codec.h

#pragma once
#include <cstdint>
#include <cstddef>

struct Order
{
    uint64_t order_id;
    uint32_t price;
    uint32_t quantity;
    uint8_t side; // SIDE_BUY or SIDE_SELL
};

enum class CodecResult
{
    OK,
    BUFFER_TOO_SMALL,
    INVALID_MSG_TYPE,
    INVALID_MSG_LEN,
    CHECKSUM_MISMATCH
};

// Returns number of bytes written, or 0 on failure
size_t encode_order(uint8_t *buf, size_t buf_len, const Order &order);

// Decodes order from buffer, returns result code
CodecResult decode_order(const uint8_t *buf, size_t buf_len, Order &out);

// Utility: compute simple XOR checksum over buffer
uint16_t compute_checksum(const uint8_t *data, size_t len);

// Get human-readable error string
const char *codec_result_str(CodecResult result);