//
// Fulcrum - A fast & nimble SPV Server for Bitcoin Cash
// Copyright (C) 2019-2020  Calin A. Culianu <calin.culianu@gmail.com>
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program (see LICENSE.txt).  If not, see
// <https://www.gnu.org/licenses/>.
//
#include "BTC.h"
#include "Common.h"
#include "Util.h"

#include "bitcoin/crypto/endian.h"
#include "bitcoin/crypto/sha256.h"
#include "bitcoin/hash.h"
#include "bitcoin/pubkey.h"
#include "bitcoin/streams.h"
#include "bitcoin/utilstrencodings.h"
#include "bitcoin/version.h"

#include <algorithm>
#include <atomic>
#include <utility>

namespace bitcoin
{
    inline void Endian_Check_In_namespace_bitcoin()
    {
        constexpr uint32_t magicWord = 0x01020304;
        const uint8_t wordBytes[4] = {0x01, 0x02, 0x03, 0x04}; // represent above as big endian
        const uint32_t bytesAsNum = *reinterpret_cast<const uint32_t *>(wordBytes);

        if (magicWord != be32toh(bytesAsNum))
        {
            throw Exception(QString("Program compiled with incorrect WORDS_BIGENDIAN setting.\n\n")
                            + "How to fix this:\n"
                            + " 1. Adjust WORDS_BIGENDIAN in the qmake .pro file to match your architecture.\n"
                            + " 2. Re-run qmake.\n"
                            + " 3. Do a full clean recompile.\n\n");
        }
    }
    extern bool TestBase58(bool silent, bool throws);
}

namespace BTC
{
    void CheckBitcoinEndiannessAndOtherSanityChecks() {
        bitcoin::Endian_Check_In_namespace_bitcoin();
        if ( ! bitcoin::CSHA256::SelfTest() )
            throw InternalError("sha256 self-test failed. Cannot proceed.");
        Tests::Base58(true, true);
        Debug() << "Using sha256 algorithm: " << bitcoin::SHA256AutoDetect();
    }


    namespace Tests {
        bool Base58(bool silent, bool throws) { return bitcoin::TestBase58(silent, throws); }
    }


    /// specialization for CTransaction which works differently
    template <> bitcoin::CTransaction Deserialize(const QByteArray &bytes, int pos)
    {
        bitcoin::GenericVectorReader<QByteArray> vr(bitcoin::SER_NETWORK, bitcoin::PROTOCOL_VERSION, bytes, pos);
        return bitcoin::CTransaction(bitcoin::deserialize, vr);
    }

    QByteArray Hash(const QByteArray &b, bool once)
    {
        bitcoin::CHash256 h(once);
        QByteArray ret(int(h.OUTPUT_SIZE), Qt::Initialization::Uninitialized);
        h.Write(reinterpret_cast<const uint8_t *>(b.constData()), size_t(b.length()));
        h.Finalize(reinterpret_cast<uint8_t *>(ret.data()));
        return ret;
    }

    QByteArray HashRev(const QByteArray &b, bool once)
    {
        QByteArray ret = Hash(b, once);
        std::reverse(std::begin(ret), std::end(ret));
        return ret;
    }

    QByteArray Hash160(const QByteArray &b) {
        bitcoin::CHash160 h;
        QByteArray ret(int(h.OUTPUT_SIZE), Qt::Initialization::Uninitialized);
        h.Write(reinterpret_cast<const uint8_t *>(b.constData()), size_t(b.length()));
        h.Finalize(reinterpret_cast<uint8_t *>(ret.data()));
        return ret;
    }

    // HeaderVerifier helper
    bool HeaderVerifier::operator()(const QByteArray & header, QString *err)
    {
        const long height = prevHeight+1;
        if (header.size() != BTC::GetBlockHeaderSize()) {
            if (err) *err = QString("Header verification failed for header at height %1: wrong size").arg(height);
            return false;
        }
        bitcoin::CBlockHeader curHdr = Deserialize<bitcoin::CBlockHeader>(header);
        if (!checkInner(height, curHdr, err))
            return false;
        prevHeight = height;
        prev = header;
        if (err) err->clear();
        return true;
    }
    bool HeaderVerifier::operator()(const bitcoin::CBlockHeader &curHdr, QString *err)
    {
        const long height = prevHeight+1;
        QByteArray header = Serialize(curHdr);
        if (header.size() != BTC::GetBlockHeaderSize()) {
            if (err) *err = QString("Header verification failed for header at height %1: wrong size").arg(height);
            return false;
        }
        if (!checkInner(height, curHdr, err))
            return false;
        prevHeight = height;
        prev = header;
        if (err) err->clear();
        return true;
    }

    bool HeaderVerifier::checkInner(long height, const bitcoin::CBlockHeader &curHdr, QString *err)
    {
        if (curHdr.IsNull()) {
            if (err) *err = QString("Header verification failed for header at height %1: failed to deserialize").arg(height);
            return false;
        }
        if (!prev.isEmpty() && Hash(prev) != QByteArray::fromRawData(reinterpret_cast<const char *>(curHdr.hashPrevBlock.begin()), int(curHdr.hashPrevBlock.width())) ) {
            if (err) *err = QString("Header %1 'hashPrevBlock' does not match the contents of the previous block").arg(height);
            return false;
        }
        return true;
    }
    std::pair<int, QByteArray> HeaderVerifier::lastHeaderProcessed() const
    {
        return { int(prevHeight), prev };
    }

} // end namespace BTC