#include "wal.hpp"

#include "../json_parse.hpp"

#include <algorithm>
#include <chrono>
#include <cstring>
#include <iomanip>
#include <sstream>

namespace smartbotic::database {

// ===== CRC32 Implementation =====

namespace crc32 {

// CRC32 lookup table (polynomial 0xEDB88320)
static const uint32_t table[256] = {
    0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA, 0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,
    0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988, 0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,
    0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE, 0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,
    0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC, 0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,
    0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172, 0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,
    0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940, 0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,
    0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116, 0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,
    0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924, 0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,
    0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A, 0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,
    0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818, 0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,
    0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E, 0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,
    0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C, 0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,
    0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2, 0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,
    0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0, 0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,
    0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086, 0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,
    0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4, 0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,
    0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A, 0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,
    0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8, 0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,
    0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE, 0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,
    0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC, 0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,
    0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252, 0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,
    0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60, 0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,
    0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236, 0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,
    0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04, 0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,
    0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A, 0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,
    0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38, 0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,
    0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E, 0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,
    0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C, 0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,
    0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2, 0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,
    0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0, 0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,
    0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6, 0xBAD03605, 0xCDD706B3, 0x54DE5729, 0x23D967BF,
    0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94, 0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D
};

uint32_t calculate(const void* data, size_t length) {
    uint32_t crc = 0xFFFFFFFF;
    const uint8_t* bytes = static_cast<const uint8_t*>(data);
    for (size_t i = 0; i < length; ++i) {
        crc = table[(crc ^ bytes[i]) & 0xFF] ^ (crc >> 8);
    }
    return crc ^ 0xFFFFFFFF;
}

uint32_t calculate(const std::string& str) {
    return calculate(str.data(), str.size());
}

} // namespace crc32

// ===== WalEntry Implementation =====

std::vector<uint8_t> WalEntry::serialize() const {
    std::vector<uint8_t> result;

    // Reserve space for length prefix (will be set at the end)
    result.resize(4);

    // Write sequence (8 bytes)
    for (int i = 0; i < 8; ++i) {
        result.push_back(static_cast<uint8_t>((sequence >> (i * 8)) & 0xFF));
    }

    // Write timestamp (8 bytes)
    for (int i = 0; i < 8; ++i) {
        result.push_back(static_cast<uint8_t>((timestamp >> (i * 8)) & 0xFF));
    }

    // Write opType (1 byte)
    result.push_back(static_cast<uint8_t>(opType));

    // Write collection (2 bytes length + data)
    uint16_t collLen = static_cast<uint16_t>(collection.size());
    result.push_back(static_cast<uint8_t>(collLen & 0xFF));
    result.push_back(static_cast<uint8_t>((collLen >> 8) & 0xFF));
    result.insert(result.end(), collection.begin(), collection.end());

    // Write documentId (2 bytes length + data)
    uint16_t docIdLen = static_cast<uint16_t>(documentId.size());
    result.push_back(static_cast<uint8_t>(docIdLen & 0xFF));
    result.push_back(static_cast<uint8_t>((docIdLen >> 8) & 0xFF));
    result.insert(result.end(), documentId.begin(), documentId.end());

    // Write data flag and data (1 byte flag + 4 bytes length + data)
    if (data) {
        result.push_back(1);
        std::string dataStr = data->dump();
        uint32_t dataLen = static_cast<uint32_t>(dataStr.size());
        for (int i = 0; i < 4; ++i) {
            result.push_back(static_cast<uint8_t>((dataLen >> (i * 8)) & 0xFF));
        }
        result.insert(result.end(), dataStr.begin(), dataStr.end());
    } else {
        result.push_back(0);
    }

    // Write collectionOptions flag and data
    if (collectionOptions) {
        result.push_back(1);
        std::string optsStr = collectionOptions->toJson().dump();
        uint32_t optsLen = static_cast<uint32_t>(optsStr.size());
        for (int i = 0; i < 4; ++i) {
            result.push_back(static_cast<uint8_t>((optsLen >> (i * 8)) & 0xFF));
        }
        result.insert(result.end(), optsStr.begin(), optsStr.end());
    } else {
        result.push_back(0);
    }

    // Write vectorData flag and data (1 byte flag + 4 bytes dim + dim * sizeof(float) bytes)
    if (vectorData) {
        result.push_back(1);
        uint32_t dim = static_cast<uint32_t>(vectorData->size());
        for (int i = 0; i < 4; ++i) {
            result.push_back(static_cast<uint8_t>((dim >> (i * 8)) & 0xFF));
        }
        const uint8_t* floatBytes = reinterpret_cast<const uint8_t*>(vectorData->data());
        result.insert(result.end(), floatBytes, floatBytes + dim * sizeof(float));
    } else {
        result.push_back(0);
    }

    // v1.8.0 — origin nodeId trailer (1 byte flag + 2 byte len + bytes).
    // Always emitted by current writer. Older readers stop after vectorData
    // and never observe this section; new readers handle missing trailer.
    if (!nodeId.empty()) {
        result.push_back(1);
        uint16_t nodeLen = static_cast<uint16_t>(nodeId.size());
        result.push_back(static_cast<uint8_t>(nodeLen & 0xFF));
        result.push_back(static_cast<uint8_t>((nodeLen >> 8) & 0xFF));
        result.insert(result.end(), nodeId.begin(), nodeId.end());
    } else {
        result.push_back(0);
    }

    // Calculate and append checksum (excluding length prefix and checksum itself)
    uint32_t crc = crc32::calculate(result.data() + 4, result.size() - 4);
    for (int i = 0; i < 4; ++i) {
        result.push_back(static_cast<uint8_t>((crc >> (i * 8)) & 0xFF));
    }

    // Set length prefix (total size minus 4 bytes for length prefix)
    uint32_t totalLen = static_cast<uint32_t>(result.size() - 4);
    result[0] = static_cast<uint8_t>(totalLen & 0xFF);
    result[1] = static_cast<uint8_t>((totalLen >> 8) & 0xFF);
    result[2] = static_cast<uint8_t>((totalLen >> 16) & 0xFF);
    result[3] = static_cast<uint8_t>((totalLen >> 24) & 0xFF);

    return result;
}

std::optional<WalEntry> WalEntry::deserialize(const std::vector<uint8_t>& data) {
    if (data.size() < 4) {
        return std::nullopt;
    }

    size_t offset = 0;

    // Read length prefix
    uint32_t length = 0;
    for (int i = 0; i < 4; ++i) {
        length |= static_cast<uint32_t>(data[offset++]) << (i * 8);
    }

    if (data.size() < length + 4) {
        return std::nullopt;
    }

    // Verify checksum
    uint32_t storedCrc = 0;
    for (int i = 0; i < 4; ++i) {
        storedCrc |= static_cast<uint32_t>(data[data.size() - 4 + i]) << (i * 8);
    }
    uint32_t calculatedCrc = crc32::calculate(data.data() + 4, length - 4);
    if (storedCrc != calculatedCrc) {
        return std::nullopt;  // Checksum mismatch
    }

    WalEntry entry;

    // Read sequence
    for (int i = 0; i < 8; ++i) {
        entry.sequence |= static_cast<uint64_t>(data[offset++]) << (i * 8);
    }

    // Read timestamp
    for (int i = 0; i < 8; ++i) {
        entry.timestamp |= static_cast<uint64_t>(data[offset++]) << (i * 8);
    }

    // Read opType
    entry.opType = static_cast<WalOpType>(data[offset++]);

    // Read collection
    uint16_t collLen = 0;
    collLen |= static_cast<uint16_t>(data[offset++]);
    collLen |= static_cast<uint16_t>(data[offset++]) << 8;
    entry.collection = std::string(reinterpret_cast<const char*>(&data[offset]), collLen);
    offset += collLen;

    // Read documentId
    uint16_t docIdLen = 0;
    docIdLen |= static_cast<uint16_t>(data[offset++]);
    docIdLen |= static_cast<uint16_t>(data[offset++]) << 8;
    entry.documentId = std::string(reinterpret_cast<const char*>(&data[offset]), docIdLen);
    offset += docIdLen;

    // Read data
    uint8_t hasData = data[offset++];
    if (hasData) {
        uint32_t dataLen = 0;
        for (int i = 0; i < 4; ++i) {
            dataLen |= static_cast<uint32_t>(data[offset++]) << (i * 8);
        }
        std::string dataStr(reinterpret_cast<const char*>(&data[offset]), dataLen);
        offset += dataLen;
        try {
            entry.data = smartbotic::db::parse_to_nlohmann(dataStr);
        } catch (const nlohmann::json::exception&) {
            return std::nullopt;
        }
    }

    // Read collectionOptions
    uint8_t hasOpts = data[offset++];
    if (hasOpts) {
        uint32_t optsLen = 0;
        for (int i = 0; i < 4; ++i) {
            optsLen |= static_cast<uint32_t>(data[offset++]) << (i * 8);
        }
        std::string optsStr(reinterpret_cast<const char*>(&data[offset]), optsLen);
        offset += optsLen;
        try {
            entry.collectionOptions = CollectionOptions::fromJson(smartbotic::db::parse_to_nlohmann(optsStr));
        } catch (const nlohmann::json::exception&) {
            return std::nullopt;
        }
    }

    // Read vectorData (present for VEC_PUT, but flag byte always written)
    if (offset < data.size() - 4) {  // at least 1 flag byte + 4 checksum bytes remain
        uint8_t hasVec = data[offset++];
        if (hasVec) {
            uint32_t dim = 0;
            for (int i = 0; i < 4; ++i) {
                dim |= static_cast<uint32_t>(data[offset++]) << (i * 8);
            }
            if (offset + dim * sizeof(float) > data.size() - 4) {
                return std::nullopt;  // Truncated vector data
            }
            std::vector<float> vec(dim);
            std::memcpy(vec.data(), &data[offset], dim * sizeof(float));
            offset += dim * sizeof(float);
            entry.vectorData = std::move(vec);
        }
    }

    // v1.8.0 — origin nodeId (optional trailer). Pre-v1.8 entries don't have
    // this section; we leave entry.nodeId empty so the persistence layer can
    // treat it as "origin unknown / assume local".
    if (offset < data.size() - 4) {
        uint8_t hasNode = data[offset++];
        if (hasNode) {
            if (offset + 2 > data.size() - 4) {
                return std::nullopt;  // Truncated nodeId length
            }
            uint16_t nodeLen = static_cast<uint16_t>(data[offset]) |
                               (static_cast<uint16_t>(data[offset + 1]) << 8);
            offset += 2;
            if (offset + nodeLen > data.size() - 4) {
                return std::nullopt;  // Truncated nodeId
            }
            entry.nodeId.assign(reinterpret_cast<const char*>(&data[offset]), nodeLen);
            offset += nodeLen;
        }
    }

    entry.checksum = storedCrc;
    return entry;
}

uint32_t WalEntry::calculateChecksum() const {
    auto serialized = serialize();
    // Exclude length prefix and checksum
    return crc32::calculate(serialized.data() + 4, serialized.size() - 8);
}

// ===== WriteAheadLog Implementation =====

WriteAheadLog::WriteAheadLog(Config config)
    : config_(std::move(config)) {
}

WriteAheadLog::~WriteAheadLog() {
    close();
}

bool WriteAheadLog::open() {
    std::lock_guard<std::mutex> lock(writeMutex_);

    if (isOpen_.load()) {
        return true;
    }

    // Create WAL directory if it doesn't exist
    std::error_code ec;
    std::filesystem::create_directories(config_.walDir, ec);
    if (ec) {
        return false;
    }

    // Find existing WAL files and determine highest sequence
    auto walFiles = getWalFiles();
    if (!walFiles.empty()) {
        // Read the last file to get the highest sequence
        for (auto it = walFiles.rbegin(); it != walFiles.rend(); ++it) {
            std::ifstream file(*it, std::ios::binary);
            if (!file) continue;

            auto header = readHeader(file);
            if (!header) continue;

            // Read entries to find highest sequence
            while (file) {
                uint32_t length;
                file.read(reinterpret_cast<char*>(&length), 4);
                if (!file || length == 0) break;

                std::vector<uint8_t> entryData(length + 4);
                std::memcpy(entryData.data(), &length, 4);
                file.read(reinterpret_cast<char*>(entryData.data() + 4), length);
                if (!file) break;

                auto entry = WalEntry::deserialize(entryData);
                if (entry && entry->sequence > sequence_.load()) {
                    sequence_.store(entry->sequence);
                }
            }
        }
    }

    // Open current WAL file for appending
    auto currentPath = currentFilePath();
    bool fileExists = std::filesystem::exists(currentPath);

    currentFile_.open(currentPath, std::ios::binary | std::ios::app);
    if (!currentFile_) {
        return false;
    }

    if (!fileExists) {
        // Write header for new file
        currentFileStartSequence_ = sequence_.load() + 1;
        writeHeader();
    } else {
        // Read existing header
        std::ifstream readFile(currentPath, std::ios::binary);
        auto header = readHeader(readFile);
        if (header) {
            currentFileStartSequence_ = header->startSequence;
        }
    }

    currentFileSize_ = std::filesystem::file_size(currentPath);
    isOpen_.store(true);
    return true;
}

void WriteAheadLog::close() {
    std::lock_guard<std::mutex> lock(writeMutex_);

    if (!isOpen_.load()) {
        return;
    }

    if (currentFile_.is_open()) {
        currentFile_.flush();
        currentFile_.close();
    }

    isOpen_.store(false);
}

void WriteAheadLog::setSequenceFloor(uint64_t seq) {
    // CAS loop — monotonically raise sequence_ to at least `seq`.
    // Concurrent appends (which `++` the same atomic) are tolerated
    // because compare_exchange_weak retries until it observes a
    // current value that's already ≥ seq, in which case we leave it.
    uint64_t current = sequence_.load();
    while (current < seq && !sequence_.compare_exchange_weak(current, seq)) {
        // current was updated by compare_exchange_weak — loop and retest.
    }
}

uint64_t WriteAheadLog::append(WalEntry entry) {
    std::lock_guard<std::mutex> lock(writeMutex_);

    if (!isOpen_.load() || !currentFile_.is_open()) {
        return 0;
    }

    // Assign sequence number and timestamp
    entry.sequence = ++sequence_;
    entry.timestamp = static_cast<uint64_t>(
        std::chrono::duration_cast<std::chrono::milliseconds>(
            std::chrono::system_clock::now().time_since_epoch()
        ).count()
    );

    // Serialize and write
    auto data = entry.serialize();
    currentFile_.write(reinterpret_cast<const char*>(data.data()), static_cast<std::streamsize>(data.size()));
    currentFileSize_ += data.size();

    if (config_.syncOnWrite) {
        currentFile_.flush();
        sync();
    }

    // Rotate if file is too large
    if (currentFileSize_ >= config_.maxFileSizeBytes) {
        rotate();
    }

    return entry.sequence;
}

void WriteAheadLog::sync() {
    if (currentFile_.is_open()) {
        currentFile_.flush();
        // Note: For true durability, we'd use fsync() here
        // std::filesystem doesn't provide this, would need OS-specific code
    }
}

uint64_t WriteAheadLog::replay(uint64_t fromSequence, std::function<void(const WalEntry&)> callback) {
    auto walFiles = getWalFiles();
    uint64_t count = 0;

    for (const auto& file : walFiles) {
        count += replayFile(file, fromSequence, callback);
    }

    return count;
}

uint64_t WriteAheadLog::totalSizeBytes() const {
    uint64_t total = 0;
    auto walFiles = getWalFiles();
    for (const auto& file : walFiles) {
        std::error_code ec;
        total += std::filesystem::file_size(file, ec);
    }
    return total;
}

void WriteAheadLog::truncateBefore(uint64_t sequence) {
    std::lock_guard<std::mutex> lock(writeMutex_);

    auto walFiles = getWalFiles();
    for (const auto& file : walFiles) {
        // Read header to get start sequence
        std::ifstream readFile(file, std::ios::binary);
        auto header = readHeader(readFile);
        readFile.close();

        if (header && header->startSequence < sequence) {
            // Check if all entries in this file are before the sequence
            bool canDelete = true;
            uint64_t maxSeqInFile = 0;

            std::ifstream scanFile(file, std::ios::binary);
            scanFile.seekg(sizeof(Header));

            while (scanFile) {
                uint32_t length;
                scanFile.read(reinterpret_cast<char*>(&length), 4);
                if (!scanFile || length == 0) break;

                std::vector<uint8_t> entryData(length + 4);
                std::memcpy(entryData.data(), &length, 4);
                scanFile.read(reinterpret_cast<char*>(entryData.data() + 4), length);
                if (!scanFile) break;

                auto entry = WalEntry::deserialize(entryData);
                if (entry) {
                    maxSeqInFile = std::max(maxSeqInFile, entry->sequence);
                }
            }

            if (maxSeqInFile < sequence) {
                // Safe to delete this file
                std::error_code ec;
                std::filesystem::remove(file, ec);
            }
        }
    }
}

WalEntry WriteAheadLog::makeInsertEntry(const std::string& collection, const Document& doc,
                                         const std::string& originNodeId) {
    WalEntry entry;
    entry.opType = WalOpType::INSERT;
    entry.collection = collection;
    entry.documentId = doc.id;
    entry.data = doc.toJson();
    entry.nodeId = originNodeId;
    return entry;
}

WalEntry WriteAheadLog::makeUpdateEntry(const std::string& collection, const Document& doc,
                                         const std::string& originNodeId) {
    WalEntry entry;
    entry.opType = WalOpType::UPDATE;
    entry.collection = collection;
    entry.documentId = doc.id;
    entry.data = doc.toJson();
    entry.nodeId = originNodeId;
    return entry;
}

WalEntry WriteAheadLog::makeDeleteEntry(const std::string& collection, const std::string& id,
                                         const std::string& originNodeId) {
    WalEntry entry;
    entry.opType = WalOpType::DELETE;
    entry.collection = collection;
    entry.documentId = id;
    entry.nodeId = originNodeId;
    return entry;
}

WalEntry WriteAheadLog::makeUpsertEntry(const std::string& collection, const Document& doc,
                                         const std::string& originNodeId) {
    WalEntry entry;
    entry.opType = WalOpType::UPSERT;
    entry.collection = collection;
    entry.documentId = doc.id;
    entry.data = doc.toJson();
    entry.nodeId = originNodeId;
    return entry;
}

WalEntry WriteAheadLog::makeCreateCollectionEntry(const std::string& collection, const CollectionOptions& options,
                                                   const std::string& originNodeId) {
    WalEntry entry;
    entry.opType = WalOpType::CREATE_COLLECTION;
    entry.collection = collection;
    entry.collectionOptions = options;
    entry.nodeId = originNodeId;
    return entry;
}

WalEntry WriteAheadLog::makeDropCollectionEntry(const std::string& collection,
                                                 const std::string& originNodeId) {
    WalEntry entry;
    entry.opType = WalOpType::DROP_COLLECTION;
    entry.collection = collection;
    entry.nodeId = originNodeId;
    return entry;
}

WalEntry WriteAheadLog::makeVecPutEntry(const std::string& collection,
    const std::string& docId, const std::vector<float>& vec,
    const std::string& originNodeId) {
    WalEntry entry;
    entry.opType = WalOpType::VEC_PUT;
    entry.collection = collection;
    entry.documentId = docId;
    entry.vectorData = vec;
    entry.nodeId = originNodeId;
    return entry;
}

WalEntry WriteAheadLog::makeVecDeleteEntry(const std::string& collection,
    const std::string& docId,
    const std::string& originNodeId) {
    WalEntry entry;
    entry.opType = WalOpType::VEC_DELETE;
    entry.collection = collection;
    entry.documentId = docId;
    entry.nodeId = originNodeId;
    return entry;
}

std::filesystem::path WriteAheadLog::currentFilePath() const {
    return config_.walDir / "wal-current.log";
}

std::vector<std::filesystem::path> WriteAheadLog::getWalFiles() const {
    std::vector<std::filesystem::path> files;

    std::error_code ec;
    for (const auto& entry : std::filesystem::directory_iterator(config_.walDir, ec)) {
        if (entry.is_regular_file()) {
            const auto& path = entry.path();
            if (path.filename().string().starts_with("wal-") &&
                path.extension() == ".log") {
                files.push_back(path);
            }
        }
    }

    // Sort by filename (which includes sequence number for archived files)
    std::sort(files.begin(), files.end());
    return files;
}

void WriteAheadLog::rotate() {
    if (currentFile_.is_open()) {
        currentFile_.flush();
        currentFile_.close();
    }

    // Rename current file with sequence range
    auto currentPath = currentFilePath();
    std::ostringstream oss;
    oss << "wal-" << std::setfill('0') << std::setw(16) << currentFileStartSequence_
        << "-" << std::setw(16) << sequence_.load() << ".log";
    auto archivePath = config_.walDir / oss.str();

    std::error_code ec;
    std::filesystem::rename(currentPath, archivePath, ec);

    // Open new current file
    currentFileStartSequence_ = sequence_.load() + 1;
    currentFile_.open(currentPath, std::ios::binary | std::ios::app);
    if (currentFile_) {
        writeHeader();
        currentFileSize_ = sizeof(Header);
    }
}

std::optional<WriteAheadLog::Header> WriteAheadLog::readHeader(std::ifstream& file) {
    Header header;
    file.read(reinterpret_cast<char*>(&header), sizeof(Header));
    if (!file) {
        return std::nullopt;
    }

    // Verify magic
    if (std::memcmp(header.magic, "CALWAL01", 8) != 0) {
        return std::nullopt;
    }

    return header;
}

void WriteAheadLog::writeHeader() {
    Header header;
    std::memcpy(header.magic, "CALWAL01", 8);
    header.startSequence = currentFileStartSequence_;
    currentFile_.write(reinterpret_cast<const char*>(&header), sizeof(Header));
    currentFile_.flush();
}

uint64_t WriteAheadLog::replayFile(const std::filesystem::path& path, uint64_t fromSequence,
                                    const std::function<void(const WalEntry&)>& callback) {
    std::ifstream file(path, std::ios::binary);
    if (!file) {
        return 0;
    }

    auto header = readHeader(file);
    if (!header) {
        return 0;
    }

    uint64_t count = 0;

    while (file) {
        // Read entry length
        uint32_t length;
        file.read(reinterpret_cast<char*>(&length), 4);
        if (!file || length == 0) break;

        // Read entry data
        std::vector<uint8_t> entryData(length + 4);
        std::memcpy(entryData.data(), &length, 4);
        file.read(reinterpret_cast<char*>(entryData.data() + 4), length);
        if (!file) break;

        // Deserialize and invoke callback
        auto entry = WalEntry::deserialize(entryData);
        if (entry && entry->sequence > fromSequence) {
            callback(*entry);
            count++;
        }
    }

    return count;
}

} // namespace smartbotic::database