// SPDX-License-Identifier: MIT OR Apache-2.0
//
// Copyright (c) 2020-2022 Andre Richter <andre.o.richter@gmail.com>

//! Asynchronous exception handling.

#[cfg(target_arch = "aarch64")]
#[path = "../_arch/aarch64/exception/asynchronous.rs"]
mod arch_asynchronous;

use core::{fmt, marker::PhantomData};

//--------------------------------------------------------------------------------------------------
// Architectural Public Reexports
//--------------------------------------------------------------------------------------------------
pub use arch_asynchronous::{
    is_local_irq_masked, local_irq_mask, local_irq_mask_save, local_irq_restore, local_irq_unmask,
    print_state,
};

//--------------------------------------------------------------------------------------------------
// Public Definitions
//--------------------------------------------------------------------------------------------------

/// Interrupt descriptor.
#[derive(Copy, Clone)]
pub struct IRQDescriptor {
    /// Descriptive name.
    pub name: &'static str,

    /// Reference to handler trait object.
    pub handler: &'static (dyn interface::IRQHandler + Sync),
}

/// IRQContext token.
///
/// An instance of this type indicates that the local core is currently executing in IRQ
/// context, aka executing an interrupt vector or subcalls of it.
///
/// Concept and implementation derived from the `CriticalSection` introduced in
/// <https://github.com/rust-embedded/bare-metal>
#[derive(Clone, Copy)]
pub struct IRQContext<'irq_context> {
    _0: PhantomData<&'irq_context ()>,
}

/// Asynchronous exception handling interfaces.
pub mod interface {

    /// Implemented by types that handle IRQs.
    pub trait IRQHandler {
        /// Called when the corresponding interrupt is asserted.
        fn handle(&self) -> Result<(), &'static str>;
    }

    /// IRQ management functions.
    ///
    /// The `BSP` is supposed to supply one global instance. Typically implemented by the
    /// platform's interrupt controller.
    pub trait IRQManager {
        /// The IRQ number type depends on the implementation.
        type IRQNumberType;

        /// Register a handler.
        fn register_handler(
            &self,
            irq_number: Self::IRQNumberType,
            descriptor: super::IRQDescriptor,
        ) -> Result<(), &'static str>;

        /// Enable an interrupt in the controller.
        fn enable(&self, irq_number: Self::IRQNumberType);

        /// Handle pending interrupts.
        ///
        /// This function is called directly from the CPU's IRQ exception vector. On AArch64,
        /// this means that the respective CPU core has disabled exception handling.
        /// This function can therefore not be preempted and runs start to finish.
        ///
        /// Takes an IRQContext token to ensure it can only be called from IRQ context.
        #[allow(clippy::trivially_copy_pass_by_ref)]
        fn handle_pending_irqs<'irq_context>(
            &'irq_context self,
            ic: &super::IRQContext<'irq_context>,
        );

        /// Print list of registered handlers.
        fn print_handler(&self);
    }
}

/// A wrapper type for IRQ numbers with integrated range sanity check.
#[derive(Copy, Clone)]
pub struct IRQNumber<const MAX_INCLUSIVE: usize>(usize);

//--------------------------------------------------------------------------------------------------
// Public Code
//--------------------------------------------------------------------------------------------------

impl<'irq_context> IRQContext<'irq_context> {
    /// Creates an IRQContext token.
    ///
    /// # Safety
    ///
    /// - This must only be called when the current core is in an interrupt context and will not
    ///   live beyond the end of it. That is, creation is allowed in interrupt vector functions. For
    ///   example, in the ARMv8-A case, in `extern "C" fn current_elx_irq()`.
    /// - Note that the lifetime `'irq_context` of the returned instance is unconstrained. User code
    ///   must not be able to influence the lifetime picked for this type, since that might cause it
    ///   to be inferred to `'static`.
    #[inline(always)]
    pub unsafe fn new() -> Self {
        IRQContext { _0: PhantomData }
    }
}

impl<const MAX_INCLUSIVE: usize> IRQNumber<{ MAX_INCLUSIVE }> {
    /// Creates a new instance if number <= MAX_INCLUSIVE.
    pub const fn new(number: usize) -> Self {
        assert!(number <= MAX_INCLUSIVE);

        Self(number)
    }

    /// Return the wrapped number.
    pub const fn get(self) -> usize {
        self.0
    }
}

impl<const MAX_INCLUSIVE: usize> fmt::Display for IRQNumber<{ MAX_INCLUSIVE }> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.0)
    }
}

/// Executes the provided closure while IRQs are masked on the executing core.
///
/// While the function temporarily changes the HW state of the executing core, it restores it to the
/// previous state before returning, so this is deemed safe.
#[inline(always)]
pub fn exec_with_irq_masked<T>(f: impl FnOnce() -> T) -> T {
    let ret: T;

    unsafe {
        let saved = local_irq_mask_save();
        ret = f();
        local_irq_restore(saved);
    }

    ret
}