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

#define PIN_LED 0b1000
#define PIN_BUTTON 0b0001
#define PIN_TRIM 0b0001

void init_ports(void) {
  // all outputs, swallows noise
  DDRB = 0xff;
  DDRC = 0xff;
  DDRD = 0xff;

  DDRD |= PIN_LED;
  PORTB |= PIN_BUTTON; // pull-up
  DDRB &= ~PIN_BUTTON;
  DDRC &= ~PIN_TRIM;
}

void init_pwm(void) {
  // page 84
  //  7-6: ouput A, 5-4: output B, 3-2: res, 1-0: waveform
  TCCR2A = 0b00100011;
  // 7-6: force output A/B, 5-4: res, 3: waveform, 2-0: clock source
  TCCR2B = 0b01000001;
  // duty
  OCR2B = 0;
}

void deinit_pwm(void) {
  TCCR2A = 0;
  TCCR2B = 0;
  OCR2B = 0;
}

void pwm_fade_in(int until, int step) {
  int i;
  for (i = 0; i < until; i += step) {
    OCR2B = i;
    _delay_ms(0.5);
  }
}

void pwm_fade_out(int until, int step) {
  int i;
  for (i = OCR2B; i > until; i -= step) {
    OCR2B = i;
    _delay_ms(0.25);
  }
}
/*
int analog_read(void) {
  ADCSRA |= ADEN;
  ADCSRA |= ADSC;
}*/

int main(void) {
  init_ports();

  while (1) {
    if (!(PINB & PIN_BUTTON)) {
      init_pwm();
      pwm_fade_in(0x7f >> 5, 1);
      _delay_ms(300);
      OCR2B = 0x7f >> 3;
      _delay_ms(150);
      pwm_fade_out(32, 4);
      _delay_ms(50);
      pwm_fade_out(0, 4);
    }
    deinit_pwm();
    PORTD &= ~PIN_LED;
  }
  return 0;
}