/* globals window document mat4 */

const internals = {

  // Constants

  kEntrypointElementId: 'entrypoint',  // The id of the canvas element where we will render
  kWidthRatio: 2.76,
  kHeightRatio: 1,
  kTargetVerticalResolution: 32 + Math.round(Math.random() * 1024),
  kFieldOfView: 45,
  kNearLimit: 0.1,
  kFarLimit: 100,
  kBackgroundColor: [0.811, 0.73, 0.48, 1.0],
  kRotationValues: [Math.random(), Math.random(), Math.random()],
  kFPS: 30,

  // Constants: Shaders

  kVertexShader: `

    attribute vec4 aVertexPosition;
    attribute vec4 aColor;

    varying vec4 vColor;

    uniform mat4 uModelViewMatrix;
    uniform mat4 uProjectionMatrix;

    void main() {

      gl_Position = uProjectionMatrix * uModelViewMatrix * aVertexPosition;
      vColor = aColor;
    }
  `,

  kFragmentShader: `

  precision mediump float;
  varying vec4 vColor;

  void main() {

    gl_FragColor = vColor;
  }
  `,

  // Properties: Animation

  currentTime: 0,

  // Runs on load, Initializes WebGL and starts the animation loop.

  onLoad() {


    const canvas = internals.initializeCanvas();
    const { gl, programInfo, buffers } = internals.initializeWebGL(canvas);

    window.requestAnimationFrame(internals.animate.bind(this, gl, programInfo, buffers));
  },

  // Gets a canvas element and sets up resizing events.

  initializeCanvas() {

    const canvas = document.getElementById(internals.kEntrypointElementId);
    internals.resizeCanvas(canvas);
    window.addEventListener('resize', () => internals.resizeCanvas(canvas));

    return canvas;
  },

  // Given a canvas, it will initialize the webgl context and set up the shaders.

  initializeWebGL(canvas) {

    const gl = canvas.getContext('webgl', {
      preserveDrawingBuffer: true
    });
    const shaderProgram = internals.initializeShaderProgram(gl, internals.kVertexShader, internals.kFragmentShader);

    const programInfo = {
      program: shaderProgram,
      attribLocations: {
        vertexPosition: gl.getAttribLocation(shaderProgram, 'aVertexPosition'),
        vertexColor: gl.getAttribLocation(shaderProgram, 'aColor')
      },
      uniformLocations: {
        projectionMatrix: gl.getUniformLocation(shaderProgram, 'uProjectionMatrix'),
        modelViewMatrix: gl.getUniformLocation(shaderProgram, 'uModelViewMatrix')
      }
    };

    const buffers = internals.initializeBuffers(gl);

    return { gl, programInfo, buffers };
  },

  // Methods: Canvas

  resizeCanvas(canvas) {

    let width = window.innerWidth;
    let height = Math.round(width * internals.kHeightRatio / internals.kWidthRatio);

    if (window.innerHeight < height) {
      height = window.innerHeight;
      width = Math.round(height * internals.kWidthRatio / internals.kHeightRatio);
      console.log(width, height);
    }

    canvas.style.width = `${width}px`;
    canvas.style.height = `${height}px`;

    canvas.width = internals.kTargetVerticalResolution * internals.kWidthRatio;
    canvas.height = internals.kTargetVerticalResolution;
  },

  // Methods: Shader / GL Related

  initializeShaderProgram(gl, vertexShaderSource, fragmentShaderSource) {

    const vertexShader = internals.loadShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
    const fragmentShader = internals.loadShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);

    const shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);

    gl.linkProgram(shaderProgram);

    if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
      console.error(`Unable to initialize shader program: ${gl.getProgramInfoLog(shaderProgram)}`);
      return null;
    }

    return shaderProgram;
  },

  loadShader(gl, type, source) {

    const shader = gl.createShader(type);
    gl.shaderSource(shader, source);
    gl.compileShader(shader);

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
      console.error(`Unable to compile shader: ${gl.getShaderInfoLog(shader)}`);
      gl.deleteShader(shader);
      return null;
    }

    return shader;
  },

  initializeBuffers(gl) {

    const positionBuffer = gl.createBuffer();

    gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);

    const positions = [
      -1.0, 1.0, 1.0,     // Front-top-left
      1.0, 1.0, 1.0,      // Front-top-right
      -1.0, -1.0, 1.0,    // Front-bottom-left
      1.0, -1.0, 1.0,     // Front-bottom-right
      1.0, -1.0, -1.0,    // Back-bottom-right
      1.0, 1.0, 1.0,      // Front-top-right
      1.0, 1.0, -1.0,     // Back-top-right
      -1.0, 1.0, 1.0,     // Front-top-left
      -1.0, 1.0, -1.0,    // Back-top-left
      -1.0, -1.0, 1.0,    // Front-bottom-left
      -1.0, -1.0, -1.0,   // Back-bottom-left
      1.0, -1.0, -1.0,    // Back-bottom-right
      -1.0, 1.0, -1.0,    // Back-top-left
      1.0, 1.0, -1.0      // Back-top-right
    ];

    gl.bufferData(gl.ARRAY_BUFFER,
      new Float32Array(positions),
      gl.STATIC_DRAW);

    return {
      position: positionBuffer
    };
  },

  // Methods: Utility

  createMatrix() {

    const matrix = mat4.create();

    mat4.translate(
      matrix,
      matrix,
      [-0.0, 0.0, -6.0]
    );

    return matrix;
  },

  // Methods: Animation

  rotate(matrix) {

    mat4.rotate(internals.modelViewMatrix, internals.modelViewMatrix, internals.kRotationValues[0], [1, 0, 0]);
    mat4.rotate(internals.modelViewMatrix, internals.modelViewMatrix, internals.kRotationValues[1], [0, 1, 0]);
    mat4.rotate(internals.modelViewMatrix, internals.modelViewMatrix, internals.kRotationValues[2], [0, 0, 1]);
  },

  drawScene(gl, programInfo, buffers) {

    gl.clearColor(...internals.kBackgroundColor);
    gl.clearDepth(1.0);
    gl.enable(gl.DEPTH_TEST);
    gl.depthFunc(gl.LEQUAL);

    const fieldOfView = internals.kFieldOfView * Math.PI / 180;
    const aspectRatio = internals.kWidthRatio / internals.kHeightRatio;
    const projectionMatrix = mat4.create();

    mat4.perspective(
      projectionMatrix,
      fieldOfView,
      aspectRatio,
      internals.kNearLimit,
      internals.kFarLimit
    );

    internals.modelViewMatrix = internals.modelViewMatrix || internals.createMatrix();

    internals.rotate(internals.modelViewMatrix);

    {
      const numberOfComponents = 3;
      const type = gl.FLOAT;
      const normalize = false;
      const stride = 0;
      const offset = 0;

      gl.bindBuffer(gl.ARRAY_BUFFER, buffers.position);
      gl.vertexAttribPointer(
        programInfo.attribLocations.vertexPosition,
        numberOfComponents,
        type,
        normalize,
        stride,
        offset
      );
      gl.enableVertexAttribArray(programInfo.attribLocations.vertexPosition);
    }

    {
      // ATTEMPT TO SEND COLOR DATA

      const colorBuffer = gl.createBuffer();

      gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);

      const colors = [
        1.0, 0.0, 0.5, 1.0, // Front-top-left
        1.0, 0.3, 0.8, 1.0, // Front-top-right
        1.0, 1.0, 0.7, 1.0, // Front-bottom-left
        0.0, 0.3, 0.5, 1.0, // Front-bottom-right
        0.0, 0.3, 0.5, 1.0, // Back-bottom-right
        1.0, 0.3, 0.8, 1.0, // Front-top-right
        1.0, 0.3, 0.8, 1.0, // Back-top-right
        1.0, 0.0, 0.5, 1.0, // Front-top-left
        1.0, 0.0, 0.5, 1.0, // Back-top-left
        1.0, 1.0, 0.7, 1.0, // Front-bottom-left
        1.0, 1.0, 0.7, 1.0, // Back-bottom-left
        0.0, 0.3, 0.5, 1.0, // Back-bottom-right
        1.0, 0.0, 0.5, 1.0, // Back-top-left
        1.0, 0.3, 0.8, 1.0  // Back-top-right
      ];

      gl.bufferData(gl.ARRAY_BUFFER,
        new Float32Array(colors),
        gl.STATIC_DRAW);

      const numberOfComponents = 4;
      const type = gl.FLOAT;
      const normalize = false;
      const stride = 0;
      const offset = 0;

      gl.bindBuffer(gl.ARRAY_BUFFER, colorBuffer);
      gl.vertexAttribPointer(
        programInfo.attribLocations.vertexColor,
        numberOfComponents,
        type,
        normalize,
        stride,
        offset
      );
      gl.enableVertexAttribArray(programInfo.attribLocations.vertexColor);

      // END ATTEMPT
    }

    gl.useProgram(programInfo.program);

    gl.uniformMatrix4fv(
      programInfo.uniformLocations.projectionMatrix,
      false,
      projectionMatrix
    );
    gl.uniformMatrix4fv(
      programInfo.uniformLocations.modelViewMatrix,
      false,
      internals.modelViewMatrix
    );

    {
      const offset = 0;
      const vertexCount = 14;
      gl.drawArrays(gl.TRIANGLE_STRIP, offset, vertexCount);
    }
  },

  animate(gl, programInfo, buffers, time) {

    const delta = time - internals.currentTime;
    const interval = 1000 / internals.kFPS;

    if (delta >= interval) {
      internals.drawScene(gl, programInfo, buffers, delta);
      internals.currentTime = time;
    }

    window.requestAnimationFrame(internals.animate.bind(this, gl, programInfo, buffers));
  }
};

window.addEventListener('load', internals.onLoad);