feat: refactor inventory and recipe services for improved error handling and code reuse; add systematic backend review plan

backend/src/meal-plan/meal-plan.service.ts

@@ -68,11 +68,8 @@ export class MealPlanService {
     return this.prisma.mealPlanEntry.delete({ where: { id: entry.id } });
   }
 
-  /** Samlad ingredienslista för ett datumintervall */
-  async shoppingList(userId: number, from: string, to: string) {
-    const entries = await this.findByRange(userId, from, to);
-
-    // Summera ingredienser per produkt+enhet (skalat per portionsantal)
+  /** Aggregerar ingredienser per produkt+enhet från matplansposter, skalat per portionsantal */
+  private aggregateIngredients(entries: Awaited<ReturnType<typeof this.findByRange>>) {
     const map = new Map<string, { productId: number; name: string; quantity: number; unit: string }>();
     for (const entry of entries) {
       const recipeServings = (entry.recipe as any).servings as number | null;
@@ -80,8 +77,8 @@ export class MealPlanService {
       const scale = recipeServings && entryServings ? entryServings / recipeServings : 1;
       for (const ing of entry.recipe.ingredients) {
         const key = `${ing.product.id}-${ing.unit}`;
-        const existing = map.get(key);
         const qty = Number(ing.quantity) * scale;
+        const existing = map.get(key);
         if (existing) {
           existing.quantity += qty;
         } else {
@@ -94,8 +91,13 @@ export class MealPlanService {
         }
       }
     }
+    return Array.from(map.values());
+  }
 
-    return Array.from(map.values()).sort((a, b) => a.name.localeCompare(b.name, 'sv'));
+  /** Samlad ingredienslista för ett datumintervall */
+  async shoppingList(userId: number, from: string, to: string) {
+    const entries = await this.findByRange(userId, from, to);
+    return this.aggregateIngredients(entries).sort((a, b) => a.name.localeCompare(b.name, 'sv'));
   }
 
   /** Jämför veckans ingrediensbehov mot inventariet */
@@ -109,32 +111,16 @@ export class MealPlanService {
     });
     const pantryProductIds = new Set(pantryItems.map((p) => p.productId));
 
-    // Aggregera ingredienser per produkt+enhet (skalat per portionsantal)
-    const map = new Map<string, { productId: number; name: string; required: number; unit: string }>();
-    for (const entry of entries) {
-      const recipeServings = (entry.recipe as any).servings as number | null;
-      const entryServings = (entry as any).servings as number | null;
-      const scale = recipeServings && entryServings ? entryServings / recipeServings : 1;
-      for (const ing of entry.recipe.ingredients) {
-        const key = `${ing.product.id}-${ing.unit}`;
-        const qty = Number(ing.quantity) * scale;
-        const existing = map.get(key);
-        if (existing) {
-          existing.required += qty;
-        } else {
-          map.set(key, {
-            productId: ing.product.id,
-            name: ing.product.canonicalName || ing.product.name,
-            required: qty,
-            unit: ing.unit,
-          });
-        }
-      }
-    }
+    const aggregated = this.aggregateIngredients(entries).map((item) => ({
+      productId: item.productId,
+      name: item.name,
+      required: item.quantity,
+      unit: item.unit,
+    }));
 
     // Kontrollera inventariet för varje ingrediens
     const result = await Promise.all(
-      Array.from(map.values()).map(async (item) => {
+      aggregated.map(async (item) => {
         // Pantry-varor anses alltid tillgängliga — visa inte i inköpslistan
         if (pantryProductIds.has(item.productId)) {
           return {