// -----------------------------------------------------------------------------

let counter     = 0.0;
let frameNumber = 0;
let fpsTime     = performance.now();


let cameraAt   = [ 0, 0, 0 ];
let cameraDir  = [ 0, 0, 1 ];
let yaw        = 0.0;
let cameraEye  = [ cameraAt[0]-cameraDir[0], 
                   cameraAt[1]-cameraDir[1],  
                   cameraAt[2]-cameraDir[2] ];


function frame() 
{
  var startTime = performance.now();

  // setup a transform for triangle 
  const t = { p:{x:0,y:0,z:0}, r:{x:0,y:0.0,z:0.0}, s:{x:1.0, y:1.0,z:1.0} };

  let modelMatrix = buildMatrix(t.p, t.r, t.s);
  // update the local matrix for each triangle draw differently
  device.queue.writeBuffer(mvpUniformBuffer,      0,      modelMatrix);

  // Rotate the camera around the origin in the circle
  mat4.lookAt(viewMatrix, cameraEye,  cameraAt, [0, 1, 0]);
  device.queue.writeBuffer(mvpUniformBuffer,      64,     viewMatrix);

  // simple counter
  counter += 0.001;

  const k = 0;
  const renderPassDescription = {
    colorAttachments: [{
      view: context.getCurrentTexture().createView(),
      loadOp: (k==0 ? "clear":"load"), 
      clearValue: [0, 0.5, 0.5, 1], // clear screen to color
      storeOp: 'store'
    }],
    depthStencilAttachment: {
      view: depthTexture.createView(),
      depthLoadOp: (k==0 ? "clear":"load"), 
      depthClearValue: 1,
      depthStoreOp: "store",
    }
  };

  renderPassDescription.colorAttachments[0].view = context.getCurrentTexture().createView();
  const commandEncoder = device.createCommandEncoder();
  const renderPass = commandEncoder.beginRenderPass(renderPassDescription);

  renderPass.setBindGroup(0, uniformBindGroup);
  renderPass.setPipeline(pipeline);
  renderPass.setVertexBuffer(0, positionBuffer);
  renderPass.setVertexBuffer(1, colorBuffer);
  renderPass.setIndexBuffer(indexBuffer, 'uint16');
  renderPass.drawIndexed(3,1);
  renderPass.end();
  device.queue.submit([commandEncoder.finish()]);

  // animate - keep updating
  requestAnimationFrame(frame);
  
  // --------- Timing Information -------------------------
  frameNumber++;
  var endTime = performance.now();

  var updateFPS = 1000.0 / ( endTime - fpsTime);
  var maxFPS    = 1000.0 / ( endTime - startTime);
  
      
  fpsTime = endTime;
  
  
  divInfo.innerHTML = `
  Cursor Keys 'A/D' Yaw - Rotation<br>
  Frame Number: ${frameNumber}<br>
  Current FPS: ${updateFPS.toFixed(1)},<br>
  Max FPS: ${maxFPS.toFixed(2)}
  `;
} 

onkeydown = function( e )
{
  let dt = 0.2;
  
  switch (event.key) 
  {
    case 'a':        
    {
        yaw -= dt * 0.1;
    }
    break;
      
    case 'd':
    {
       yaw += dt * 0.1;
    }
    break;
      
    case "ArrowLeft":
    {
        cameraAt[0] += dt;
    }
    break;
    
    case "ArrowRight":
    {
       cameraAt[0] -= dt;
    }  
    break;
      
    case "ArrowUp":
    {
       cameraAt[2] += dt;
    }
    break;
    
    case "ArrowDown":
    {
       cameraAt[2] -= dt;
    }
    break;
  }// end switch(..)
  
  
  cameraDir = [ Math.sin(yaw), 0, Math.cos(yaw) ];
  
  cameraEye = [ cameraAt[0]-cameraDir[0], 
                cameraAt[1]-cameraDir[1],  
                cameraAt[2]-cameraDir[2] ];

}// end onkeydown(..)

frame();