/**
 * @author   Ikaros Kappler
 * @date     2019-09-18
 * @modified 2019-10-03 Added the beginDrawCycle hook.
 * @modified 2020-03-25 Ported stub to Typescript.
 * @modified 2020-10-15 Re-added the text() function.
 * @modified 2021-01-24 Added the `setCurrentId` function.
 * @modified 2021-05-31 Added the `setConfiguration` function from `DrawLib`.
 * @modified 2022-02-03 Added the `lineWidth` param to the `crosshair` function.
 * @modified 2022-02-03 Added the `cross(...)` function.
 * @modified 2022-03-27 Added the `texturedPoly` function.
 * @modified 2022-07-26 Adding `alpha` to the `image(...)` function.
 * @modified 2023-02-10 The methods `setCurrentClassName` and `setCurrentId` also accept `null` now.
 * @modified 2023-09-29 Downgrading all `Vertex` param type to the more generic `XYCoords` type in these render functions: line, arrow, texturedPoly, cubicBezier, cubicBezierPath, handle, handleLine, dot, point, circle, circleArc, ellipse, grid, raster.
 * @modified 2023-09-29 Added the `headLength` parameter to the 'DrawLib.arrow()` function.
 * @modified 2023-09-29 Added the `arrowHead(...)` function to the 'DrawLib.arrow()` interface.
 * @modified 2023-09-29 Added the `cubicBezierArrow(...)` function to the 'DrawLib.arrow()` interface.
 * @modified 2023-09-29 Added the `lineDashes` attribute.
 * @version  0.0.10
 **/

import { Polygon } from "./Polygon";
import { Vertex } from "./Vertex";
import { DrawLib, XYCoords, SVGPathParams, UID, DrawLibConfiguration, FontStyle, FontWeight } from "./interfaces";
import { Bounds } from "./Bounds";

/**
 * @classdesc A wrapper class for basic drawing operations. This is the WebGL
 * implementation whih sould work with shaders.
 *
 * @requires CubicBzierCurvce
 * @requires Polygon
 * @requires SVGSerializable
 * @requires Vertex
 * @requires XYCoords
 */
export class drawutilsgl implements DrawLib<void> {
  // Vertex shader source code
  private static vertCode: string = `
    precision mediump float;

    attribute vec3 position;

    uniform vec2 uRotationVector;

    void main(void) {
	vec2 rotatedPosition = vec2(
	    position.x * uRotationVector.y +
		position.y * uRotationVector.x,
	    position.y * uRotationVector.y -
		position.x * uRotationVector.x
	);

	gl_Position = vec4(rotatedPosition, position.z, 1.0);
    }`;

  // Fragment shader source code
  private static fragCode: string = `
    precision highp float;

    void main(void) {
	gl_FragColor = vec4(0.0,0.75,1.0,1.0);
    }`;

  gl: WebGLRenderingContext;

  readonly offset: Vertex;
  readonly scale: Vertex;

  fillShapes: boolean;

  private _zindex: number;

  private glutils: GLU;

  private _vertShader: WebGLShader; // TODO (what's the type?)
  private _fragShader: WebGLShader; // TODO
  private _program: WebGLProgram;
  private vertex_buffer: WebGLBuffer; // TODO

  private curId: UID | null;
  private renderTime: number;

  /**
   * The constructor.
   *
   * @constructor
   * @name drawutils
   * @param {WebGLRenderingContext|null} context - The drawing context.
   * @param {boolean} fillShaped - Indicates if the constructed drawutils should fill all drawn shapes (if possible).
   **/
  constructor(context: WebGLRenderingContext, fillShapes: boolean) {
    this.gl = context;
    this.offset = new Vertex(0, 0);
    this.scale = new Vertex(1, 1);
    this.fillShapes = fillShapes;

    this._zindex = 0.0;

    if (context == null || typeof context === "undefined") return;

    this.glutils = new GLU(context);
    // PROBLEM: CANNOT USE MULTIPLE SHADER PROGRAM INSTANCES ON THE SAME CONTEXT!
    // SOLUTION: USE SHARED SHADER PROGRAM!!! ... somehow ...
    // This needs to be considered in the overlying component; both draw-instances need to
    // share their gl context.
    // That's what the copyInstace(boolean) method is good for.
    this._vertShader = this.glutils.compileShader(drawutilsgl.vertCode, this.gl.VERTEX_SHADER) as WebGLShader;
    this._fragShader = this.glutils.compileShader(drawutilsgl.fragCode, this.gl.FRAGMENT_SHADER) as WebGLShader;
    this._program = this.glutils.makeProgram(this._vertShader, this._fragShader);

    // Create an empty buffer object
    this.vertex_buffer = this.gl.createBuffer() as WebGLBuffer;
    // Bind appropriate array buffer to it
    // this.gl.bindBuffer(this.gl.ARRAY_BUFFER, this.vertex_buffer);

    console.log("gl initialized");
  }

  _x2rel(x: number): number {
    return ((this.scale.x * x + this.offset.x) / this.gl.canvas.width) * 2.0 - 1.0;
  }
  _y2rel(y: number): number {
    return ((this.offset.y - this.scale.y * y) / this.gl.canvas.height) * 2.0 - 1.0;
  }

  /**
   * Creates a 'shallow' (non deep) copy of this instance. This implies
   * that under the hood the same gl context and gl program will be used.
   */
  copyInstance(fillShapes: boolean): drawutilsgl {
    var copy: drawutilsgl = new drawutilsgl(null as any as WebGLRenderingContext, fillShapes);
    copy.gl = this.gl;
    copy.glutils = this.glutils;
    copy._vertShader = this._vertShader;
    copy._fragShader = this._fragShader;
    copy._program = this._program;
    return copy;
  }

  /**
   * Called before each draw cycle.
   * @param {number} renderTime
   **/
  beginDrawCycle(renderTime: number) {
    this._zindex = 0.0;
    this.renderTime = renderTime;
  }

  /**
   * Called after each draw cycle.
   *
   * This is required for compatibility with other draw classes in the library (like drawgl).
   *
   * @name endDrawCycle
   * @method
   * @param {number} renderTime
   * @instance
   **/
  endDrawCycle(renderTime: number) {
    // NOOP
  }

  /**
   * Set the current drawlib configuration.
   *
   * @name setConfiguration
   * @method
   * @param {DrawLibConfiguration} configuration - The new configuration settings to use for the next render methods.
   */
  setConfiguration(configuration: DrawLibConfiguration): void {
    // TODO
  }

  // /**
  //  * Set or clear the line-dash configuration. Pass `null` for un-dashed lines.
  //  *
  //  * See https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/stroke-dasharray
  //  * and https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/setLineDash
  //  * for how line dashes work.
  //  *
  //  * @method
  //  * @param {Array<number> lineDashes - The line-dash array configuration.
  //  * @returns {void}
  //  */
  // setLineDash(lineDashes: Array<number>) {
  //   // TODO
  // }

  /**
   * This method shouled be called each time the currently drawn `Drawable` changes.
   * It is used by some libraries for identifying elemente on re-renders.
   *
   * @name setCurrentId
   * @method
   * @param {UID|null} uid - A UID identifying the currently drawn element(s).es.
   **/
  setCurrentId(uid: UID | null): void {
    // NOOP
    this.curId = uid;
  }

  /**
   * This method shouled be called each time the currently drawn `Drawable` changes.
   * Determine the class name for further usage here.
   *
   * @name setCurrentClassName
   * @method
   * @param {string|null} className - A class name for further custom use cases.
   **/
  setCurrentClassName(className: string | null): void {
    // NOOP
  }

  /**
   * Draw the line between the given two points with the specified (CSS-) color.
   *
   * @method line
   * @param {XYCoords} zA - The start point of the line.
   * @param {XYCoords} zB - The end point of the line.
   * @param {string} color - Any valid CSS color string.
   * @return {void}
   * @instance
   * @memberof drawutils
   **/
  line(zA: XYCoords, zB: XYCoords, color: string) {
    const vertices: Float32Array = new Float32Array(6);
    vertices[0] = this._x2rel(zA.x);
    vertices[1] = this._y2rel(zA.y);
    vertices[2] = this._zindex;
    vertices[3] = this._x2rel(zB.x);
    vertices[4] = this._y2rel(zB.y);
    vertices[5] = this._zindex;
    this._zindex += 0.001;

    // Create an empty buffer object
    // const vertex_buffer = this.gl.createBuffer();
    // Bind appropriate array buffer to it
    this.gl.bindBuffer(this.gl.ARRAY_BUFFER, this.vertex_buffer);
    // Pass the vertex data to the buffer
    this.gl.bufferData(this.gl.ARRAY_BUFFER, vertices, this.gl.STATIC_DRAW);
    // Bind vertex buffer object
    // this.gl.bindBuffer(this.gl.ARRAY_BUFFER, vertex_buffer);
    // Get the attribute location
    var coord = this.gl.getAttribLocation(this._program, "position");
    // Point an attribute to the currently bound VBO
    this.gl.vertexAttribPointer(coord, 3, this.gl.FLOAT, false, 0, 0);
    // Enable the attribute
    this.gl.enableVertexAttribArray(coord);
    // Unbind the buffer?
    //this.gl.bindBuffer(this.gl.ARRAY_BUFFER, null);
    // Set the view port
    this.gl.viewport(0, 0, this.gl.canvas.width, this.gl.canvas.height);

    let uRotationVector = this.gl.getUniformLocation(this._program, "uRotationVector");
    // let radians = currentAngle * Math.PI / 180.0;
    let currentRotation = [0.0, 1.0];
    //currentRotation[0] = Math.sin(radians);
    //currentRotation[1] = Math.cos(radians);
    this.gl.uniform2fv(uRotationVector, currentRotation);

    this.gl.lineWidth(5);

    // Draw the line
    this.gl.drawArrays(this.gl.LINES, 0, vertices.length / 3);
    // POINTS, LINE_STRIP, LINE_LOOP, LINES,
    // TRIANGLE_STRIP,TRIANGLE_FAN, TRIANGLES
  }

  /**
   * Draw a line and an arrow at the end (zB) of the given line with the specified (CSS-) color.
   *
   * @method arrow
   * @param {XYCoords} zA - The start point of the arrow-line.
   * @param {XYCoords} zB - The end point of the arrow-line.
   * @param {string} color - Any valid CSS color string.
   * @param {headLength=8} headLength - (optional) The length of the arrow head (default is 8 units).
   * @return {void}
   * @instance
   * @memberof drawutils
   **/
  arrow(zA: XYCoords, zB: XYCoords, color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a cubic Bézier curve and and an arrow at the end (endControlPoint) of the given line width the specified (CSS-) color and arrow size.
   *
   * @method cubicBezierArrow
   * @param {XYCoords} startPoint - The start point of the cubic Bézier curve
   * @param {XYCoords} endPoint   - The end point the cubic Bézier curve.
   * @param {XYCoords} startControlPoint - The start control point the cubic Bézier curve.
   * @param {XYCoords} endControlPoint   - The end control point the cubic Bézier curve.
   * @param {string} color - The CSS color to draw the curve with.
   * @param {number} lineWidth - (optional) The line width to use.
   * @param {headLength=8} headLength - (optional) The length of the arrow head (default is 8 units).
   *
   * @return {void}
   * @instance
   * @memberof DrawLib
   */
  cubicBezierArrow(
    startPoint: XYCoords,
    endPoint: XYCoords,
    startControlPoint: XYCoords,
    endControlPoint: XYCoords,
    color: string,
    lineWidth?: number,
    headLength?: number
  ) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw just an arrow head a the end of an imaginary line (zB) of the given line width the specified (CSS-) color and size.
   *
   * @method arrow
   * @param {XYCoords} zA - The start point of the arrow-line.
   * @param {XYCoords} zB - The end point of the arrow-line.
   * @param {string} color - Any valid CSS color string.
   * @param {number=1} lineWidth - (optional) The line width to use; default is 1.
   * @param {number=8} headLength - (optional) The length of the arrow head (default is 8 pixels).
   * @return {void}
   * @instance
   * @memberof DrawLib
   **/
  arrowHead(zA: XYCoords, zB: XYCoords, color: string, lineWidth?: number, headLength?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw an image at the given position with the given size.<br>
   * <br>
   * Note: SVG images may have resizing issues at the moment.Draw a line and an arrow at the end (zB) of the given line with the specified (CSS-) color.
   *
   * @method image
   * @param {Image} image - The image object to draw.
   * @param {XYCoords} position - The position to draw the the upper left corner at.
   * @param {XYCoords} size - The x/y-size to draw the image with.
   * @param {number=0.0} alpha - (optional, default=0.0) The transparency (0.0=opaque, 1.0=transparent).
   * @return {void}
   * @instance
   * @memberof drawutils
   **/
  image(image: HTMLImageElement, position: XYCoords, size: XYCoords, alpha: number = 0.0) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw an image at the given position with the given size.<br>
   * <br>
   * Note: SVG images may have resizing issues at the moment.Draw a line and an arrow at the end (zB) of the given line with the specified (CSS-) color.
   *
   * @method texturedPoly
   * @param {Image} textureImage - The image object to draw.
   * @param {Bounds} textureSize - The texture size to use; these are the original bounds to map the polygon vertices to.
   * @param {Polygon} polygon - The polygon to use as clip path.
   * @param {XYCoords} polygonPosition - The polygon's position (relative), measured at the bounding box's center.
   * @param {number} rotation - The rotation to use for the polygon (and for the texture).
   * @return {void}
   * @instance
   * @memberof drawutilsgl
   **/
  texturedPoly(
    textureImage: HTMLImageElement,
    textureSize: Bounds,
    polygon: Polygon,
    polygonPosition: XYCoords,
    rotation: number
  ) {
    // NOT YET IMPLEMENTED
  }

  // +---------------------------------------------------------------------------------
  // | This is the final helper function for drawing and filling stuff. It is not
  // | intended to be used from the outside.
  // |
  // | When in draw mode it draws the current shape.
  // | When in fill mode it fills the current shape.
  // |
  // | This function is usually only called internally.
  // |
  // | @param color A stroke/fill color to use.
  // +-------------------------------
  _fillOrDraw(color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw the given (cubic) bézier curve.
   *
   * @method cubicBezier
   * @param {XYCoords} startPoint - The start point of the cubic Bézier curve
   * @param {XYCoords} endPoint   - The end point the cubic Bézier curve.
   * @param {XYCoords} startControlPoint - The start control point the cubic Bézier curve.
   * @param {VertXYCoordsex} endControlPoint   - The end control point the cubic Bézier curve.
   * @param {string} color - The CSS color to draw the curve with.
   * @param {number=} lineWidth - (optional) The line width to use; default is 1.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  cubicBezier(
    startPoint: XYCoords,
    endPoint: XYCoords,
    startControlPoint: XYCoords,
    endControlPoint: XYCoords,
    color: string,
    lineWidth?: number
  ) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw the given (cubic) Bézier path.
   *
   * The given path must be an array with n*3+1 vertices, where n is the number of
   * curves in the path:
   * <pre> [ point1, point1_startControl, point2_endControl, point2, point2_startControl, point3_endControl, point3, ... pointN_endControl, pointN ]</pre>
   *
   * @method cubicBezierPath
   * @param {XYCoords[]} path - The cubic bezier path as described above.
   * @param {string} color - The CSS colot to draw the path with.
   * @param {number=} lineWidth - (optional) The line width to use; default is 1.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  cubicBezierPath(path: Array<XYCoords>, color: string, lineWidth?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw the given handle and handle point (used to draw interactive Bézier curves).
   *
   * The colors for this are fixed and cannot be specified.
   *
   * @method handle
   * @param {XYCoords} startPoint - The start of the handle.
   * @param {XYCoords} endPoint - The end point of the handle.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  handle(startPoint: XYCoords, endPoint: XYCoords) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a handle line (with a light grey).
   *
   * @method handleLine
   * @param {XYCoords} startPoint - The start point to draw the handle at.
   * @param {XYCoords} endPoint - The end point to draw the handle at.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  handleLine(startPoint: XYCoords, endPoint: XYCoords) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a 1x1 dot with the specified (CSS-) color.
   *
   * @method dot
   * @param {XYCoords} p - The position to draw the dot at.
   * @param {string} color - The CSS color to draw the dot with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  dot(p: XYCoords, color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw the given point with the specified (CSS-) color and radius 3.
   *
   * @method point
   * @param {XYCoords} p - The position to draw the point at.
   * @param {string} color - The CSS color to draw the point with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  point(p: XYCoords, color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a circle with the specified (CSS-) color and radius.<br>
   * <br>
   * Note that if the x- and y- scales are different the result will be an ellipse rather than a circle.
   *
   * @method circle
   * @param {XYCoords} center - The center of the circle.
   * @param {number} radius - The radius of the circle.
   * @param {string} color - The CSS color to draw the circle with.
   * @param {number=} lineWidth - (optional) The line width to use; default is 1.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  circle(center: XYCoords, radius: number, color: string, lineWidth?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a circular arc (section of a circle) with the given CSS color.
   *
   * @method circleArc
   * @param {XYCoords} center - The center of the circle.
   * @param {number} radius - The radius of the circle.
   * @param {number} startAngle - The angle to start at.
   * @param {number} endAngle - The angle to end at.
   * @param {string} color - The CSS color to draw the circle with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  circleArc(center: XYCoords, radius: number, startAngle: number, endAngle: number, color: string, lineWidth?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw an ellipse with the specified (CSS-) color and thw two radii.
   *
   * @method ellipse
   * @param {XYCoords} center - The center of the ellipse.
   * @param {number} radiusX - The radius of the ellipse.
   * @param {number} radiusY - The radius of the ellipse.
   * @param {string} color - The CSS color to draw the ellipse with.
   * @param {number=} lineWidth - (optional) The line width to use; default is 1.
   * @param {number=} rotation - (optional, default=0) The rotation of the ellipse.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  ellipse(center: XYCoords, radiusX: number, radiusY: number, color: string, lineWidth?: number, rotation?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw square at the given center, size and with the specified (CSS-) color.<br>
   * <br>
   * Note that if the x-scale and the y-scale are different the result will be a rectangle rather than a square.
   *
   * @method square
   * @param {XYCords} center - The center of the square.
   * @param {number} size - The size of the square.
   * @param {string} color - The CSS color to draw the square with.
   * @param {number=} lineWidth - (optional) The line width to use; default is 1.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  square(center: XYCoords, size: number, color: string, lineWidth?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a rectangle.
   *
   * @param {XYCoords} position - The upper left corner of the rectangle.
   * @param {number} width - The width of the rectangle.
   * @param {number} height - The height of the rectangle.
   * @param {string} color - The color to use.
   * @param {number=1} lineWidth - (optional) The line with to use (default is 1).
   **/
  rect(position: XYCoords, width: number, height: number, color: string, lineWidth?: number): void {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a grid of horizontal and vertical lines with the given (CSS-) color.
   *
   * @method grid
   * @param {XYCoords} center - The center of the grid.
   * @param {number} width - The total width of the grid (width/2 each to the left and to the right).
   * @param {number} height - The total height of the grid (height/2 each to the top and to the bottom).
   * @param {number} sizeX - The horizontal grid size.
   * @param {number} sizeY - The vertical grid size.
   * @param {string} color - The CSS color to draw the grid with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  grid(center: XYCoords, width: number, height: number, sizeX: number, sizeY: number, color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a raster of crosshairs in the given grid.<br>
   *
   * This works analogue to the grid() function
   *
   * @method raster
   * @param {XYCoords} center - The center of the raster.
   * @param {number} width - The total width of the raster (width/2 each to the left and to the right).
   * @param {number} height - The total height of the raster (height/2 each to the top and to the bottom).
   * @param {number} sizeX - The horizontal raster size.
   * @param {number} sizeY - The vertical raster size.
   * @param {string} color - The CSS color to draw the raster with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  raster(center: XYCoords, width: number, height: number, sizeX: number, sizeY: number, color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a diamond handle (square rotated by 45°) with the given CSS color.
   *
   * It is an inherent featur of the handle functions that the drawn elements are not scaled and not
   * distorted. So even if the user zooms in or changes the aspect ratio, the handles will be drawn
   * as even shaped diamonds.
   *
   * @method diamondHandle
   * @param {XYCoords} center - The center of the diamond.
   * @param {number} size - The x/y-size of the diamond.
   * @param {string} color - The CSS color to draw the diamond with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  diamondHandle(center: XYCoords, size: number, color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a square handle with the given CSS color.<br>
   * <br>
   * It is an inherent featur of the handle functions that the drawn elements are not scaled and not
   * distorted. So even if the user zooms in or changes the aspect ratio, the handles will be drawn
   * as even shaped squares.
   *
   * @method squareHandle
   * @param {XYCoords} center - The center of the square.
   * @param {number} size - The x/y-size of the square.
   * @param {string} color - The CSS color to draw the square with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  squareHandle(center: XYCoords, size: number, color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a circle handle with the given CSS color.<br>
   * <br>
   * It is an inherent featur of the handle functions that the drawn elements are not scaled and not
   * distorted. So even if the user zooms in or changes the aspect ratio, the handles will be drawn
   * as even shaped circles.
   *
   * @method circleHandle
   * @param {XYCoords} center - The center of the circle.
   * @param {number} radius - The radius of the circle.
   * @param {string} color - The CSS color to draw the circle with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  circleHandle(center: XYCoords, size: number, color: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a crosshair with given radius and color at the given position.<br>
   * <br>
   * Note that the crosshair radius will not be affected by scaling.
   *
   * @method crosshair
   * @param {XYCoords} center - The center of the crosshair.
   * @param {number} radius - The radius of the crosshair.
   * @param {string} color - The CSS color to draw the crosshair with.
   * @param {number=0.5} lineWidth - (optional, default=0.5) The line width to use.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  crosshair(center: XYCoords, radius: number, color: string, lineWidth?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a cross with diagonal axes with given radius, color and lineWidth at the given position.<br>
   * <br>
   * Note that the x's radius will not be affected by scaling.
   *
   * @method crosshair
   * @param {XYCoords} center - The center of the crosshair.
   * @param {number} radius - The radius of the crosshair.
   * @param {string} color - The CSS color to draw the crosshair with.
   * @param {number=1} lineWidth - (optional, default=1.0) The line width to use.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  cross(center: XYCoords, radius: number, color: string, lineWidth?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a polygon.
   *
   * @method polygon
   * @param {Polygon} polygon - The polygon to draw.
   * @param {string} color - The CSS color to draw the polygon with.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  polygon(polygon: Polygon, color: string, lineWidth?: number) {
    const vertices: Float32Array = new Float32Array(polygon.vertices.length * 3);
    for (var i = 0; i < polygon.vertices.length; i++) {
      vertices[i * 3 + 0] = this._x2rel(polygon.vertices[i].x);
      vertices[i * 3 + 1] = this._y2rel(polygon.vertices[i].y);
      vertices[i * 3 + 2] = this._zindex;
    }
    this._zindex += 0.001;
    //console.log( vertices );

    // Create an empty buffer object
    // const vertex_buffer = this.gl.createBuffer();
    // Bind appropriate array buffer to it
    this.gl.bindBuffer(this.gl.ARRAY_BUFFER, this.vertex_buffer);
    // Pass the vertex data to the buffer
    this.gl.bufferData(this.gl.ARRAY_BUFFER, vertices, this.gl.STATIC_DRAW);
    // Bind vertex buffer object
    // this.gl.bindBuffer(this.gl.ARRAY_BUFFER, vertex_buffer);
    // Get the attribute location
    var coord = this.gl.getAttribLocation(this._program, "position");
    // Point an attribute to the currently bound VBO
    this.gl.vertexAttribPointer(coord, 3, this.gl.FLOAT, false, 0, 0);
    // Enable the attribute
    this.gl.enableVertexAttribArray(coord);
    // Unbind the buffer?
    this.gl.bindBuffer(this.gl.ARRAY_BUFFER, null);
    // Set the view port
    this.gl.viewport(0, 0, this.gl.canvas.width, this.gl.canvas.height);

    let uRotationVector = this.gl.getUniformLocation(this._program, "uRotationVector");
    // let radians = currentAngle * Math.PI / 180.0;
    let currentRotation = [0.0, 1.0];
    //currentRotation[0] = Math.sin(radians);
    //currentRotation[1] = Math.cos(radians);
    this.gl.uniform2fv(uRotationVector, currentRotation);

    // Draw the polygon
    this.gl.drawArrays(this.gl.TRIANGLE_FAN, 0, vertices.length / 3);
    // POINTS, LINE_STRIP, LINE_LOOP, LINES,
    // TRIANGLE_STRIP,TRIANGLE_FAN, TRIANGLES
  }

  /**
   * Draw a polygon line (alternative function to the polygon).
   *
   * @method polyline
   * @param {XYCoords[]} vertices - The polygon vertices to draw.
   * @param {boolan}   isOpen   - If true the polyline will not be closed at its end.
   * @param {string}   color    - The CSS color to draw the polygon with.
   * @param {number=}  lineWidth - (optional) The line width to use; default is 1.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  polyline(vertices: Array<XYCoords>, isOpen: boolean, color: string, lineWidth?: number) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a text at the given relative position.
   *
   * @method text
   * @param {string} text - The text to draw.
   * @param {number} x - The x-position to draw the text at.
   * @param {number} y - The y-position to draw the text at.
   * @param {string=} options.color - The Color to use.
   * @param {string=} options.fontFamily - The font family to use.
   * @param {number=} options.fontSize - The font size (in pixels) to use.
   * @param {FontStyle=} options.fontStyle - The font style to use.
   * @param {FontWeight=} options.fontWeight - The font weight to use.
   * @param {number=} options.lineHeight - The line height (in pixels) to use.
   * @param {number=} options.rotation - The (optional) rotation in radians.
   * @param {string=} options.textAlign - The text align to use. According to the specifiactions (https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/textAlign) valid values are `"left" || "right" || "center" || "start" || "end"`.
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  text(
    text: string,
    x: number,
    y: number,
    options?: {
      color?: string;
      fontFamily?: string;
      fontSize?: number;
      fontStyle?: FontStyle;
      fontWeight?: FontWeight;
      lineHeight?: number;
      textAlign?: CanvasRenderingContext2D["textAlign"];
      rotation?: number;
    }
  ) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw a non-scaling text label at the given position.
   *
   * @method label
   * @param {string} text - The text to draw.
   * @param {number} x - The x-position to draw the text at.
   * @param {number} y - The y-position to draw the text at.
   * @param {number=} rotation - The (aoptional) rotation in radians.
   * @param {string="black"} color - The color to use (default is black).
   * @return {void}
   * @instance
   * @memberof drawutils
   */
  label(text: string, x: number, y: number, rotation?: number, color?: string) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Draw an SVG-like path given by the specified path data.
   *
   * @method path
   * @param {SVGPathData} pathData - An array of path commands and params.
   * @param {string=null} color - (optional) The color to draw this path with (default is null).
   * @param {number=1} lineWidth - (optional) the line width to use (default is 1).
   * @param {boolean=false} options.inplace - (optional) If set to true then path transforamtions (scale and translate) will be done in-place in the array. This can boost the performance.
   * @instance
   * @memberof drawutils
   * @return {R} An instance representing the drawn path.
   */
  path(pathData: SVGPathParams, color?: string, lineWidth?: number, options?: { inplace?: boolean }) {
    // NOT YET IMPLEMENTED
  }

  /**
   * Due to gl compatibility there is a generic 'clear' function required
   * to avoid accessing the context object itself directly.
   *
   * This function just fills the whole canvas with a single color.
   *
   * @param {string} color - The color to clear with.
   **/
  clear(color: string) {
    // NOT YET IMPLEMENTED

    // if( typeof color == 'string' )
    // color = Color.parse(color); // Color class does not yet exist in TS

    // Clear the canvas
    this.gl.clearColor(1.0, 1.0, 1.0, 1.0);

    // Enable the depth test
    this.gl.enable(this.gl.DEPTH_TEST);

    // Clear the color and depth buffer
    this.gl.clear(this.gl.COLOR_BUFFER_BIT | this.gl.DEPTH_BUFFER_BIT);
  }
}

/**
 * Some GL helper utils.
 **/
class GLU {
  gl: WebGLRenderingContext;

  constructor(gl: WebGLRenderingContext) {
    this.gl = gl;
  }

  bufferData(verts: Float32Array): WebGLBuffer {
    // Create an empty buffer object
    var vbuffer: WebGLBuffer = this.gl.createBuffer() as WebGLBuffer;
    // Bind appropriate array buffer to it
    this.gl.bindBuffer(this.gl.ARRAY_BUFFER, vbuffer);
    // Pass the vertex data to the buffer
    this.gl.bufferData(this.gl.ARRAY_BUFFER, verts, this.gl.STATIC_DRAW);
    // Unbind the buffer
    this.gl.bindBuffer(this.gl.ARRAY_BUFFER, null);
    return vbuffer;
  }

  /*=================== Shaders ====================*/
  compileShader(shaderCode: string, shaderType: any): WebGLShader | null {
    // Create a vertex shader object
    var shader: WebGLShader = this.gl.createShader(shaderType) as WebGLShader;
    // Attach vertex shader source code
    this.gl.shaderSource(shader, shaderCode);
    // Compile the vertex shader
    this.gl.compileShader(shader);
    const vertStatus = this.gl.getShaderParameter(shader, this.gl.COMPILE_STATUS);
    if (!vertStatus) {
      console.warn("Error in shader:" + this.gl.getShaderInfoLog(shader));
      this.gl.deleteShader(shader);
      return null;
    }
    return shader;
  }

  makeProgram(vertShader: WebGLShader, fragShader: WebGLShader): WebGLProgram {
    // Create a shader program object to store
    // the combined shader program
    var program: WebGLProgram = this.gl.createProgram() as WebGLProgram;

    // Attach a vertex shader
    this.gl.attachShader(program, vertShader);

    // Attach a fragment shader
    this.gl.attachShader(program, fragShader);

    // Link both the programs
    this.gl.linkProgram(program);

    // Use the combined shader program object
    this.gl.useProgram(program);

    /*======= Do some cleanup ======*/
    this.gl.detachShader(program, vertShader);
    this.gl.detachShader(program, fragShader);
    this.gl.deleteShader(vertShader);
    this.gl.deleteShader(fragShader);

    return program;
  }
}