// Wave keyframe generator based on trigonometry functions.
@mixin keyframes($animation-name, $func, $type: "", $segments: "", $length: "", $amplitude: "", $frequency: "", $mirrored: "") {
  will-change: transform;
  transform-style: preserve-3d;
  backface-visibility: hidden;

  // Exterior by default.
  $element-width: 0%;
  $element-height: 0%;

  @if $type == "interior" {
    $element-width: 100%;
    $element-height: 50%;
  }

  @if $segments == "" {
    $segments: 1;
  }

  @if $length == "" {
    $length: 100cqw;
  }

  @if $amplitude == "" {
    $amplitude: 50cqh;
  }

  @if $frequency == "" {
    $frequency: 1;
  }
  
  --frequency: #{$frequency};
  
  @if $mirrored == "" {
    $mirrored: -1;
  }
  @else {
    $mirrored: 1;
  }
  
  // Take in account that the length and amplitude is reduced by the current element size.
  @keyframes #{$animation-name} {
    @for $i from 0 through $segments {
      $key-frame: ($i / $segments * 100) + '%';
      #{$key-frame} {
        transform: translate3d(calc((#{$length} - #{$element-width}) * #{$i} / #{$segments}), calc((#{$amplitude} - #{$element-height}) * #{$mirrored} * #{$func}(#{$i} * (360deg * #{$frequency} / #{$segments}))), 0);
      }
    }
  }
}

// Default styles.
* {
  box-sizing: border-box;
}

body {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 0;
  margin: 0;
  min-height: 100vh;
  min-height: 100svh;
  color: white;
  background-color: black;
}

.box {
  position: relative;
  // This is a "must have" requisite to make work the animation.
  container-type: size;
  width: 500px;
  height: 300px;
  margin-top: 1rem;
  background-color: #D3D3D3;
  margin-bottom: 100px;
}

.x-axis {
  position: absolute;
  top: 50%;
  left: 0;
  z-index: 2;
  width: 100%;
  height: 2px;
  background-color: red;
  transform: translate(0, -50%);
}

.y-axis {
  position: absolute;
  top: 0;
  left: 0;
  z-index: 2;
  width: 2px;
  height: 100%;
  background-color: red;
}

.marker {
  position: absolute;
  top: calc(50% - 10px);
  left: -10px;
  z-index: 3;
  display: block;
  width: 20px;
  height: 20px;
  border-radius: 50%;
  background-color: cyan;
  animation-name: sine;
  animation-duration: 5s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
  
  @include keyframes('sine', sin, 'exterior', 60, '', '', 3, '');
}

canvas {
  position: absolute;
  width: 100%;
  height: 100%;
  z-index: 1;
}

// Example.
.example {
  width: 100%;
  height: 300px;
  padding: 50px 0;
  margin-bottom: 100px;
  background-image: url('https://images.pexels.com/photos/1341279/pexels-photo-1341279.jpeg');
  background-size: cover;
  background-position: center center;
  background-repeat: no-repeat;
  overflow: hidden;
}

.animation-area {
  position: relative;
  // This is a "must have" requisite to make work the animation.
  container-type: size;
  width: 100%;
  height: 100%;
}

.star {
  position: absolute;
  top: calc(50% - 15px);
  left: 0;
  z-index: 3;
  display: block;
  width: 30px;
  height: 30px;
  animation-duration: 5s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
}

.star-1 {
  animation-name: star-1;
  @include keyframes('star-1', sin, 'interior', 60, '', '', 3, '');  
}

.star-2 {
  animation-name: star-2;
  @include keyframes('star-2', sin, 'interior', 60, '', '', 3, 'mirrored');
}

// Get the canvas element and its context
const canvas = document.getElementById('myCanvas');
const marker = document.getElementsByClassName('marker')[0];

// Check if canvas and marker exist.
if (canvas && marker) {
  const ctx = canvas.getContext('2d');

  // Get the CSS variable value of the previous sibling
  const computedStyles = getComputedStyle(marker);
  const cssVariableValue = parseFloat(computedStyles.getPropertyValue('--frequency'));

  // Set the canvas width and height
  canvas.width = canvas.offsetWidth;
  canvas.height = canvas.offsetHeight;

  // Calculate the frequency based on canvas size
  const frequency = (2 * Math.PI) / canvas.width * cssVariableValue;

  // Define the properties for drawing the sine function
  const amplitude = canvas.height / 2;  // Set the amplitude of the sine wave
  const phaseShift = 0;  // Set the phase shift of the sine wave
  const yOffset = canvas.height / 2;  // Set the y offset for centering the sine wave

  // Clear the canvas
  ctx.clearRect(0, 0, canvas.width, canvas.height);

  // Start drawing the sine wave
  ctx.beginPath();
  ctx.moveTo(0, yOffset);

  // Calculate and draw the points of the sine wave
  for (let x = 0; x < canvas.width; x++) {
    const y = (-1) * amplitude * Math.sin(frequency * x + phaseShift) + yOffset;
    ctx.lineTo(x, y);
  }

  // Set the line color and width
  ctx.strokeStyle = 'blue';
  ctx.lineWidth = 2;

  // Set the line style to dashed
  ctx.setLineDash([5, 3]); // The first number represents the length of the dash, and the second number represents the length of the gap

  // Draw the sine wave with the dashed line style
  ctx.stroke();
}