//! # Queue
//!
//! Queue structure
use crate::sync::interface::Mutex;
use crate::sync::NullLock;
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_lifo_queue {
	($name:tt,$size:tt,$default:tt,$type:ty) => {
		init_lifo_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: LifoQueue<'static, $type, {$size+1}> = LifoQueue::new(NullLock::new([Node::new($default); {$size+1}]));
	};
}

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

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

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

impl<'a, T: Sized, const COUNT: usize> crate::util::queue::Queue<'a> for LifoQueue<'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 1..COUNT {
                if idx != COUNT - 1 {
                    queue[idx].next = Some(&mut queue[idx + 1] as *mut Node<'a, T>);
                } else {
                    queue[idx].next = None;
                }
            }
            queue[0].next = Some(&mut queue[1] as *mut Node<'a, T>);
        });
    }

    /// # Pop
    ///
    /// Get an item from the queue
    fn pop(&self) -> Option<&mut Node<'a, T>> {
        return self.inner.lock(|pool| {
            if let Some(entry) = pool[0].next {
                unsafe {
                    pool[0].next = (*entry).next;
                    (*entry).next = None;
                    return Some(&mut *entry as &mut Node<'a, T>);
                }
            } else {
                return None;
            }
        });
    }

    /// # Push
    ///
    /// Add the item to the start of the queue.
    fn push(&self, freed_item: &mut Node<'a, T>) {
        self.inner.lock(|pool| {
            freed_item.next = pool[0].next;
            pool[0].next = Some(freed_item as *mut Node<'a, T>);
        });
    }
}

impl<T: Debug, const COUNT: usize> Debug for LifoQueue<'_, 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);
        })
    }
}