use crate::error;
use std::cell::RefCell;
use std::marker::PhantomData;
use std::sync::Arc;
use windows::Win32::Graphics::Direct3D12::{
    ID3D12DescriptorHeap, ID3D12Device, D3D12_CPU_DESCRIPTOR_HANDLE, D3D12_DESCRIPTOR_HEAP_DESC,
    D3D12_DESCRIPTOR_HEAP_FLAG_NONE, D3D12_DESCRIPTOR_HEAP_FLAG_SHADER_VISIBLE,
    D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV, D3D12_DESCRIPTOR_HEAP_TYPE_SAMPLER,
    D3D12_GPU_DESCRIPTOR_HANDLE,
};

#[const_trait]
pub trait D3D12HeapType {
    fn get_desc(size: usize) -> D3D12_DESCRIPTOR_HEAP_DESC;
}

pub trait D3D12ShaderVisibleHeapType: D3D12HeapType {}

pub struct SamplerPaletteHeap;
pub struct LutTextureHeap;

impl D3D12ShaderVisibleHeapType for SamplerPaletteHeap {}

impl const D3D12HeapType for SamplerPaletteHeap {
    // sampler palettes just get set directly
    fn get_desc(size: usize) -> D3D12_DESCRIPTOR_HEAP_DESC {
        D3D12_DESCRIPTOR_HEAP_DESC {
            Type: D3D12_DESCRIPTOR_HEAP_TYPE_SAMPLER,
            NumDescriptors: size as u32,
            Flags: D3D12_DESCRIPTOR_HEAP_FLAG_SHADER_VISIBLE,
            NodeMask: 0,
        }
    }
}

impl const D3D12HeapType for LutTextureHeap {
    // Lut texture heaps are CPU only and get bound to the descriptor heap of the shader.
    fn get_desc(size: usize) -> D3D12_DESCRIPTOR_HEAP_DESC {
        D3D12_DESCRIPTOR_HEAP_DESC {
            Type: D3D12_DESCRIPTOR_HEAP_TYPE_CBV_SRV_UAV,
            NumDescriptors: size as u32,
            Flags: D3D12_DESCRIPTOR_HEAP_FLAG_NONE,
            NodeMask: 0,
        }
    }
}

pub struct D3D12DescriptorHeapSlot<T> {
    cpu_handle: D3D12_CPU_DESCRIPTOR_HANDLE,
    gpu_handle: Option<D3D12_GPU_DESCRIPTOR_HANDLE>,
    heap: Arc<RefCell<D3D12DescriptorHeapInner>>,
    slot: usize,
    _pd: PhantomData<T>,
}

impl<T> D3D12DescriptorHeapSlot<T> {
    /// Get the index of the resource within the heap.
    pub fn index(&self) -> usize {
        self.slot
    }
}

impl<T> AsRef<D3D12_CPU_DESCRIPTOR_HANDLE> for D3D12DescriptorHeapSlot<T> {
    fn as_ref(&self) -> &D3D12_CPU_DESCRIPTOR_HANDLE {
        &self.cpu_handle
    }
}

impl<T: D3D12ShaderVisibleHeapType> AsRef<D3D12_GPU_DESCRIPTOR_HANDLE>
    for D3D12DescriptorHeapSlot<T>
{
    fn as_ref(&self) -> &D3D12_GPU_DESCRIPTOR_HANDLE {
        self.gpu_handle.as_ref().unwrap()
    }
}

struct D3D12DescriptorHeapInner {
    heap: ID3D12DescriptorHeap,
    desc: D3D12_DESCRIPTOR_HEAP_DESC,
    cpu_start: D3D12_CPU_DESCRIPTOR_HANDLE,
    gpu_start: Option<D3D12_GPU_DESCRIPTOR_HANDLE>,
    handle_size: usize,
    start: usize,
    // Bit flag representation of available handles in the heap.
    //
    //  0 - Occupied
    //  1 - free

    // todo: actually use a bitset here.
    map: Box<[bool]>,
}

pub struct D3D12DescriptorHeap<T>(Arc<RefCell<D3D12DescriptorHeapInner>>, PhantomData<T>);

impl<T: D3D12HeapType> D3D12DescriptorHeap<T> {
    pub fn new(device: &ID3D12Device, size: usize) -> error::Result<D3D12DescriptorHeap<T>> {
        let desc = T::get_desc(size);
        unsafe { D3D12DescriptorHeap::new_with_desc(device, desc) }
    }
}

impl<T> D3D12DescriptorHeap<T> {
    pub unsafe fn new_with_desc(
        device: &ID3D12Device,
        desc: D3D12_DESCRIPTOR_HEAP_DESC,
    ) -> error::Result<D3D12DescriptorHeap<T>> {
        unsafe {
            let heap: ID3D12DescriptorHeap = device.CreateDescriptorHeap(&desc)?;
            let cpu_start = heap.GetCPUDescriptorHandleForHeapStart();

            let gpu_start = if (desc.Flags & D3D12_DESCRIPTOR_HEAP_FLAG_SHADER_VISIBLE).0 != 0 {
                Some(heap.GetGPUDescriptorHandleForHeapStart())
            } else {
                None
            };

            Ok(D3D12DescriptorHeap(
                Arc::new(RefCell::new(D3D12DescriptorHeapInner {
                    heap,
                    desc,
                    cpu_start,
                    gpu_start,
                    handle_size: device.GetDescriptorHandleIncrementSize(desc.Type) as usize,
                    start: 0,
                    map: vec![false; desc.NumDescriptors as usize].into_boxed_slice(),
                })),
                PhantomData::default(),
            ))
        }
    }

    pub fn alloc_slot(&mut self) -> error::Result<D3D12DescriptorHeapSlot<T>> {
        let mut handle = D3D12_CPU_DESCRIPTOR_HANDLE { ptr: 0 };

        let mut inner = self.0.borrow_mut();
        for i in inner.start..inner.desc.NumDescriptors as usize {
            if !inner.map[i] {
                inner.map[i] = true;
                handle.ptr = inner.cpu_start.ptr + (i * inner.handle_size);
                inner.start = i + 1;

                let gpu_handle = inner
                    .gpu_start
                    .map(|gpu_start| D3D12_GPU_DESCRIPTOR_HANDLE {
                        ptr: (handle.ptr as u64 - inner.cpu_start.ptr as u64 + gpu_start.ptr),
                    });

                return Ok(D3D12DescriptorHeapSlot {
                    cpu_handle: handle,
                    slot: i,
                    heap: Arc::clone(&self.0),
                    gpu_handle,
                    _pd: Default::default(),
                });
            }
        }

        todo!("error need to fail");
    }
}

impl<T> Drop for D3D12DescriptorHeapSlot<T> {
    fn drop(&mut self) {
        let mut inner = self.heap.borrow_mut();
        inner.map[self.slot] = false;
        if inner.start > self.slot {
            inner.start = self.slot
        }
    }
}