//! # FIFO Queue
//!
//! Provides the FIFO queue structure for allocations
use crate::sync::NullLock;
use crate::sync::interface::Mutex;
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_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(NullLock::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: NullLock<[Node<'a, T>;COUNT]>,
}

impl<'a, T: Sized, const COUNT: usize> FifoQueue<'a, T, COUNT> {
    /// # Create new Fifo Queue
    pub const fn new(initial: NullLock<[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> FifoQueue<'a, T, COUNT> {
	/// # 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`
	pub 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, T>);
				} else {
					queue[idx].next = None;
				}
			}
			queue[0].next = Some(&mut queue[2] as *mut Node<'a, T>);
			queue[1].next = Some(&mut queue[COUNT-1] as *mut Node<'a, T>);
		});
	}

	/// # Allocate Data
	///
	/// If there is a data chunk available,
	/// return it, otherwise return `None`
	#[allow(dead_code)]
	pub fn alloc(&self) -> Option<&mut Node<'a,T>> {
		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,T>});
			} else {
				return None;
			}
		});
	}

	/// # Free
	///
	/// Add the item to the end of the queue.
	/// If there were no items, set it as the head.
	#[allow(dead_code)]
	pub fn free(&self, freed_item: &mut Node<'a,T>) {
		self.inner.lock(|pool| {
			freed_item.next = None;
			match pool[1].next {
				None => {
					pool[0].next = Some(freed_item as *mut Node<'a,T>);
				}
				Some(entry) => {
					unsafe {
						(*entry).next = Some(freed_item as *mut Node<'a,T>);
					}
				}
			}
			pool[1].next = Some(freed_item as *mut Node<'a,T>);
		});
	}
}

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);
		})
	}
}