use core::marker::{PhantomData, PhantomPinned};
use core::pin::Pin;

use embassy::interrupt::{Interrupt, InterruptExt};

use crate::peripheral::can_be_preempted;

/// A type which can be used as state with `Peripheral`.
///
/// It needs to be `Sync` because references are shared between the 'thread' which owns the `Peripheral` and the interrupt.
///
/// It also requires `'static` to be used safely with `Peripheral::register_interrupt`,
/// because although `Pin` guarantees that the memory of the state won't be invalidated,
/// it doesn't guarantee that the lifetime will last.
pub trait PeripheralState: Sync {
    type Interrupt: Interrupt;
    fn on_interrupt(&self);
}

pub struct Peripheral<S: PeripheralState> {
    state: S,

    irq_setup_done: bool,
    irq: S::Interrupt,

    _not_send: PhantomData<*mut ()>,
    _pinned: PhantomPinned,
}

impl<S: PeripheralState + 'static> Peripheral<S> {
    /// Registers `on_interrupt` as the wrapped interrupt's interrupt handler and enables it.
    ///
    /// This requires this `Peripheral`'s `PeripheralState` to live for `'static`,
    /// because `Pin` only guarantees that it's memory won't be repurposed,
    /// not that it's lifetime will last.
    ///
    /// To use non-`'static` `PeripheralState`, use the unsafe `register_interrupt_unchecked`.
    ///
    /// Note: `'static` doesn't mean it _has_ to live for the entire program, like an `&'static T`;
    /// it just means it _can_ live for the entire program - for example, `u8` lives for `'static`.
    pub fn register_interrupt(self: Pin<&mut Self>) {
        // SAFETY: `S: 'static`, so there's no way it's lifetime can expire.
        unsafe { self.register_interrupt_unchecked() }
    }
}

impl<S: PeripheralState> Peripheral<S> {
    pub fn new(irq: S::Interrupt, state: S) -> Self {
        if can_be_preempted(&irq) {
            panic!("`Peripheral` cannot be created in an interrupt with higher priority than the interrupt it wraps");
        }

        Self {
            irq,
            irq_setup_done: false,

            state,
            _not_send: PhantomData,
            _pinned: PhantomPinned,
        }
    }

    /// Registers `on_interrupt` as the wrapped interrupt's interrupt handler and enables it.
    ///
    /// # Safety
    /// The lifetime of any data in `PeripheralState` that is accessed by the interrupt handler
    /// must not end without `Drop` being called on this `Peripheral`.
    ///
    /// This can be accomplished by either not accessing any data with a lifetime in `on_interrupt`,
    /// or making sure that nothing like `mem::forget` is used on the `Peripheral`.
    pub unsafe fn register_interrupt_unchecked(self: Pin<&mut Self>) {
        let this = self.get_unchecked_mut();
        if this.irq_setup_done {
            return;
        }

        this.irq.disable();
        this.irq.set_handler(|p| {
            // The state can't have been dropped, otherwise the interrupt would have been disabled.
            // We checked in `new` that the thread owning the `Peripheral` can't preempt the interrupt,
            // so someone can't have preempted us before this point and dropped the `Peripheral`.
            let state = unsafe { &*(p as *const S) };
            state.on_interrupt();
        });
        this.irq
            .set_handler_context((&this.state) as *const _ as *mut ());
        this.irq.enable();

        this.irq_setup_done = true;
    }

    pub fn state(self: Pin<&mut Self>) -> &S {
        &self.into_ref().get_ref().state
    }

    /// Returns whether the wrapped interrupt is currently in a pending state.
    pub fn is_pending(&self) -> bool {
        self.irq.is_pending()
    }

    /// Forces the wrapped interrupt into a pending state.
    pub fn pend(&self) {
        self.irq.pend()
    }

    /// Forces the wrapped interrupt out of a pending state.
    pub fn unpend(&self) {
        self.irq.unpend()
    }

    /// Gets the priority of the wrapped interrupt.
    pub fn priority(&self) -> <S::Interrupt as Interrupt>::Priority {
        self.irq.get_priority()
    }
}

impl<S: PeripheralState> Drop for Peripheral<S> {
    fn drop(&mut self) {
        self.irq.disable();
        self.irq.remove_handler();
    }
}