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#![no_std]
extern crate core;
use core::alloc::{GlobalAlloc, Layout};
use core::cell::UnsafeCell;
use core::mem::MaybeUninit;
use core::ptr::null_mut;

pub struct Heap<const P: usize> {
    playarea: usize,
    len:      UnsafeCell<usize>,
    header:   UnsafeCell<[MaybeUninit<(*mut u8, usize)>; P]>
}

fn is_allocated(pointer: *mut u8, size: usize) -> bool {
    if (pointer..pointer.wrapping_add(size)).contains(&pointer) {
	true
    } else {
	false
    }
}

impl<const P: usize> Heap<P> {
    const HEADER_ITEM: MaybeUninit<(*mut u8, usize)> = MaybeUninit::uninit();
    const HEADER_INIT: [MaybeUninit<(*mut u8, usize)>; P] = [Self::HEADER_ITEM; P];

    pub const fn new() -> Self {
	Heap {
	    playarea: P,
	    len: UnsafeCell::new(0),
	    header: UnsafeCell::new(Self::HEADER_INIT)
	}
    }
}

unsafe impl<const P: usize> GlobalAlloc for Heap<P> {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
	let size = layout.size();
	let mut ptr = null_mut();
	for pointer in 0..self.playarea {
	    if !is_allocated(pointer as *mut u8, size) {
		ptr = pointer as *mut u8;
		break;
	    }
	};
	let header_mut = self.header.get();
	*header_mut.as_mut().unwrap().get_unchecked_mut(*self.len.get())  = MaybeUninit::new((ptr, size));
	*self.len.get() += 1;

	ptr
    }

    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {}
}

unsafe impl<const P: usize> Sync for Heap<P> {}