Add ingredient scaling

src/commands/groceries.rs

@@ -34,7 +34,9 @@ pub async fn with(
     };
 
     let ids = map_events_to_recipe_ids(api_client, calendar_name, &date_range).await?;
-    let ingredients = get_ingredients(api_client, ids).await?;
+
+    // TODO: make required_yield configurable!
+    let ingredients = get_ingredients(api_client, ids, 4.0).await?;
     let ingredients = merge_ingredients(ingredients);
     let md = prepare_grocery_list(&date_range, &ingredients)?;
     log::debug!("Saving the following grocery list:\n\n{}", &md);
@@ -68,6 +70,7 @@ where
 async fn get_ingredients<RecipeIds>(
     api_client: &ApiClient,
     recipe_ids: RecipeIds,
+    required_yield: f64,
 ) -> Result<Vec<(Ingredient, String)>>
 where
     RecipeIds: IntoIterator<Item = usize>,
@@ -88,9 +91,10 @@ where
         response.json::<Recipe>().await.map(|r| {
             log::info!("Retrieved ingredients for '{}'", r.name);
             let recipe_name = r.name.clone();
+            let scale = required_yield / r.recipe_yield as f64;
             r.ingredients
                 .into_iter()
-                .map(move |i| (i, recipe_name.clone()))
+                .map(move |i| (i * scale, recipe_name.clone()))
         })
     });
 

src/recipe.rs

@@ -283,6 +283,15 @@ impl core::fmt::Display for Ingredient {
     }
 }
 
+impl std::ops::Mul<f64> for Ingredient {
+    type Output = Ingredient;
+
+    fn mul(mut self, rhs: f64) -> Self::Output {
+        self.amount *= rhs;
+        self
+    }
+}
+
 impl core::fmt::Display for Unit {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let u: &dyn core::fmt::Display = match self {