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class Bezier {
  constructor(ctx) {
    this.ctx = ctx;
  }

  
  draw(controlPoints, t = 1) {
    if (!controlPoints.length) return;
    const curvePoints = [];
    let i = 0;
    while (i <= t) {
      this.drawLines(controlPoints, i, curvePoints, false, null, "blue");
      i += 0.01;
    }
    
    this.drawLines(controlPoints, t, curvePoints, false, null, "blue");
    return curvePoints;
  }

  
  drawAnimation(controlPoints, t = 1) {
    if (!controlPoints.length) return Promise.resolve([]);
    return new Promise((resolve) => {
      const curvePoints = [];
      let i = 0;
      const p2d = new Path2D();
      const draw = () => {
        ctx.clearRect(0, 0, canvas.width, canvas.height);
        if (i > t) {
          
          this.drawLines(controlPoints, t, curvePoints, true, p2d, "blue");
          resolve(curvePoints);
          return;
        }
        ctx.fillText(`t = (${i.toFixed(2)})`, 10, 20);
        this.drawLines(controlPoints, i, curvePoints, true, p2d, "blue");
        i += 0.01;
        requestAnimationFrame(draw);
      };
      draw();
    });
  }

  
  drawLines(points, t, curvePoints, isAnimation, p2d, color) {
    
    if (points.length < 2) {
      curvePoints.push({ ...points[0] });
      this.drawCurve(curvePoints, isAnimation, p2d);
      return;
    }
    if (isAnimation) {
      
      this.ctx.save();
      for (let i = 0; i < points.length; i++) {
        
        this.ctx.beginPath();
        this.ctx.strokeStyle = color ?? "red";
        this.ctx.lineWidth = 2;
        i > 0 && this.ctx.moveTo(points[i - 1].x, points[i - 1].y);
        this.ctx.lineTo(points[i].x, points[i].y);
        this.ctx.stroke();
        
        this.ctx.beginPath();
        this.ctx.strokeStyle = "black";
        this.ctx.lineWidth = 1;
        this.ctx.arc(points[i].x, points[i].y, 5, 0, 2 * Math.PI);
        this.ctx.stroke();
      }
      this.ctx.restore();
    }
    
    const newPoints = [];
    
    for (let i = 0; i < points.length - 1; i++) {
      newPoints.push(this.calcMotionPoint(points[i], points[i + 1], t));
    }
    
    this.drawLines(newPoints, t, curvePoints, isAnimation, p2d, null);
  }

  
  drawCurve(curvePoints, isAnimation, p2d) {
    
    const len = curvePoints.length;
    if (isAnimation) {
      const x = curvePoints[len - 1].x;
      const y = curvePoints[len - 1].y;
      
      p2d.lineTo(x, y);
      this.ctx.stroke(p2d);
      
      this.ctx.save();
      this.ctx.beginPath();
      this.ctx.strokeStyle = "blue";
      this.ctx.lineWidth = 1;
      this.ctx.arc(x, y, 5, 0, 2 * Math.PI);
      this.ctx.stroke();
      this.ctx.restore();
    } else {
      
      if (len < 3) return;
      this.ctx.beginPath();
      this.ctx.moveTo(curvePoints[len - 3].x, curvePoints[len - 3].y);
      this.ctx.lineTo(curvePoints[len - 2].x, curvePoints[len - 2].y);
      this.ctx.lineTo(curvePoints[len - 1].x, curvePoints[len - 1].y);
      this.ctx.stroke();
    }
  }

  
  calcMotionPoint(p1, p2, t) {
    
    return {
      x: (1 - t) * p1.x + t * p2.x,
      y: (1 - t) * p1.y + t * p2.y,
    };
  }
}