//! # FIFO Queue
//!
//! Provides the FIFO queue structure for allocations
use crate::sync::NullLock;
use crate::sync::interface::Mutex;
use crate::vprintln;
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_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: QueueAllocator<'static, $type, {$size+2}> = QueueAllocator::<$type, {$size+2}>{inner: NullLock::new([QueueItem::new($default); {$size+2}])};
	};
}

#[derive(Copy,Clone)]
/// # Queue Item
///
/// Encapsulates a data element and a pointer to
/// the next `Queue` item
pub struct QueueItem<'a, T: Sized> {
	/// # Data
	///
	/// The encapsulated data
	data: T,
	/// # Pointer to the next item
	///
	/// Stores either `None` or points
	/// to the next item.
	next: Option<*mut QueueItem<'a, T>>,
}

impl<T> QueueItem<'_,T> {
	/// # Constructor
	pub const fn new(data: T) -> Self {
		Self {
			data: data,
			next: None,
		}
	}
	/// # Get the inner data
	///
	/// Returns a borrow of the underlying data.
	pub fn inner(&mut self) -> &mut T {
		&mut self.data
	}
	/// # Get pointer to inner data
	pub fn ptr(&mut self) -> *mut u8 {
		self.inner() as *mut T as *mut u8
	}
}

/// # Sharing Thread Safety for QueueItem
unsafe impl<T> Send for QueueItem<'_,T> {}

impl<T: Debug> Debug for QueueItem<'_,T> {
	/// # Debug formatter for `QueueItem`
	///
	/// Output the encapsulated data
	fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
		#[cfg(feature="verbose")]
		return write!(f, "{:?} {:x} {:?}", self.data, self as *const QueueItem<'_,T> as usize, self.next);

		#[cfg(not(feature="verbose"))]
		return write!(f, "{:?}", self.data);
	}
}

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

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

impl<'a, T: Sized,const COUNT: usize> QueueAllocator<'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) {
		vprintln!("QA: Initializing Queue Allocator!");
		self.inner.lock(|queue| {
			vprintln!("QA: Clearing internal references...");
			for idx in 2..COUNT {
				if idx != COUNT-1 {
					queue[idx].next = Some(&mut queue[idx+1] as *mut QueueItem<'a, T>);
				} else {
					queue[idx].next = None;
				}
			}
			vprintln!("QA: Initializing head and tail...");
			queue[0].next = Some(&mut queue[2] as *mut QueueItem<'a, T>);
			queue[1].next = Some(&mut queue[COUNT-1] as *mut QueueItem<'a, T>);
		});
		vprintln!("QA: Initialized Queue Allocator!");
	}

	/// # Allocate Data
	///
	/// If there is a data chunk available,
	/// return it, otherwise return `None`
	#[allow(dead_code)]
	pub fn alloc(&self) -> Option<&mut QueueItem<'a,T>> {
		vprintln!("QA: Allocating chunk!");
		return self.inner.lock(|pool| {
			if let Some(entry) = pool[0].next {
				vprintln!("QA: Found chunk!");
				pool[0].next = unsafe { (*entry).next };
				unsafe {
					(*entry).next = None;
				}
				match pool[0].next {
					None => {
						pool[1].next = None
					}
					_ => {}
				}
				vprintln!("QA: \x1b[92mAllocated {:x}\x1b[0m", unsafe{(*entry).ptr() as usize});
				return Some(unsafe{&mut *entry as &mut QueueItem<'a,T>});
			} else {
				vprintln!("QA: No chunks available!");
				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 QueueItem<'a,T>) {
		vprintln!("QA: Deallocating chunk!");
		self.inner.lock(|pool| {
			freed_item.next = None;
			match pool[1].next {
				None => {
					pool[0].next = Some(freed_item as *mut QueueItem<'a,T>);
				}
				Some(entry) => {
					unsafe {
						(*entry).next = Some(freed_item as *mut QueueItem<'a,T>);
					}
				}
			}
			pool[1].next = Some(freed_item as *mut QueueItem<'a,T>);
			vprintln!("QA: \x1b[91mDeallocated {:x}\x1b[0m", freed_item.ptr() as usize);
		});
	}
}

impl<T: Debug,const COUNT: usize> Debug for QueueAllocator<'_,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| {
			#[cfg(feature="verbose")]
			return write!(f, "{:?}", queue);

			#[cfg(not(feature="verbose"))]
			return write!(f, "{:?}", queue);
		})
	}
}