//! Stack Resource Policy

#![deny(missing_docs)]
#![deny(warnings)]
#![feature(asm)]
#![feature(const_fn)]
#![no_std]

extern crate cortex_m;
extern crate static_ref;
extern crate typenum;

use core::cell::UnsafeCell;
use core::marker::PhantomData;

use cortex_m::ctxt::Context;
use cortex_m::interrupt::Nr;
#[cfg(not(thumbv6m))]
use cortex_m::register::{basepri, basepri_max};
use static_ref::Ref;
use typenum::{Cmp, Unsigned};
#[cfg(not(thumbv6m))]
use typenum::{Greater, Less};

pub use cortex_m::ctxt::Local;
pub use cortex_m::asm::{bkpt, wfi};

#[doc(hidden)]
pub use cortex_m::peripheral::NVIC;

macro_rules! barrier {
    () => {
        asm!(""
             :
             :
             : "memory"
             : "volatile");
    }
}

/// A resource
pub struct Resource<T, CEILING> {
    _ceiling: PhantomData<CEILING>,
    data: UnsafeCell<T>,
}

impl<T, C> Resource<T, C> {
    /// Creates a new resource with ceiling `C`
    pub const fn new(data: T) -> Self
    where
        C: Ceiling,
    {
        Resource {
            _ceiling: PhantomData,
            data: UnsafeCell::new(data),
        }
    }
}

impl<T, CEILING> Resource<T, C<CEILING>> {
    /// Borrows the resource for the duration of another resource's critical
    /// section
    ///
    /// This operation is zero cost and doesn't impose any additional blocking
    pub fn borrow<'cs, PRIORITY, SCEILING>(
        &'static self,
        _priority: &P<PRIORITY>,
        _system_ceiling: &'cs C<SCEILING>,
    ) -> Ref<'cs, T>
    where
        SCEILING: GreaterThanOrEqual<CEILING>,
        CEILING: GreaterThanOrEqual<PRIORITY>,
    {
        unsafe { Ref::new(&*self.data.get()) }
    }

    /// Locks the resource for the duration of the critical section `f`
    ///
    /// For the duration of the critical section, tasks whose priority level is
    /// smaller than or equal to the resource `CEILING` will be prevented from
    /// preempting the current task.
    ///
    /// Within this critical section, resources with ceiling equal to or smaller
    /// than `CEILING` can be borrowed at zero cost. See
    /// [Resource.borrow](struct.Resource.html#method.borrow).
    #[cfg(not(thumbv6m))]
    pub fn lock<R, PRIORITY, F>(&'static self, _priority: &P<PRIORITY>, f: F) -> R
        where F: FnOnce(Ref<T>, &C<CEILING>) -> R,
              CEILING: Cmp<PRIORITY, Output = Greater> + Cmp<UMAX, Output = Less> + Level
    {
        unsafe {
            let old_basepri = basepri::read();
            basepri_max::write(<CEILING>::hw());
            barrier!();
            let ret =
                f(Ref::new(&*self.data.get()), &C { _marker: PhantomData });
            barrier!();
            basepri::write(old_basepri);
            ret
        }
    }
}

unsafe impl<T, C> Sync for Resource<T, C>
where
    C: Ceiling,
{
}

/// A hardware peripheral as a resource
pub struct Peripheral<P, CEILING>
where
    P: 'static,
{
    peripheral: cortex_m::peripheral::Peripheral<P>,
    _ceiling: PhantomData<CEILING>,
}

impl<P, C> Peripheral<P, C>
where
    C: Ceiling,
{
    /// Assigns a ceiling `C` to the `peripheral`
    ///
    /// # Safety
    ///
    /// You MUST not create two resources that point to the same peripheral
    pub const unsafe fn new(peripheral: cortex_m::peripheral::Peripheral<P>,)
        -> Self {
        Peripheral {
            _ceiling: PhantomData,
            peripheral: peripheral,
        }
    }
}

impl<Periph, CEILING> Peripheral<Periph, C<CEILING>> {
    /// See [Resource.borrow](./struct.Resource.html#method.borrow)
    pub fn borrow<'cs, PRIORITY, SCEILING>(
        &'static self,
        _priority: &P<PRIORITY>,
        _system_ceiling: &'cs C<SCEILING>,
    ) -> Ref<'cs, Periph>
    where
        SCEILING: GreaterThanOrEqual<CEILING>,
        CEILING: GreaterThanOrEqual<PRIORITY>,
    {
        unsafe { Ref::new(&*self.peripheral.get()) }
    }

    /// See [Resource.lock](./struct.Resource.html#method.lock)
    #[cfg(not(thumbv6m))]
    pub fn lock<R, PRIORITY, F>(&'static self, _priority: &P<PRIORITY>, f: F) -> R
        where F: FnOnce(Ref<Periph>, &C<CEILING>) -> R,
              CEILING: Cmp<PRIORITY, Output = Greater> + Cmp<UMAX, Output = Less> + Level
    {
        unsafe {
            let old_basepri = basepri::read();
            basepri_max::write(<CEILING>::hw());
            barrier!();
            let ret = f(
                Ref::new(&*self.peripheral.get()),
                &C { _marker: PhantomData },
            );
            barrier!();
            basepri::write(old_basepri);
            ret
        }
    }
}

unsafe impl<T, C> Sync for Peripheral<T, C>
where
    C: Ceiling,
{
}

/// A global critical section
///
/// No task can preempt this critical section
pub fn critical<R, F>(f: F) -> R
where
    F: FnOnce(&CMAX) -> R,
{
    let primask = ::cortex_m::register::primask::read();
    ::cortex_m::interrupt::disable();

    let r = f(&C { _marker: PhantomData });

    // If the interrupts were active before our `disable` call, then re-enable
    // them. Otherwise, keep them disabled
    if primask.is_active() {
        ::cortex_m::interrupt::enable();
    }

    r
}

/// Requests the execution of a `task`
pub fn request<T, P>(_task: fn(T, P))
where
    T: Context + Nr,
    P: Priority,
{
    let nvic = unsafe { &*NVIC.get() };

    match () {
        #[cfg(debug_assertions)]
        () => {
            // NOTE(safe) zero sized type
            let task = unsafe { core::ptr::read(0x0 as *const T) };
            // NOTE(safe) atomic read
            assert!(!nvic.is_pending(task),
                    "Task is already in the pending state");
        }
        #[cfg(not(debug_assertions))]
        () => {}
    }

    // NOTE(safe) zero sized type
    let task = unsafe { core::ptr::read(0x0 as *const T) };
    // NOTE(safe) atomic write
    nvic.set_pending(task);
}

/// A type-level ceiling
pub struct C<T> {
    _marker: PhantomData<T>,
}

/// A type-level priority
pub struct P<T> {
    _marker: PhantomData<T>,
}

impl<T> P<T>
where
    T: Level,
{
    #[doc(hidden)]
    pub fn hw() -> u8 {
        T::hw()
    }
}

/// A valid resource ceiling
///
/// DO NOT IMPLEMENT THIS TRAIT YOURSELF
pub unsafe trait Ceiling {}

/// Type-level `>=` operator
///
/// DO NOT IMPLEMENT THIS TRAIT YOURSELF
pub unsafe trait GreaterThanOrEqual<RHS> {}

/// Interrupt hardware level
///
/// DO NOT IMPLEMENT THIS TRAIT YOURSELF
pub unsafe trait Level {
    /// Interrupt hardware level
    fn hw() -> u8;
}

/// A valid task priority
///
/// DO NOT IMPLEMENT THIS TRAIT YOURSELF
pub unsafe trait Priority {}


/// Convert a logical priority to a shifted hardware prio
/// as used by the NVIC and basepri registers
/// Notice, wrapping causes a panic due to u8
pub fn logical2hw(logical: u8) -> u8 {
    ((1 << PRIORITY_BITS) - logical) << (8 - PRIORITY_BITS)
}

/// Convert a shifted hardware prio to a logical priority
/// as used by the NVIC and basepri registers
/// Notice, wrapping causes a panic due to u8
pub fn hw2logical(hw: u8) -> u8 {
    (1 << PRIORITY_BITS) - (hw >> (8 - PRIORITY_BITS))
}


/// Priority 0, the lowest priority
pub type P0 = P<::typenum::U0>;

/// Declares tasks
#[macro_export]
macro_rules! tasks {
    ($krate:ident, {
        $($task:ident: ($Interrupt:ident, $P:ident),)*
    }) => {
        fn main() {
            $crate::critical(|cmax| {
                fn signature(_: fn($crate::P0, &$crate::CMAX)) {}

                signature(init);
                let p0 = unsafe { ::core::ptr::read(0x0 as *const _) };
                init(p0, cmax);
                set_priorities();
                enable_tasks();
            });

            fn signature(_: fn($crate::P0) -> !) {}

            signature(idle);
            let p0 = unsafe { ::core::ptr::read(0x0 as *const _) };
            idle(p0);

            fn set_priorities() {
                // NOTE(safe) this function runs in an interrupt free context
                let _nvic = unsafe { &*$crate::NVIC.get() };

                $(
                    {
                        let hw = $crate::$P::hw();
                        if hw != 0 {
                            unsafe {
                                _nvic.set_priority
                                    (::$krate::interrupt::Interrupt::$Interrupt,
                                     hw,
                                    );
                            }
                        }
                    }
                )*

                // TODO freeze the NVIC.IPR register using the MPU, if available
            }

            fn enable_tasks() {
                // NOTE(safe) this function runs in an interrupt free context
                let _nvic = unsafe { &*$crate::NVIC.get() };

                $(
                    _nvic.enable(::$krate::interrupt::Interrupt::$Interrupt);
                )*
            }

            #[allow(dead_code)]
            fn is_priority<P>()
            where
                P: $crate::Priority,
            {
            }

            #[allow(dead_code)]
            #[link_section = ".rodata.interrupts"]
            #[used]
            static INTERRUPTS: ::$krate::interrupt::Handlers =
                ::$krate::interrupt::Handlers {
                $(
                    $Interrupt: {
                        extern "C" fn $task(
                            task: ::$krate::interrupt::$Interrupt
                        ) {
                            is_priority::<$crate::$P>();
                            ::$task(
                                task, unsafe {
                                    ::core::ptr::read(0x0 as *const $crate::$P)
                                }
                            )
                        }

                        $task
                    },
                )*
                    ..::$krate::interrupt::DEFAULT_HANDLERS
                };
        }
    }
}

include!(concat!(env!("OUT_DIR"), "/prio.rs"));