// Copyright (c) 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.

#include <node/txreconciliation.h>

#include <util/check.h>
#include <util/system.h>

#include <unordered_map>
#include <variant>


namespace {

/**
 * Keeps track of txreconciliation-related per-peer state.
 */
class TxReconciliationState
{
};

} // namespace

/** Actual implementation for TxReconciliationTracker's data structure. */
class TxReconciliationTracker::Impl
{
private:
    mutable Mutex m_txreconciliation_mutex;

    /**
     * Keeps track of txreconciliation states of eligible peers.
     * For pre-registered peers, the locally generated salt is stored.
     * For registered peers, the locally generated salt is forgotten, and the state (including
     * "full" salt) is stored instead.
     */
    std::unordered_map<NodeId, std::variant<uint64_t, TxReconciliationState>> m_states GUARDED_BY(m_txreconciliation_mutex);

public:
    explicit Impl() {}

    uint64_t PreRegisterPeer(NodeId peer_id) EXCLUSIVE_LOCKS_REQUIRED(!m_txreconciliation_mutex)
    {
        AssertLockNotHeld(m_txreconciliation_mutex);
        LOCK(m_txreconciliation_mutex);
        // We do not support txreconciliation salt/version updates.
        assert(m_states.find(peer_id) == m_states.end());

        LogPrintLevel(BCLog::TXRECONCILIATION, BCLog::Level::Debug, "Pre-register peer=%d\n", peer_id);
        const uint64_t local_salt{GetRand(UINT64_MAX)};

        // We do this exactly once per peer (which are unique by NodeId, see GetNewNodeId) so it's
        // safe to assume we don't have this record yet.
        Assert(m_states.emplace(peer_id, local_salt).second);
        return local_salt;
    }

    void ForgetPeer(NodeId peer_id) EXCLUSIVE_LOCKS_REQUIRED(!m_txreconciliation_mutex)
    {
        AssertLockNotHeld(m_txreconciliation_mutex);
        LOCK(m_txreconciliation_mutex);
        if (m_states.erase(peer_id)) {
            LogPrintLevel(BCLog::TXRECONCILIATION, BCLog::Level::Debug, "Forget txreconciliation state of peer=%d\n", peer_id);
        }
    }
};

TxReconciliationTracker::TxReconciliationTracker() : m_impl{std::make_unique<TxReconciliationTracker::Impl>()} {}

TxReconciliationTracker::~TxReconciliationTracker() = default;

uint64_t TxReconciliationTracker::PreRegisterPeer(NodeId peer_id)
{
    return m_impl->PreRegisterPeer(peer_id);
}

void TxReconciliationTracker::ForgetPeer(NodeId peer_id)
{
    m_impl->ForgetPeer(peer_id);
}