// Copyright (c) 2012 Pieter Wuille
// Copyright (c) 2012-2020 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_ADDRMAN_H
#define BITCOIN_ADDRMAN_H

#include <netaddress.h>
#include <protocol.h>
#include <streams.h>
#include <timedata.h>

#include <cstdint>
#include <memory>
#include <optional>
#include <utility>
#include <vector>

class AddrManImpl;

/** Default for -checkaddrman */
static constexpr int32_t DEFAULT_ADDRMAN_CONSISTENCY_CHECKS{0};

/** Stochastic address manager
 *
 * Design goals:
 *  * Keep the address tables in-memory, and asynchronously dump the entire table to peers.dat.
 *  * Make sure no (localized) attacker can fill the entire table with his nodes/addresses.
 *
 * To that end:
 *  * Addresses are organized into buckets that can each store up to 64 entries.
 *    * Addresses to which our node has not successfully connected go into 1024 "new" buckets.
 *      * Based on the address range (/16 for IPv4) of the source of information, or if an asmap is provided,
 *        the AS it belongs to (for IPv4/IPv6), 64 buckets are selected at random.
 *      * The actual bucket is chosen from one of these, based on the range in which the address itself is located.
 *      * The position in the bucket is chosen based on the full address.
 *      * One single address can occur in up to 8 different buckets to increase selection chances for addresses that
 *        are seen frequently. The chance for increasing this multiplicity decreases exponentially.
 *      * When adding a new address to an occupied position of a bucket, it will not replace the existing entry
 *        unless that address is also stored in another bucket or it doesn't meet one of several quality criteria
 *        (see IsTerrible for exact criteria).
 *    * Addresses of nodes that are known to be accessible go into 256 "tried" buckets.
 *      * Each address range selects at random 8 of these buckets.
 *      * The actual bucket is chosen from one of these, based on the full address.
 *      * When adding a new good address to an occupied position of a bucket, a FEELER connection to the
 *        old address is attempted. The old entry is only replaced and moved back to the "new" buckets if this
 *        attempt was unsuccessful.
 *    * Bucket selection is based on cryptographic hashing, using a randomly-generated 256-bit key, which should not
 *      be observable by adversaries.
 *    * Several indexes are kept for high performance. Setting m_consistency_check_ratio with the -checkaddrman
 *      configuration option will introduce (expensive) consistency checks for the entire data structure.
 */
class AddrMan
{
    const std::unique_ptr<AddrManImpl> m_impl;

public:
    explicit AddrMan(std::vector<bool> asmap, bool deterministic, int32_t consistency_check_ratio);

    ~AddrMan();

    template <typename Stream>
    void Serialize(Stream& s_) const;

    template <typename Stream>
    void Unserialize(Stream& s_);

    //! Return the number of (unique) addresses in all tables.
    size_t size() const;

    //! Add addresses to addrman's new table.
    bool Add(const std::vector<CAddress>& vAddr, const CNetAddr& source, int64_t nTimePenalty = 0);

    //! Mark an entry as accessible, possibly moving it from "new" to "tried".
    void Good(const CService& addr, int64_t nTime = GetAdjustedTime());

    //! Mark an entry as connection attempted to.
    void Attempt(const CService& addr, bool fCountFailure, int64_t nTime = GetAdjustedTime());

    //! See if any to-be-evicted tried table entries have been tested and if so resolve the collisions.
    void ResolveCollisions();

    /**
     * Randomly select an address in the tried table that another address is
     * attempting to evict.
     *
     * @return CAddress The record for the selected tried peer.
     *         int64_t  The last time we attempted to connect to that peer.
     */
    std::pair<CAddress, int64_t> SelectTriedCollision();

    /**
     * Choose an address to connect to.
     *
     * @param[in] newOnly  Whether to only select addresses from the new table.
     * @return    CAddress The record for the selected peer.
     *            int64_t  The last time we attempted to connect to that peer.
     */
    std::pair<CAddress, int64_t> Select(bool newOnly = false) const;

    /**
     * Return all or many randomly selected addresses, optionally by network.
     *
     * @param[in] max_addresses  Maximum number of addresses to return (0 = all).
     * @param[in] max_pct        Maximum percentage of addresses to return (0 = all).
     * @param[in] network        Select only addresses of this network (nullopt = all).
     *
     * @return                   A vector of randomly selected addresses from vRandom.
     */
    std::vector<CAddress> GetAddr(size_t max_addresses, size_t max_pct, std::optional<Network> network) const;

    /** We have successfully connected to this peer. Calling this function
     *  updates the CAddress's nTime, which is used in our IsTerrible()
     *  decisions and gossiped to peers. Callers should be careful that updating
     *  this information doesn't leak topology information to network spies.
     *
     *  net_processing calls this function when it *disconnects* from a peer to
     *  not leak information about currently connected peers.
     *
     * @param[in]   addr     The address of the peer we were connected to
     * @param[in]   nTime    The time that we were last connected to this peer
     */
    void Connected(const CService& addr, int64_t nTime = GetAdjustedTime());

    //! Update an entry's service bits.
    void SetServices(const CService& addr, ServiceFlags nServices);

    const std::vector<bool>& GetAsmap() const;

    friend class AddrManTest;
    friend class AddrManDeterministic;
};

#endif // BITCOIN_ADDRMAN_H