Feat: convert() method to expose calculate() - allows for complex calcs

src/UnitConverter/Unit/AbstractUnit.php

@@ -67,14 +67,27 @@ protected function configure () : void
   /**
    * Calculate the amount of required base units to make up 1 unit.
    *
-   * @param mixed $value Unused. Supposed to help determine conversion if using calculate.
+   * @param float $value
+   * @param UnitInterface $to
    * @return null|float
    */
-  protected function calculate ($value) : ?float
+  protected function calculate (float $value, UnitInterface $to) : ?float
   {
     return null;
   }
 
+  /**
+   * Exposes access to the ::calculate() method.
+   *
+   * @param float $value
+   * @param UnitInterface $to
+   * @return null|float
+   */
+  public function convert (float $value, UnitInterface $to)
+  {
+    return $this->calculate($value, $to);
+  }
+
   public function setName (string $name) : UnitInterface
   {
     $this->name = $name;
@@ -125,8 +138,13 @@ public function setUnits (float $units) : UnitInterface
     return $this;
   }
 
-  public function getUnits ($value = null) : float
+  public function getUnits () : float
+  {
+    return $this->units;
+  }
+
+  public function getBaseUnits () : float
   {
-    return $this->calculate($value) ?? $this->units;
+    return $this->getBase()->getUnits();
   }
 }

src/UnitConverter/UnitConverter.php

@@ -92,6 +92,9 @@ protected function loadUnit(string $symbol) : UnitInterface
   /**
    * Calculate the conversion from one unit to another.
    *
+   * @FIXME Gross use of a check for a null calculate() method ... 😑 Gotta
+   * figure out a better way to use the calulate method.
+   *
    * @internal
    * @param float $value The initial value being converted.
    * @param UnitInterface $from The unit of measure being converted **from**.
@@ -100,6 +103,12 @@ protected function loadUnit(string $symbol) : UnitInterface
    */
   protected function calculate (float $value, UnitInterface $from, UnitInterface $to): float
   {
+    $selfConversion = $from->convert($value, $to);
+
+    if ($selfConversion)
+      return $selfConversion;
+
+    # If the unit does not implement the calculate() method, convert it manually.
     return ($value * $from->getUnits()) / $to->getUnits();
   }
 
@@ -125,6 +134,7 @@ public function from (string $unit)
   public function to (string $unit)
   {
     $this->to = $this->loadUnit($unit);
+
     return $this->calculate($this->convert, $this->from, $this->to);
   }
 }