// Copyright (c) 2009-2010 Satoshi Nakamoto

// Copyright (c) 2009-present 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 <chain.h>

#include <tinyformat.h>

#include <util/check.h>

std::string CBlockIndex::ToString() const

{

    return strprintf("CBlockIndex(pprev=%p, nHeight=%d, merkle=%s, hashBlock=%s)",

                     pprev, nHeight, hashMerkleRoot.ToString(), GetBlockHash().ToString());

}

void CChain::SetTip(CBlockIndex& block)

{

    CBlockIndex* pindex = █

    vChain.resize(pindex->nHeight + 1);

    while (pindex && vChain[pindex->nHeight] != pindex) {

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        vChain[pindex->nHeight] = pindex;

        pindex = pindex->pprev;

    }

}

std::vector<uint256> LocatorEntries(const CBlockIndex* index)

{

    int step = 1;

    std::vector<uint256> have;

    if (index == nullptr) return have;

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    have.reserve(32);

    while (index) {

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        have.emplace_back(index->GetBlockHash());

        if (index->nHeight == 0) break;

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        // Exponentially larger steps back, plus the genesis block.

        int height = std::max(index->nHeight - step, 0);

        // Use skiplist.

        index = index->GetAncestor(height);

        if (have.size() > 10) step *= 2;

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    }

    return have;

}

CBlockLocator GetLocator(const CBlockIndex* index)

{

    return CBlockLocator{LocatorEntries(index)};

}

const CBlockIndex* CChain::FindFork(const CBlockIndex& index) const

{

    const auto* pindex{&index};

    if (pindex->nHeight > Height())

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        pindex = pindex->GetAncestor(Height());

    while (pindex && !Contains(*pindex))

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        pindex = pindex->pprev;

    return pindex;

}

CBlockIndex* CChain::FindEarliestAtLeast(int64_t nTime, int height) const

{

    std::pair<int64_t, int> blockparams = std::make_pair(nTime, height);

    std::vector<CBlockIndex*>::const_iterator lower = std::lower_bound(vChain.begin(), vChain.end(), blockparams,

        [](CBlockIndex* pBlock, const std::pair<int64_t, int>& blockparams) -> bool { return pBlock->GetBlockTimeMax() < blockparams.first || pBlock->nHeight < blockparams.second; });

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    return (lower == vChain.end() ? nullptr : *lower);

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}

/** Turn the lowest '1' bit in the binary representation of a number into a '0'. */

int static inline InvertLowestOne(int n) { return n & (n - 1); }

/** Compute what height to jump back to with the CBlockIndex::pskip pointer. */

int static inline GetSkipHeight(int height) {

    if (height < 2)

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        return 0;

    // Determine which height to jump back to. Any number strictly lower than height is acceptable,

    // but the following expression seems to perform well in simulations (max 110 steps to go back

    // up to 2**18 blocks).

    return (height & 1) ? InvertLowestOne(InvertLowestOne(height - 1)) + 1 : InvertLowestOne(height);

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}

const CBlockIndex* CBlockIndex::GetAncestor(int height) const

{

    if (height > nHeight || height < 0) {

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        return nullptr;

    }

    const CBlockIndex* pindexWalk = this;

    int heightWalk = nHeight;

    while (heightWalk > height) {

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        int heightSkip = GetSkipHeight(heightWalk);

        int heightSkipPrev = GetSkipHeight(heightWalk - 1);

        if (pindexWalk->pskip != nullptr &&

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            (heightSkip == height ||

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             (heightSkip > height && !(heightSkipPrev < heightSkip - 2 &&

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                                       heightSkipPrev >= height)))) {

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            // Only follow pskip if pprev->pskip isn't better than pskip->pprev.

            pindexWalk = pindexWalk->pskip;

            heightWalk = heightSkip;

        } else {

            assert(pindexWalk->pprev);

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            pindexWalk = pindexWalk->pprev;

            heightWalk--;

        }

    }

    return pindexWalk;

}

CBlockIndex* CBlockIndex::GetAncestor(int height)

{

    return const_cast<CBlockIndex*>(static_cast<const CBlockIndex*>(this)->GetAncestor(height));

}

void CBlockIndex::BuildSkip()

{

    if (pprev)

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        pskip = pprev->GetAncestor(GetSkipHeight(nHeight));

}

arith_uint256 GetBitsProof(uint32_t bits)

{

    arith_uint256 bnTarget;

    bool fNegative;

    bool fOverflow;

    bnTarget.SetCompact(bits, &fNegative, &fOverflow);

    if (fNegative || fOverflow || bnTarget == 0)

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        return 0;

    // We need to compute 2**256 / (bnTarget+1), but we can't represent 2**256

    // as it's too large for an arith_uint256. However, as 2**256 is at least as large

    // as bnTarget+1, it is equal to ((2**256 - bnTarget - 1) / (bnTarget+1)) + 1,

    // or ~bnTarget / (bnTarget+1) + 1.

    return (~bnTarget / (bnTarget + 1)) + 1;

}

int64_t GetBlockProofEquivalentTime(const CBlockIndex& to, const CBlockIndex& from, const CBlockIndex& tip, const Consensus::Params& params)

{

    arith_uint256 r;

    int sign = 1;

    if (to.nChainWork > from.nChainWork) {

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        r = to.nChainWork - from.nChainWork;

    } else {

        r = from.nChainWork - to.nChainWork;

        sign = -1;

    }

    r = r * arith_uint256(params.nPowTargetSpacing) / GetBlockProof(tip);

    if (r.bits() > 63) {

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        return sign * std::numeric_limits<int64_t>::max();

    }

    return sign * int64_t(r.GetLow64());

}

/** Find the last common ancestor two blocks have.

 *  Both pa and pb must be non-nullptr. */

const CBlockIndex* LastCommonAncestor(const CBlockIndex* pa, const CBlockIndex* pb) {

    // First rewind to the last common height (the forking point cannot be past one of the two).

    if (pa->nHeight > pb->nHeight) {

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        pa = pa->GetAncestor(pb->nHeight);

    } else if (pb->nHeight > pa->nHeight) {

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        pb = pb->GetAncestor(pa->nHeight);

    }

    while (pa != pb) {

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        // Jump back until pa and pb have a common "skip" ancestor.

        while (pa->pskip != pb->pskip) {

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            // This logic relies on the property that equal-height blocks have equal-height skip

            // pointers.

            Assume(pa->nHeight == pb->nHeight);

            Assume(pa->pskip->nHeight == pb->pskip->nHeight);

            pa = pa->pskip;

            pb = pb->pskip;

        }

        // At this point, pa and pb are different, but have equal pskip. The forking point lies in

        // between pa/pb on the one end, and pa->pskip/pb->pskip on the other end.

        pa = pa->pprev;

        pb = pb->pprev;

    }

    return pa;

}