discounts

src/models/_entities/products.rs

@@ -16,6 +16,7 @@ pub struct Model {
     #[sea_orm(column_type = "Text", nullable)]
     pub description: Option<String>,
     pub price_cents: i64,
+    pub sale_price_cents: Option<i64>,
     pub currency: String,
     pub sku: Option<String>,
     pub stock: i32,

src/models/orders.rs

@@ -61,13 +61,15 @@ pub async fn place(ctx: &AppContext, items: &[(i32, i32)], details: Checkout) ->
             )));
         }
         currency = product.currency.clone();
-        subtotal += product.price_cents * i64::from(*qty);
+        // Snapshot the effective price (honouring any active discount).
+        let unit_price_cents = product.effective_price_cents();
+        subtotal += unit_price_cents * i64::from(*qty);
 
         let mut active = product.clone().into_active_model();
         active.stock = Set(product.stock - *qty);
         active.update(&txn).await?;
 
-        snapshots.push((product.id, product.name, product.price_cents, *qty));
+        snapshots.push((product.id, product.name, unit_price_cents, *qty));
     }
 
     let order = ActiveModel {

src/models/products.rs

@@ -19,7 +19,25 @@ impl ActiveModelBehavior for ActiveModel {
 }
 
 // implement your read-oriented logic here
-impl Model {}
+impl Model {
+    /// Whether a discount is currently active: a sale price is set and is
+    /// strictly below the regular price.
+    #[must_use]
+    pub fn on_sale(&self) -> bool {
+        matches!(self.sale_price_cents, Some(sale) if sale < self.price_cents)
+    }
+
+    /// The price actually charged: the sale price when [`Model::on_sale`],
+    /// otherwise the regular price.
+    #[must_use]
+    pub fn effective_price_cents(&self) -> i64 {
+        if self.on_sale() {
+            self.sale_price_cents.unwrap_or(self.price_cents)
+        } else {
+            self.price_cents
+        }
+    }
+}
 
 // implement your write-oriented logic here
 impl ActiveModel {}