// Copyright (c) 2016-2022 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_VERSIONBITS_H

#define BITCOIN_VERSIONBITS_H

#include <chain.h>

#include <sync.h>

#include <map>

/** What block version to use for new blocks (pre versionbits) */

static const int32_t VERSIONBITS_LAST_OLD_BLOCK_VERSION = 4;

/** What bits to set in version for versionbits blocks */

static const int32_t VERSIONBITS_TOP_BITS = 0x20000000UL;

/** What bitmask determines whether versionbits is in use */

static const int32_t VERSIONBITS_TOP_MASK = 0xE0000000UL;

/** Total bits available for versionbits */

static const int32_t VERSIONBITS_NUM_BITS = 29;

/** BIP 9 defines a finite-state-machine to deploy a softfork in multiple stages.

 *  State transitions happen during retarget period if conditions are met

 *  In case of reorg, transitions can go backward. Without transition, state is

 *  inherited between periods. All blocks of a period share the same state.

 */

enum class ThresholdState {

    DEFINED,   // First state that each softfork starts out as. The genesis block is by definition in this state for each deployment.

    STARTED,   // For blocks past the starttime.

    LOCKED_IN, // For at least one retarget period after the first retarget period with STARTED blocks of which at least threshold have the associated bit set in nVersion, until min_activation_height is reached.

    ACTIVE,    // For all blocks after the LOCKED_IN retarget period (final state)

    FAILED,    // For all blocks once the first retarget period after the timeout time is hit, if LOCKED_IN wasn't already reached (final state)

};

// A map that gives the state for blocks whose height is a multiple of Period().

// The map is indexed by the block's parent, however, so all keys in the map

// will either be nullptr or a block with (height + 1) % Period() == 0.

typedef std::map<const CBlockIndex*, ThresholdState> ThresholdConditionCache;

/** Display status of an in-progress BIP9 softfork */

struct BIP9Stats {

    /** Length of blocks of the BIP9 signalling period */

    int period;

    /** Number of blocks with the version bit set required to activate the softfork */

    int threshold;

    /** Number of blocks elapsed since the beginning of the current period */

    int elapsed;

    /** Number of blocks with the version bit set since the beginning of the current period */

    int count;

    /** False if there are not enough blocks left in this period to pass activation threshold */

    bool possible;

};

/**

 * Abstract class that implements BIP9-style threshold logic, and caches results.

 */

class AbstractThresholdConditionChecker {

protected:

    virtual bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const =0;

    virtual int64_t BeginTime(const Consensus::Params& params) const =0;

    virtual int64_t EndTime(const Consensus::Params& params) const =0;

    virtual int MinActivationHeight(const Consensus::Params& params) const { return 0; }

    virtual int Period(const Consensus::Params& params) const =0;

    virtual int Threshold(const Consensus::Params& params) const =0;

public:

    /** Returns the numerical statistics of an in-progress BIP9 softfork in the period including pindex

     * If provided, signalling_blocks is set to true/false based on whether each block in the period signalled

     */

    BIP9Stats GetStateStatisticsFor(const CBlockIndex* pindex, const Consensus::Params& params, std::vector<bool>* signalling_blocks = nullptr) const;

    /** Returns the state for pindex A based on parent pindexPrev B. Applies any state transition if conditions are present.

     *  Caches state from first block of period. */

    ThresholdState GetStateFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;

    /** Returns the height since when the ThresholdState has started for pindex A based on parent pindexPrev B, all blocks of a period share the same */

    int GetStateSinceHeightFor(const CBlockIndex* pindexPrev, const Consensus::Params& params, ThresholdConditionCache& cache) const;

};

/** BIP 9 allows multiple softforks to be deployed in parallel. We cache

 *  per-period state for every one of them. */

class VersionBitsCache

{

private:

    Mutex m_mutex;

    ThresholdConditionCache m_caches[Consensus::MAX_VERSION_BITS_DEPLOYMENTS] GUARDED_BY(m_mutex);

public:

    /** Get the numerical statistics for a given deployment for the signalling period that includes pindex.

     * If provided, signalling_blocks is set to true/false based on whether each block in the period signalled

     */

    static BIP9Stats Statistics(const CBlockIndex* pindex, const Consensus::Params& params, Consensus::DeploymentPos pos, std::vector<bool>* signalling_blocks = nullptr);

    static uint32_t Mask(const Consensus::Params& params, Consensus::DeploymentPos pos);

    /** Get the BIP9 state for a given deployment for the block after pindexPrev. */

    ThresholdState State(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    /** Get the block height at which the BIP9 deployment switched into the state for the block after pindexPrev. */

    int StateSinceHeight(const CBlockIndex* pindexPrev, const Consensus::Params& params, Consensus::DeploymentPos pos) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    /** Determine what nVersion a new block should use

     */

    int32_t ComputeBlockVersion(const CBlockIndex* pindexPrev, const Consensus::Params& params) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

    void Clear() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex);

};

#endif // BITCOIN_VERSIONBITS_H