//! # FIFO Queue
//!
//! Provides the FIFO queue structure for allocations
use crate::sync::interface::Mutex;
use crate::sync::NullLock;
use crate::serial_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) {
        serial_vprintln!("QA: Initializing Queue Allocator!");
        self.inner.lock(|queue| {
            serial_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;
                }
            }
            serial_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>);
        });
        serial_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>> {
        serial_vprintln!("QA: Allocating chunk!");
        return self.inner.lock(|pool| {
            if let Some(entry) = pool[0].next {
                serial_vprintln!("QA: Found chunk!");
                pool[0].next = unsafe { (*entry).next };
                unsafe {
                    (*entry).next = None;
                }
                match pool[0].next {
                    None => pool[1].next = None,
                    _ => {}
                }
                serial_vprintln!("QA: \x1b[92mAllocated {:x}\x1b[0m", unsafe {
                    (*entry).ptr() as usize
                });
                return Some(unsafe { &mut *entry as &mut QueueItem<'a, T> });
            } else {
                serial_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>) {
        serial_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>);
            serial_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);
        })
    }
}