#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#define F_CPU 16000000UL
#define RESET_BUTTON PB0
#define STOP_BUTTON PB1
#define PLAY_BUTTON PB2
#define DISPLAY_PORT PORTD
#define DISPLAY_DDR DDRD

const uint8_t digitPatterns[] = {
    // abcdefg
    0b00111111, // 0
    0b00000110, // 1
    0b01011011, // 2
    0b01001111, // 3
    0b01100110, // 4
    0b01101101, // 5
    0b01111101, // 6
    0b00000111, // 7
    0b01111111, // 8
    0b01101111  // 9
};
volatile uint16_t timerValue = 0;
volatile uint8_t running = 0;
volatile uint8_t displayDigit = 0;

void initializeDisplay() {
    DISPLAY_DDR = 0xFF;
    DDRC = 0xFF;
}

void initializeButtons() {
    PCICR |= (1 << PCIE0);
    PCMSK0 |= (1 << PCINT0) | (1 << PCINT1) | (1 << PCINT2);
}

void updateDisplay() {
    uint8_t ones = timerValue % 10;
    uint8_t tens = (timerValue / 10) % 10;

    DISPLAY_PORT = digitPatterns[ones];
    PORTC |= (1 << PC0);
    _delay_ms(5);
    PORTC = 0x00;
    displayDigit = !displayDigit;
    DISPLAY_PORT = !digitPatterns[tens];
    PORTC |= (1 << PC1);
    _delay_ms(5);
    PORTC = 0x00;
}
ISR(PCINT0_vect) {
    if (!(PINB & (1 << RESET_BUTTON))) {
        timerValue = 0;
        running = 0;
        updateDisplay();
    } else if (!(PINB & (1 << STOP_BUTTON))) {
        running = 0;
    } else if (!(PINB & (1 << PLAY_BUTTON))) {
        running = 1;
    }
}

void initializeTimer() {
    TCCR1B |= (1 << WGM12);    // CTC mode
    OCR1A = 15624;              // Compare value for 1-second interval at 16 MHz (16,000,000 / 1024)
    TIMSK1 |= (1 << OCIE1A);    // Enable Timer1 compare match interrupt
    TCCR1B |= (1 << CS12) | (1 << CS10); // Set prescaler to 1024, starts the timer
}

ISR(TIMER1_COMPA_vect) {
    if (running) {
        timerValue++;
    }
}

int main() {
    initializeDisplay();
    initializeButtons();
    initializeTimer();

    sei();

    while (1) {
        updateDisplay();
    }

    return 0;
}