptedTx(const CTransactionRef& tx);

    /** Respond to transaction rejected from mempool */

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

    /** Respond to package rejected from mempool */

    void MempoolRejectedPackage(const Package& package);

    /** Marks a tx as ReceivedResponse in txrequest and checks whether AlreadyHaveTx.

     * Return a bool indicating whether this tx should be validated. If false, optionally, a

     * PackageToValidate. */

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

    /** Whether there are any orphans to reconsider for this peer. */

    bool HaveMoreWork(NodeId nodeid) const;

    /** Returns next orphan tx to consider, or nullptr if none exist. */

    CTransactionRef GetTxToReconsider(NodeId nodeid);

    /** Check that all data structures are empty. */

    void CheckIsEmpty() const;

    /** Check that all data structures that track per-peer information have nothing for this peer. */

    void CheckIsEmpty(NodeId nodeid) const;

    /** Wrapper for TxOrphanage::GetOrphanTransactions */

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

};

} // namespace node

#endif // BITCOIN_NODE_TXDOWNLOADMAN_H