use core::slice;
use std::{
    ops::{Deref, DerefMut},
    usize,
};

use crate::allocator::ALLOCATOR;

#[derive(Debug)]
pub struct SharedPtr<const N: usize>([u8; N]);

impl<const N: usize> SharedPtr<N> {
    pub fn new() -> Option<Self> {
        let mut allocator = ALLOCATOR.lock().unwrap();

        let buf = unsafe {
            let buf = allocator.allocate(N)?;
            slice::from_raw_parts_mut(buf, N)
        };

        Some(SharedPtr(buf.try_into().expect("Should never fail")))
    }

    pub fn get_offset(&self) -> usize {
        let allocator = ALLOCATOR.lock().unwrap();

        unsafe { allocator.get_offset(self.as_ptr()) }
    }
}

impl<const N: usize> Deref for SharedPtr<N> {
    type Target = [u8; N];

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

impl<'a, const N: usize> DerefMut for SharedPtr<N> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        &mut self.0
    }
}

impl<const N: usize> Drop for SharedPtr<N> {
    fn drop(&mut self) {
        let mut allocator = ALLOCATOR.lock().unwrap();

        unsafe {
            allocator.deallocate(self.0.as_mut_ptr());
        }
    }
}

#[cfg(test)]
mod tests {
    use super::SharedPtr;

    #[test]
    fn test() {
        let mut x = SharedPtr::<10>::new().unwrap();
        x[0] = 1;
        assert_eq!(x[0], 1);
        drop(x);
    }

    #[test]
    fn slice() {
        let mut x = SharedPtr::<10>::new().unwrap();
        x[0] = 1;
        x[1] = 2;
        assert_eq!(x[0..=1], [1, 2]);
    }
}