#include <SPI.h>

#define SPI_MASTER_SLAVE_SEL_PIN (2)
#define SS_PIN                   (53)

boolean is_spi_master;
volatile boolean slave_received = false;
volatile uint8_t slave_recv_data = 0xff;

void setup() {
  Serial.begin(115200);
  pinMode(SPI_MASTER_SLAVE_SEL_PIN, INPUT_PULLUP);
  
  if (digitalRead(SPI_MASTER_SLAVE_SEL_PIN) == LOW) {
    is_spi_master = true;
  } else {
    is_spi_master = false;
  }

  if (is_spi_master) {
    pinMode(SS_PIN, OUTPUT);
    digitalWrite(SS_PIN, HIGH);
    SPI.begin();
    SPI.setDataMode(SPI_MODE0); // Corrected from SPI_MPDE0 to SPI_MODE0
    SPI.setBitOrder(MSBFIRST);
    SPI.setClockDivider(SPI_CLOCK_DIV16);
    Serial.println(F("SPI Master..."));
    delay(100);
  } else {
    pinMode(SS_PIN, INPUT_PULLUP); // Moved this line to the correct place
    pinMode(MISO, OUTPUT); // Corrected the syntax for pinMode
    SPCR &= ~_BV(MSTR); // Ensure this is set correctly for slave mode
    SPCR &= ~_BV(CPOL); // Corrected from CP0L to CPOL
    SPCR &= ~_BV(CPHA);
    SPCR &= ~_BV(DORD);
    SPCR |= _BV(SPE); // Set SPE to enable SPI
    Serial.println(F("SPI Slave..."));
  }
}

void loop() {
  if (is_spi_master) {
    static uint8_t send_data = 0x00, recv_data;
    Serial.print(F("Master> sent: 0x"));
    Serial.print(send_data, HEX);

    digitalWrite(SS_PIN, LOW);
    recv_data = SPI.transfer(send_data);
    digitalWrite(SS_PIN, HIGH);
    
    Serial.print(F(", received: 0x"));
    Serial.println(recv_data, HEX);
    send_data += 1;
    delay(100); // Corrected from dalay to delay
  } else {
    if (slave_received) {
      SPDR = slave_recv_data; // Send data to master
      slave_received = false;
      Serial.print(F("Slave: received 0x"));
      Serial.println(slave_recv_data, HEX);
    }
    delay(1);
  }
}

ISR(SPI_STC_vect) {
  slave_recv_data = SPDR; // Read data from master
  slave_received = true;
}