import Cocoa
import MetalKit

// Self-contained MetalViewController based on https://metalbyexample.com/modern-metal-1/
class MetalViewController: NSViewController {
    var mtkView: MTKView!

    var device: MTLDevice!
    var commandQueue: MTLCommandQueue!
    var pipelineState: MTLRenderPipelineState!

    override func viewDidLoad() {
        super.viewDidLoad()

        mtkView = MTKView()
        mtkView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(mtkView)
        view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "|[mtkView]|", options: [], metrics: nil, views: ["mtkView": mtkView!]))
        view.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[mtkView]|", options: [], metrics: nil, views: ["mtkView": mtkView!]))

        device = MTLCreateSystemDefaultDevice()!
        mtkView.device = device
        mtkView.delegate = self

        commandQueue = device.makeCommandQueue()
        let shaders = """
        #include <metal_stdlib>
        using namespace metal;
        struct VertexIn {
            packed_float3 position;
            packed_float3 color;
        };
        struct VertexOut {
            float4 position [[position]];
            float4 color;
        };
        vertex VertexOut vertex_main(device const VertexIn *vertices [[buffer(0)]],
                                     uint vertexId [[vertex_id]]) {
            VertexOut out;
            out.position = float4(vertices[vertexId].position, 1);
            out.color = float4(vertices[vertexId].color, 1);
            return out;
        }
        fragment float4 fragment_main(VertexOut in [[stage_in]]) {
            return in.color;
        }
        """
        do {
            let library = try device.makeLibrary(source: shaders, options: nil)
            let pipelineDescriptor = MTLRenderPipelineDescriptor()
            pipelineDescriptor.colorAttachments[0].pixelFormat = mtkView.colorPixelFormat
            pipelineDescriptor.vertexFunction = library.makeFunction(name: "vertex_main")
            pipelineDescriptor.fragmentFunction = library.makeFunction(name: "fragment_main")
            pipelineState = try device.makeRenderPipelineState(descriptor: pipelineDescriptor)
        } catch {
            fatalError()
        }
    }
}

extension MetalViewController: MTKViewDelegate {
    func mtkView(_ view: MTKView, drawableSizeWillChange size: CGSize) {}

    func draw(in view: MTKView) {
        guard let commandBuffer = commandQueue.makeCommandBuffer() else { return }
        guard let passDescriptor = view.currentRenderPassDescriptor else { return }
        guard let encoder = commandBuffer.makeRenderCommandEncoder(descriptor: passDescriptor) else { return }
        let vertexData: [Float] = [-0.5, -0.5, 0, 1, 0, 0,
                                   0.5, -0.5, 0, 0, 1, 0,
                                   0, 0.5, 0, 0, 0, 1]
        encoder.setVertexBytes(vertexData, length: vertexData.count * MemoryLayout<Float>.stride, index: 0)
        encoder.setRenderPipelineState(pipelineState)
        encoder.drawPrimitives(type: .triangle, vertexStart: 0, vertexCount: 3)
        encoder.endEncoding()
        commandBuffer.present(view.currentDrawable!)
        commandBuffer.commit()
    }
}