Dynamically create thumbnails

thumbnail_create.php

<?php
class ImgUtils {
  /**
   * Creates and returns image resource if type is supported.
   * Currently supported types (JPEG, GIF, PNG)
   * @param string $file URL to the file
   * @return bool|resource image resource if image type supported, otherwise false
   */
  private static function OpenImage( $file )
  {
    $size = getimagesize( $file ); // detect type and process accordingly
    switch ( $size[ "mime" ] ) {
      case "image/jpeg":
        $im = imagecreatefromjpeg( $file ); // jpeg file
        break;
      case "image/gif":
        $im = imagecreatefromgif( $file ); // gif file
        break;
      case "image/png":
        $im = imagecreatefrompng( $file ); // png file
        break;
      default:
        $im = false; // not supported type
        break;
    }
    return $im;
  }

  /**
   * Resizes image and returns URL to the resized image (thumbnail).
   * @param string $fileUrl   URL to the file
   * @param int    $newWidth  new width (smaller than original)
   * @param int    $newHeight new height (smaller than original)
   * @return bool|string URL to the resized image (thumbnail) if success, otherwise false
   */
  public static function ResizeImage( $fileUrl, $newWidth = 150, $newHeight = 150 )
  {
    $image = self::OpenImage( $fileUrl ); // get image resource
    if ( $image === false ) return false;
    $imageW = imagesx( $image );
    $imageH = imagesy( $image );

    // calculate new image dimensions (preserve aspect)
    if ( $newWidth && !$newHeight ) {
      $new_w = $newWidth;
      $new_h = $new_w * ( $imageH / $imageW );
    }
    elseif ( $newHeight && !$newWidth ) {
      $new_h = $newHeight;
      $new_w = $new_h * ( $imageW / $imageH );
    }
    else {
      $new_w = $newWidth ? $newWidth : 150;
      $new_h = $newHeight ? $newHeight : 150;
      if ( ( $imageW / $imageH ) > ( $new_w / $new_h ) ) {
        $new_h = $new_w * ( $imageH / $imageW );
      }
      else {
        $new_w = $new_h * ( $imageW / $imageH );
      }
    }

    $fileNewUrl = self::GetThumbnailPath( $fileUrl, $newWidth, $newHeight );

    $newImage = imagecreatetruecolor( $new_w, $new_h ); // create resource
    imagecopyresampled( $newImage, $image, 0, 0, 0, 0, $new_w, $new_h, $imageW, $imageH ); // copy
    imagejpeg( $newImage, $fileNewUrl ); // save
    return $fileNewUrl; // return URL to the thumbnail
  }

  /**
   * Generates thumbnail URL from original file URL and its dimensions.
   * @param string $fileUrl   URL to the file
   * @param int    $newWidth  width of the thumbnail
   * @param int    $newHeight height of the thumbnail
   * @return string URL to the thumbnail
   */
  public static function GetThumbnailPath( $fileUrl, $newWidth, $newHeight )
  {
    $pi = pathinfo( $fileUrl ); // get file URL parts
    // create new URL for thumbnail, for ex in DIR/FILENAME_150x150.EXT format
    $fileNewUrl = sprintf( "%s/%s_%dx%d.%s", $pi[ 'dirname' ], $pi[ 'filename' ], $newWidth, $newHeight, $pi[ 'extension' ] );
    return $fileNewUrl;
  }

  /**
   * Generates if thumbnail not found, or found but regenerate equal to true and returns URL to the thumbnail.
   * @param string $fileUrl    URL to the file
   * @param int    $width      width of the thumbnail
   * @param int    $height     height of the thumbnail
   * @param bool   $regenerate if true forces regenerate thumbnail, otherwise returns existing one
   * @return bool|string thumbnail URL if success, false otherwise
   */
  public static function GetThumbnail( $fileUrl, $width = 150, $height = 150, $regenerate = false )
  {
    $thumbPath = self::GetThumbnailPath( $fileUrl, $width, $height );
    if ( file_exists( $thumbPath ) && is_file( $thumbPath ) && !$regenerate ) {
      user_error( 'not generated' );
      return $thumbPath;
    }
    else {
      user_error( 'generated' );
      return self::ResizeImage( $fileUrl, $width, $height );
    }
  }
}

?>

<?php
$myImagUrl = '/home/user1/www/uploads/images/myimage.jpg';
$thumbnail = ImgUtils::GetThumbnail( $myImagUrl ); // return url to the 150x150 thumbnail, if not exists generates it
// $thumbnail = ImgUtils::GetThumbnail( $myImagUrl, 200, 200, true ); // return 200x200 thumbnail url forcing regenerate it
if ( $thumbnail ) {
  ?>
  <img src="<?= str_replace( $_SERVER[ 'DOCUMENT_ROOT' ], '', $thumbnail ) ?>" alt=""/>
<?
}
?>