#include <libopencm3/cm3/nvic.h>
#include <libopencm3/stm32/exti.h>
#include <libopencm3/stm32/rtc.h>

static inline uint32_t rtc_to_sec(uint32_t rtc)
{
	uint32_t sec;

	sec = (rtc & 0xf) + ((rtc >> 4) & 0xf) * 10;
	sec += (((rtc >> 8) & 0xf) + ((rtc >> 12) & 0xf) * 10) * 60;
	sec += (((rtc >> 16) & 0xf) + ((rtc >> 20) & 0xf) * 10) * 3600;

	return sec;
}

static inline uint32_t sec_to_rtc(uint32_t sec)
{
	uint32_t rtc;
	uint32_t hour, min;

	hour = sec / 3600;
	min = (sec % 3600) / 60;
	sec = sec % 60;

	rtc = ((hour / 10) << 20) | ((hour % 10) << 16);
	rtc |= ((min / 10) << 12) | ((min % 10) << 8);
	rtc |= ((sec / 10) << 4) | (sec % 10);

	return rtc;
}

void rtc_alarm_isr(void)
{
	uint32_t alarm_sec;

	exti_reset_request(EXTI17);

	rtc_unlock();

	/* Disable the alarm. */
	RTC_CR &= ~RTC_CR_ALRAE;
	while (!(RTC_ISR & RTC_ISR_ALRAWF));
	RTC_ISR &= ~RTC_ISR_ALRAF;

	/* Set the alarm time. */
	alarm_sec = rtc_to_sec(RTC_TR) + 10;
	RTC_ALRMAR = sec_to_rtc(alarm_sec);
	RTC_ALRMAR |= 0xc0000000;

	/* Enable the alarm. */
	EXTI_IMR |= EXTI17;
	exti_set_trigger(EXTI17, EXTI_TRIGGER_RISING);
	RTC_CR |= RTC_CR_ALRAE;

	rtc_lock();
}

int alarm_init(void)
{
	uint32_t alarm_sec;

	rtc_unlock();

	/* Set the alarm time. */
	alarm_sec = rtc_to_sec(RTC_TR) + 10;
	RTC_ALRMAR = sec_to_rtc(alarm_sec);
	RTC_ALRMAR |= 0xc0000000;

	RTC_CR |= RTC_CR_ALRAIE | RTC_CR_BYPSHAD;

	nvic_enable_irq(NVIC_RTC_IRQ);
	EXTI_IMR |= EXTI17;
	exti_set_trigger(EXTI17, EXTI_TRIGGER_RISING);

	rtc_lock();

	return 0;
}