// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2015 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 "sigcache.h"

#include "pubkey.h"
#include "random.h"
#include "uint256.h"
#include "util.h"

#include <boost/thread.hpp>
#include <boost/tuple/tuple_comparison.hpp>

namespace {

/**
 * Valid signature cache, to avoid doing expensive ECDSA signature checking
 * twice for every transaction (once when accepted into memory pool, and
 * again when accepted into the block chain)
 */
class CSignatureCache
{
private:
     //! sigdata_type is (signature hash, signature, public key):
    typedef boost::tuple<uint256, std::vector<unsigned char>, CPubKey> sigdata_type;
    std::set< sigdata_type> setValid;
    boost::shared_mutex cs_sigcache;

public:
    bool
    Get(const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubKey)
    {
        boost::shared_lock<boost::shared_mutex> lock(cs_sigcache);

        sigdata_type k(hash, vchSig, pubKey);
        std::set<sigdata_type>::iterator mi = setValid.find(k);
        if (mi != setValid.end())
            return true;
        return false;
    }

    void Set(const uint256 &hash, const std::vector<unsigned char>& vchSig, const CPubKey& pubKey)
    {
        // DoS prevention: limit cache size to less than 10MB
        // (~200 bytes per cache entry times 50,000 entries)
        // Since there are a maximum of 20,000 signature operations per block
        // 50,000 is a reasonable default.
        int64_t nMaxCacheSize = GetArg("-maxsigcachesize", 50000);
        if (nMaxCacheSize <= 0) return;

        boost::unique_lock<boost::shared_mutex> lock(cs_sigcache);

        while (static_cast<int64_t>(setValid.size()) > nMaxCacheSize)
        {
            // Evict a random entry. Random because that helps
            // foil would-be DoS attackers who might try to pre-generate
            // and re-use a set of valid signatures just-slightly-greater
            // than our cache size.
            uint256 randomHash = GetRandHash();
            std::vector<unsigned char> unused;
            std::set<sigdata_type>::iterator it =
                setValid.lower_bound(sigdata_type(randomHash, unused, unused));
            if (it == setValid.end())
                it = setValid.begin();
            setValid.erase(*it);
        }

        sigdata_type k(hash, vchSig, pubKey);
        setValid.insert(k);
    }
};

}

bool CachingTransactionSignatureChecker::VerifySignature(const std::vector<unsigned char>& vchSig, const CPubKey& pubkey, const uint256& sighash) const
{
    static CSignatureCache signatureCache;

    if (signatureCache.Get(sighash, vchSig, pubkey))
        return true;

    if (!TransactionSignatureChecker::VerifySignature(vchSig, pubkey, sighash))
        return false;

    if (store)
        signatureCache.Set(sighash, vchSig, pubkey);
    return true;
}
