//! # FIFO Queue
//!
//! Provides the FIFO queue structure for allocations
use crate::sync::interface::Mutex;
#[allow(unused_imports)]
use crate::sync::NullLock;
#[allow(unused_imports)]
use crate::sync::SpinLock;
use crate::util::node::*;
use core::fmt;
use core::fmt::{Debug, Formatter};

/// # Initialize Queue
/// - Name: Symbol name
/// - Size: Number of elements
/// - Default: Default value
/// - Type: Data Type
#[macro_export]
macro_rules! init_fifo_queue {
	($name:tt,$size:tt,$default:tt,$type:ty) => {
		init_fifo_queue!{@gen [$name,$size,$default,$type,concat!("# ", stringify!($type), " Queue Allocator")]}
	};
	(@gen [$name:tt,$size:tt,$default:tt,$type:ty,$doc:expr]) => {
		#[doc = $doc]
		#[link_section = ".data.alloc"]
		pub static $name: FifoQueue<'static, $type, {$size+1}> = FifoQueue::new(SpinLock::new([Node::new($default); {$size+1}]));
	};
}

/// # Queue Allocator
///
/// Structure to store a pool of allocated data structures.
pub struct FifoQueue<'a, T: Sized, const COUNT: usize> {
    /// # Synchronized Pool of items
    ///
    /// Stores synchronization wrapper around the data pool
    pub inner: SpinLock<[Node<'a, T>; COUNT]>,
}

impl<'a, T: Sized, const COUNT: usize> FifoQueue<'a, T, COUNT> {
    /// # Create new Fifo Queue
    pub const fn new(initial: SpinLock<[Node<'a, T>; COUNT]>) -> Self {
        Self { inner: initial }
    }
}

/// # Sharing Thread Safety for FifoQueue
unsafe impl<T, const COUNT: usize> Send for FifoQueue<'_, T, COUNT> {}

impl<'a, T: Sized, const COUNT: usize> crate::util::queue::Queue<'a> for FifoQueue<'a, T, COUNT> {
    type Data = T;
    /// # Initialization of Fixed-Size Pool
    ///
    /// Establishes the header and footer of the queue
    /// as the first and second elements respectively.
    /// All of the internal elements point to the next
    /// one and the final element points to `None`
    fn init(&self) {
        self.inner.lock(|queue| {
            for idx in 2..COUNT {
                if idx != COUNT - 1 {
                    queue[idx].next = Some(&mut queue[idx + 1] as *mut Node<'a, Self::Data>);
                } else {
                    queue[idx].next = None;
                }
            }
            queue[0].next = Some(&mut queue[2] as *mut Node<'a, Self::Data>);
            queue[1].next = Some(&mut queue[COUNT - 1] as *mut Node<'a, Self::Data>);
        });
    }

    /// # Pop
    ///
    /// If there is a data chunk available,
    /// return it, otherwise return `None`
    fn pop(&self) -> Option<&mut Node<'a, Self::Data>> {
        return self.inner.lock(|pool| {
            if let Some(entry) = pool[0].next {
                pool[0].next = unsafe { (*entry).next };
                unsafe {
                    (*entry).next = None;
                }
                match pool[0].next {
                    None => pool[1].next = None,
                    _ => {}
                }
                return Some(unsafe { &mut *entry as &mut Node<'a, Self::Data> });
            } else {
                return None;
            }
        });
    }

    /// # Push
    ///
    /// Add the item to the end of the queue.
    /// If there were no items, set it as the head.
    fn push(&self, freed_item: &mut Node<'a, Self::Data>) {
        self.inner.lock(|pool| {
            freed_item.next = None;
            match pool[1].next {
                None => {
                    pool[0].next = Some(freed_item as *mut Node<'a, Self::Data>);
                }
                Some(entry) => unsafe {
                    (*entry).next = Some(freed_item as *mut Node<'a, Self::Data>);
                },
            }
            pool[1].next = Some(freed_item as *mut Node<'a, Self::Data>);
        });
    }
}

impl<T: Debug, const COUNT: usize> Debug for FifoQueue<'_, T, COUNT> {
    /// # Debug Formatted Output
    ///
    /// Output each data point in the array with
    /// its debug formatter.
    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
        self.inner.lock(|queue| {
            return write!(f, "{:?}", queue);
        })
    }
}