Implement FDA guideline-based rounding

Rounding is left out of Food nutrients for now to prevent rounding up before
summing in certain places.

app/Models/IngredientAmount.php

@@ -103,7 +103,7 @@ final class IngredientAmount extends Model
     public function getNutrientsSummaryAttribute(): string {
         $summary = [];
         foreach (Nutrients::all() as $nutrient) {
-            $amount = round($this->{$nutrient['value']}(), 2);
+            $amount = Nutrients::round($this->{$nutrient['value']}(), $nutrient['value']);
             $summary[] = "{$nutrient['label']}: {$amount}{$nutrient['unit']}";
         }
         return implode(', ', $summary);

app/Models/Recipe.php

@@ -7,6 +7,7 @@ use App\Models\Traits\Ingredient;
 use App\Models\Traits\Journalable;
 use App\Models\Traits\Sluggable;
 use App\Models\Traits\Taggable;
+use App\Support\Nutrients;
 use ElasticScoutDriverPlus\QueryDsl;
 use Illuminate\Database\Eloquent\Factories\HasFactory;
 use Illuminate\Database\Eloquent\Model;
@@ -165,7 +166,7 @@ final class Recipe extends Model implements HasMedia
         if (empty($this->weight)) {
             return null;
         }
-        return round($this->weight / $this->servings, 2);
+        return round($this->weight / $this->servings);
     }
 
     /**
@@ -209,13 +210,6 @@ final class Recipe extends Model implements HasMedia
 
     /**
      * Add nutrient calculations handling to overloading.
-     *
-     * @param string $method
-     * @param array $parameters
-     *
-     * @return mixed
-     *
-     * @noinspection PhpMissingParamTypeInspection
      */
     public function __call($method, $parameters): mixed {
         if (in_array($method, $this->nutrientTotalMethods)) {
@@ -223,15 +217,7 @@ final class Recipe extends Model implements HasMedia
         }
         elseif (in_array($method, $this->nutrientPerServingMethods)) {
             $sum = $this->sumNutrient(substr($method, 0, -10)) / $this->servings;
-
+            return Nutrients::round($sum, substr($method, 0, -10));
-            // Per-serving calculations are rounded, though actual food label
-            // rounding standards are more complex.
-            if ($sum > 1) {
-                return round($sum);
-            }
-            else {
-                return round($sum, 2);
-            }
         }
         else {
             return parent::__call($method, $parameters);

app/Support/Nutrients.php

@@ -188,4 +188,24 @@ class Nutrients
             throw new \DomainException("Unsupported recipe unit: {$fromUnit}");
         }
     }
+
+    /**
+     * Round a nutrient amount according to FDA guidelines.
+     *
+     * Note: this stays mostly true to the guidelines except that carbohydrates
+     * and protein are meant to state "less than 1 gram" when the amount is less
+     * than 1 gram. Instead, this method treats anything less than 1 gram as
+     * zero.
+     *
+     * @url https://labelcalc.com/food-labeling/a-guide-to-using-fda-rounding-rules-for-your-food-label/
+     */
+    public static function round(float $amount, string $nutrient): float {
+        return match ($nutrient) {
+            'calories' => ($amount < 5 ? 0 : ($amount <= 50 ? round( $amount / 5 ) * 5 : round( $amount / 10 ) * 10)),
+            'carbohydrates', 'protein' => ($amount < 1 ? 0 : round( $amount)),
+            'cholesterol', 'fat'  => ($amount < 0.5 ? 0 : ($amount <= 5 ? round( $amount / 5, 1 ) * 5 : round($amount))),
+            'sodium' => ($amount < 5 ? 0 : ($amount <= 140 ? round( $amount / 5 ) * 5 : round( $amount / 10 ) * 10)),
+            default => throw new \UnexpectedValueException()
+        };
+    }
 }

resources/views/journal-entries/index.blade.php

@@ -104,7 +104,7 @@
                         </div>
                         <span class="text-sm text-gray-500">
                         @foreach(\App\Support\Nutrients::all()->sortBy('weight') as $nutrient)
-                                {{ round($entries->where('meal', $meal)->sum($nutrient['value']), 2) }}{{ $nutrient['unit'] }}
+                                {{ \App\Support\Nutrients::round($entries->where('meal', $meal)->sum($nutrient['value']), $nutrient['value']) }}{{ $nutrient['unit'] }}
                                 {{ $nutrient['value'] }}@if(!$loop->last), @endif
                             @endforeach
                     </span>
@@ -124,7 +124,7 @@
                                 <div>
                                     <span class="font-bold">nutrients:</span>
                                     @foreach(\App\Support\Nutrients::all()->sortBy('weight') as $nutrient)
-                                        {{ round($entry->{$nutrient['value']}, 2) }}{{ $nutrient['unit'] }}
+                                        {{ \App\Support\Nutrients::round($entry->{$nutrient['value']}, $nutrient['value']) }}{{ $nutrient['unit'] }}
                                         {{ $nutrient['value'] }}@if(!$loop->last), @endif
                                     @endforeach
                                 </div>