// 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 <policy/packages.h>
#include <txorphanage.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;
    /** Maximum number of transactions allowed in orphanage. */
    const uint32_t m_max_orphan_txs;
    /** 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<uint256>& txhashes);

    /** 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::OrphanTxBase> GetOrphanTransactions() const;
};
} // namespace node
#endif // BITCOIN_NODE_TXDOWNLOADMAN_H