use std::{cell::Cell, fmt, marker::PhantomData, mem};
use wasmer_runtime_core::{
    memory::Memory,
    types::{Type, ValueError, ValueType, WasmExternType},
};

pub struct Array;
pub struct Item;

#[repr(transparent)]
pub struct WasmPtr<T: Copy, Ty = Item> {
    offset: u32,
    _phantom: PhantomData<(T, Ty)>,
}

impl<T: Copy, Ty> WasmPtr<T, Ty> {
    #[inline]
    pub fn new(offset: u32) -> Self {
        Self {
            offset,
            _phantom: PhantomData,
        }
    }

    #[inline]
    pub fn offset(self) -> u32 {
        self.offset
    }
}

impl<T: Copy + ValueType> WasmPtr<T, Item> {
    #[inline]
    pub fn deref<'a>(self, memory: &'a Memory) -> Option<&'a Cell<T>> {
        if (self.offset as usize) + mem::size_of::<T>() >= memory.size().bytes().0 {
            return None;
        }
        unsafe {
            let cell_ptr = memory
                .view::<T>()
                .get_unchecked((self.offset() as usize) / mem::size_of::<T>())
                as *const _;
            Some(&*cell_ptr)
        }
    }
}

impl<T: Copy + ValueType> WasmPtr<T, Array> {
    #[inline]
    pub fn deref<'a>(self, memory: &'a Memory, index: u32, length: u32) -> Option<&'a [Cell<T>]> {
        if (self.offset as usize) + (mem::size_of::<T>() * ((index + length) as usize))
            >= memory.size().bytes().0
        {
            return None;
        }

        unsafe {
            let cell_ptrs = memory.view::<T>().get_unchecked(
                ((self.offset as usize) / mem::size_of::<T>()) + (index as usize)
                    ..((self.offset() as usize) / mem::size_of::<T>())
                        + ((index + length) as usize),
            ) as *const _;
            Some(&*cell_ptrs)
        }
    }
}

unsafe impl<T: Copy, Ty> WasmExternType for WasmPtr<T, Ty> {
    const TYPE: Type = Type::I32;
}

impl<T: Copy, Ty> ValueType for WasmPtr<T, Ty> {
    fn into_le(self, buffer: &mut [u8]) {
        buffer[..mem::size_of::<u32>()].copy_from_slice(&self.offset.to_le_bytes());
    }
    fn from_le(buffer: &[u8]) -> Result<Self, ValueError> {
        if buffer.len() >= mem::size_of::<Self>() {
            let mut array = [0u8; mem::size_of::<u32>()];
            array.copy_from_slice(&buffer[..mem::size_of::<u32>()]);
            Ok(Self {
                offset: u32::from_le_bytes(array),
                _phantom: PhantomData,
            })
        } else {
            Err(ValueError::BufferTooSmall)
        }
    }
}

impl<T: Copy, Ty> Clone for WasmPtr<T, Ty> {
    fn clone(&self) -> Self {
        Self {
            offset: self.offset,
            _phantom: PhantomData,
        }
    }
}

impl<T: Copy, Ty> Copy for WasmPtr<T, Ty> {}

impl<T: Copy, Ty> PartialEq for WasmPtr<T, Ty> {
    fn eq(&self, other: &Self) -> bool {
        self.offset == other.offset
    }
}

impl<T: Copy, Ty> Eq for WasmPtr<T, Ty> {}

impl<T: Copy, Ty> fmt::Debug for WasmPtr<T, Ty> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "WasmPtr({:#x})", self.offset)
    }
}