use arduino_hal::{clock::Clock, pac::TC0, DefaultClock};

// Prescaler set for the timer (see tccr0b)
const TIMER_PRESCALE: u32 = 64;
// Timer clock tick rate per second
const TIMER_FREQ: u32 = DefaultClock::FREQ / TIMER_PRESCALE;

const fn us_to_ticks(us: u32) -> u32 {
    TIMER_FREQ * us / 1_000_000
}

// Timer 0 (8bit)
pub struct SegmentTimer(TC0);

impl SegmentTimer {
    // Sets up timer to rise interrupts:
    // 1. TIMER0_COMPA - segment_switch_us - time in μs to switch to next segment
    // 2. TIMER0_COMPB - set by set_segment_on_time to keep segment LEDs on
    pub fn init(tc0: TC0, segment_switch_us: u32) -> SegmentTimer {
        // 16_000_000 / 64 * 1000 / 1_000_000 => 250
        let ocra = us_to_ticks(segment_switch_us);

        // Use CTC mode: reset counter when matches compare value
        tc0.tccr0a.write(|w| w.wgm0().ctc());
        // Set the compare value for TOP (reset)
        tc0.ocr0a.write(|w| {
            w.bits(
                ocra.try_into()
                    .expect("timer init segment_switch_us out of rage"),
            )
        });
        // Slow down the timer (CLK / prescale)
        tc0.tccr0b.write(|w| w.cs0().prescale_64());
        // Raise interrupt on TOP (reset)
        // Raise interrupt on B match
        tc0.timsk0
            .write(|w| w.ocie0a().set_bit().ocie0b().set_bit());

        SegmentTimer(tc0)
    }

    // Set for how long the segment LEDs should be on in μs
    // Controls TIMER0_COMPB interrupt time after TIMER0_COMPA
    pub fn segment_on_time(&mut self, segment_on_us: u32) {
        let ocrb = us_to_ticks(segment_on_us);
        // Set the compare value for B match
        self.0.ocr0b.write(|w| {
            w.bits(
                ocrb.try_into()
                    .expect("timer init segment_on_us out of rage"),
            )
        });
    }
}