#include <avr/io.h>
#include <avr/interrupt.h> 
#include <util/delay.h>
#include <stdbool.h>

// ----- Pin Map -----
#define IR_SIG   2      // PB2, active LOW when tripped
#define RUN_BTN  3      // PB3, active LOW
#define STOP_BTN 4      // PB4, active LOW
#define RUN_SIG  0      // PB0, output
#define RUN_LED  1      // PB1, output (active LOW)

volatile bool events = false;

static inline void respond();

int main(void) {
  // ----- Pin Configuration -----
  // Configure IR_SIG, RUN_BTN_ and STOP_BTN as inputs
  DDRB &= ~((1 << IR_SIG) | (1 << RUN_BTN) | (1 << STOP_BTN));

  // Enable internal pull-up resistors
  PORTB |= (1 << IR_SIG) | (1 << RUN_BTN) | (1 << STOP_BTN);

  // Configure RUN_SIG and RUN_LED as outputs
  DDRB |= (1 << RUN_SIG) | (1 << RUN_LED);

  // Initialize RUN_LED to OFF (active LOW)
  PORTB |= (1 << RUN_LED);
  PORTB &= ~(1 << RUN_SIG);

  // Enable pin change interrupts
  GIMSK |= (1 << PCIE);
  PCMSK |= (1 << PCINT2) | (1 << PCINT3) | (1 << PCINT4); // Unmask pins

  sei(); // Enable global interrupts
  
  // ---- Wait for events ----
  for (;;) {
    // Check for events
      if (events) {
        respond();
        events = false;
      }
      _delay_ms(10);
    }
}

static inline void respond() {
  // Flip run bit to 1 on START_BTN active low
  if (!(PINB & (1 << RUN_BTN))) {
    PORTB &= ~(1 << RUN_LED);
    PORTB |= (1 << RUN_SIG);
  }
  // Flip run bit to 0 on IR_SIG or STOP_BTN active low
  if (!(PINB & (1 << STOP_BTN)) || !(PINB & (1 << IR_SIG))) {
    PORTB |= (1 << RUN_LED);
    PORTB &= ~(1 << RUN_SIG);
  }
}

// ISR for pin change pn PB0-PB5
ISR(PCINT0_vect) {
  events = true;
}