#include <SPI.h>

// Pin definitions (adjust to your schematic)
#define SS 5            // Chip select for SX1278
#define RST 14          // Reset pin for SX1278
#define DIO0 26         // DIO0 pin (used for IRQ flags)
#define MOTION_SENSOR 4 // PIR sensor pin

// Set this to 'true' for transmitter mode, 'false' for receiver mode.
bool isTransmitter = true;

// Write a value to an SX1278 register via SPI
void writeRegister(byte addr, byte value) {
  digitalWrite(SS, LOW);
  SPI.transfer(addr | 0x80);  // MSB=1 for write
  SPI.transfer(value);
  digitalWrite(SS, HIGH);
}

// Read a value from an SX1278 register via SPI
byte readRegister(byte addr) {
  digitalWrite(SS, LOW);
  SPI.transfer(addr & 0x7F);  // MSB=0 for read
  byte value = SPI.transfer(0x00);
  digitalWrite(SS, HIGH);
  return value;
}

// Reset the SX1278 using the RST pin
void resetSX1278() {
  digitalWrite(RST, LOW);
  delay(100);
  digitalWrite(RST, HIGH);
  delay(100);
}

// Initialize the SX1278 in LoRa mode and set frequency to ~433 MHz
void initSX1278() {
  // Put the SX1278 in sleep mode with LoRa enabled (RegOpMode = 0x80)
  writeRegister(0x01, 0x80);
  delay(10);
  
  // Set frequency registers for ~433 MHz.
  // Calculation: FRF = Frequency / FSTEP, where FSTEP ≈ 61.035 Hz.
  // For 433 MHz, FRF ≈ 433e6 / 61.035 ≈ 7090667 (0x6C, 0x80, 0x00)
  writeRegister(0x06, 0x6C);
  writeRegister(0x07, 0x80);
  writeRegister(0x08, 0x00);
  
  // Put the SX1278 in standby mode (RegOpMode = 0x81)
  writeRegister(0x01, 0x81);
  delay(10);
  
  // If receiver, switch to continuous RX mode (RegOpMode = 0x85)
  if (!isTransmitter) {
    writeRegister(0x01, 0x85);
  }
  
  Serial.println("SX1278 configured in LoRa mode.");
}

void setup() {
  Serial.begin(115200);
  pinMode(MOTION_SENSOR, INPUT_PULLUP);
  pinMode(SS, OUTPUT);
  pinMode(RST, OUTPUT);
  pinMode(DIO0, INPUT);
  
  SPI.begin(); // Uses default SPI pins (SCK=18, MISO=19, MOSI=23 on ESP32)
  
  resetSX1278();
  initSX1278();
  
  if (isTransmitter) {
    Serial.println("Device set as TRANSMITTER");
  } else {
    Serial.println("Device set as RECEIVER");
  }
}

void loop() {
  if (isTransmitter) {
    sendLoRaMessage();
    delay(2000); // Wait 2 seconds between transmissions
  } else {
    receiveLoRaMessage();
    delay(100);  // Small delay for polling in RX mode
  }
}

// Function to send a LoRa message based on the PIR sensor state
void sendLoRaMessage() {
  int motionState = digitalRead(MOTION_SENSOR);
  char payload = (motionState == HIGH) ? 'M' : 'N';
  
  Serial.println("Transmitting...");
  if (motionState == HIGH) {
    Serial.println("Motion detected! Sending LoRa message...");
  } else {
    Serial.println("No motion detected. Sending LoRa message...");
  }
  
  // Set FIFO pointer to 0 (RegFifoAddrPtr at 0x0D)
  writeRegister(0x0D, 0x00);
  // Write the payload to FIFO (RegFifo at 0x00)
  writeRegister(0x00, payload);
  // Set payload length to 1 byte (RegPayloadLength at 0x22)
  writeRegister(0x22, 0x01);
  
  // Set SX1278 to TX mode (RegOpMode = 0x83)
  writeRegister(0x01, 0x83);
  
  // Wait for TxDone flag (bit 3 in RegIrqFlags at 0x12, mask 0x08)
  while (!(readRegister(0x12) & 0x08)) {
    // Wait until transmission is complete
  }
  
  // Clear TxDone flag by writing 0x08 to RegIrqFlags
  writeRegister(0x12, 0x08);
  
  // Return to standby mode (RegOpMode = 0x81)
  writeRegister(0x01, 0x81);
}

// Function to receive a LoRa message and display it
void receiveLoRaMessage() {
  // Check the RxDone flag (bit 6 in RegIrqFlags at 0x12, mask 0x40)
  if (readRegister(0x12) & 0x40) {
    // Clear RxDone flag
    writeRegister(0x12, 0x40);
    
    // Read current FIFO address from RegFifoRxCurrentAddr (0x10)
    byte currentAddr = readRegister(0x10);
    // Set FIFO pointer to current address (RegFifoAddrPtr at 0x0D)
    writeRegister(0x0D, currentAddr);
    
    // Get number of received bytes from RegRxNbBytes (0x13)
    byte nbBytes = readRegister(0x13);
    String msg = "";
    for (byte i = 0; i < nbBytes; i++) {
      msg += (char)readRegister(0x00);
    }
    
    Serial.print("Received: ");
    Serial.println(msg);
  } else {
    Serial.println("No LoRa packet received.");
  }
}