#ifndef ENCRYPTION_H
#define ENCRYPTION_H

#include <QDataStream>
#include <QFile>
#include <QDebug>
#include <QCryptographicHash>

#include "ecrypt-sync.h"
#include "QtZlib/zlib.h"

class Encryption {
public:
    static const int VECTOR_SIZE = 16;        // 16 32-bit words
    static const int NUM_OF_BLOCKS_PER_CHUNK = 8192;

    //--------------------------------------------------------------------
    // Helper functions (assuming little–endian order)

    static void Convert32BitTo8Bit(quint32 value, quint8* array) {
        array[0] = static_cast<quint8>(value >> 0);
        array[1] = static_cast<quint8>(value >> 8);
        array[2] = static_cast<quint8>(value >> 16);
        array[3] = static_cast<quint8>(value >> 24);
    }

    static quint32 ConvertArrayTo32Bit(const QByteArray &array) {
        return ((static_cast<quint32>(static_cast<uchar>(array[0])) << 0)  |
                (static_cast<quint32>(static_cast<uchar>(array[1])) << 8)  |
                (static_cast<quint32>(static_cast<uchar>(array[2])) << 16) |
                (static_cast<quint32>(static_cast<uchar>(array[3])) << 24));
    }

    static quint32 Rotate(quint32 value, quint32 numBits) {
        return (value << numBits) | (value >> (32 - numBits));
    }

    // Build the IV table from a 0x20–byte feed. The table is 0xFB0 bytes.
    static QByteArray InitIVTable(const QByteArray &feed) {
        const int tableSize = 0xFB0;
        QByteArray table;
        table.resize(tableSize);
        int ptr = 0;
        for (int i = 0; i < 200; ++i) {
            for (int x = 0; x < 5; ++x) {
                if (static_cast<uchar>(feed.at(ptr)) == 0x00)
                    ptr = 0;
                int base = i * 20 + x * 4;
                table[base]     = feed.at(ptr);
                table[base + 1] = feed.at(ptr);
                table[base + 2] = feed.at(ptr);
                table[base + 3] = feed.at(ptr);
                ++ptr;
            }
        }
        // Copy block numbers [1,0,0,0] into the last 16 bytes
        QByteArray oneBlock;
        oneBlock.append(char(1)); oneBlock.append(char(0)); oneBlock.append(char(0)); oneBlock.append(char(0));
        table.replace(0xFA0, 4, oneBlock);
        table.replace(0xFA4, 4, oneBlock);
        table.replace(0xFA8, 4, oneBlock);
        table.replace(0xFAC, 4, oneBlock);
        return table;
    }

    // "unk" function as in the C# code.
    static int unk(quint64 arg1, quint8 arg2) {
        if (arg2 >= 0x40)
            return 0;
        return static_cast<int>(arg1 >> arg2);
    }

    // Compute the IV for a given section index using the IV table.
    static QByteArray GetIV(const QByteArray &table, int index) {
        int num1 = 0xFA0 + index;
        int num2 = unk(0x51EB851FLL * num1, 0x20);
        int adjust = ((num2 >> 6) + (num2 >> 31));
        int startIndex = 20 * (num1 - 200 * adjust);
        // Return 8 bytes from that location.
        return table.mid(startIndex, 8);
    }

    // Update the IV table given the section's SHA1 hash.
    static void UpdateIVTable(QByteArray &table, int index, const QByteArray &sectionHash) {
        int blockNumIndex = index % 4;
        int baseOffset = 0xFA0 + blockNumIndex * 4;
        quint32 blockNumVal = (static_cast<uchar>(table.at(baseOffset))      ) |
                              (static_cast<uchar>(table.at(baseOffset + 1)) << 8 ) |
                              (static_cast<uchar>(table.at(baseOffset + 2)) << 16) |
                              (static_cast<uchar>(table.at(baseOffset + 3)) << 24);
        int blockNum = blockNumVal * 4 + index;
        int num2 = unk(0x51EB851FLL * blockNum, 0x20);
        int adjust = ((num2 >> 6) + (num2 >> 31));
        int startIndex = 20 * (blockNum - 200 * adjust) + 1;
        int hashIndex = 0;
        for (int x = 0; x < 4; ++x) {
            table[startIndex - 1] = table.at(startIndex - 1) ^ sectionHash.at(hashIndex);
            table[startIndex]     = table.at(startIndex)     ^ sectionHash.at(hashIndex + 1);
            table[startIndex + 1] = table.at(startIndex + 1) ^ sectionHash.at(hashIndex + 2);
            table[startIndex + 2] = table.at(startIndex + 2) ^ sectionHash.at(hashIndex + 3);
            table[startIndex + 3] = table.at(startIndex + 3) ^ sectionHash.at(hashIndex + 4);
            startIndex += 5;
            hashIndex += 5;
        }
    }

    static quint32 ToUInt32(const QByteArray &data, int offset) {
        // Converts 4 bytes (starting at offset) from data into a 32-bit unsigned integer (little-endian)
        return ((static_cast<quint32>(static_cast<uchar>(data[offset]))      ) |
                (static_cast<quint32>(static_cast<uchar>(data[offset+1])) << 8 ) |
                (static_cast<quint32>(static_cast<uchar>(data[offset+2])) << 16) |
                (static_cast<quint32>(static_cast<uchar>(data[offset+3])) << 24));
    }

    //--------------------------------------------------------------------
    // Salsa20 decryption for one section.
    // This function resets the counter for each section.
    static QByteArray salsa20DecryptSection(const QByteArray &sectionData, const QByteArray &key, const QByteArray &iv, int blockSize = 64)
    {
        // Choose the appropriate constant based on key length.
        QByteArray constants;
        if (key.size() == 32)
            constants = "expand 32-byte k";
        else if (key.size() == 16)
            constants = "expand 16-byte k";
        else {
            qWarning() << "Invalid key size:" << key.size() << "; expected 16 or 32 bytes.";
            return QByteArray();
        }

        QVector<quint32> state(VECTOR_SIZE);

        // Set state[0] using the first 4 bytes of the constant.
        state[0] = ConvertArrayTo32Bit(constants.mid(0, 4));

        // state[1] through state[4] come from the first 16 bytes of the key.
        state[1] = ToUInt32(key, 0);
        state[2] = ToUInt32(key, 4);
        state[3] = ToUInt32(key, 8);
        state[4] = ToUInt32(key, 12);

        // state[5] comes from the next 4 bytes of the constant.
        state[5] = ConvertArrayTo32Bit(constants.mid(4, 4));

        // state[6] and state[7] come from the IV (which must be 8 bytes).
        state[6] = ConvertArrayTo32Bit(iv.mid(0, 4));
        state[7] = ConvertArrayTo32Bit(iv.mid(4, 4));

        // state[8] and state[9] are the 64-bit block counter (start at 0).
        state[8] = 0;
        state[9] = 0;

        // state[10] comes from the next 4 bytes of the constant.
        state[10] = ConvertArrayTo32Bit(constants.mid(8, 4));

        // For state[11] through state[14]:
        // If the key is 32 bytes, use bytes 16..31; if 16 bytes, reuse the first 16 bytes.
        if (key.size() == 32) {
            state[11] = ToUInt32(key, 16);
            state[12] = ToUInt32(key, 20);
            state[13] = ToUInt32(key, 24);
            state[14] = ToUInt32(key, 28);
        } else { // key.size() == 16
            state[11] = ToUInt32(key, 0);
            state[12] = ToUInt32(key, 4);
            state[13] = ToUInt32(key, 8);
            state[14] = ToUInt32(key, 12);
        }

        // state[15] comes from the last 4 bytes of the constant.
        state[15] = ConvertArrayTo32Bit(constants.mid(12, 4));

        // Prepare the output buffer.
        QByteArray output(sectionData.size(), Qt::Uninitialized);
        int numBlocks = sectionData.size() / blockSize;
        int remainder = sectionData.size() % blockSize;

        // Process each full block.
        for (int blockIndex = 0; blockIndex < numBlocks; ++blockIndex) {
            QVector<quint32> x = state; // make a copy of the current state for this block

            // Run 20 rounds (10 iterations) of Salsa20.
            for (int round = 20; round > 0; round -= 2) {
                x[4]  ^= Rotate(x[0]  + x[12], 7);
                x[8]  ^= Rotate(x[4]  + x[0], 9);
                x[12] ^= Rotate(x[8]  + x[4], 13);
                x[0]  ^= Rotate(x[12] + x[8], 18);

                x[9]  ^= Rotate(x[5]  + x[1], 7);
                x[13] ^= Rotate(x[9]  + x[5], 9);
                x[1]  ^= Rotate(x[13] + x[9], 13);
                x[5]  ^= Rotate(x[1]  + x[13], 18);

                x[14] ^= Rotate(x[10] + x[6], 7);
                x[2]  ^= Rotate(x[14] + x[10], 9);
                x[6]  ^= Rotate(x[2]  + x[14], 13);
                x[10] ^= Rotate(x[6]  + x[2], 18);

                x[3]  ^= Rotate(x[15] + x[11], 7);
                x[7]  ^= Rotate(x[3]  + x[15], 9);
                x[11] ^= Rotate(x[7]  + x[3], 13);
                x[15] ^= Rotate(x[11] + x[7], 18);

                x[1]  ^= Rotate(x[0]  + x[3], 7);
                x[2]  ^= Rotate(x[1]  + x[0], 9);
                x[3]  ^= Rotate(x[2]  + x[1], 13);
                x[0]  ^= Rotate(x[3]  + x[2], 18);

                x[6]  ^= Rotate(x[5]  + x[4], 7);
                x[7]  ^= Rotate(x[6]  + x[5], 9);
                x[4]  ^= Rotate(x[7]  + x[6], 13);
                x[5]  ^= Rotate(x[4]  + x[7], 18);

                x[11] ^= Rotate(x[10] + x[9], 7);
                x[8]  ^= Rotate(x[11] + x[10], 9);
                x[9]  ^= Rotate(x[8]  + x[11], 13);
                x[10] ^= Rotate(x[9]  + x[8], 18);

                x[12] ^= Rotate(x[15] + x[14], 7);
                x[13] ^= Rotate(x[12] + x[15], 9);
                x[14] ^= Rotate(x[13] + x[12], 13);
                x[15] ^= Rotate(x[14] + x[13], 18);
            }

            // Produce the 64-byte keystream block by adding the original state.
            QVector<quint8> keyStreamBlock(blockSize);
            for (int i = 0; i < VECTOR_SIZE; ++i) {
                x[i] += state[i];
                Convert32BitTo8Bit(x[i], keyStreamBlock.data() + 4 * i);
            }

            // XOR the keystream block with the corresponding block of sectionData.
            const uchar* inBlock = reinterpret_cast<const uchar*>(sectionData.constData()) + blockIndex * blockSize;
            uchar* outBlock = reinterpret_cast<uchar*>(output.data()) + blockIndex * blockSize;
            for (int j = 0; j < blockSize; ++j) {
                outBlock[j] = inBlock[j] ^ keyStreamBlock[j];
            }
            // Increment the 64-bit block counter.
            state[8]++;
            if (state[8] == 0)
                state[9]++;
        }

        // Process any remaining bytes.
        if (remainder > 0) {
            QVector<quint32> x = state;
            for (int round = 20; round > 0; round -= 2) {
                x[4]  ^= Rotate(x[0]  + x[12], 7);
                x[8]  ^= Rotate(x[4]  + x[0], 9);
                x[12] ^= Rotate(x[8]  + x[4], 13);
                x[0]  ^= Rotate(x[12] + x[8], 18);

                x[9]  ^= Rotate(x[5]  + x[1], 7);
                x[13] ^= Rotate(x[9]  + x[5], 9);
                x[1]  ^= Rotate(x[13] + x[9], 13);
                x[5]  ^= Rotate(x[1]  + x[13], 18);

                x[14] ^= Rotate(x[10] + x[6], 7);
                x[2]  ^= Rotate(x[14] + x[10], 9);
                x[6]  ^= Rotate(x[2]  + x[14], 13);
                x[10] ^= Rotate(x[6]  + x[2], 18);

                x[3]  ^= Rotate(x[15] + x[11], 7);
                x[7]  ^= Rotate(x[3]  + x[15], 9);
                x[11] ^= Rotate(x[7]  + x[3], 13);
                x[15] ^= Rotate(x[11] + x[7], 18);

                x[1]  ^= Rotate(x[0]  + x[3], 7);
                x[2]  ^= Rotate(x[1]  + x[0], 9);
                x[3]  ^= Rotate(x[2]  + x[1], 13);
                x[0]  ^= Rotate(x[3]  + x[2], 18);

                x[6]  ^= Rotate(x[5]  + x[4], 7);
                x[7]  ^= Rotate(x[6]  + x[5], 9);
                x[4]  ^= Rotate(x[7]  + x[6], 13);
                x[5]  ^= Rotate(x[4]  + x[7], 18);

                x[11] ^= Rotate(x[10] + x[9], 7);
                x[8]  ^= Rotate(x[11] + x[10], 9);
                x[9]  ^= Rotate(x[8]  + x[11], 13);
                x[10] ^= Rotate(x[9]  + x[8], 18);

                x[12] ^= Rotate(x[15] + x[14], 7);
                x[13] ^= Rotate(x[12] + x[15], 9);
                x[14] ^= Rotate(x[13] + x[12], 13);
                x[15] ^= Rotate(x[14] + x[13], 18);
            }
            QVector<quint8> keyStreamBlock(blockSize);
            for (int i = 0; i < VECTOR_SIZE; ++i) {
                x[i] += state[i];
                Convert32BitTo8Bit(x[i], keyStreamBlock.data() + 4 * i);
            }
            const uchar* inBlock = reinterpret_cast<const uchar*>(sectionData.constData()) + numBlocks * blockSize;
            uchar* outBlock = reinterpret_cast<uchar*>(output.data()) + numBlocks * blockSize;
            for (int j = 0; j < remainder; ++j)
                outBlock[j] = inBlock[j] ^ keyStreamBlock[j];
        }

        return output;
    }

    static void fillIVTable(QByteArray fastFileData, QByteArray& ivTable, quint32 ivTableLength)
    {
        QDataStream stream(fastFileData);
        stream.skipRawData(24);

        quint32 nameKeyLength = 0;
        for (int i = 0; i < 32 && !stream.atEnd(); i++) {
            if (!stream.atEnd() && stream.device()->peek(1).toHex() != "00") {
                nameKeyLength++;
                stream.skipRawData(1);
            } else {
                break;
            }
        }

        if (nameKeyLength < 32) {
            stream.skipRawData(32 - nameKeyLength);
        }

        if (ivTableLength < 16) {
            qWarning() << "IV table length too small!";
            return;
        }

        for (quint32 i = 0; i < ivTableLength - 16; i++) {
            if (stream.atEnd()) {
                qWarning() << "Stream ended while filling IV table!";
                return;
            }
            quint8 ivVal;
            stream >> ivVal;
            ivTable[i] = ivVal;
        }
    }

    static void fillIV(int index, QByteArray& ivPtr, const QByteArray& ivTable, const QVector<quint32>& ivCounter)
    {
        if (index < 0 || index >= ivCounter.size()) {
            qWarning() << "Invalid IV index: " << index;
            return;
        }

        int ivOffset = ((index + 4 * (ivCounter[index] - 1)) % 800) * 20;

        if (ivOffset + 8 > ivTable.size()) {
            qWarning() << "IV offset out of bounds! Offset: " << ivOffset;
            return;
        }

        ivPtr = ivTable.mid(ivOffset, 8);
    }


    static void generateNewIV(int index, const QByteArray& hash, QByteArray& ivTable, QVector<quint32>& ivCounter)
    {
        if (index < 0 || index >= ivCounter.size()) {
            qWarning() << "Invalid index: " << index;
            return;
        }

        quint32 safeCounter = fmin(ivCounter[index], 800u - 1);
        int ivOffset = (index + 4 * safeCounter) % 800 * 5;

        for (int i = 0; i < 20; i++) {
            if (ivOffset + i >= ivTable.size()) {
                qWarning() << "Index out of bounds for IV table!";
                return;
            }
            ivTable[ivOffset + i] ^= hash[i];
        }

        ivCounter[index]++;
    }

    static QByteArray decryptFastFile(const QByteArray& fastFileData)
    {
        const QByteArray bo2_salsa20_key = QByteArray::fromHex("641D8A2FE31D3AA63622BBC9CE8587229D42B0F8ED9B924130BF88B65EDC50BE");

        QByteArray fileData = fastFileData;
        QByteArray finalFastFile;

        QByteArray ivTable(16000, 0);
        fillIVTable(fileData, ivTable, 16000 - 1);

        QVector<quint32> ivCounter(4, 1);
        QDataStream stream(fileData);
        stream.setByteOrder(QDataStream::LittleEndian);
        stream.skipRawData(0x138);

        QByteArray sha1Hash(20, 0);
        QByteArray ivPtr(8, 0);
        int chunkIndex = 0;

        while (!stream.atEnd()) {
            quint32 dataLength;
            stream >> dataLength;

            if (dataLength == 0 || dataLength > fileData.size() - stream.device()->pos()) {
                qWarning() << "Invalid data length at offset: " << stream.device()->pos();
                break;
            }

            fillIV(chunkIndex % 4, ivPtr, ivTable, ivCounter);

            ECRYPT_ctx x;
            ECRYPT_keysetup(&x, reinterpret_cast<const u8*>(bo2_salsa20_key.constData()), 256, 0);
            ECRYPT_ivsetup(&x, reinterpret_cast<const u8*>(ivPtr.constData()));

            QByteArray encryptedBlock = fileData.mid(stream.device()->pos(), dataLength);
            QByteArray decryptedBlock;
            decryptedBlock.resize(dataLength);

            ECRYPT_decrypt_bytes(&x, reinterpret_cast<const u8*>(encryptedBlock.constData()),
                                 reinterpret_cast<u8*>(decryptedBlock.data()), dataLength);

            QCryptographicHash sha1(QCryptographicHash::Sha1);
            sha1.addData(decryptedBlock);
            sha1Hash = sha1.result();

            z_stream strm = {};
            strm.zalloc = Z_NULL;
            strm.zfree = Z_NULL;
            strm.opaque = Z_NULL;
            strm.avail_in = static_cast<uInt>(decryptedBlock.size());
            strm.next_in = reinterpret_cast<Bytef*>(decryptedBlock.data());

            QByteArray decompressedData;
            decompressedData.resize(fmax(dataLength * 2, 4096));
            strm.avail_out = decompressedData.size();
            strm.next_out = reinterpret_cast<Bytef*>(decompressedData.data());

            int zReturn = inflateInit2(&strm, -15);
            if (zReturn != Z_OK) {
                qWarning() << "inflateInit2 failed with error code" << zReturn;
                break;
            }

            zReturn = inflate(&strm, Z_FINISH);
            inflateEnd(&strm);

            if (zReturn != Z_STREAM_END) {
                qDebug() << "Error decompressing at offset: " << stream.device()->pos() << " : " << zReturn;
                decompressedData.clear();
            } else {
                decompressedData.resize(strm.total_out);
            }

            finalFastFile.append(decompressedData);

            generateNewIV(chunkIndex % 4, sha1Hash, ivTable, ivCounter);

            if (stream.device()->pos() + static_cast<qint64>(dataLength) > fileData.size()) {
                qWarning() << "Skipping past file size!";
                break;
            }

            stream.skipRawData(dataLength);
            chunkIndex++;
        }

        return finalFastFile;
    }
};

#endif // ENCRYPTION_H