#![cfg_attr(feature = "const_mut_refs", feature(const_mut_refs))]
#![cfg_attr(
    feature = "alloc_ref",
    feature(allocator_api, alloc_layout_extra, nonnull_slice_from_raw_parts)
)]
#![no_std]

#[cfg(test)]
#[macro_use]
extern crate std;

#[cfg(feature = "use_spin")]
extern crate spinning_top;

#[cfg(feature = "use_spin")]
use core::alloc::GlobalAlloc;
use core::alloc::Layout;
#[cfg(feature = "alloc_ref")]
use core::alloc::{AllocError, Allocator};
#[cfg(feature = "use_spin")]
use core::ops::Deref;
use core::ptr::NonNull;
#[cfg(test)]
use hole::Hole;
use hole::HoleList;
#[cfg(feature = "use_spin")]
use spinning_top::Spinlock;

pub mod hole;
#[cfg(test)]
mod test;

/// A fixed size heap backed by a linked list of free memory blocks.
pub struct Heap {
    bottom: usize,
    size: usize,
    used: usize,
    holes: HoleList,
}

impl Heap {
    /// Creates an empty heap. All allocate calls will return `None`.
    #[cfg(not(feature = "const_mut_refs"))]
    pub fn empty() -> Heap {
        Heap {
            bottom: 0,
            size: 0,
            used: 0,
            holes: HoleList::empty(),
        }
    }

    #[cfg(feature = "const_mut_refs")]
    pub const fn empty() -> Heap {
        Heap {
            bottom: 0,
            size: 0,
            used: 0,
            holes: HoleList::empty(),
        }
    }

    /// Initializes an empty heap
    ///
    /// # Unsafety
    ///
    /// This function must be called at most once and must only be used on an
    /// empty heap.
    pub unsafe fn init(&mut self, heap_bottom: usize, heap_size: usize) {
        self.bottom = heap_bottom;
        self.size = heap_size;
        self.used = 0;
        self.holes = HoleList::new(heap_bottom, heap_size);
    }

    /// Creates a new heap with the given `bottom` and `size`. The bottom address must be valid
    /// and the memory in the `[heap_bottom, heap_bottom + heap_size)` range must not be used for
    /// anything else. This function is unsafe because it can cause undefined behavior if the
    /// given address is invalid.
    pub unsafe fn new(heap_bottom: usize, heap_size: usize) -> Heap {
        if heap_size < HoleList::min_size() {
            Self::empty()
        } else {
            Heap {
                bottom: heap_bottom,
                size: heap_size,
                used: 0,
                holes: HoleList::new(heap_bottom, heap_size),
            }
        }
    }

    /// Allocates a chunk of the given size with the given alignment. Returns a pointer to the
    /// beginning of that chunk if it was successful. Else it returns `None`.
    /// This function scans the list of free memory blocks and uses the first block that is big
    /// enough. The runtime is in O(n) where n is the number of free blocks, but it should be
    /// reasonably fast for small allocations.
    pub fn allocate_first_fit(&mut self, layout: Layout) -> Result<NonNull<u8>, ()> {
        match self.holes.allocate_first_fit(layout) {
            Ok((ptr, aligned_layout)) => {
                self.used += aligned_layout.size();
                Ok(ptr)
            }
            Err(err) => Err(err),
        }
    }

    /// Frees the given allocation. `ptr` must be a pointer returned
    /// by a call to the `allocate_first_fit` function with identical size and alignment. Undefined
    /// behavior may occur for invalid arguments, thus this function is unsafe.
    ///
    /// This function walks the list of free memory blocks and inserts the freed block at the
    /// correct place. If the freed block is adjacent to another free block, the blocks are merged
    /// again. This operation is in `O(n)` since the list needs to be sorted by address.
    pub unsafe fn deallocate(&mut self, ptr: NonNull<u8>, layout: Layout) {
        self.used -= self.holes.deallocate(ptr, layout).size();
    }

    /// Returns the bottom address of the heap.
    pub fn bottom(&self) -> usize {
        self.bottom
    }

    /// Returns the size of the heap.
    pub fn size(&self) -> usize {
        self.size
    }

    /// Return the top address of the heap
    pub fn top(&self) -> usize {
        self.bottom + self.size
    }

    /// Returns the size of the used part of the heap
    pub fn used(&self) -> usize {
        self.used
    }

    /// Returns the size of the free part of the heap
    pub fn free(&self) -> usize {
        self.size - self.used
    }

    /// Extends the size of the heap by creating a new hole at the end
    ///
    /// # Unsafety
    ///
    /// The new extended area must be valid
    pub unsafe fn extend(&mut self, by: usize) {
        let top = self.top();
        let layout = Layout::from_size_align(by, 1).unwrap();
        self.holes
            .deallocate(NonNull::new_unchecked(top as *mut u8), layout);
        self.size += by;
    }
}

#[cfg(all(feature = "alloc_ref", feature = "use_spin"))]
unsafe impl Allocator for LockedHeap {
    fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, AllocError> {
        if layout.size() == 0 {
            return Ok(NonNull::slice_from_raw_parts(layout.dangling(), 0));
        }
        match self.0.lock().allocate_first_fit(layout) {
            Ok(ptr) => Ok(NonNull::slice_from_raw_parts(ptr, layout.size())),
            Err(()) => Err(AllocError),
        }
    }

    unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
        if layout.size() != 0 {
            self.0.lock().deallocate(ptr, layout);
        }
    }
}

#[cfg(feature = "use_spin")]
pub struct LockedHeap(Spinlock<Heap>);

#[cfg(feature = "use_spin")]
impl LockedHeap {
    /// Creates an empty heap. All allocate calls will return `None`.
    #[cfg(feature = "use_spin_nightly")]
    pub const fn empty() -> LockedHeap {
        LockedHeap(Spinlock::new(Heap::empty()))
    }

    /// Creates an empty heap. All allocate calls will return `None`.
    #[cfg(not(feature = "use_spin_nightly"))]
    pub fn empty() -> LockedHeap {
        LockedHeap(Spinlock::new(Heap::empty()))
    }

    /// Creates a new heap with the given `bottom` and `size`. The bottom address must be valid
    /// and the memory in the `[heap_bottom, heap_bottom + heap_size)` range must not be used for
    /// anything else. This function is unsafe because it can cause undefined behavior if the
    /// given address is invalid.
    pub unsafe fn new(heap_bottom: usize, heap_size: usize) -> LockedHeap {
        LockedHeap(Spinlock::new(Heap {
            bottom: heap_bottom,
            size: heap_size,
            used: 0,
            holes: HoleList::new(heap_bottom, heap_size),
        }))
    }
}

#[cfg(feature = "use_spin")]
impl Deref for LockedHeap {
    type Target = Spinlock<Heap>;

    fn deref(&self) -> &Spinlock<Heap> {
        &self.0
    }
}

#[cfg(feature = "use_spin")]
unsafe impl GlobalAlloc for LockedHeap {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        self.0
            .lock()
            .allocate_first_fit(layout)
            .ok()
            .map_or(0 as *mut u8, |allocation| allocation.as_ptr())
    }

    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        self.0
            .lock()
            .deallocate(NonNull::new_unchecked(ptr), layout)
    }
}

/// Align downwards. Returns the greatest x with alignment `align`
/// so that x <= addr. The alignment must be a power of 2.
pub fn align_down(addr: usize, align: usize) -> usize {
    if align.is_power_of_two() {
        addr & !(align - 1)
    } else if align == 0 {
        addr
    } else {
        panic!("`align` must be a power of 2");
    }
}

/// Align upwards. Returns the smallest x with alignment `align`
/// so that x >= addr. The alignment must be a power of 2.
pub fn align_up(addr: usize, align: usize) -> usize {
    align_down(addr + align - 1, align)
}