Auto-deduct spice inventory when batch is created/updated/deleted

- Add size_id, units_produced, quantity_g to batches table
- quantity_g auto-calculated from units × packing size on save
- Batch model deducts spice quantities on create, reverses on delete,
  recalculates on update when relevant fields change
- Batch form shows live total weight preview
- Chargen table shows units + grams produced

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/Models/Batch.php

@@ -6,7 +6,10 @@ use Illuminate\Database\Eloquent\Model;
 
 class Batch extends Model
 {
-    protected $fillable = ['lot_number', 'product_id', 'recipe_id', 'produced_at', 'expires_at'];
+    protected $fillable = [
+        'lot_number', 'product_id', 'size_id', 'recipe_id',
+        'units_produced', 'quantity_g', 'produced_at', 'expires_at',
+    ];
 
     protected $casts = [
         'produced_at' => 'date',
@@ -18,6 +21,11 @@ class Batch extends Model
         return $this->belongsTo(Product::class);
     }
 
+    public function size()
+    {
+        return $this->belongsTo(ProductSize::class);
+    }
+
     public function recipe()
     {
         return $this->belongsTo(Recipe::class);
@@ -27,4 +35,61 @@ class Batch extends Model
     {
         return $this->hasMany(BatchOrigin::class);
     }
+
+    protected static function booted(): void
+    {
+        // Auto-calculate quantity_g before saving
+        static::saving(function (Batch $batch) {
+            if ($batch->units_produced && $batch->size_id) {
+                $gramsPerUnit = $batch->size?->packing?->size ?? 0;
+                $batch->quantity_g = $batch->units_produced * $gramsPerUnit;
+            }
+        });
+
+        static::created(function (Batch $batch) {
+            $batch->deductSpices();
+        });
+
+        static::updated(function (Batch $batch) {
+            if ($batch->wasChanged(['recipe_id', 'size_id', 'units_produced'])) {
+                $batch->restoreSpices(
+                    $batch->getOriginal('recipe_id'),
+                    $batch->getOriginal('quantity_g'),
+                );
+                $batch->deductSpices();
+            }
+        });
+
+        static::deleting(function (Batch $batch) {
+            $batch->restoreSpices($batch->recipe_id, $batch->quantity_g);
+        });
+    }
+
+    private function deductSpices(): void
+    {
+        if (! $this->quantity_g || ! $this->recipe_id) {
+            return;
+        }
+
+        $recipe = Recipe::with('spices')->find($this->recipe_id);
+
+        foreach ($recipe->spices as $spice) {
+            $grams = $this->quantity_g * $spice->pivot->amount_in_percent / 100;
+            $spice->decrement('quantity', $grams);
+        }
+    }
+
+    private function restoreSpices(int $recipeId, float $quantityG): void
+    {
+        if (! $quantityG || ! $recipeId) {
+            return;
+        }
+
+        $recipe = Recipe::with('spices')->find($recipeId);
+
+        foreach ($recipe->spices as $spice) {
+            $grams = $quantityG * $spice->pivot->amount_in_percent / 100;
+            $spice->increment('quantity', $grams);
+        }
+    }
 }