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

#define DUTY 20
#define LED_PIN PB0
#define ONTIME 7210
#define OFFTIME 10101
//#define ONTIME 213
//#define OFFTIME 425
//#define ONTIME 5
//#define OFFTIME 5

#define BIT(x)	(1<<x)

#define N_1 (_BV(CS00))
#define N_8 (_BV(CS01))
#define N_64 (_BV(CS01) | _BV(CS00))
#define N_256 (_BV(CS02))
#define N_1024 (_BV(CS02) | _BV(CS00))

static void setPrescaler(uint8_t mode) {
  cli();
  CLKPR = bit(CLKPCE);
  CLKPR = mode;
  sei();
}
uint8_t onoff = 1;
volatile uint16_t seccount = 0;
volatile uint16_t lastsec = 0;
uint8_t daycount = 0;


static void pwm_init(void) {
  DDRB |= _BV(PB0);                   // set PWM pin as OUTPUT
  TCCR0A |= _BV(WGM01) | _BV(WGM00);  // set timer mode to FAST PWM
  TCCR0A |= _BV(COM0A1);              // connect PWM signal to pin (AC0A => PB0)
}

/* When timer is set to Fast PWM Mode, the freqency can be
calculated using equation: F = F_CPU / (N * 256) 
Posible frequencies (@1.2MHz):
 -> F(N_1) = 4.687kHz
 -> F(N_8) = 585Hz
 -> F(N_64) = 73Hz
 -> F(N_256) = 18Hz
 -> F(N_1024) = 4Hz */
static void pwm_set_frequency(uint32_t N) {
  TCCR0B = (TCCR0B & ~((1 << CS02) | (1 << CS01) | (1 << CS00))) | N;  // set prescaler
}

static void pwm_set_duty(uint8_t duty) {
  OCR0A = duty;  // set the OCRnx
}

static void pwm_stop(void) {
  TCCR0B &= ~((1 << CS02) | (1 << CS01) | (1 << CS00));  // stop the timer
}

ISR(WDT_vect) {
  cli();
  seccount++;
  // set prescaler to "4s" (measured 5s on my attiny13) and enable Watchdog Timer
  WDTCR |= (1 << WDCE);
  WDTCR = (1 << WDTIE) | (0 << WDE) | (1 << WDP3) | (0 << WDP2) | (0 << WDP1) | (0 << WDP0);
  sei();                // enable global interrupts
  // start the lights
  if(!onoff && (seccount > OFFTIME))
  {
    onoff=1;
    seccount=0;
    lastsec=0;
    pwm_set_frequency(N_8);
    pwm_init();
    pwm_set_duty(DUTY);
    set_sleep_mode(SLEEP_MODE_ADC);
    return;        
  }
  // stop the lights
  if(onoff && seccount > ONTIME){
     onoff=0;
    seccount=0;
    lastsec=0;
    pwm_set_duty(0);
    pwm_stop();
    digitalWrite(PB0,0);    
    MCUCR = BIT(SE) + BIT(SM1);   // Power-Down wählen
    sleep_cpu();                  // und stoppen bis WDT aufweckt
  }
}

void setup() {
  _delay_ms(5000);  /* setup */
  pinMode(LED_PIN, OUTPUT);
  setPrescaler(4);
  pwm_set_frequency(N_8);
  pwm_init();
  pwm_set_duty(DUTY);
  onoff=1;  
  seccount = 0;
  cli();
  WDTCR |= (1 << WDCE);
  WDTCR = (1 << WDTIE) | (0 << WDE) | (1 << WDP3) | (0 << WDP2) | (0 << WDP1) | (0 << WDP0);
  sei();                // enable global interrupts
}

void loop() {
  // todo check light conditions and change duty
  // todo check battery state and switch off
}