#pragma once
#include <Arduino.h>

// ============================================================================
// Protocol Constants
// ============================================================================

// Sync bytes (distinguishable from Feetech 0xFF 0xFF)
constexpr uint8_t SYNC0 = 0xA5;
constexpr uint8_t SYNC1 = 0x5A;

// Packet structure:
// [SYNC0][SYNC1][TAG 4 bytes][LENGTH 2 bytes][SEQ 2 bytes][PAYLOAD...][CRC16 2 bytes]
// Total overhead: 12 bytes

constexpr uint16_t MAX_PAYLOAD_SIZE = 6000;
constexpr uint16_t PACKET_HEADER_SIZE = 10;  // sync(2) + tag(4) + len(2) + seq(2)
constexpr uint16_t PACKET_CRC_SIZE = 2;

// ============================================================================
// Packet Tags (4 bytes each, human-readable)
// ============================================================================

namespace Tag {
  // Identity & Config
  constexpr char IDENT[4] = {'I','D','N','T'};  // Identity request/response
  constexpr char CONFG[4] = {'C','O','N','F'};  // Config update
  
  // File Operations
  constexpr char FLIST[4] = {'F','L','S','T'};  // File list
  constexpr char FLOAD[4] = {'F','L','O','D'};  // File load
  constexpr char FSAVE[4] = {'F','S','A','V'};  // File save
  constexpr char FDELE[4] = {'F','D','E','L'};  // File delete
  constexpr char FPLAY[4] = {'F','P','L','Y'};  // Play animation file
  
  // Motor Control
  constexpr char MSET[4]  = {'M','S','E','T'};  // Set motor positions
  constexpr char MPOS[4]  = {'M','P','O','S'};  // Motor position stream
  constexpr char MSCAN[4] = {'M','S','C','N'};  // Scan for motors
  constexpr char MWRIT[4] = {'M','W','R','T'};  // Write motor register
  constexpr char MSTRM[4] = {'M','S','T','M'};  // Motor stream control
  
  // Sensors
  constexpr char IMU[4]   = {'I','M','U','0'};  // ADXL acceleration data (x,y,z)
  constexpr char RADAR[4] = {'R','D','A','R'};  // Radar targets
  constexpr char FRAME[4] = {'F','R','M','E'};  // Animation frame events (frame, mode, status)
  
  // System
  constexpr char STATE[4] = {'S','T','A','T'};  // System state/heartbeat
  constexpr char MSGE[4]  = {'M','S','G','E'};  // Log/debug message
  constexpr char BOOT[4]  = {'B','O','O','T'};  // Enter bootloader
  constexpr char ACK[4]   = {'A','C','K','!'};  // Acknowledge
  constexpr char NACK[4]  = {'N','A','C','K'};  // Negative acknowledge
}

// ============================================================================
// Play Modes (for FPLAY command)
// ============================================================================

enum PlayMode : uint8_t {
  PLAY_IDLE   = 0x00,
  PLAY_ONCE   = 0x01,
  PLAY_LOOP   = 0x02,
  PLAY_REPEAT = 0x03
};

// ============================================================================
// Packet Buffer
// ============================================================================

extern uint8_t g_rxBuffer[MAX_PAYLOAD_SIZE + PACKET_HEADER_SIZE + PACKET_CRC_SIZE];
extern uint16_t g_rxBufferLen;

// ============================================================================
// CRC16-CCITT
// ============================================================================

uint16_t crc16Update(uint16_t crc, const uint8_t* data, uint16_t len);
uint16_t crc16Compute(const uint8_t* data, uint16_t len);

// ============================================================================
// Packet Sending
// ============================================================================

// Send a tagged packet with auto-incrementing sequence number
void sendPacket(const char tag[4], const uint8_t* payload, uint16_t len);

// Convenience: send string as MSGE packet
void sendMessage(const String& msg);

// Convenience: send ACK/NACK
void sendAck(const char originalTag[4]);
void sendNack(const char originalTag[4], const String& reason = "");

// ============================================================================
// Packet Receiving
// ============================================================================

// Packet receive state machine - call from loop()
// Returns true when a complete valid packet is ready
bool receivePacket();

// Get received packet info (valid after receivePacket returns true)
const char* getReceivedTag();
const uint8_t* getReceivedPayload();
uint16_t getReceivedPayloadLen();
uint16_t getReceivedSeq();

// Check if received tag matches
bool tagMatches(const char* received, const char expected[4]);

// ============================================================================
// Utility
// ============================================================================

// Compare tags
inline bool tagsEqual(const char a[4], const char b[4]) {
  return memcmp(a, b, 4) == 0;
}