<?php
//
// SimpleImage
//
//  A PHP class that makes working with images as simple as possible.
//
//  Developed and maintained by Cory LaViska <https://github.com/claviska>.
//
//  Copyright A Beautiful Site, LLC.
//
//  Source: https://github.com/claviska/SimpleImage
//
//  Licensed under the MIT license <http://opensource.org/licenses/MIT>
//

namespace claviska;

/**
 * A PHP class that makes working with images as simple as possible.
 */
class SimpleImage {

  const
    ERR_FILE_NOT_FOUND = 1,
    ERR_FONT_FILE = 2,
    ERR_FREETYPE_NOT_ENABLED = 3,
    ERR_GD_NOT_ENABLED = 4,
    ERR_INVALID_COLOR = 5,
    ERR_INVALID_DATA_URI = 6,
    ERR_INVALID_IMAGE = 7,
    ERR_LIB_NOT_LOADED = 8,
    ERR_UNSUPPORTED_FORMAT = 9,
    ERR_WEBP_NOT_ENABLED = 10,
    ERR_WRITE = 11,
    ERR_INVALID_FLAG = 12;

  protected $flags;
  protected $image;
  protected $mimeType;
  protected $exif;

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Magic methods
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Creates a new SimpleImage object.
   *
   * @param string $image An image file or a data URI to load.
   * @param array $flags Optional override of default flags.
   * @throws \Exception Thrown if the GD library is not found; file|URI or image data is invalid.
   */
  public function __construct($image = '', $flags = []) {
    // Check for the required GD extension
    if(extension_loaded('gd')) {
      // Ignore JPEG warnings that cause imagecreatefromjpeg() to fail
      ini_set('gd.jpeg_ignore_warning', 1);
    } else {
      throw new \Exception('Required extension GD is not loaded.', self::ERR_GD_NOT_ENABLED);
    }

    // Associative array of flags.
    $this->flags = [
      "sslVerify" => true // Skip SSL peer validation
    ];

    // Override default flag values.
    foreach($flags as $flag => $value) {
      $this->setFlag($flag, $value);
    }

    // Load an image through the constructor
    if(preg_match('/^data:(.*?);/', $image)) {
      $this->fromDataUri($image);
    } elseif($image) {
      $this->fromFile($image);
    }
  }

  /**
   * Destroys the image resource.
   */
  public function __destruct() {
    //Check for a valid GDimage instance
    $type_check = (gettype($this->image) == "object" && get_class($this->image) == "GdImage");

    if($this->image !== null && is_resource($this->image) && $type_check) {
      imagedestroy($this->image);
    }
  }

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Helper functions
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Set flag value.
   *
   * @param string $flag Name of the flag to set.
   * @param boolean $value State of the flag.
   * @throws \Exception Thrown if flag does not exist (no default value).
   */
  public function setFlag($flag, $value) {
    // Throw if flag does not exist
    if(!in_array($flag, array_keys($this->flags))) {
      throw new \Exception('Invalid flag.', self::ERR_INVALID_FLAG);
    }

    // Set flag value by name
    $this->flags[$flag] = $value;
  }

  /**
   * Get flag value.
   *
   * @param string $flag Name of the flag to get.
   * @return boolean|null
   */
  public function getFlag($flag) {
    return in_array($flag, array_keys($this->flags)) ? $this->flags[$flag] : null;
  }

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Loaders
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Loads an image from a data URI.
   *
   * @param string $uri A data URI.
   * @throws \Exception Thrown if URI or image data is invalid.
   * @return \claviska\SimpleImage
   */
  public function fromDataUri($uri) {
    // Basic formatting check
    preg_match('/^data:(.*?);/', $uri, $matches);
    if(!count($matches)) {
      throw new \Exception('Invalid data URI.', self::ERR_INVALID_DATA_URI);
    }

    // Determine mime type
    $this->mimeType = $matches[1];
    if(!preg_match('/^image\/(gif|jpeg|png)$/', $this->mimeType)) {
      throw new \Exception(
        'Unsupported format: ' . $this->mimeType,
        self::ERR_UNSUPPORTED_FORMAT
      );
    }

    // Get image data
    $uri = base64_decode(preg_replace('/^data:(.*?);base64,/', '', $uri));
    $this->image = imagecreatefromstring($uri);
    if(!$this->image) {
      throw new \Exception("Invalid image data.", self::ERR_INVALID_IMAGE);
    }

    return $this;
  }

  /**
   * Loads an image from a file.
   *
   * @param string $file The image file to load.
   * @param boolean $sslVerify Set to false to skip SSL validation.
   * @throws \Exception Thrown if file or image data is invalid.
   * @return \claviska\SimpleImage
   */
  public function fromFile($file) {
    // Set fopen options.
    $sslVerify = $this->getFlag("sslVerify"); // Don't perform peer validation when true
    $opts = [
      "ssl" => [
        "verify_peer"      => $sslVerify,
        "verify_peer_name" => $sslVerify
      ]
    ];

    // Check if the file exists and is readable.
    $file = @file_get_contents($file, false, stream_context_create($opts));
    if($file === false) {
      throw new \Exception("File not found: $file", self::ERR_FILE_NOT_FOUND);
    }

    // Create image object from string
    $this->image = imagecreatefromstring($file);

    // Get image info
    $info = @getimagesizefromstring($file);
    if($info === false) {
      throw new \Exception("Invalid image file: $file", self::ERR_INVALID_IMAGE);
    }
    $this->mimeType = $info['mime'];

    if(!$this->image) {
      throw new \Exception("Unsupported format: " . $this->mimeType, self::ERR_UNSUPPORTED_FORMAT);
    }

    switch($this->mimeType) {
      case 'image/gif':
        // Copy the gif over to a true color image to preserve its transparency. This is a
        // workaround to prevent imagepalettetotruecolor() from borking transparency.
        $width = imagesx($this->image);
        $height = imagesx($this->image);

        $gif = imagecreatetruecolor((int) $width, (int) $height);
        $alpha = imagecolorallocatealpha($gif, 0, 0, 0, 127);
        imagecolortransparent($gif, $alpha);
        imagefill($gif, 0, 0, $alpha);

        imagecopy($this->image, $gif, 0, 0, 0, 0, $width, $height);
        imagedestroy($gif);
        break;
      case 'image/jpeg':
        // Load exif data from JPEG images
        if(function_exists('exif_read_data')) {
          $this->exif = @exif_read_data("data://image/jpeg;base64," . base64_encode($file));
        }
        break;
    }

    // Convert pallete images to true color images
    imagepalettetotruecolor($this->image);

    return $this;
  }

  /**
   * Creates a new image.
   *
   * @param integer $width The width of the image.
   * @param integer $height The height of the image.
   * @param string|array $color Optional fill color for the new image (default 'transparent').
   * @return \claviska\SimpleImage
   */
  public function fromNew($width, $height, $color = 'transparent') {
    $this->image = imagecreatetruecolor((int) $width, (int) $height);

    // Use PNG for dynamically created images because it's lossless and supports transparency
    $this->mimeType = 'image/png';

    // Fill the image with color
    $this->fill($color);

    return $this;
  }

  /**
   * Creates a new image from a string.
   *
   * @param string $string The raw image data as a string.
   * @example
   *    $string = file_get_contents('image.jpg');
   * @return \claviska\SimpleImage
   */
  public function fromString($string) {
    return $this->fromFile('data://;base64,' . base64_encode($string));
  }

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Savers
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Generates an image.
   *
   * @param string $mimeType The image format to output as a mime type (defaults to the original mime type).
   * @param integer $quality Image quality as a percentage (default 100).
   * @throws \Exception Thrown when WEBP support is not enabled or unsupported format.
   * @return array Returns an array containing the image data and mime type ['data' => '', 'mimeType' => ''].
   */
  protected function generate($mimeType = null, $quality = 100) {
    // Format defaults to the original mime type
    $mimeType = $mimeType ?: $this->mimeType;

    // Ensure quality is a valid integer
    if($quality === null) $quality = 100;
    $quality = self::keepWithin((int) $quality, 0, 100);

    // Capture output
    ob_start();

    // Generate the image
    switch($mimeType) {

      case 'image/gif':
        imagesavealpha($this->image, true);
        imagegif($this->image, null);
        break;
      case 'image/jpeg':
        imageinterlace($this->image, true);
        imagejpeg($this->image, null, $quality);
        break;
      case 'image/png':
        imagesavealpha($this->image, true);
        imagepng($this->image);
        break;
      case 'image/webp':
        // Not all versions of PHP will have webp support enabled
        if(!function_exists('imagewebp')) {
          throw new \Exception(
            'WEBP support is not enabled in your version of PHP.',
            self::ERR_WEBP_NOT_ENABLED
          );
        }
        imagesavealpha($this->image, true);
        imagewebp($this->image, null, $quality);
        break;
      case 'image/bmp':
      case 'image/x-ms-bmp':
      case 'image/x-windows-bmp':
        // Not all versions of PHP support bmp
        if(!function_exists('imagebmp')) {
          throw new \Exception(
            'BMP support is not available in your version of PHP.',
            self::ERR_UNSUPPORTED_FORMAT
          );
        }
        imageinterlace($this->image, true);
        imagebmp($this->image, null, $quality);
        break;
      default:
        throw new \Exception('Unsupported format: ' . $mimeType, self::ERR_UNSUPPORTED_FORMAT);
    }

    // Stop capturing
    $data = ob_get_contents();
    ob_end_clean();

    return [
      'data' => $data,
      'mimeType' => $mimeType
    ];
  }

  /**
   * Generates a data URI.
   *
   * @param string $mimeType The image format to output as a mime type (defaults to the original mime type).
   * @param integer $quality Image quality as a percentage (default 100).
   * @return string Returns a string containing a data URI.
   */
  public function toDataUri($mimeType = null, $quality = 100) {
    $image = $this->generate($mimeType, $quality);

    return 'data:' . $image['mimeType'] . ';base64,' . base64_encode($image['data']);
  }

  /**
   * Forces the image to be downloaded to the clients machine. Must be called before any output is sent to the screen.
   *
   * @param string $filename The filename (without path) to send to the client (e.g. 'image.jpeg').
   * @param string $mimeType The image format to output as a mime type (defaults to the original mime type).
   * @param integer $quality Image quality as a percentage (default 100).
   * @return \claviska\SimpleImage
   */
  public function toDownload($filename, $mimeType = null, $quality = 100) {
    $image = $this->generate($mimeType, $quality);

    // Set download headers
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Content-Description: File Transfer');
    header('Content-Length: ' . strlen($image['data']));
    header('Content-Transfer-Encoding: Binary');
    header('Content-Type: application/octet-stream');
    header("Content-Disposition: attachment; filename=\"$filename\"");

    echo $image['data'];

    return $this;
  }

  /**
   * Writes the image to a file.
   *
   * @param string $file The image format to output as a mime type (defaults to the original mime type).
   * @param string $mimeType Image quality as a percentage (default 100).
   * @param integer $quality Image quality as a percentage (default 100).
   * @throws \Exception Thrown if failed write to file.
   * @return \claviska\SimpleImage
   */
  public function toFile($file, $mimeType = null, $quality = 100) {
    $image = $this->generate($mimeType, $quality);

    // Save the image to file
    if(!file_put_contents($file, $image['data'])) {
      throw new \Exception("Failed to write image to file: $file", self::ERR_WRITE);
    }

    return $this;
  }

  /**
   * Outputs the image to the screen. Must be called before any output is sent to the screen.
   *
   * @param string $mimeType The image format to output as a mime type (defaults to the original mime type).
   * @param integer $quality Image quality as a percentage (default 100).
   * @return \claviska\SimpleImage
   */
  public function toScreen($mimeType = null, $quality = 100) {
    $image = $this->generate($mimeType, $quality);

    // Output the image to stdout
    header('Content-Type: ' . $image['mimeType']);
    echo $image['data'];

    return $this;
  }

  /**
   * Generates an image string.
   *
   * @param string $mimeType The image format to output as a mime type (defaults to the original mime type).
   * @param integer $quality Image quality as a percentage (default 100).
   * @return string
   */
  public function toString($mimeType = null, $quality = 100) {
    return $this->generate($mimeType, $quality)['data'];
  }

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Utilities
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Ensures a numeric value is always within the min and max range.
   *
   * @param integer|float $value A numeric value to test.
   * @param integer|float $min The minimum allowed value.
   * @param integer|float $max The maximum allowed value.
   * @return integer|float
   */
  protected static function keepWithin($value, $min, $max) {
    if($value < $min) return $min;
    if($value > $max) return $max;
    return $value;
  }

  /**
   * Gets the image's current aspect ratio.
   *
   * @return float Returns the aspect ratio as a float.
   */
  public function getAspectRatio() {
    return $this->getWidth() / $this->getHeight();
  }

  /**
   * Gets the image's exif data.
   *
   * @return array|NULL Returns an array of exif data or null if no data is available.
   */
  public function getExif() {
    return isset($this->exif) ? $this->exif : null;
  }

  /**
   * Gets the image's current height.
   *
   * @return integer
   */
  public function getHeight() {
    return (int) imagesy($this->image);
  }

  /**
   * Gets the mime type of the loaded image.
   *
   * @return string
   */
  public function getMimeType() {
    return $this->mimeType;
  }

  /**
   * Gets the image's current orientation.
   *
   * @return string One of the values: 'landscape', 'portrait', or 'square'
   */
  public function getOrientation() {
    $width = $this->getWidth();
    $height = $this->getHeight();

    if($width > $height) return 'landscape';
    if($width < $height) return 'portrait';
    return 'square';
  }

  /**
   * Gets the resolution of the image
   *
   * @return mixed The resolution as an array of integers: [96, 96]
   */
  public function getResolution() {
    return imageresolution($this->image);
  }

  /**
   * Gets the image's current width.
   *
   * @return integer
   */
  public function getWidth() {
    return (int) imagesx($this->image);
  }

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Manipulation
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Same as PHP's imagecopymerge, but works with transparent images. Used internally for overlay.
   *
   * @param resource $dstIm Destination image link resource.
   * @param resource $srcIm Source image link resource.
   * @param integer $dstX x-coordinate of destination point.
   * @param integer $dstY y-coordinate of destination point.
   * @param integer $srcX x-coordinate of source point.
   * @param integer $srcY y-coordinate of source point.
   * @param integer $srcW Source width.
   * @param integer $srcH Source height.
   * @param integer $pct
   * @return boolean true if success.
   */
  protected static function imageCopyMergeAlpha($dstIm, $srcIm, $dstX, $dstY, $srcX, $srcY, $srcW, $srcH, $pct) {
    // Are we merging with transparency?
    if($pct < 100) {
      // Disable alpha blending and "colorize" the image using a transparent color
      imagealphablending($srcIm, false);
      imagefilter($srcIm, IMG_FILTER_COLORIZE, 0, 0, 0, round(127 * ((100 - $pct) / 100)));
    }

    imagecopy($dstIm, $srcIm, (int) $dstX, (int) $dstY, (int) $srcX, (int) $srcY, (int) $srcW, (int) $srcH);

    return true;
  }

  /**
   * Rotates an image so the orientation will be correct based on its exif data. It is safe to call
   * this method on images that don't have exif data (no changes will be made).
   *
   * @return \claviska\SimpleImage
   */
  public function autoOrient() {
    $exif = $this->getExif();

    if(!$exif || !isset($exif['Orientation'])){
      return $this;
    }

    switch($exif['Orientation']) {
    case 1: // Do nothing!
      break;
    case 2: // Flip horizontally
      $this->flip('x');
      break;
    case 3: // Rotate 180 degrees
      $this->rotate(180);
      break;
    case 4: // Flip vertically
      $this->flip('y');
      break;
    case 5: // Rotate 90 degrees clockwise and flip vertically
      $this->flip('y')->rotate(90);
      break;
    case 6: // Rotate 90 clockwise
      $this->rotate(90);
      break;
    case 7: // Rotate 90 clockwise and flip horizontally
      $this->flip('x')->rotate(90);
      break;
    case 8: // Rotate 90 counterclockwise
      $this->rotate(-90);
      break;
    }

    return $this;
  }

  /**
   * Proportionally resize the image to fit inside a specific width and height.
   *
   * @param integer $maxWidth The maximum width the image can be.
   * @param integer $maxHeight The maximum height the image can be.
   * @return \claviska\SimpleImage
   */
  public function bestFit($maxWidth, $maxHeight) {
    // If the image already fits, there's nothing to do
    if($this->getWidth() <= $maxWidth && $this->getHeight() <= $maxHeight) {
      return $this;
    }

    // Calculate max width or height based on orientation
    if($this->getOrientation() === 'portrait') {
      $height = $maxHeight;
      $width = $maxHeight * $this->getAspectRatio();
    } else {
      $width = $maxWidth;
      $height = $maxWidth / $this->getAspectRatio();
    }

    // Reduce to max width
    if($width > $maxWidth) {
      $width = $maxWidth;
      $height = $width / $this->getAspectRatio();
    }

    // Reduce to max height
    if($height > $maxHeight) {
      $height = $maxHeight;
      $width = $height * $this->getAspectRatio();
    }

    return $this->resize($width, $height);
  }

  /**
   * Crop the image.
   *
   * @param integer|float $x1 Top left x coordinate.
   * @param integer|float $y1 Top left y coordinate.
   * @param integer|float $x2 Bottom right x coordinate.
   * @param integer|float $y2 Bottom right x coordinate.
   * @return \claviska\SimpleImage
   */
  public function crop($x1, $y1, $x2, $y2) {
    // Keep crop within image dimensions
    $x1 = self::keepWithin($x1, 0, $this->getWidth());
    $x2 = self::keepWithin($x2, 0, $this->getWidth());
    $y1 = self::keepWithin($y1, 0, $this->getHeight());
    $y2 = self::keepWithin($y2, 0, $this->getHeight());

    // Avoid using native imagecrop() because of a bug with PNG transparency
    $dstW = abs($x2 - $x1);
    $dstH = abs($y2 - $y1);
    $newImage = imagecreatetruecolor((int) $dstW, (int) $dstH);
    $transparentColor = imagecolorallocatealpha($newImage, 0, 0, 0, 127);
    imagecolortransparent($newImage, $transparentColor);
    imagefill($newImage, 0, 0, $transparentColor);

    // Crop it
    imagecopyresampled(
      $newImage,
      $this->image,
      0, 0, min($x1, $x2), min($y1, $y2),
      (int) $dstW,
      (int) $dstH,
      (int) $dstW,
      (int) $dstH
    );

    // Swap out the new image
    $this->image = $newImage;

    return $this;
  }

  /**
   * Applies a duotone filter to the image.
   *
   * @param string|array $lightColor The lightest color in the duotone.
   * @param string|array $darkColor The darkest color in the duotone.
   * @return \claviska\SimpleImage
   */
  function duotone($lightColor, $darkColor) {
    $lightColor = self::normalizeColor($lightColor);
    $darkColor = self::normalizeColor($darkColor);

    // Calculate averages between light and dark colors
    $redAvg = $lightColor['red'] - $darkColor['red'];
    $greenAvg = $lightColor['green'] - $darkColor['green'];
    $blueAvg = $lightColor['blue'] - $darkColor['blue'];

    // Create a matrix of all possible duotone colors based on gray values
    $pixels = [];
    for($i = 0; $i <= 255; $i++) {
      $grayAvg = $i / 255;
      $pixels['red'][$i] = $darkColor['red'] + $grayAvg * $redAvg;
      $pixels['green'][$i] = $darkColor['green'] + $grayAvg * $greenAvg;
      $pixels['blue'][$i] = $darkColor['blue'] + $grayAvg * $blueAvg;
    }

    // Apply the filter pixel by pixel
    for($x = 0; $x < $this->getWidth(); $x++) {
      for($y = 0; $y < $this->getHeight(); $y++) {
        $rgb = $this->getColorAt($x, $y);
        $gray = min(255, round(0.299 * $rgb['red'] + 0.114 * $rgb['blue'] + 0.587 * $rgb['green']));
        $this->dot($x, $y, [
          'red' => $pixels['red'][$gray],
          'green' => $pixels['green'][$gray],
          'blue' => $pixels['blue'][$gray]
        ]);
      }
    }

    return $this;
  }

  /**
   * Proportionally resize the image to a specific height.
   *
   * @deprecated
   *    This method was deprecated in version 3.2.2 and will be removed in version 4.0.
   *    Please use `resize(null, $height)` instead.
   * @param integer $height
   * @return \claviska\SimpleImage
   */
  public function fitToHeight($height) {
    return $this->resize(null, $height);
  }

  /**
   * Proportionally resize the image to a specific width.
   *
   * @deprecated
   *    This method was deprecated in version 3.2.2 and will be removed in version 4.0.
   *    Please use `resize(null, $height)` instead.
   * @param integer $width The width to resize the image to.
   * @return \claviska\SimpleImage
   */
  public function fitToWidth($width) {
    return $this->resize($width, null);
  }

  /**
   * Flip the image horizontally or vertically.
   *
   * @param string $direction The direction to flip: x|y|both.
   * @return \claviska\SimpleImage
   */
  public function flip($direction) {
    switch($direction) {
    case 'x':
      imageflip($this->image, IMG_FLIP_HORIZONTAL);
      break;
    case 'y':
      imageflip($this->image, IMG_FLIP_VERTICAL);
      break;
    case 'both':
      imageflip($this->image, IMG_FLIP_BOTH);
      break;
    }

    return $this;
  }

  /**
   * Reduces the image to a maximum number of colors.
   *
   * @param integer $max The maximum number of colors to use.
   * @param boolean $dither Whether or not to use a dithering effect (default true).
   * @return \claviska\SimpleImage
   */
  public function maxColors($max, $dither = true) {
    imagetruecolortopalette($this->image, $dither, max(1, $max));

    return $this;
  }

  /**
   * Place an image on top of the current image.
   *
   * @param string|SimpleImage $overlay The image to overlay. This can be a filename, a data URI, or a SimpleImage object.
   * @param string $anchor The anchor point: 'center', 'top', 'bottom', 'left', 'right', 'top left', 'top right', 'bottom left', 'bottom right' (default 'center').
   * @param float $opacity The opacity level of the overlay 0-1 (default 1).
   * @param integer $xOffset Horizontal offset in pixels (default 0).
   * @param integer $yOffset Vertical offset in pixels (default 0).
   * @param bool $calculateOffsetFromEdge Calculate Offset referring to the edges of the image (default false).
   * @return \claviska\SimpleImage
   */
  public function overlay($overlay, $anchor = 'center', $opacity = 1, $xOffset = 0, $yOffset = 0, $calculateOffsetFromEdge = false) {
    // Load overlay image
    if(!($overlay instanceof SimpleImage)) $overlay = new SimpleImage($overlay);

    // Convert opacity
    $opacity = self::keepWithin($opacity, 0, 1) * 100;

    // Get available space
    $spaceX = $this->getWidth() - $overlay->getWidth();
    $spaceY = $this->getHeight() - $overlay->getHeight();

    // Set default center
    $x = ($spaceX / 2) + ($calculateOffsetFromEdge ? 0 : $xOffset);
    $y = ($spaceY / 2) + ($calculateOffsetFromEdge ? 0 : $yOffset);

    // Determine if top|bottom
    if (strpos($anchor, 'top') !== false) {
      $y = $yOffset;
    } elseif (strpos($anchor, 'bottom') !== false) {
      $y = $spaceY + ($calculateOffsetFromEdge ? -$yOffset : $yOffset);
    }

    // Determine if left|right
    if (strpos($anchor, 'left') !== false) {
      $x = $xOffset;
    } elseif (strpos($anchor, 'right') !== false) {
      $x = $spaceX + ($calculateOffsetFromEdge ? -$xOffset : $xOffset);
    }

    // Perform the overlay
    self::imageCopyMergeAlpha(
      $this->image,
      $overlay->image,
      $x, $y,
      0, 0,
      $overlay->getWidth(),
      $overlay->getHeight(),
      $opacity
    );

    return $this;
  }

  /**
   * Resize an image to the specified dimensions. If only one dimension is specified, the image will be resized proportionally.
   *
   * @param integer $width The new image width.
   * @param integer $height The new image height.
   * @return \claviska\SimpleImage
   */
  public function resize($width = null, $height = null) {
    // No dimentions specified
    if(!$width && !$height) {
      return $this;
    }

    // Resize to width
    if($width && !$height) {
      $height = $width / $this->getAspectRatio();
    }

    // Resize to height
    if(!$width && $height) {
      $width = $height * $this->getAspectRatio();
    }

    // If the dimensions are the same, there's no need to resize
    if($this->getWidth() === $width && $this->getHeight() === $height) {
      return $this;
    }

    // We can't use imagescale because it doesn't seem to preserve transparency properly. The
    // workaround is to create a new truecolor image, allocate a transparent color, and copy the
    // image over to it using imagecopyresampled.
    $newImage = imagecreatetruecolor((int) $width, (int) $height);
    $transparentColor = imagecolorallocatealpha($newImage, 0, 0, 0, 127);
    imagecolortransparent($newImage, $transparentColor);
    imagefill($newImage, 0, 0, $transparentColor);
    imagecopyresampled(
      $newImage,
      $this->image,
      0, 0, 0, 0,
      (int) $width,
      (int) $height,
      $this->getWidth(),
      $this->getHeight()
    );

    // Swap out the new image
    $this->image = $newImage;

    return $this;
  }

  /**
   * Sets an image's resolution, as per https://www.php.net/manual/en/function.imageresolution.php
   *
   * @param integer $res_x The horizontal resolution in DPI.
   * @param integer $res_y The vertical resolution in DPI
   * @return \claviska\SimpleImage
   */
  public function resolution($res_x, $res_y = null) {
    if(is_null($res_y)) {
      imageresolution($this->image, $res_x);
    } else {
      imageresolution($this->image, $res_x, $res_y);
    }

    return $this;
  }

  /**
   * Rotates the image.
   *
   * @param integer $angle The angle of rotation (-360 - 360).
   * @param string|array $backgroundColor The background color to use for the uncovered zone area after rotation (default 'transparent').
   * @return \claviska\SimpleImage
   */
  public function rotate($angle, $backgroundColor = 'transparent') {
    // Rotate the image on a canvas with the desired background color
    $backgroundColor = $this->allocateColor($backgroundColor);

    $this->image = imagerotate(
      $this->image,
      -(self::keepWithin($angle, -360, 360)),
      $backgroundColor
    );
    imagecolortransparent($this->image, imagecolorallocatealpha($this->image, 0, 0, 0, 127));

    return $this;
  }

  /**
   * Adds text to the image.
   *
   * @param string $text The desired text.
   * @param array $options
   *    An array of options.
   *       - fontFile* (string) - The TrueType (or compatible) font file to use.
   *       - size (integer) - The size of the font in pixels (default 12).
   *       - color (string|array) - The text color (default black).
   *       - anchor (string) - The anchor point: 'center', 'top', 'bottom', 'left', 'right', 'top left', 'top right', 'bottom left', 'bottom right' (default 'center').
   *       - xOffset (integer) - The horizontal offset in pixels (default 0).
   *       - yOffset (integer) - The vertical offset in pixels (default 0).
   *       - shadow (array) - Text shadow params.
   *          - x* (integer) - Horizontal offset in pixels.
   *          - y* (integer) - Vertical offset in pixels.
   *          - color* (string|array) - The text shadow color.
   *       - $calculateOffsetFromEdge (bool) - Calculate offsets from the edge of the image (default false).
   *       - $baselineAlign (bool) - Align the text font with the baseline. (default true).
   * @param array $boundary
   *    If passed, this variable will contain an array with coordinates that surround the text: [x1, y1, x2, y2, width, height].
   *    This can be used for calculating the text's position after it gets added to the image.
   * @throws \Exception
   * @return \claviska\SimpleImage
   */
  public function text($text, $options, &$boundary = null) {
    // Check for freetype support
    if(!function_exists('imagettftext')) {
      throw new \Exception(
        'Freetype support is not enabled in your version of PHP.',
        self::ERR_FREETYPE_NOT_ENABLED
      );
    }

    // Default options
    $options = array_merge([
      'fontFile' => null,
      'size' => 12,
      'color' => 'black',
      'anchor' => 'center',
      'xOffset' => 0,
      'yOffset' => 0,
      'shadow' => null,
      'calculateOffsetFromEdge' => false,
      'baselineAlign' => true
    ], $options);

    // Extract and normalize options
    $fontFile = $options['fontFile'];
    $size = ($options['size'] / 96) * 72; // Convert px to pt (72pt per inch, 96px per inch)
    $color = $this->allocateColor($options['color']);
    $anchor = $options['anchor'];
    $xOffset = $options['xOffset'];
    $yOffset = $options['yOffset'];
    $calculateOffsetFromEdge = $options['calculateOffsetFromEdge'];
    $baselineAlign = $options['baselineAlign'];
    $angle = 0;

    // Calculate the bounding box dimensions
    //
    // Since imagettfbox() returns a bounding box from the text's baseline, we can end up with
    // different heights for different strings of the same font size. For example, 'type' will often
    // be taller than 'text' because the former has a descending letter.
    //
    // To compensate for this, we created a temporary bounding box to measure the maximum height
    // that the font used can occupy. Based on this, we can adjust the text vertically so that it
    // appears inside the box with a good consistency.
    //
    // See: https://github.com/claviska/SimpleImage/issues/165
    //

    $boxText = imagettfbbox($size, $angle, $fontFile, $text);
    if(!$boxText) throw new \Exception("Unable to load font file: $fontFile", self::ERR_FONT_FILE);

    $boxWidth = abs($boxText[4] - $boxText[0]);
    $boxHeight = abs($boxText[5] - $boxText[1]);

    // Calculate Offset referring to the edges of the image.
    // Just invert the value for bottom|right;
    if ($calculateOffsetFromEdge == true) {
      if (strpos($anchor, 'bottom') !== false) $yOffset *= -1;
      if (strpos($anchor, 'right') !== false) $xOffset *= -1;
    }

    // Align the text font with the baseline.
    // I use $yOffset to inject the vertical alignment correction value.
    if ($baselineAlign == true) {
      // Create a temporary box to obtain the maximum height that this font can use.
      $boxFull = imagettfbbox($size, $angle, $fontFile, 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890');
      // Based on the maximum height, the text is aligned.
      if (strpos($anchor, 'bottom') !== false) {
        $yOffset -= $boxFull[1];
      } elseif (strpos($anchor, 'top') !== false) {
        $yOffset += abs($boxFull[5]) - $boxHeight;
      } else { // center
        $boxFullHeight = abs($boxFull[1]) + abs($boxFull[5]);
        $yOffset += ($boxFullHeight/2) - ($boxHeight/2) - abs($boxFull[1]);
      }

    } else {
      // Prevents fonts rendered outside the box boundary from being cut.
      // Example: 'Scriptina' font, some letters invade the space of the previous or subsequent letter.
      $yOffset -= $boxText[1];
    }

    // Prevents fonts rendered outside the box boundary from being cut.
    // Example: 'Scriptina' font, some letters invade the space of the previous or subsequent letter.
    $xOffset -= $boxText[0];

    // Determine position
    switch($anchor) {
      case 'top left':
        $x = $xOffset;
        $y = $yOffset + $boxHeight;
        break;
      case 'top right':
        $x = $this->getWidth() - $boxWidth + $xOffset;
        $y = $yOffset + $boxHeight;
        break;
      case 'top':
        $x = ($this->getWidth() / 2) - ($boxWidth / 2) + $xOffset;
        $y = $yOffset + $boxHeight;
        break;
      case 'bottom left':
        $x = $xOffset;
        $y = $this->getHeight() + $yOffset ;
        break;
      case 'bottom right':
        $x = $this->getWidth() - $boxWidth + $xOffset;
        $y = $this->getHeight() + $yOffset;
        break;
      case 'bottom':
        $x = ($this->getWidth() / 2) - ($boxWidth / 2) + $xOffset;
        $y = $this->getHeight() + $yOffset;
        break;
      case 'left':
        $x = $xOffset;
        $y = ($this->getHeight() / 2) - (($boxHeight / 2) - $boxHeight) + $yOffset;
        break;
      case 'right';
        $x = $this->getWidth() - $boxWidth + $xOffset;
        $y = ($this->getHeight() / 2) - (($boxHeight / 2) - $boxHeight) + $yOffset;
        break;
      default: // center
        $x = ($this->getWidth() / 2) - ($boxWidth / 2) + $xOffset;
        $y = ($this->getHeight() / 2) - (($boxHeight / 2) - $boxHeight) + $yOffset;
        break;
    }
    $x = (int) round($x);
    $y = (int) round($y);

    // Pass the boundary back by reference
    $boundary = [
      'x1' => $x + $boxText[0],
      'y1' => $y + $boxText[1] - $boxHeight, // $y is the baseline, not the top!
      'x2' => $x + $boxWidth + $boxText[0],
      'y2' => $y + $boxText[1],
      'width' => $boxWidth,
      'height' => $boxHeight
    ];

    // Text shadow
    if(is_array($options['shadow'])) {
      imagettftext(
        $this->image,
        $size,
        $angle,
        $x + $options['shadow']['x'],
        $y + $options['shadow']['y'],
        $this->allocateColor($options['shadow']['color']),
        $fontFile,
        $text
      );
    }

    // Draw the text
    imagettftext($this->image, $size, $angle, $x, $y, $color, $fontFile, $text);

    return $this;
  }

  /**
  * Adds text with a line break to the image.
  *
  * @param string $text The desired text.
  * @param array $options
  *  An array of options.
  *     - fontFile* (string) - The TrueType (or compatible) font file to use.
  *     - size (integer) - The size of the font in pixels (default 12).
  *     - color (string|array) - The text color (default black).
  *     - anchor (string) - The anchor point: 'center', 'top', 'bottom', 'left', 'right', 'top left', 'top right', 'bottom left', 'bottom right' (default 'center').
  *     - xOffset (integer) - The horizontal offset in pixels (default 0). Has no effect when anchor is 'center'.
  *     - yOffset (integer) - The vertical offset in pixels (default 0). Has no effect when anchor is 'center'.
  *     - shadow (array) - Text shadow params.
  *       - x* (integer) - Horizontal offset in pixels.
  *       - y* (integer) - Vertical offset in pixels.
  *       - color* (string|array) - The text shadow color.
  *     - $calculateOffsetFromEdge (bool) - Calculate offsets from the edge of the image (default false).
  *     - width (int) - Width of text box (default image width).
  *     - align (string) - How to align text: 'left', 'right', 'center', 'justify' (default 'left').
  *     - leading (float) - Increase/decrease spacing between lines of text (default 0).
  *     - opacity (float) - The opacity level of the text 0-1 (default 1).
  * @throws \Exception
  * @return \claviska\SimpleImage
  */
  public function textBox($text, $options) {
    // default width of image
    $maxWidth = $this->getWidth();
    // Default options
    $options = array_merge([
      'fontFile' => null,
      'size' => 12,
      'color' => 'black',
      'anchor' => 'center',
      'xOffset' => 0,
      'yOffset' => 0,
      'shadow' => null,
      'calculateOffsetFromEdge' => false,
      'width' => $maxWidth,
      'align' => 'left',
      'leading' => 0,
      'opacity' => 1
    ], $options);

    // Extract and normalize options
    $fontFile = $options['fontFile'];
    $fontSize = $fontSizePx = $options['size'];
    $fontSize = ($fontSize / 96) * 72; // Convert px to pt (72pt per inch, 96px per inch)
    $color = $options['color'];
    $anchor = $options['anchor'];
    $xOffset = $options['xOffset'];
    $yOffset = $options['yOffset'];
    $shadow = $options['shadow'];
    $calculateOffsetFromEdge = $options['calculateOffsetFromEdge'];
    $angle = 0;
    $maxWidth = $options['width'];
    $leading = $options['leading'];
    $leading = self::keepWithin($leading, ($fontSizePx * -1), $leading);
    $opacity = $options['opacity'];

    $align = $options['align'];
    if ($align == 'right') {
      $align = 'top right';
    } elseif ($align == 'center') {
      $align = 'top';
    } elseif ($align == 'justify') {
      $align = 'justify';
    } else {
      $align = 'top left';
    }

    list($lines, $isLastLine, $lastLineHeight) = self::textSeparateLines($text, $fontFile, $fontSize, $maxWidth);

    $maxHeight = (count($lines) - 1) * ($fontSizePx * 1.2 + $leading) + $lastLineHeight;

    $imageText = new SimpleImage();
    $imageText->fromNew($maxWidth, $maxHeight);

    // Align left/center/right
    if ($align <> 'justify') {
      foreach ($lines as $key => $line) {
        if( $align == 'top' ) $line = trim($line); // If is justify = 'center'
        $imageText->text($line, array(
          'fontFile' => $fontFile,
          'size' => $fontSizePx,
          'color' => $color,
          'anchor' => $align,
          'xOffset' => 0,
          'yOffset' => $key * ($fontSizePx * 1.2 + $leading),
          'shadow' => $shadow,
          'calculateOffsetFromEdge' => true
        ));
      }

    // Justify
    } else {
      foreach ($lines as $keyLine => $line) {
        // Check if there are spaces at the beginning of the sentence
        $spaces = 0;
        if (preg_match("/^\s+/", $line, $match)) {
          // Count spaces
          $spaces = strlen($match[0]);
          $line = ltrim($line);
        }

        // Separate words
        $words = preg_split("/\s+/", $line);
        // Include spaces with the first word
        $words[0] = str_repeat(' ', $spaces) . $words[0];

        // Calculates the space occupied by all words
        $wordsSize = array();
        foreach ($words as $key => $word) {
          $wordBox = imagettfbbox($fontSize, 0, $fontFile, $word);
          $wordWidth = abs($wordBox[4] - $wordBox[0]);
          $wordsSize[$key] = $wordWidth;
        }
        $wordsSizeTotal = array_sum($wordsSize);

        // Calculates the required space between words
        $countWords = count($words);
        $wordSpacing = 0;
        if ($countWords > 1) {
          $wordSpacing = ($maxWidth - $wordsSizeTotal) / ($countWords - 1);
          $wordSpacing = round($wordSpacing, 3);
        }

        $xOffsetJustify = 0;
        foreach ($words as $key => $word) {
          if ($isLastLine[$keyLine] == true) {
            if ($key < (count($words) - 1)) continue;
            $word = $line;
          }
          $imageText->text($word, array(
            'fontFile' => $fontFile,
            'size' => $fontSizePx,
            'color' => $color,
            'anchor' => 'top left',
            'xOffset' => $xOffsetJustify,
            'yOffset' => $keyLine * ($fontSizePx * 1.2 + $leading),
            'shadow' => $shadow,
            'calculateOffsetFromEdge' => true,
            )
          );
          // Calculate offset for next word
          $xOffsetJustify += $wordsSize[$key] + $wordSpacing;
        }
      }
    }

    $this->overlay($imageText, $anchor, $opacity, $xOffset, $yOffset, $calculateOffsetFromEdge);

    return $this;
  }

  /**
  * Receives a text and breaks into LINES.
  *
  * @param integer $text
  * @param string $fontFile
  * @param int $fontSize
  * @param int $maxWidth
  * @return array
  */
  private function textSeparateLines($text, $fontFile, $fontSize, $maxWidth) {
    $words = self::textSeparateWords($text);
    $countWords = count($words) - 1;
    $lines[0] = '';
    $lineKey = 0;
    $isLastLine = [];
    for ($i = 0; $i < $countWords; $i++) {
      $word = $words[$i];
      $isLastLine[$lineKey] = false;
      if ($word === PHP_EOL) {
        $isLastLine[$lineKey] = true;
        $lineKey++;
        $lines[$lineKey] = '';
        continue;
      }
      $lineBox = imagettfbbox($fontSize, 0, $fontFile, $lines[$lineKey] . $word);
      if (abs($lineBox[4] - $lineBox[0]) < $maxWidth) {
        $lines[$lineKey] .= $word . ' ';
      } else {
        $lineKey++;
        $lines[$lineKey] = $word . ' ';
      }
    }
    $isLastLine[$lineKey] = true;
    // Exclude space of right
    $lines = array_map('rtrim', $lines);
    // Calculate height of last line
    $boxFull = imagettfbbox($fontSize, 0, $fontFile, 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890');
    $lineBox = imagettfbbox($fontSize, 0, $fontFile, $lines[$lineKey]);
    // Height of last line = ascender of $boxFull + descender of $lineBox
    $lastLineHeight = abs($lineBox[1]) + abs($boxFull[5]);

    return array($lines, $isLastLine, $lastLineHeight);
  }

  /**
  * Receives a text and breaks into WORD / SPACE / NEW LINE.
  *
  * @param integer $text
  * @return array
  */
  private function textSeparateWords($text) {
    // Normalizes line break
    $text = preg_replace('/(\r\n|\n|\r)/', PHP_EOL, $text);
    $text = explode(PHP_EOL, $text);
    $newText = array();
    foreach ($text as $key => $line) {
      $newText = array_merge($newText, explode(' ', $line), [PHP_EOL]);
    }

    return $newText;
  }

  /**
   * Creates a thumbnail image. This function attempts to get the image as close to the provided
   * dimensions as possible, then crops the remaining overflow to force the desired size. Useful
   * for generating thumbnail images.
   *
   * @param integer $width The thumbnail width.
   * @param integer $height The thumbnail height.
   * @param string $anchor The anchor point: 'center', 'top', 'bottom', 'left', 'right', 'top left', 'top right', 'bottom left', 'bottom right' (default 'center').
   * @return \claviska\SimpleImage
   */
  public function thumbnail($width, $height, $anchor = 'center') {
    // Determine aspect ratios
    $currentRatio = $this->getHeight() / $this->getWidth();
    $targetRatio = $height / $width;

    // Fit to height/width
    if($targetRatio > $currentRatio) {
      $this->resize(null, $height);
    } else {
      $this->resize($width, null);
    }

    switch($anchor) {
    case 'top':
      $x1 = floor(($this->getWidth() / 2) - ($width / 2));
      $x2 = $width + $x1;
      $y1 = 0;
      $y2 = $height;
      break;
    case 'bottom':
      $x1 = floor(($this->getWidth() / 2) - ($width / 2));
      $x2 = $width + $x1;
      $y1 = $this->getHeight() - $height;
      $y2 = $this->getHeight();
      break;
    case 'left':
      $x1 = 0;
      $x2 = $width;
      $y1 = floor(($this->getHeight() / 2) - ($height / 2));
      $y2 = $height + $y1;
      break;
    case 'right':
      $x1 = $this->getWidth() - $width;
      $x2 = $this->getWidth();
      $y1 = floor(($this->getHeight() / 2) - ($height / 2));
      $y2 = $height + $y1;
      break;
    case 'top left':
      $x1 = 0;
      $x2 = $width;
      $y1 = 0;
      $y2 = $height;
      break;
    case 'top right':
      $x1 = $this->getWidth() - $width;
      $x2 = $this->getWidth();
      $y1 = 0;
      $y2 = $height;
      break;
    case 'bottom left':
      $x1 = 0;
      $x2 = $width;
      $y1 = $this->getHeight() - $height;
      $y2 = $this->getHeight();
      break;
    case 'bottom right':
      $x1 = $this->getWidth() - $width;
      $x2 = $this->getWidth();
      $y1 = $this->getHeight() - $height;
      $y2 = $this->getHeight();
      break;
    default:
      $x1 = floor(($this->getWidth() / 2) - ($width / 2));
      $x2 = $width + $x1;
      $y1 = floor(($this->getHeight() / 2) - ($height / 2));
      $y2 = $height + $y1;
      break;
    }

    // Return the cropped thumbnail image
    return $this->crop($x1, $y1, $x2, $y2);
  }

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Drawing
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Draws an arc.
   *
   * @param integer $x The x coordinate of the arc's center.
   * @param integer $y The y coordinate of the arc's center.
   * @param integer $width The width of the arc.
   * @param integer $height The height of the arc.
   * @param integer $start The start of the arc in degrees.
   * @param integer $end The end of the arc in degrees.
   * @param string|array $color The arc color.
   * @param integer|string $thickness Line thickness in pixels or 'filled' (default 1).
   * @return \claviska\SimpleImage
   */
  public function arc($x, $y, $width, $height, $start, $end, $color, $thickness = 1) {
    // Allocate the color
    $tempColor = $this->allocateColor($color);
    imagesetthickness($this->image, 1);

    // Draw an arc
    if($thickness === 'filled') {
      imagefilledarc($this->image, $x, $y, $width, $height, $start, $end, $tempColor, IMG_ARC_PIE);

    } else if ($thickness === 1) {
      imagearc($this->image, $x, $y, $width, $height, $start, $end, $tempColor);

    } else {
      // New temp image
      $tempImage = new SimpleImage();
      $tempImage->fromNew($this->getWidth(), $this->getHeight(), 'transparent');

      // Draw a large ellipse filled with $color (+$thickness pixels)
      $tempColor = $tempImage->allocateColor($color);
      imagefilledarc($tempImage->image, $x, $y, $width+$thickness, $height+$thickness, $start, $end, $tempColor, IMG_ARC_PIE);

      // Draw a smaller ellipse filled with red|blue (-$thickness pixels)
      $tempColor = (self::normalizeColor($color)['red'] == 255) ? 'blue' : 'red';
      $tempColor = $tempImage->allocateColor($tempColor);
      imagefilledarc($tempImage->image, $x, $y, $width-$thickness, $height-$thickness, $start, $end, $tempColor, IMG_ARC_PIE);

      // Replace the color of the smaller ellipse with 'transparent'
      $tempImage->excludeInsideColor($x, $y, $color);

      // Apply the temp image
      $this->overlay($tempImage);
    }

    return $this;
  }

  /**
   * Draws a border around the image.
   *
   * @param string|array $color The border color.
   * @param integer $thickness The thickness of the border (default 1).
   * @return \claviska\SimpleImage
   */
  public function border($color, $thickness = 1) {
    $x1 = -1;
    $y1 = 0;
    $x2 = $this->getWidth();
    $y2 = $this->getHeight()-1;

    $color = $this->allocateColor($color);
    imagesetthickness($this->image, $thickness*2);
    imagerectangle($this->image, $x1, $y1, $x2, $y2, $color);

    return $this;
  }

  /**
   * Draws a single pixel dot.
   *
   * @param integer $x The x coordinate of the dot.
   * @param integer $y The y coordinate of the dot.
   * @param string|array $color The dot color.
   * @return \claviska\SimpleImage
   */
  public function dot($x, $y, $color) {
    $color = $this->allocateColor($color);
    imagesetpixel($this->image, $x, $y, $color);

    return $this;
  }

  /**
   * Draws an ellipse.
   *
   * @param integer $x The x coordinate of the center.
   * @param integer $y The y coordinate of the center.
   * @param integer $width The ellipse width.
   * @param integer $height The ellipse height.
   * @param string|array $color The ellipse color.
   * @param integer|array $thickness Line thickness in pixels or 'filled' (default 1).
   * @return \claviska\SimpleImage
   */
  public function ellipse($x, $y, $width, $height, $color, $thickness = 1) {
    // Allocate the color
    $tempColor = $this->allocateColor($color);
    imagesetthickness($this->image, 1);

    // Draw an ellipse
    if($thickness === 'filled') {
      imagefilledellipse($this->image, $x, $y, $width, $height, $tempColor);

    } else if ($thickness === 1) {
      imageellipse($this->image, $x, $y, $width, $height, $tempColor);

    } else {
      // New temp image
      $tempImage = new SimpleImage();
      $tempImage->fromNew($this->getWidth(), $this->getHeight(), 'transparent');

      // Draw a large ellipse filled with $color (+$thickness pixels)
      $tempColor = $tempImage->allocateColor($color);
      imagefilledellipse($tempImage->image, $x, $y, $width+$thickness, $height+$thickness, $tempColor);

      // Draw a smaller ellipse filled with red|blue (-$thickness pixels)
      $tempColor = (self::normalizeColor($color)['red'] == 255) ? 'blue' : 'red';
      $tempColor = $tempImage->allocateColor($tempColor);
      imagefilledellipse($tempImage->image, $x, $y, $width-$thickness, $height-$thickness, $tempColor);

      // Replace the color of the smaller ellipse with 'transparent'
      $tempImage->excludeInsideColor($x, $y, $color);

      // Apply the temp image
      $this->overlay($tempImage);
    }

    return $this;
  }

  /**
   * Fills the image with a solid color.
   *
   * @param string|array $color The fill color.
   * @return \claviska\SimpleImage
   */
  public function fill($color) {
    // Draw a filled rectangle over the entire image
    $this->rectangle(0, 0, $this->getWidth(), $this->getHeight(), 'white', 'filled');

    // Now flood it with the appropriate color
    $color = $this->allocateColor($color);
    imagefill($this->image, 0, 0, $color);

    return $this;
  }

  /**
   * Draws a line.
   *
   * @param integer $x1 The x coordinate for the first point.
   * @param integer $y1 The y coordinate for the first point.
   * @param integer $x2 The x coordinate for the second point.
   * @param integer $y2 The y coordinate for the second point.
   * @param string|array $color The line color.
   * @param integer $thickness The line thickness (default 1).
   * @return \claviska\SimpleImage
   */
  public function line($x1, $y1, $x2, $y2, $color, $thickness = 1) {
    // Allocate the color
    $color = $this->allocateColor($color);

    // Draw a line
    imagesetthickness($this->image, $thickness);
    imageline($this->image, $x1, $y1, $x2, $y2, $color);

    return $this;
  }

  /**
   * Draws a polygon.
   *
   * @param array $vertices
   *    The polygon's vertices in an array of x/y arrays.
   *    Example:
   *        [
   *            ['x' => x1, 'y' => y1],
   *            ['x' => x2, 'y' => y2],
   *            ['x' => xN, 'y' => yN]
   *        ]
   * @param string|array $color The polygon color.
   * @param integer|array $thickness Line thickness in pixels or 'filled' (default 1).
   * @return \claviska\SimpleImage
   */
  public function polygon($vertices, $color, $thickness = 1) {
    // Allocate the color
    $color = $this->allocateColor($color);

    // Convert [['x' => x1, 'y' => x1], ['x' => x1, 'y' => y2], ...] to [x1, y1, x2, y2, ...]
    $points = [];
    foreach($vertices as $vals) {
      $points[] = $vals['x'];
      $points[] = $vals['y'];
    }

    // Draw a polygon
    if($thickness === 'filled') {
      imagesetthickness($this->image, 1);
      imagefilledpolygon($this->image, $points, count($vertices), $color);
    } else {
      imagesetthickness($this->image, $thickness);
      imagepolygon($this->image, $points, count($vertices), $color);
    }

    return $this;
  }

  /**
   * Draws a rectangle.
   *
   * @param integer $x1 The upper left x coordinate.
   * @param integer $y1 The upper left y coordinate.
   * @param integer $x2 The bottom right x coordinate.
   * @param integer $y2 The bottom right y coordinate.
   * @param string|array $color The rectangle color.
   * @param integer|array $thickness Line thickness in pixels or 'filled' (default 1).
   * @return \claviska\SimpleImage
   */
  public function rectangle($x1, $y1, $x2, $y2, $color, $thickness = 1) {
    // Allocate the color
    $color = $this->allocateColor($color);

    // Draw a rectangle
    if($thickness === 'filled') {
      imagesetthickness($this->image, 1);
      imagefilledrectangle($this->image, $x1, $y1, $x2, $y2, $color);
    } else {
      imagesetthickness($this->image, $thickness);
      imagerectangle($this->image, $x1, $y1, $x2, $y2, $color);
    }

    return $this;
  }

  /**
   * Draws a rounded rectangle.
   *
   * @param integer $x1 The upper left x coordinate.
   * @param integer $y1 The upper left y coordinate.
   * @param integer $x2 The bottom right x coordinate.
   * @param integer $y2 The bottom right y coordinate.
   * @param integer $radius The border radius in pixels.
   * @param string|array $color The rectangle color.
   * @param integer|array $thickness Line thickness in pixels or 'filled' (default 1).
   * @return \claviska\SimpleImage
   */
  public function roundedRectangle($x1, $y1, $x2, $y2, $radius, $color, $thickness = 1) {
    if($thickness === 'filled') {
      // Draw the filled rectangle without edges
      $this->rectangle($x1 + $radius + 1, $y1, $x2 - $radius - 1, $y2, $color, 'filled');
      $this->rectangle($x1, $y1 + $radius + 1, $x1 + $radius, $y2 - $radius - 1, $color, 'filled');
      $this->rectangle($x2 - $radius, $y1 + $radius + 1, $x2, $y2 - $radius - 1, $color, 'filled');

      // Fill in the edges with arcs
      $this->arc($x1 + $radius, $y1 + $radius, $radius * 2, $radius * 2, 180, 270, $color, 'filled');
      $this->arc($x2 - $radius, $y1 + $radius, $radius * 2, $radius * 2, 270, 360, $color, 'filled');
      $this->arc($x1 + $radius, $y2 - $radius, $radius * 2, $radius * 2, 90, 180, $color, 'filled');
      $this->arc($x2 - $radius, $y2 - $radius, $radius * 2, $radius * 2, 360, 90, $color, 'filled');
    } else {
      $offset = $thickness / 2;
      $x1 -= $offset;
      $x2 += $offset;
      $y1 -= $offset;
      $y2 += $offset;
      $radius = self::keepWithin($radius, 0, min(($x2 - $x1) / 2, ($y2 - $y1) / 2 ) - 1);
      $radius = floor($radius);
      $thickness = self::keepWithin($thickness, 1, min(($x2 - $x1) / 2, ($y2 - $y1) / 2));

      // New temp image
      $tempImage = new SimpleImage();
      $tempImage->fromNew($this->getWidth(), $this->getHeight(), 'transparent');

      // Draw a large rectangle filled with $color
      $tempImage->roundedRectangle($x1, $y1, $x2, $y2, $radius, $color,'filled');

      // Draw a smaller rectangle filled with red|blue (-$thickness pixels on each side)
      $tempColor = (self::normalizeColor($color)['red'] == 255) ? 'blue' : 'red';
      $radius = $radius - $thickness;
      $radius = self::keepWithin($radius, 0, $radius);
      $tempImage->roundedRectangle(
        $x1 + $thickness,
        $y1 + $thickness,
        $x2 - $thickness,
        $y2 - $thickness,
        $radius,
        $tempColor,
        'filled'
      );

      // Replace the color of the smaller rectangle with 'transparent'
      $tempImage->excludeInsideColor(($x2 + $x1) / 2, ($y2 + $y1) / 2, $color);

      // Apply the temp image
      $this->overlay($tempImage);
    }

    return $this;
  }

  /**
   * Exclude inside color.
   * Used for roundedRectangle(), ellipse() and arc()
   *
   * @param number $x certer x of rectangle.
   * @param number $y certer y of rectangle.
   * @param string|array $borderColor The color of border.
   */
  private function excludeInsideColor($x, $y, $borderColor) {
    $borderColor = $this->allocateColor($borderColor);
    $transparent = $this->allocateColor('transparent');
    imagefilltoborder($this->image, $x, $y, $borderColor, $transparent);
    return $this;
  }

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Filters
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Applies the blur filter.
   *
   * @param string $type The blur algorithm to use: 'selective', 'gaussian' (default 'gaussian').
   * @param number $passes The number of time to apply the filter, enhancing the effect (default 1).
   * @return \claviska\SimpleImage
   */
  public function blur($type = 'selective', $passes = 1) {
    $filter = $type === 'gaussian' ? IMG_FILTER_GAUSSIAN_BLUR : IMG_FILTER_SELECTIVE_BLUR;

    for($i = 0; $i < $passes; $i++) {
      imagefilter($this->image, $filter);
    }

    return $this;
  }

  /**
   * Applies the brightness filter to brighten the image.
   *
   * @param integer $percentage Percentage to brighten the image (0 - 100).
   * @return \claviska\SimpleImage
   */
  public function brighten($percentage) {
    $percentage = self::keepWithin(255 * $percentage / 100, 0, 255);

    imagefilter($this->image, IMG_FILTER_BRIGHTNESS, $percentage);

    return $this;
  }

  /**
   * Applies the colorize filter.
   *
   * @param string|array $color The filter color.
   * @return \claviska\SimpleImage
   */
  public function colorize($color) {
    $color = self::normalizeColor($color);

    imagefilter(
      $this->image,
      IMG_FILTER_COLORIZE,
      $color['red'],
      $color['green'],
      $color['blue'],
      127 - ($color['alpha'] * 127)
    );

    return $this;
  }

  /**
   * Applies the contrast filter.
   *
   * @param integer $percentage Percentage to adjust (-100 - 100).
   * @return \claviska\SimpleImage
   */
  public function contrast($percentage) {
    imagefilter($this->image, IMG_FILTER_CONTRAST, self::keepWithin($percentage, -100, 100));

    return $this;
  }

  /**
   * Applies the brightness filter to darken the image.
   *
   * @param integer $percentage Percentage to darken the image (0 - 100).
   * @return \claviska\SimpleImage
   */
  public function darken($percentage) {
    $percentage = self::keepWithin(255 * $percentage / 100, 0, 255);

    imagefilter($this->image, IMG_FILTER_BRIGHTNESS, -$percentage);

    return $this;
  }

  /**
   * Applies the desaturate (grayscale) filter.
   *
   * @return \claviska\SimpleImage
   */
  public function desaturate() {
    imagefilter($this->image, IMG_FILTER_GRAYSCALE);

    return $this;
  }

  /**
   * Applies the edge detect filter.
   *
   * @return \claviska\SimpleImage
   */
  public function edgeDetect() {
    imagefilter($this->image, IMG_FILTER_EDGEDETECT);

    return $this;
  }

  /**
   * Applies the emboss filter.
   *
   * @return \claviska\SimpleImage
   */
  public function emboss() {
    imagefilter($this->image, IMG_FILTER_EMBOSS);

    return $this;
  }

  /**
   * Inverts the image's colors.
   *
   * @return \claviska\SimpleImage
   */
  public function invert() {
    imagefilter($this->image, IMG_FILTER_NEGATE);

    return $this;
  }

  /**
   * Changes the image's opacity level.
   *
   * @param float $opacity The desired opacity level (0 - 1).
   * @return \claviska\SimpleImage
   */
  public function opacity($opacity) {
    // Create a transparent image
    $newImage = new SimpleImage();
    $newImage->fromNew($this->getWidth(), $this->getHeight());

    // Copy the current image (with opacity) onto the transparent image
    self::imageCopyMergeAlpha(
      $newImage->image,
      $this->image,
      0, 0,
      0, 0,
      $this->getWidth(),
      $this->getHeight(),
      self::keepWithin($opacity, 0, 1) * 100
    );

    return $this;
  }

  /**
   * Applies the pixelate filter.
   *
   * @param integer $size The size of the blocks in pixels (default 10).
   * @return \claviska\SimpleImage
   */
  public function pixelate($size = 10) {
    imagefilter($this->image, IMG_FILTER_PIXELATE, $size, true);

    return $this;
  }

  /**
   * Simulates a sepia effect by desaturating the image and applying a sepia tone.
   *
   * @return \claviska\SimpleImage
   */
  public function sepia() {
    imagefilter($this->image, IMG_FILTER_GRAYSCALE);
    imagefilter($this->image, IMG_FILTER_COLORIZE, 70, 35, 0);

    return $this;
  }

  /**
   * Sharpens the image.
   *
   * @param integer $amount Sharpening amount (default 50).
   * @return \claviska\SimpleImage
   */
  public function sharpen($amount = 50) {
    // Normalize amount
    $amount = max(1, min(100, $amount)) / 100;

    $sharpen = [
      [-1, -1, -1],
      [-1,  8 / $amount, -1],
      [-1, -1, -1],
    ];
    $divisor = array_sum(array_map('array_sum', $sharpen));

    imageconvolution($this->image, $sharpen, $divisor, 0);

    return $this;
  }

  /**
   * Applies the mean remove filter to produce a sketch effect.
   *
   * @return \claviska\SimpleImage
   */
  public function sketch() {
    imagefilter($this->image, IMG_FILTER_MEAN_REMOVAL);

    return $this;
  }

  //////////////////////////////////////////////////////////////////////////////////////////////////
  // Color utilities
  //////////////////////////////////////////////////////////////////////////////////////////////////

  /**
   * Converts a "friendly color" into a color identifier for use with GD's image functions.
   *
   * @param string|array $color The color to allocate.
   * @return integer
   */
  protected function allocateColor($color) {
    $color = self::normalizeColor($color);

    // Was this color already allocated?
    $index = imagecolorexactalpha(
      $this->image,
      $color['red'],
      $color['green'],
      $color['blue'],
      (int) (127 - ($color['alpha'] * 127))
    );
    if($index > -1) {
      // Yes, return this color index
      return $index;
    }

    // Allocate a new color index
    return imagecolorallocatealpha(
      $this->image,
      $color['red'],
      $color['green'],
      $color['blue'],
      127 - ($color['alpha'] * 127)
    );
  }

  /**
   * Adjusts a color by increasing/decreasing red/green/blue/alpha values independently.
   *
   * @param string|array $color The color to adjust.
   * @param integer $red Red adjustment (-255 - 255).
   * @param integer $green Green adjustment (-255 - 255).
   * @param integer $blue Blue adjustment (-255 - 255).
   * @param integer $alpha Alpha adjustment (-1 - 1).
   * @return integer[] An RGBA color array.
   */
  public static function adjustColor($color, $red, $green, $blue, $alpha) {
    // Normalize to RGBA
    $color = self::normalizeColor($color);

    // Adjust each channel
    return self::normalizeColor([
      'red' => $color['red'] + $red,
      'green' => $color['green'] + $green,
      'blue' => $color['blue'] + $blue,
      'alpha' => $color['alpha'] + $alpha
    ]);
  }

  /**
   * Darkens a color.
   *
   * @param string|array $color The color to darken.
   * @param integer $amount Amount to darken (0 - 255).
   * @return integer[] An RGBA color array.
   */
  public static function darkenColor($color, $amount) {
    return self::adjustColor($color, -$amount, -$amount, -$amount, 0);
  }

  /**
   * Extracts colors from an image like a human would do.™ This method requires the third-party
   * library \League\ColorExtractor. If you're using Composer, it will be installed for you
   * automatically.
   *
   * @param integer $count The max number of colors to extract (default 5).
   * @param string|array $backgroundColor
   *    By default any pixel with alpha value greater than zero will
   *    be discarded. This is because transparent colors are not perceived as is. For example, fully
   *    transparent black would be seen white on a white background. So if you want to take
   *    transparency into account, you have to specify a default background color.
   * @throws \Exception Thrown if library \League\ColorExtractor is missing.
   * @return integer[] An array of RGBA colors arrays.
   */
  public function extractColors($count = 5, $backgroundColor = null) {
    // Check for required library
    if(!class_exists('\League\ColorExtractor\ColorExtractor')) {
      throw new \Exception(
        'Required library \League\ColorExtractor is missing.',
        self::ERR_LIB_NOT_LOADED
      );
    }

    // Convert background color to an integer value
    if($backgroundColor) {
      $backgroundColor = self::normalizeColor($backgroundColor);
      $backgroundColor = \League\ColorExtractor\Color::fromRgbToInt([
        'r' => $backgroundColor['red'],
        'g' => $backgroundColor['green'],
        'b' => $backgroundColor['blue']
      ]);
    }

    // Extract colors from the image
    $palette = \League\ColorExtractor\Palette::fromGD($this->image, $backgroundColor);
    $extractor = new \League\ColorExtractor\ColorExtractor($palette);
    $colors = $extractor->extract($count);

    // Convert colors to an RGBA color array
    foreach($colors as $key => $value) {
      $colors[$key] = self::normalizeColor(\League\ColorExtractor\Color::fromIntToHex($value));
    }

    return $colors;
  }

  /**
   * Gets the RGBA value of a single pixel.
   *
   * @param integer $x The horizontal position of the pixel.
   * @param integer $y The vertical position of the pixel.
   * @return integer[] An RGBA color array or false if the x/y position is off the canvas.
   */
  public function getColorAt($x, $y) {
    // Coordinates must be on the canvas
    if($x < 0 || $x > $this->getWidth() || $y < 0 || $y > $this->getHeight()) {
      return false;
    }

    // Get the color of this pixel and convert it to RGBA
    $color = imagecolorat($this->image, $x, $y);
    $rgba = imagecolorsforindex($this->image, $color);
    $rgba['alpha'] = 127 - ($color >> 24) & 0xFF;

    return $rgba;
  }

  /**
   * Lightens a color.
   *
   * @param string|array $color The color to lighten.
   * @param integer $amount Amount to lighten (0 - 255).
   * @return integer[] An RGBA color array.
   */
  public static function lightenColor($color, $amount) {
    return self::adjustColor($color, $amount, $amount, $amount, 0);
  }

  /**
   * Normalizes a hex or array color value to a well-formatted RGBA array.
   *
   * @param string|array $color
   *    A CSS color name, hex string, or an array [red, green, blue, alpha].
   *    You can pipe alpha transparency through hex strings and color names. For example:
   *        #fff|0.50 <-- 50% white
   *        red|0.25 <-- 25% red
   * @throws \Exception Thrown if color value is invalid.
   * @return array [red, green, blue, alpha].
   */
  public static function normalizeColor($color) {
    // 140 CSS color names and hex values
    $cssColors = [
      'aliceblue' => '#f0f8ff', 'antiquewhite' => '#faebd7', 'aqua' => '#00ffff',
      'aquamarine' => '#7fffd4', 'azure' => '#f0ffff', 'beige' => '#f5f5dc', 'bisque' => '#ffe4c4',
      'black' => '#000000', 'blanchedalmond' => '#ffebcd', 'blue' => '#0000ff',
      'blueviolet' => '#8a2be2', 'brown' => '#a52a2a', 'burlywood' => '#deb887',
      'cadetblue' => '#5f9ea0', 'chartreuse' => '#7fff00', 'chocolate' => '#d2691e',
      'coral' => '#ff7f50', 'cornflowerblue' => '#6495ed', 'cornsilk' => '#fff8dc',
      'crimson' => '#dc143c', 'cyan' => '#00ffff', 'darkblue' => '#00008b', 'darkcyan' => '#008b8b',
      'darkgoldenrod' => '#b8860b', 'darkgray' => '#a9a9a9', 'darkgrey' => '#a9a9a9',
      'darkgreen' => '#006400', 'darkkhaki' => '#bdb76b', 'darkmagenta' => '#8b008b',
      'darkolivegreen' => '#556b2f', 'darkorange' => '#ff8c00', 'darkorchid' => '#9932cc',
      'darkred' => '#8b0000', 'darksalmon' => '#e9967a', 'darkseagreen' => '#8fbc8f',
      'darkslateblue' => '#483d8b', 'darkslategray' => '#2f4f4f', 'darkslategrey' => '#2f4f4f',
      'darkturquoise' => '#00ced1', 'darkviolet' => '#9400d3', 'deeppink' => '#ff1493',
      'deepskyblue' => '#00bfff', 'dimgray' => '#696969', 'dimgrey' => '#696969',
      'dodgerblue' => '#1e90ff', 'firebrick' => '#b22222', 'floralwhite' => '#fffaf0',
      'forestgreen' => '#228b22', 'fuchsia' => '#ff00ff', 'gainsboro' => '#dcdcdc',
      'ghostwhite' => '#f8f8ff', 'gold' => '#ffd700', 'goldenrod' => '#daa520', 'gray' => '#808080',
      'grey' => '#808080', 'green' => '#008000', 'greenyellow' => '#adff2f',
      'honeydew' => '#f0fff0', 'hotpink' => '#ff69b4', 'indianred ' => '#cd5c5c',
      'indigo ' => '#4b0082', 'ivory' => '#fffff0', 'khaki' => '#f0e68c', 'lavender' => '#e6e6fa',
      'lavenderblush' => '#fff0f5', 'lawngreen' => '#7cfc00', 'lemonchiffon' => '#fffacd',
      'lightblue' => '#add8e6', 'lightcoral' => '#f08080', 'lightcyan' => '#e0ffff',
      'lightgoldenrodyellow' => '#fafad2', 'lightgray' => '#d3d3d3', 'lightgrey' => '#d3d3d3',
      'lightgreen' => '#90ee90', 'lightpink' => '#ffb6c1', 'lightsalmon' => '#ffa07a',
      'lightseagreen' => '#20b2aa', 'lightskyblue' => '#87cefa', 'lightslategray' => '#778899',
      'lightslategrey' => '#778899', 'lightsteelblue' => '#b0c4de', 'lightyellow' => '#ffffe0',
      'lime' => '#00ff00', 'limegreen' => '#32cd32', 'linen' => '#faf0e6', 'magenta' => '#ff00ff',
      'maroon' => '#800000', 'mediumaquamarine' => '#66cdaa', 'mediumblue' => '#0000cd',
      'mediumorchid' => '#ba55d3', 'mediumpurple' => '#9370db', 'mediumseagreen' => '#3cb371',
      'mediumslateblue' => '#7b68ee', 'mediumspringgreen' => '#00fa9a',
      'mediumturquoise' => '#48d1cc', 'mediumvioletred' => '#c71585', 'midnightblue' => '#191970',
      'mintcream' => '#f5fffa', 'mistyrose' => '#ffe4e1', 'moccasin' => '#ffe4b5',
      'navajowhite' => '#ffdead', 'navy' => '#000080', 'oldlace' => '#fdf5e6', 'olive' => '#808000',
      'olivedrab' => '#6b8e23', 'orange' => '#ffa500', 'orangered' => '#ff4500',
      'orchid' => '#da70d6', 'palegoldenrod' => '#eee8aa', 'palegreen' => '#98fb98',
      'paleturquoise' => '#afeeee', 'palevioletred' => '#db7093', 'papayawhip' => '#ffefd5',
      'peachpuff' => '#ffdab9', 'peru' => '#cd853f', 'pink' => '#ffc0cb', 'plum' => '#dda0dd',
      'powderblue' => '#b0e0e6', 'purple' => '#800080', 'rebeccapurple' => '#663399',
      'red' => '#ff0000', 'rosybrown' => '#bc8f8f', 'royalblue' => '#4169e1',
      'saddlebrown' => '#8b4513', 'salmon' => '#fa8072', 'sandybrown' => '#f4a460',
      'seagreen' => '#2e8b57', 'seashell' => '#fff5ee', 'sienna' => '#a0522d',
      'silver' => '#c0c0c0', 'skyblue' => '#87ceeb', 'slateblue' => '#6a5acd',
      'slategray' => '#708090', 'slategrey' => '#708090', 'snow' => '#fffafa',
      'springgreen' => '#00ff7f', 'steelblue' => '#4682b4', 'tan' => '#d2b48c', 'teal' => '#008080',
      'thistle' => '#d8bfd8', 'tomato' => '#ff6347', 'turquoise' => '#40e0d0',
      'violet' => '#ee82ee', 'wheat' => '#f5deb3', 'white' => '#ffffff', 'whitesmoke' => '#f5f5f5',
      'yellow' => '#ffff00', 'yellowgreen' => '#9acd32'
    ];

    // Parse alpha from '#fff|.5' and 'white|.5'
    if(is_string($color) && strstr($color, '|')) {
      $color = explode('|', $color);
      $alpha = (float) $color[1];
      $color = trim($color[0]);
    } else {
      $alpha = 1;
    }

    // Translate CSS color names to hex values
    if(is_string($color) && array_key_exists(strtolower($color), $cssColors)) {
      $color = $cssColors[strtolower($color)];
    }

    // Translate transparent keyword to a transparent color
    if($color === 'transparent') {
      $color = ['red' => 0, 'green' => 0, 'blue' => 0, 'alpha' => 0];
    }

    // Convert hex values to RGBA
    if(is_string($color)) {
      // Remove #
      $hex = preg_replace('/^#/', '', $color);

      // Support short and standard hex codes
      if(strlen($hex) === 3) {
        list($red, $green, $blue) = [
          $hex[0] . $hex[0],
          $hex[1] . $hex[1],
          $hex[2] . $hex[2]
        ];
      } elseif(strlen($hex) === 6) {
        list($red, $green, $blue) = [
          $hex[0] . $hex[1],
          $hex[2] . $hex[3],
          $hex[4] . $hex[5]
        ];
      } else {
        throw new \Exception("Invalid color value: $color", self::ERR_INVALID_COLOR);
      }

      // Turn color into an array
      $color = [
        'red' => hexdec($red),
        'green' => hexdec($green),
        'blue' => hexdec($blue),
        'alpha' => $alpha
      ];
    }

    // Enforce color value ranges
    if(is_array($color)) {
      // RGB default to 0
      $color['red'] = isset($color['red']) ? $color['red'] : 0;
      $color['green'] = isset($color['green']) ? $color['green'] : 0;
      $color['blue'] = isset($color['blue']) ? $color['blue'] : 0;

      // Alpha defaults to 1
      $color['alpha'] = isset($color['alpha']) ? $color['alpha'] : 1;

      return [
        'red' => (int) self::keepWithin((int) $color['red'], 0, 255),
        'green' => (int) self::keepWithin((int) $color['green'], 0, 255),
        'blue' => (int) self::keepWithin((int) $color['blue'], 0, 255),
        'alpha' => self::keepWithin($color['alpha'], 0, 1)
      ];
    }

    throw new \Exception("Invalid color value: $color", self::ERR_INVALID_COLOR);
  }

}
