#define F_CPU 8000000UL

#include "../avr-i2c-slave/I2CSlave.h"
#include <util/delay.h>
#include <avr/io.h>

#include <avr/interrupt.h>

#define BAUDRATE 9600
#define BAUD_PRESCALLER (((F_CPU / (BAUDRATE * 16UL))) - 1)

#define I2C_ADDR 0x20

void USART_init(void){
  UBRR0H = (uint8_t)(BAUD_PRESCALLER>>8);
  UBRR0L = (uint8_t)(BAUD_PRESCALLER);
  UCSR0B = (1<<RXEN0)|(1<<TXEN0);
  UCSR0C = (3<<UCSZ00);
}

void USART_send( unsigned char data){
  while(!(UCSR0A & (1<<UDRE0)));
  UDR0 = data;
}
 
void USART_putstring(char* StringPtr){
  while(*StringPtr != 0x00){
    USART_send(*StringPtr);
    StringPtr++;
  }
}

volatile uint8_t challenge = 0; // Use 0 as 'challenge not sent' condition
uint16_t time_open = 0;

uint8_t check_challenge(uint8_t arg) {
  return (arg >> 3);
}

void I2C_received(uint8_t received_data) {
  uint8_t solution;
  char message[100] = {0};

  solution = check_challenge(challenge);
  sprintf(message, "Response: %d. Expected: %d\n", received_data, solution);
  USART_putstring(message);
  if (received_data == solution) { // Check validity of response
    // Open lock
    time_open = 5000;
  }
}

void I2C_requested() {
  challenge = (uint8_t)(TCNT1 & 0xff);
  I2C_transmitByte(challenge);
  char message[100] = {0};
  sprintf(message, "Request received. Sending %d\n", challenge);
  USART_putstring(message);
}

void setup() {
  // set received/requested callbacks
  I2C_setCallbacks(I2C_received, I2C_requested);
  // init I2C
  I2C_init(I2C_ADDR);
  // init output gpio
  DDRC = 0b00000100; // PC2
  TCNT1 = 0;
  TCCR1B |= (1 << CS10) | (1 << CS11); // No prescaling
}

int main() {
  int i = 0;
  setup();
  USART_init();
  while (1) {
    i++;
    if (time_open > 0) {
      PORTC |= 2 << 1;
      time_open -= 1;
    } else {
      PORTC = 0;
    }
    _delay_ms(1);
    if (i > 1000) {
      char message[] = "Alive\n";
      USART_putstring(message);
      i = 0;
    }
  }
}