// Copyright (c) 2021-2022 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_TXORPHANAGE_H
#define BITCOIN_TXORPHANAGE_H

#include <net.h>
#include <primitives/block.h>
#include <primitives/transaction.h>
#include <sync.h>
#include <util/time.h>

#include <map>
#include <set>

/** Expiration time for orphan transactions */
static constexpr auto ORPHAN_TX_EXPIRE_TIME{20min};
/** Minimum time between orphan transactions expire time checks */
static constexpr auto ORPHAN_TX_EXPIRE_INTERVAL{5min};

/** A class to track orphan transactions (failed on TX_MISSING_INPUTS)
 * Since we cannot distinguish orphans from bad transactions with
 * non-existent inputs, we heavily limit the number of orphans
 * we keep and the duration we keep them for.
 * Not thread-safe. Requires external synchronization.
 */
class TxOrphanage {
public:
    /** Add a new orphan transaction */
    bool AddTx(const CTransactionRef& tx, NodeId peer);

    /** Check if we already have an orphan transaction (by wtxid only) */
    bool HaveTx(const Wtxid& wtxid) const;

    /** Extract a transaction from a peer's work set
     *  Returns nullptr if there are no transactions to work on.
     *  Otherwise returns the transaction reference, and removes
     *  it from the work set.
     */
    CTransactionRef GetTxToReconsider(NodeId peer);

    /** Erase an orphan by wtxid */
    int EraseTx(const Wtxid& wtxid);

    /** Erase all orphans announced by a peer (eg, after that peer disconnects) */
    void EraseForPeer(NodeId peer);

    /** Erase all orphans included in or invalidated by a new block */
    void EraseForBlock(const CBlock& block);

    /** Limit the orphanage to the given maximum */
    void LimitOrphans(unsigned int max_orphans, FastRandomContext& rng);

    /** Add any orphans that list a particular tx as a parent into the from peer's work set */
    void AddChildrenToWorkSet(const CTransaction& tx);

    /** Does this peer have any work to do? */
    bool HaveTxToReconsider(NodeId peer);

    /** Get all children that spend from this tx and were received from nodeid. Sorted from most
     * recent to least recent. */
    std::vector<CTransactionRef> GetChildrenFromSamePeer(const CTransactionRef& parent, NodeId nodeid) const;

    /** Get all children that spend from this tx but were not received from nodeid. Also return
     * which peer provided each tx. */
    std::vector<std::pair<CTransactionRef, NodeId>> GetChildrenFromDifferentPeer(const CTransactionRef& parent, NodeId nodeid) const;

    /** Return how many entries exist in the orphange */
    size_t Size()
    {
        return m_orphans.size();
    }

protected:
    struct OrphanTx {
        CTransactionRef tx;
        NodeId fromPeer;
        NodeSeconds nTimeExpire;
        size_t list_pos;
    };

    /** Map from wtxid to orphan transaction record. Limited by
     *  -maxorphantx/DEFAULT_MAX_ORPHAN_TRANSACTIONS */
    std::map<Wtxid, OrphanTx> m_orphans;

    /** Which peer provided the orphans that need to be reconsidered */
    std::map<NodeId, std::set<Wtxid>> m_peer_work_set;

    using OrphanMap = decltype(m_orphans);

    struct IteratorComparator
    {
        template<typename I>
        bool operator()(const I& a, const I& b) const
        {
            return a->first < b->first;
        }
    };

    /** Index from the parents' COutPoint into the m_orphans. Used
     *  to remove orphan transactions from the m_orphans */
    std::map<COutPoint, std::set<OrphanMap::iterator, IteratorComparator>> m_outpoint_to_orphan_it;

    /** Orphan transactions in vector for quick random eviction */
    std::vector<OrphanMap::iterator> m_orphan_list;

    /** Timestamp for the next scheduled sweep of expired orphans */
    NodeSeconds m_next_sweep{0s};
};

#endif // BITCOIN_TXORPHANAGE_H