secs-gem/include/secsgem/hsms/header.hpp

#pragma once

#include <array>
#include <chrono>
#include <cstdint>
#include <stdexcept>
#include <string>
#include <vector>

// HSMS wire-format primitives (SEMI E37): SType + status enums, the 10-byte
// Header, the Frame (header + body, length-prefixed on the wire), and the
// protocol timer defaults. One header keeps everything that touches the wire
// format in one place.
namespace secsgem::hsms {

// ---- Session type + status / reason enums --------------------------------

enum class SType : uint8_t {
  Data        = 0,
  SelectReq   = 1,
  SelectRsp   = 2,
  DeselectReq = 3,
  DeselectRsp = 4,
  LinktestReq = 5,
  LinktestRsp = 6,
  RejectReq   = 7,
  SeparateReq = 9,
};

const char* stype_name(SType s);

enum class SelectStatus : uint8_t {
  Ok = 0, AlreadyActive = 1, NotReady = 2, ConnectExhaust = 3,
};

enum class DeselectStatus : uint8_t {
  Ok = 0, NotEstablished = 1, Busy = 2,
};

enum class RejectReason : uint8_t {
  StypeNotSupported = 1,
  PtypeNotSupported = 2,
  TransactionNotOpen = 3,
  EntityNotSelected = 4,
};

inline constexpr uint8_t kPTypeSecsII = 0;
inline constexpr uint16_t kControlSessionId = 0xFFFF;

// HSMS protocol timer defaults (SEMI E37 §10).
struct Timers {
  std::chrono::milliseconds t3{45000};    // reply
  std::chrono::milliseconds t5{10000};    // connect separation
  std::chrono::milliseconds t6{5000};     // control transaction
  std::chrono::milliseconds t7{10000};    // not-selected
  std::chrono::milliseconds t8{5000};     // intercharacter
  std::chrono::milliseconds linktest{0};  // 0 disables
};

// ---- Header (10 bytes) ---------------------------------------------------

struct Header {
  uint16_t session_id = kControlSessionId;
  uint8_t byte2 = 0;
  uint8_t byte3 = 0;
  uint8_t ptype = kPTypeSecsII;
  SType stype = SType::Data;
  uint32_t system_bytes = 0;

  bool w_bit() const { return (byte2 & 0x80) != 0; }
  uint8_t stream() const { return byte2 & 0x7F; }
  uint8_t function() const { return byte3; }

  static Header data_message(uint16_t session_id, uint8_t stream, uint8_t function,
                             bool reply_expected, uint32_t system_bytes) {
    Header h;
    h.session_id = session_id;
    h.byte2 = static_cast<uint8_t>((reply_expected ? 0x80 : 0x00) | (stream & 0x7F));
    h.byte3 = function;
    h.ptype = kPTypeSecsII;
    h.stype = SType::Data;
    h.system_bytes = system_bytes;
    return h;
  }

  static Header control(SType stype, uint32_t system_bytes,
                        uint16_t session_id = kControlSessionId, uint8_t byte2 = 0,
                        uint8_t byte3 = 0) {
    Header h;
    h.session_id = session_id;
    h.byte2 = byte2;
    h.byte3 = byte3;
    h.ptype = kPTypeSecsII;
    h.stype = stype;
    h.system_bytes = system_bytes;
    return h;
  }

  std::array<uint8_t, 10> encode() const;
  static Header decode(const uint8_t* data);  // reads exactly 10 bytes
  std::string describe() const;

  bool operator==(const Header&) const = default;
};

// ---- Frame (header + body, length-prefixed) ------------------------------

class FrameError : public std::runtime_error {
 public:
  using std::runtime_error::runtime_error;
};

inline constexpr std::size_t kLengthPrefixSize = 4;
inline constexpr std::size_t kHeaderSize = 10;

struct Frame {
  Header header;
  std::vector<uint8_t> body;

  Frame() = default;
  explicit Frame(Header h, std::vector<uint8_t> b = {})
      : header(h), body(std::move(b)) {}

  // Full wire bytes including the 4-byte length prefix.
  std::vector<uint8_t> encode() const;

  // Decode a message from its payload (header + body, i.e. the bytes that
  // follow the length prefix). `len` must be >= kHeaderSize.
  static Frame decode(const uint8_t* payload, std::size_t len);
};

}  // namespace secsgem::hsms