// Upload this to Node 1, Node 2, etc.

// --- PIN DEFINITIONS ---
#define LED_PIN 8 

// Downstream Connection (To Next Node)
#define RxOut 0  
#define TxOut 1  

// SLAVE INPUT: Listens to Previous Node via Pins 20/21
// On C3 Super Mini, "Serial0" is hardwired to 20/21
#define PortIn Serial0 

// SLAVE OUTPUT: Talks to Next Node via Pins 0/1
HardwareSerial PortOut(1); 

// Global Variables
char cmd;
uint8_t arg, addr, address;

void setup() {
   delay(1000);

   pinMode(LED_PIN, OUTPUT);
   digitalWrite(LED_PIN, HIGH); // Start OFF

   // 1. Start Upstream Connection (Pins 20/21)
   PortIn.begin(921600); 
  //  pinMode(20, INPUT_PULLUP); // Safety: Prevent noise if wire is loose

   // 2. Start Downstream Connection (Pins 0 and 1)
   PortOut.begin(921600, SERIAL_8N1, RxOut, TxOut);
   
   // 3. Setup Sensor Pin
   pinMode(RxOut, INPUT);
}

void loop() {
  // Wait for command from Previous Node
  while (PortIn.available() == 0);
  cmd = PortIn.read();

  // --- 'L' (All LEDs) ---
  if (cmd == 'L') {
    PortOut.write(cmd); // Pass to Next Node
    while (PortIn.available() == 0);
    arg = PortIn.read();
    PortOut.write(arg); // Pass to Next Node

    if (arg & 0b1) digitalWrite(LED_PIN, LOW); else digitalWrite(LED_PIN, HIGH);
  }

  // --- 'l' (Specific LED) ---
  else if (cmd == 'l') {
    PortOut.write(cmd); 
    while (PortIn.available() == 0);
    addr = PortIn.read();
    PortOut.write(addr); 
    while (PortIn.available() == 0);
    arg = PortIn.read();
    PortOut.write(arg); 

    if (addr == address) {
      if (arg & 0b1) digitalWrite(LED_PIN, LOW); else digitalWrite(LED_PIN, HIGH);
    }
  }

  // --- 'a' (Address Assignment) ---
  else if (cmd == 'a') {
    PortOut.end(); 
    pinMode(RxOut, INPUT); 
    delay(5); 

    // Check: Do I have a neighbor?
    if (digitalRead(RxOut) == LOW) {
      // I am the Last Node
      address = 0;
      PortIn.write(0); // Tell Previous Node "I am 0"
      PortOut.begin(921600, SERIAL_8N1, RxOut, TxOut);
    }
    else {
      // I have a neighbor!
      PortOut.begin(921600, SERIAL_8N1, RxOut, TxOut);
      PortOut.write('a'); // Wake up Next Node

      while (PortOut.available() == 0);
      arg = PortOut.read(); // Wait for neighbor
      
      address = arg + 1;
      PortIn.write(address); // Tell Previous Node "I am neighbor+1"
    }
  }
}