/**
 * @title Buffer Mesh Instance
 * @category Mesh
 * @thumbnail https://mdn.alipayobjects.com/merchant_appfe/afts/img/A*jjZMTrp-vU8AAAAAAAAAAAAADiR2AQ/original
 */
import { OrbitControl } from "@galacean/engine-toolkit-controls";
import {
  Buffer,
  BufferBindFlag,
  BufferMesh,
  BufferUsage,
  Camera,
  Engine,
  IndexFormat,
  Material,
  Mesh,
  MeshRenderer,
  Shader,
  Vector3,
  VertexElement,
  VertexElementFormat,
  WebGLEngine,
} from "@galacean/engine";

// Create engine
WebGLEngine.create({ canvas: "canvas" }).then((engine) => {
  engine.canvas.resizeByClientSize();

  // Get scene and root entity
  const scene = engine.sceneManager.activeScene;
  const rootEntity = scene.createRootEntity("Root");

  // Init instance shader
  const shader = initCustomShader();

  // Create camera
  const cameraEntity = rootEntity.createChild("Camera");
  const camera = cameraEntity.addComponent(Camera);
  cameraEntity.addComponent(OrbitControl);
  cameraEntity.transform.setPosition(0, 10, 160);
  cameraEntity.transform.lookAt(new Vector3(0, 0, 0));
  camera.farClipPlane = 300;

  // Create Instance Cube
  const cubeEntity = rootEntity.createChild("Cube");
  const cubeRenderer = cubeEntity.addComponent(MeshRenderer);
  const material = new Material(engine, shader);
  cubeEntity.transform.rotate(0, 60, 0);
  cubeRenderer.mesh = createCustomMesh(engine, 1.0); // Use `createCustomMesh()` to create custom instance cube mesh.
  cubeRenderer.setMaterial(material);

  // Run engine.
  engine.run();
});

/**
 * Create cube geometry with custom BufferGeometry.
 * @param engine - Engine
 * @param size - Cube size
 * @returns Cube mesh
 */
function createCustomMesh(engine: Engine, size: number): Mesh {
  const geometry = new BufferMesh(engine, "CustomCubeGeometry");

  // Create vertices data.
  // prettier-ignore
  const vertices: Float32Array = new Float32Array([
          // Up
          -size, size, -size, 0, 1, 0, size, size, -size, 0, 1, 0, size, size, size, 0, 1, 0, -size, size, size, 0, 1, 0,
          // Down
          -size, -size, -size, 0, -1, 0, size, -size, -size, 0, -1, 0, size, -size, size, 0, -1, 0, -size, -size, size, 0, -1, 0,
          // Left
          -size, size, -size, -1, 0, 0, -size, size, size, -1, 0, 0, -size, -size, size, -1, 0, 0, -size, -size, -size, -1, 0, 0,
          // Right
          size, size, -size, 1, 0, 0, size, size, size, 1, 0, 0, size, -size, size, 1, 0, 0, size, -size, -size, 1, 0, 0,
          // Front
          -size, size, size, 0, 0, 1, size, size, size, 0, 0, 1, size, -size, size, 0, 0, 1, -size, -size, size, 0, 0, 1,
          // Back
          -size, size, -size, 0, 0, -1, size, size, -size, 0, 0, -1, size, -size, -size, 0, 0, -1, -size, -size, -size, 0, 0, -1]);

  // Create instance data.
  const instanceCount = 4000;
  const instanceStride = 6;
  const instanceData: Float32Array = new Float32Array(
    instanceCount * instanceStride
  );
  for (let i = 0; i < instanceCount; i++) {
    const offset = i * instanceStride;
    // instance offset
    instanceData[offset] = (Math.random() - 0.5) * 60;
    instanceData[offset + 1] = (Math.random() - 0.5) * 60;
    instanceData[offset + 2] = (Math.random() - 0.5) * 60;
    // instance color
    instanceData[offset + 3] = Math.random();
    instanceData[offset + 4] = Math.random();
    instanceData[offset + 5] = Math.random();
  }

  // Create indices data.
  // prettier-ignore
  const indices: Uint16Array = new Uint16Array([
          // Up
          0, 2, 1, 2, 0, 3,
          // Down
          4, 6, 7, 6, 4, 5,
          // Left
          8, 10, 9, 10, 8, 11,
          // Right
          12, 14, 15, 14, 12, 13,
          // Front
          16, 18, 17, 18, 16, 19,
          // Back
          20, 22, 23, 22, 20, 21]);

  // Create gpu vertex buffer and index buffer.
  const vertexBuffer = new Buffer(
    engine,
    BufferBindFlag.VertexBuffer,
    vertices,
    BufferUsage.Static
  );
  const instanceVertexBuffer = new Buffer(
    engine,
    BufferBindFlag.VertexBuffer,
    instanceData,
    BufferUsage.Static
  );
  const indexBuffer = new Buffer(
    engine,
    BufferBindFlag.IndexBuffer,
    indices,
    BufferUsage.Static
  );

  // Bind buffer
  geometry.setVertexBufferBinding(vertexBuffer, 24, 0);
  geometry.setVertexBufferBinding(instanceVertexBuffer, 24, 1);
  geometry.setIndexBufferBinding(indexBuffer, IndexFormat.UInt16);

  // Add vertexElements
  geometry.setVertexElements([
    new VertexElement("POSITION", 0, VertexElementFormat.Vector3, 0, 0), // Bind to VertexBuffer 0
    new VertexElement("NORMAL", 12, VertexElementFormat.Vector3, 0, 0), // Bind to VertexBuffer 0
    new VertexElement("INSTANCE_OFFSET", 0, VertexElementFormat.Vector3, 1, 1), // Bind instance offset to VertexBuffer 1, and enable instance by set instanceStepRate with 1
    new VertexElement("INSTANCE_COLOR", 12, VertexElementFormat.Vector3, 1, 1), // Bind instance color to VertexBuffer 1, and enable instance by set instanceStepRate with 1
  ]);

  // Add one sub geometry.
  geometry.addSubMesh(0, indices.length);

  geometry.instanceCount = instanceCount;

  return geometry;
}

/**
 * Create custom instance shader.
 */
function initCustomShader(): Shader {
  const shader = Shader.create(
    "CustomShader",
    `uniform mat4 renderer_MVPMat;
      attribute vec4 POSITION;
      attribute vec3 INSTANCE_OFFSET;
      attribute vec3 INSTANCE_COLOR;
      
      uniform mat4 renderer_MVMat;
      
      varying vec3 v_position;
      varying vec3 v_color;
      
      void main() {
        vec4 position = POSITION;
        position.xyz += INSTANCE_OFFSET;
        gl_Position = renderer_MVPMat * position;

        v_color = INSTANCE_COLOR;
      }`,

    `
      varying vec3 v_color;
      uniform vec4 u_color;
      
      void main() {
        vec4 color = vec4(v_color,1.0);
        gl_FragColor = color;
      }
      `
  );
  return shader;
}