#include <SPI.h>

#define NSS_PIN 5        // Chip select for SX1278
#define RST_PIN 14       // Reset pin for SX1278
#define MOTION_SENSOR 4  // PIR sensor connected to GPIO 4

// Function to write a value to a SX1278 register
void writeRegister(uint8_t reg, uint8_t value) {
  digitalWrite(NSS_PIN, LOW);
  SPI.transfer(reg | 0x80); // Set MSB for write
  SPI.transfer(value);
  digitalWrite(NSS_PIN, HIGH);
}

// Function to read a value from a SX1278 register (if needed)
uint8_t readRegister(uint8_t reg) {
  digitalWrite(NSS_PIN, LOW);
  SPI.transfer(reg & 0x7F); // Clear MSB for read
  uint8_t value = SPI.transfer(0x00);
  digitalWrite(NSS_PIN, HIGH);
  return value;
}

void setup() {
  Serial.begin(115200);
  pinMode(MOTION_SENSOR, INPUT_PULLUP);
  pinMode(NSS_PIN, OUTPUT);
  pinMode(RST_PIN, OUTPUT);
  
  // Ensure NSS is high by default
  digitalWrite(NSS_PIN, HIGH);
  
  SPI.begin();
  
  // Reset the SX1278
  digitalWrite(RST_PIN, LOW);
  delay(100);
  digitalWrite(RST_PIN, HIGH);
  delay(100);
  
  // Basic SX1278 initialization sequence:
  // 1. Put SX1278 in sleep mode with LoRa mode enabled.
  writeRegister(0x01, 0x80); // RegOpMode: Sleep mode, LoRa mode bit set
  delay(10);
  
  // 2. Switch to Standby mode.
  writeRegister(0x01, 0x81); // RegOpMode: Standby mode in LoRa mode
  delay(10);
  
  // 3. Set frequency to approximately 433 MHz.
  // The frequency is set using registers 0x06, 0x07, 0x08.
  // Formula: FRF = Frequency / FSTEP, where FSTEP ≈ 61.035 Hz.
  // For 433 MHz, FRF ≈ 433e6 / 61.035 ≈ 7090667.
  uint32_t frf = 7090667;
  writeRegister(0x06, (uint8_t)((frf >> 16) & 0xFF));
  writeRegister(0x07, (uint8_t)((frf >> 8) & 0xFF));
  writeRegister(0x08, (uint8_t)(frf & 0xFF));
  
  // Additional settings (power, bandwidth, etc.) would normally be set here.
  // For this minimal demo, we leave other registers at their defaults.
  
  Serial.println("SX1278 initialized in LoRa mode.");
}

void loop() {
  int motionState = digitalRead(MOTION_SENSOR);
  
  // Prepare a dummy payload:
  // '1' if motion detected, '0' otherwise.
  uint8_t payload = (motionState == HIGH) ? '1' : '0';
  
  // Write payload to FIFO.
  // FIFO register is at address 0x00.
  writeRegister(0x00, payload);
  
  // Switch to TX mode.
  // In a real implementation you’d configure FIFO pointers and packet parameters.
  // For our minimal demo, we simply trigger TX by writing an opmode.
  writeRegister(0x01, 0x83); // RegOpMode: TX mode (Standby -> TX, minimal demo)
  
  // Inform via Serial Monitor.
  if(motionState == HIGH){
    Serial.println("Transmitting: Motion detected");
  } else {
    Serial.println("Transmitting: No motion detected");
  }
  
  delay(1000);  // Wait 1 second between transmissions
  
  // Return to Standby mode after transmitting.
  writeRegister(0x01, 0x81);
}