Show suggested monthly savings for a piggybank

If a piggybank has both a target date and a target amount, show how much money needs to be added to the piggybank each month to achieve both targets.

Strings are currently hard-coded because I want to gauge the reaction to this :)

app/Models/PiggyBank.php

@@ -129,6 +129,17 @@ class PiggyBank extends Model
 
     }
 
+    public function getSuggestedMonthlyAmount()
+    {
+        if ($this->targetdate && $this->currentRelevantRep()->currentamount < $this->targetamount) {
+            $thisMonth = Carbon::now()->month;
+            $targetMonth = $this->targetdate->month;
+            $remainingAmount = $this->targetamount - $this->currentRelevantRep()->currentamount;
+            return $thisMonth < $targetMonth ? $remainingAmount / ($targetMonth - $thisMonth) : $remainingAmount ;
+        }
+        return 0;
+    }
+
     /**
      * Get all of the piggy bank's notes.
      */

app/Support/Twig/PiggyBank.php

@@ -39,6 +39,12 @@ class PiggyBank extends Twig_Extension
         }
         );
 
+        $functions[] = new Twig_SimpleFunction(
+            'suggestedMonthlyAmount', function (PB $piggyBank) {
+                return $piggyBank->getSuggestedMonthlyAmount();
+        }
+        );
+
         return $functions;
     }
 

resources/views/piggy-banks/show.twig

@@ -70,6 +70,14 @@
                                 {% endif %}
                             </td>
                         </tr>
+                        {% if piggyBank.targetdate %}
+                        <tr>
+                            <td>Suggested monthly amount to save</td>
+                            <td>
+                                {{ suggestedMonthlyAmount(piggyBank)|formatAmount }}
+                            </td>
+                        </tr>
+                        {% endif %}
                     </table>
                 </div>
             </div>