use crate::error;
use crate::error::assume_d3d12_init;
use std::ffi::c_void;
use std::mem::ManuallyDrop;
use std::ops::{Deref, DerefMut, Range};
use std::ptr::NonNull;
use windows::Win32::Graphics::Direct3D12::{
    ID3D12Device, ID3D12GraphicsCommandList, ID3D12Resource, D3D12_CPU_PAGE_PROPERTY_UNKNOWN,
    D3D12_HEAP_FLAG_NONE, D3D12_HEAP_PROPERTIES, D3D12_HEAP_TYPE_UPLOAD, D3D12_MEMORY_POOL_UNKNOWN,
    D3D12_RANGE, D3D12_RESOURCE_DESC, D3D12_RESOURCE_DIMENSION_BUFFER,
    D3D12_RESOURCE_STATE_GENERIC_READ, D3D12_TEXTURE_LAYOUT_ROW_MAJOR,
};
use windows::Win32::Graphics::Dxgi::Common::DXGI_SAMPLE_DESC;

pub struct D3D12Buffer {
    handle: ID3D12Resource,
    size: usize,
}

pub struct D3D12BufferMapHandle<'a> {
    pub slice: &'a mut [u8],
    pub handle: &'a ID3D12Resource,
}

impl<'a> Drop for D3D12BufferMapHandle<'a> {
    fn drop(&mut self) {
        unsafe { self.handle.Unmap(0, None) }
    }
}

impl D3D12Buffer {
    pub fn new(device: &ID3D12Device, size: usize) -> error::Result<D3D12Buffer> {
        unsafe {
            let mut buffer: Option<ID3D12Resource> = None;
            device.CreateCommittedResource(
                &D3D12_HEAP_PROPERTIES {
                    Type: D3D12_HEAP_TYPE_UPLOAD,
                    CPUPageProperty: D3D12_CPU_PAGE_PROPERTY_UNKNOWN,
                    MemoryPoolPreference: D3D12_MEMORY_POOL_UNKNOWN,
                    ..Default::default()
                },
                D3D12_HEAP_FLAG_NONE,
                &D3D12_RESOURCE_DESC {
                    Dimension: D3D12_RESOURCE_DIMENSION_BUFFER,
                    Width: size as u64,
                    Height: 1,
                    DepthOrArraySize: 1,
                    MipLevels: 1,
                    Layout: D3D12_TEXTURE_LAYOUT_ROW_MAJOR,
                    SampleDesc: DXGI_SAMPLE_DESC {
                        Count: 1,
                        Quality: 0,
                    },
                    ..Default::default()
                },
                D3D12_RESOURCE_STATE_GENERIC_READ,
                None,
                &mut buffer,
            )?;

            assume_d3d12_init!(buffer, "CreateCommittedResource");

            Ok(D3D12Buffer {
                handle: buffer,
                size,
            })
        }
    }

    pub fn gpu_address(&self) -> u64 {
        unsafe { self.handle.GetGPUVirtualAddress() }
    }

    pub fn into_raw(self) -> ID3D12Resource {
        self.handle
    }

    pub fn map(&mut self, range: Option<Range<usize>>) -> error::Result<D3D12BufferMapHandle> {
        let (range, size) = range.map_or((D3D12_RANGE { Begin: 0, End: 0 }, self.size), |range| {
            (
                D3D12_RANGE {
                    Begin: range.start,
                    End: range.end,
                },
                range.end - range.start,
            )
        });

        unsafe {
            let mut ptr = std::ptr::null_mut();
            self.handle.Map(0, Some(&range), Some(&mut ptr))?;
            let slice = std::slice::from_raw_parts_mut(ptr.cast(), size);
            Ok(D3D12BufferMapHandle {
                handle: &self.handle,
                slice,
            })
        }
    }
}

/// SAFETY: Creating the pointer should be safe in multithreaded contexts.
///
/// Mutation is guarded by DerefMut<Target=[u8]>
unsafe impl Send for RawD3D12Buffer {}
pub struct RawD3D12Buffer {
    buffer: ManuallyDrop<D3D12Buffer>,
    ptr: NonNull<c_void>,
}

impl RawD3D12Buffer {
    pub fn new(buffer: D3D12Buffer) -> error::Result<Self> {
        let buffer = ManuallyDrop::new(buffer);
        let range = D3D12_RANGE { Begin: 0, End: 0 };
        let mut ptr = std::ptr::null_mut();
        unsafe {
            buffer.handle.Map(0, Some(&range), Some(&mut ptr))?;
        }

        // panic-safety: If Map returns Ok then ptr is not null
        assert!(!ptr.is_null());

        let ptr = unsafe { NonNull::new_unchecked(ptr) };

        Ok(RawD3D12Buffer { buffer, ptr })
    }

    pub fn bind_cbv(&self, index: u32, cmd: &ID3D12GraphicsCommandList) {
        unsafe { cmd.SetGraphicsRootConstantBufferView(index, self.buffer.gpu_address()) }
    }
}

impl Drop for RawD3D12Buffer {
    fn drop(&mut self) {
        unsafe {
            self.buffer.handle.Unmap(0, None);
            ManuallyDrop::drop(&mut self.buffer);
        }
    }
}

impl Deref for RawD3D12Buffer {
    type Target = [u8];

    fn deref(&self) -> &Self::Target {
        unsafe { std::slice::from_raw_parts(self.ptr.as_ptr().cast(), self.buffer.size) }
    }
}

impl DerefMut for RawD3D12Buffer {
    fn deref_mut(&mut self) -> &mut Self::Target {
        unsafe { std::slice::from_raw_parts_mut(self.ptr.as_ptr().cast(), self.buffer.size) }
    }
}