#pragma once

#include <array>
#include <cstdint>
#include <string>

#include "secsgem/hsms/types.hpp"

namespace secsgem::hsms {

// The fixed 10-byte HSMS message header (SEMI E37). The interpretation of
// byte2/byte3 depends on `stype`: for data messages byte2 = (W<<7)|stream and
// byte3 = function; for control messages they carry status / reason codes.
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;

  // Data-message field views.
  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;
};

}  // namespace secsgem::hsms