import PlaygroundSupport
import MetalKit

guard let device = MTLCreateSystemDefaultDevice() else {
  fatalError("GPU is not supported")
}

let frame = CGRect(x: 0, y: 0, width: 600, height: 600)
let view = MTKView(frame: frame, device: device)
view.clearColor = MTLClearColor(red: 1, green: 1, blue: 0.8, alpha: 1)

let allocator = MTKMeshBufferAllocator(device: device)
let mdlMesh = MDLMesh(coneWithExtent: [1,1,1],
                      segments: [10, 10],
                      inwardNormals: false,
                      cap: true,
                      geometryType: .triangles,
                      allocator: allocator)
let mesh = try MTKMesh(mesh: mdlMesh, device: device)

// begin export code
let asset = MDLAsset()
asset.add(mdlMesh)
let fileExtension = "obj"
guard MDLAsset.canExportFileExtension(fileExtension) else {
  fatalError("Can't export a .\(fileExtension) format")
}
do {
  let url = playgroundSharedDataDirectory.appendingPathComponent("primitive.\(fileExtension)")
  try asset.export(to: url)
} catch {
  fatalError("Error \(error.localizedDescription)")
}
// end export code

guard let commandQueue = device.makeCommandQueue() else {
  fatalError("Could not create a command queue")
}

let shader = """
#include <metal_stdlib>
using namespace metal;
struct VertexIn {
float4 position [[ attribute(0) ]];
};
vertex float4 vertex_main(const VertexIn vertex_in [[ stage_in ]]) {
return vertex_in.position;
}
fragment float4 fragment_main() {
return float4(1, 0, 0, 1);
}
"""

let library = try device.makeLibrary(source: shader, options: nil)
let vertexFunction = library.makeFunction(name: "vertex_main")
let fragmentFunction = library.makeFunction(name: "fragment_main")

let pipelineDescriptor = MTLRenderPipelineDescriptor()
pipelineDescriptor.colorAttachments[0].pixelFormat = .bgra8Unorm
pipelineDescriptor.vertexFunction = vertexFunction
pipelineDescriptor.fragmentFunction = fragmentFunction

pipelineDescriptor.vertexDescriptor =
  MTKMetalVertexDescriptorFromModelIO(mesh.vertexDescriptor)

let pipelineState =
  try device.makeRenderPipelineState(descriptor: pipelineDescriptor)

guard let commandBuffer = commandQueue.makeCommandBuffer(),
  let renderPassDescriptor = view.currentRenderPassDescriptor,
  let renderEncoder =
  commandBuffer.makeRenderCommandEncoder(descriptor: renderPassDescriptor)
  else {  fatalError() }


renderEncoder.setRenderPipelineState(pipelineState)

renderEncoder.setVertexBuffer(mesh.vertexBuffers[0].buffer,
                              offset: 0, index: 0)

guard let submesh = mesh.submeshes.first else {
  fatalError()
}

renderEncoder.setTriangleFillMode(.lines)
renderEncoder.drawIndexedPrimitives(type: .triangle,
                                    indexCount: submesh.indexCount,
                                    indexType: submesh.indexType,
                                    indexBuffer: submesh.indexBuffer.buffer,
                                    indexBufferOffset: 0)
renderEncoder.endEncoding()
guard let drawable = view.currentDrawable else {
  fatalError()
}
commandBuffer.present(drawable)
commandBuffer.commit()

PlaygroundPage.current.liveView = view