//! [`Monotonic`] impl for the STM32.
//!
//! Not all timers are available on all parts. Ensure that only available
//! timers are exposed by having the correct `stm32*` feature enabled for `rtic-monotonic`.
//!
//! # Example
//!
//! ```
//! use rtic_monotonics::stm32::*;
//! use rtic_monotonics::stm32::Tim2 as Mono;
//! use rtic_monotonics::Monotonic;
//! use embassy_stm32::peripherals::TIM2;
//! use embassy_stm32::rcc::low_level::RccPeripheral;
//!
//! fn init() {
//!     // Generate timer token to ensure correct timer interrupt handler is used.
//!     let token = rtic_monotonics::create_stm32_tim2_monotonic_token!();
//!
//!     // If using `embassy-stm32` HAL, timer clock can be read out like this:
//!     let timer_clock_hz = TIM2::frequency();
//!     // Or define it manually if you are using other HAL or know correct frequency:
//!     let timer_clock_hz = 64_000_000;
//!
//!     // Start the monotonic
//!     Mono::start(timer_clock_hz, token);
//! }
//!
//! async fn usage() {
//!     loop {
//!          // Use the monotonic
//!          let timestamp = Mono::now().ticks();
//!          Mono::delay(100.millis()).await;
//!     }
//! }
//! ```

use crate::{Monotonic, TimeoutError, TimerQueue};
use atomic_polyfill::{AtomicU64, Ordering};
pub use fugit::{self, ExtU64};
use pac::metadata::METADATA;
use stm32_metapac as pac;

const TIMER_HZ: u32 = 1_000_000;

#[doc(hidden)]
#[macro_export]
macro_rules! __internal_create_stm32_timer_interrupt {
    ($mono_timer:ident, $timer:ident, $timer_token:ident) => {{
        #[no_mangle]
        #[allow(non_snake_case)]
        unsafe extern "C" fn $timer() {
            $crate::stm32::$mono_timer::__tq().on_monotonic_interrupt();
        }

        pub struct $timer_token;

        unsafe impl $crate::InterruptToken<$crate::stm32::$mono_timer> for $timer_token {}

        $timer_token
    }};
}

/// Register TIM2 interrupt for the monotonic.
#[macro_export]
macro_rules! create_stm32_tim2_monotonic_token {
    () => {{
        $crate::__internal_create_stm32_timer_interrupt!(Tim2, TIM2, Tim2Token)
    }};
}

/// Register TIM3 interrupt for the monotonic.
#[macro_export]
macro_rules! create_stm32_tim3_monotonic_token {
    () => {{
        $crate::__internal_create_stm32_timer_interrupt!(Tim3, TIM3, Tim3Token)
    }};
}

macro_rules! make_timer {
    ($mono_name:ident, $timer:ident, $bits:ident, $set_tim_en:ident, $set_tim_rst:ident, $overflow:ident, $tq:ident$(, doc: ($($doc:tt)*))?) => {
        /// Monotonic timer queue implementation.
        $(
            #[cfg_attr(docsrs, doc(cfg($($doc)*)))]
        )?

        pub struct $mono_name;

        use pac::$timer;

        static $overflow: AtomicU64 = AtomicU64::new(0);
        static $tq: TimerQueue<$mono_name> = TimerQueue::new();

        impl $mono_name {
            /// Start monotonic timer. Must be called only once.
            /// `tim_clock_hz` shows to which frequency `TIMx` clock source is configured.
            pub fn start(tim_clock_hz: u32, _interrupt_token: impl crate::InterruptToken<Self>) {
                pac::RCC.apbenr1().modify(|r| r.$set_tim_en(true));
                pac::RCC.apbrstr1().modify(|r| r.$set_tim_rst(true));
                pac::RCC.apbrstr1().modify(|r| r.$set_tim_rst(false));

                $timer.cr1().modify(|r| r.set_cen(false));

                let psc = tim_clock_hz / TIMER_HZ - 1;
                $timer.psc().write(|r| r.set_psc(psc as u16));

                // Enable update event interrupt.
                $timer.dier().modify(|r| r.set_uie(true));

                // Trigger an update event to load the prescaler value to the clock.
                $timer.egr().write(|r| r.set_ug(true));

                // The above line raises an update event which will indicate that the timer is already finished.
                // Since this is not the case, it should be cleared.
                $timer.sr().modify(|r| r.set_uif(false));

                // Start the counter.
                $timer.cr1().modify(|r| {
                    r.set_cen(true);
                });

                $tq.initialize(Self {});

                // SAFETY: We take full ownership of the peripheral and interrupt vector,
                // plus we are not using any external shared resources so we won't impact
                // basepri/source masking based critical sections.
                unsafe {
                    crate::set_monotonic_prio(METADATA.nvic_priority_bits.unwrap(), pac::Interrupt::$timer);
                    cortex_m::peripheral::NVIC::unmask(pac::Interrupt::$timer);
                }
            }

            /// Used to access the underlying timer queue
            #[doc(hidden)]
            pub fn __tq() -> &'static TimerQueue<$mono_name> {
                &$tq
            }

            fn is_overflow() -> bool {
                $timer.sr().read().uif()
            }

            /// Delay for some duration of time.
            #[inline]
            pub async fn delay(duration: <Self as Monotonic>::Duration) {
                $tq.delay(duration).await;
            }
            /// Timeout at a specific time.
            pub async fn timeout_at<F: core::future::Future>(
                instant: <Self as rtic_time::Monotonic>::Instant,
                future: F,
            ) -> Result<F::Output, TimeoutError> {
                $tq.timeout_at(instant, future).await
            }

            /// Timeout after a specific duration.
            #[inline]
            pub async fn timeout_after<F: core::future::Future>(
                duration: <Self as Monotonic>::Duration,
                future: F,
            ) -> Result<F::Output, TimeoutError> {
                $tq.timeout_after(duration, future).await
            }

            /// Delay to some specific time instant.
            #[inline]
            pub async fn delay_until(instant: <Self as Monotonic>::Instant) {
                $tq.delay_until(instant).await;
            }
        }

        impl Monotonic for $mono_name {
            type Instant = fugit::TimerInstantU64<TIMER_HZ>;
            type Duration = fugit::TimerDurationU64<TIMER_HZ>;

            const ZERO: Self::Instant = Self::Instant::from_ticks(0);

            fn now() -> Self::Instant {
                let cnt = $timer.cnt().read().cnt();

                // If the overflow bit is set, we add this to the timer value. It means the `on_interrupt`
                // has not yet happened, and we need to compensate here.
                let ovf: u64 = if Self::is_overflow() {
                    $bits::MAX as u64 + 1
                } else {
                    0
                };

                Self::Instant::from_ticks(cnt as u64 + ovf + $overflow.load(Ordering::SeqCst))
            }

            fn set_compare(instant: Self::Instant) {
                let now = Self::now();
                let max_ticks = $bits::MAX as u64;

                // Since the timer may or may not overflow based on the requested compare val, we check how many ticks are left.
                let val = match instant.checked_duration_since(now) {
                    None => 0, // In the past
                    Some(x) if x.ticks() <= max_ticks => instant.duration_since_epoch().ticks() as $bits, // Will not overflow
                    Some(_x) => $timer.cnt().read().cnt().wrapping_add($bits::MAX - 1), // Will overflow
                };

                $timer.ccr(1).write(|r| r.set_ccr(val));
            }

            fn clear_compare_flag() {
                $timer.sr().modify(|r| r.set_ccif(1, false));
            }

            fn pend_interrupt() {
                cortex_m::peripheral::NVIC::pend(pac::Interrupt::$timer);
            }

            fn enable_timer() {
                $timer.dier().modify(|r| r.set_ccie(1, true));
            }

            fn disable_timer() {
                $timer.dier().modify(|r| r.set_ccie(1, false));
            }

            fn on_interrupt() {
                if Self::is_overflow() {
                    $timer.sr().modify(|r| r.set_uif(false));

                    $overflow.fetch_add($bits::MAX as u64 + 1, Ordering::SeqCst);
                }
            }
        }
    };
}

make_timer!(
    Tim2,
    TIM2,
    u32,
    set_tim2en,
    set_tim2rst,
    TIMER2_OVERFLOWS,
    TIMER2_TQ
);
make_timer!(
    Tim3,
    TIM3,
    u16,
    set_tim3en,
    set_tim3rst,
    TIMER3_OVERFLOWS,
    TIMER3_TQ
);