using System;
using System.Numerics;
using System.Runtime.InteropServices;
using TerraFX.Interop.DirectX;

namespace Auspex.Rendering.Direct3D;

internal sealed class ClipZoneShader : IDisposable
{
	public struct Constants
	{
		public Vector2 ViewportSize;
	}

	public struct Instance
	{
		public Vector2 Min;

		public Vector2 Max;
	}

	private readonly FrameRenderContext _ctx;

	private readonly GpuBuffer<Instance> _buffer;

	private GpuBuffer<Instance>.Builder? _builder;

	private unsafe ID3D11Buffer* _constantBuffer;

	private unsafe ID3D11InputLayout* _il;

	private unsafe ID3D11VertexShader* _vs;

	private unsafe ID3D11PixelShader* _ps;

	public bool HasPending => _builder != null;

	public unsafe ClipZoneShader(FrameRenderContext ctx, int maxRects)
	{
		_ctx = ctx;
		_buffer = new GpuBuffer<Instance>("ClipZone", ctx, maxRects, 1u, dynamic: true);
		ReadOnlySpan<byte> source = "cbuffer Constants : register(b0)\n{\n    float2 viewportSize;\n};\n\nstruct Rect\n{\n    float2 rmin : RECTMIN;\n    float2 rmax : RECTMAX;\n};\n\nstruct VSOutput\n{\n    float4 pos : SV_POSITION;\n};\n\nVSOutput vs(in Rect r, uint vid : SV_VertexID)\n{\n    VSOutput o;\n    float2 px = float2(\n        (vid & 1) ? r.rmax.x : r.rmin.x,\n        (vid & 2) ? r.rmax.y : r.rmin.y);\n    float2 ndc = float2(\n        px.x / viewportSize.x * 2.0 - 1.0,\n        1.0 - px.y / viewportSize.y * 2.0);\n    o.pos = float4(ndc, 0, 1);\n    return o;\n}\n\nvoid ps(VSOutput input)\n{\n}"u8;
		TriangleFillShader.CompileShader(source, "vs"u8, "vs_5_0"u8, out var blob, "ClipZone VS");
		TriangleFillShader.CompileShader(source, "ps"u8, "ps_5_0"u8, out var blob2, "ClipZone PS");
		ID3D11VertexShader* vs = default(ID3D11VertexShader*);
		Marshal.ThrowExceptionForHR(ctx.Device->CreateVertexShader(blob->GetBufferPointer(), blob->GetBufferSize(), null, &vs));
		_vs = vs;
		ID3D11PixelShader* ps = default(ID3D11PixelShader*);
		Marshal.ThrowExceptionForHR(ctx.Device->CreatePixelShader(blob2->GetBufferPointer(), blob2->GetBufferSize(), null, &ps));
		_ps = ps;
		D3D11_BUFFER_DESC d3D11_BUFFER_DESC = new D3D11_BUFFER_DESC
		{
			ByteWidth = 16u,
			Usage = D3D11_USAGE.D3D11_USAGE_DEFAULT,
			BindFlags = 4u
		};
		ID3D11Buffer* constantBuffer = default(ID3D11Buffer*);
		Marshal.ThrowExceptionForHR(ctx.Device->CreateBuffer(&d3D11_BUFFER_DESC, null, &constantBuffer));
		_constantBuffer = constantBuffer;
		fixed (byte* semanticName = "RECTMIN"u8)
		{
			fixed (byte* semanticName2 = "RECTMAX"u8)
			{
				D3D11_INPUT_ELEMENT_DESC* ptr = stackalloc D3D11_INPUT_ELEMENT_DESC[2];
				*ptr = new D3D11_INPUT_ELEMENT_DESC
				{
					SemanticName = (sbyte*)semanticName,
					SemanticIndex = 0u,
					Format = DXGI_FORMAT.DXGI_FORMAT_R32G32_FLOAT,
					AlignedByteOffset = uint.MaxValue,
					InputSlot = 0u,
					InputSlotClass = D3D11_INPUT_CLASSIFICATION.D3D11_INPUT_PER_INSTANCE_DATA,
					InstanceDataStepRate = 1u
				};
				ptr[1] = new D3D11_INPUT_ELEMENT_DESC
				{
					SemanticName = (sbyte*)semanticName2,
					SemanticIndex = 0u,
					Format = DXGI_FORMAT.DXGI_FORMAT_R32G32_FLOAT,
					AlignedByteOffset = uint.MaxValue,
					InputSlot = 0u,
					InputSlotClass = D3D11_INPUT_CLASSIFICATION.D3D11_INPUT_PER_INSTANCE_DATA,
					InstanceDataStepRate = 1u
				};
				ID3D11InputLayout* il = default(ID3D11InputLayout*);
				Marshal.ThrowExceptionForHR(ctx.Device->CreateInputLayout(ptr, 2u, blob->GetBufferPointer(), blob->GetBufferSize(), &il));
				_il = il;
			}
		}
		blob->Release();
		blob2->Release();
	}

	public unsafe void Dispose()
	{
		_builder?.Dispose();
		_buffer.Dispose();
		if (_constantBuffer != null)
		{
			_constantBuffer->Release();
			_constantBuffer = null;
		}
		if (_il != null)
		{
			_il->Release();
			_il = null;
		}
		if (_vs != null)
		{
			_vs->Release();
			_vs = null;
		}
		if (_ps != null)
		{
			_ps->Release();
			_ps = null;
		}
		GC.SuppressFinalize(this);
	}

	public unsafe void UpdateConstants(Constants consts)
	{
		_ctx.Context->UpdateSubresource((ID3D11Resource*)_constantBuffer, 0u, null, &consts, 0u, 0u);
	}

	public void Add(Vector2 min, Vector2 max)
	{
		if (_builder == null)
		{
			_builder = _buffer.Map(_ctx);
		}
		Instance item = new Instance
		{
			Min = min,
			Max = max
		};
		_builder.Add(ref item);
	}

	public unsafe void Flush()
	{
		if (_builder != null)
		{
			_builder.Dispose();
			_builder = null;
			Bind();
			ID3D11Buffer* buffer = _buffer.Buffer;
			uint elementSize = (uint)_buffer.ElementSize;
			uint num = 0u;
			_ctx.Context->IASetVertexBuffers(0u, 1u, &buffer, &elementSize, &num);
			_ctx.Context->DrawInstanced(4u, (uint)_buffer.CurElements, 0u, 0u);
		}
	}

	public void Discard()
	{
		if (_builder != null)
		{
			_builder.Dispose();
			_builder = null;
		}
	}

	private unsafe void Bind()
	{
		_ctx.Context->IASetPrimitiveTopology(D3D_PRIMITIVE_TOPOLOGY.D3D_PRIMITIVE_TOPOLOGY_TRIANGLESTRIP);
		_ctx.Context->IASetInputLayout(_il);
		_ctx.Context->VSSetShader(_vs, null, 0u);
		ID3D11Buffer* constantBuffer = _constantBuffer;
		_ctx.Context->VSSetConstantBuffers(0u, 1u, &constantBuffer);
		_ctx.Context->PSSetShader(_ps, null, 0u);
		_ctx.Context->GSSetShader(null, null, 0u);
	}
}