<?php
  
  namespace Svg;
  
  class CssLength
  {
      /**
       * Array of valid css length units.
       * Should be pre-sorted by unit text length so no earlier length can be
       * contained within a latter (eg. 'in' within 'vmin').
       *
       * @var string[]
       */
      protected static $units = [
          'vmax',
          'vmin',
          'rem',
          'px',
          'pt',
          'cm',
          'mm',
          'in',
          'pc',
          'em',
          'ex',
          'ch',
          'vw',
          'vh',
          '%',
          'q',
      ];
  
      /**
       * A list of units that are inch-relative, and their unit division within an inch.
       *
       * @var array<string, float>
       */
      protected static $inchDivisions = [
          'in' => 1,
          'cm' => 2.54,
          'mm' => 25.4,
          'q' => 101.6,
          'pc' => 6,
          'pt' => 72,
      ];
  
      /**
       * The CSS length unit indicator.
       * Will be lower-case and one of the units listed in the '$units' array or empty.
       *
       * @var string
       */
      protected $unit = '';
  
      /**
       * The numeric value of the given length.
       *
       * @var float
       */
      protected $value = 0;
  
      /**
       * The original unparsed length provided.
       *
       * @var string
       */
      protected $unparsed;
  
      public function __construct(string $length)
      {
          $this->unparsed = $length;
          $this->parseLengthComponents($length);
      }
  
      /**
       * Parse out the unit and value components from the given string length.
       */
      protected function parseLengthComponents(string $length): void
      {
          $length = strtolower($length);
  
          foreach (self::$units as $unit) {
              $pos = strpos($length, $unit);
              if ($pos) {
                  $this->value = floatval(substr($length, 0, $pos));
                  $this->unit = $unit;
                  return;
              }
          }
  
          $this->unit = '';
          $this->value = floatval($length);
      }
  
      /**
       * Get the unit type of this css length.
       * Units are standardised to be lower-cased.
       *
       * @return string
       */
      public function getUnit(): string
      {
          return $this->unit;
      }
  
      /**
       * Get this CSS length in the equivalent pixel count size.
       *
       * @param float $referenceSize
       * @param float $dpi
       *
       * @return float
       */
      public function toPixels(float $referenceSize = 11.0, float $dpi = 96.0): float
      {
          // Standard relative units
          if (in_array($this->unit, ['em', 'rem', 'ex', 'ch'])) {
              return $this->value * $referenceSize;
          }
  
          // Percentage relative units
          if (in_array($this->unit, ['%', 'vw', 'vh', 'vmin', 'vmax'])) {
              return $this->value * ($referenceSize / 100);
          }
  
          // Inch relative units
          if (in_array($this->unit, array_keys(static::$inchDivisions))) {
              $inchValue = $this->value * $dpi;
              $division = static::$inchDivisions[$this->unit];
              return $inchValue / $division;
          }
  
          return $this->value;
      }
  }