Add summary section with product breakdown

- Show total volume, total amount, and average price per product
- Include grand total row
- Products sorted alphabetically

src/main.rs

@@ -1,5 +1,6 @@
 use askama::Template;
 use chrono::Utc;
+use std::collections::HashMap;
 use std::env;
 use std::fs;
 use std::path::Path;
@@ -12,6 +13,21 @@ fn fmt(v: f64) -> String {
     format!("{:.2}", v)
 }
 
+#[derive(Clone)]
+struct ProductSummary {
+    name: String,
+    volume: String,
+    amount: String,
+    avg_price: String,
+}
+
+#[derive(Clone)]
+struct Summary {
+    total_volume: String,
+    grand_total: String,
+    products: Vec<ProductSummary>,
+}
+
 #[derive(Clone)]
 struct CardData {
     card_number: String,
@@ -34,7 +50,7 @@ struct FormattedTransaction {
 struct PreparedCustomer {
     customer_number: String,
     cards: Vec<CardData>,
-    grand_total: String,
+    summary: Summary,
 }
 
 impl PreparedCustomer {
@@ -78,10 +94,48 @@ impl PreparedCustomer {
             .map(|c| c.total_amount.parse::<f64>().unwrap())
             .sum();
 
+        let mut product_totals: HashMap<String, (f64, f64)> = HashMap::new();
+        for card in &cards {
+            for tx in &card.transactions {
+                let volume: f64 = tx.volume.parse().unwrap();
+                let amount: f64 = tx.amount.parse().unwrap();
+                let entry = product_totals
+                    .entry(tx.quality_name.clone())
+                    .or_insert((0.0, 0.0));
+                entry.0 += volume;
+                entry.1 += amount;
+            }
+        }
+
+        let mut products: Vec<ProductSummary> = product_totals
+            .into_iter()
+            .map(|(name, (volume, amount))| {
+                let avg_price = if volume > 0.0 { amount / volume } else { 0.0 };
+                ProductSummary {
+                    name,
+                    volume: fmt(volume),
+                    amount: fmt(amount),
+                    avg_price: fmt(avg_price),
+                }
+            })
+            .collect();
+        products.sort_by(|a, b| a.name.cmp(&b.name));
+
+        let total_volume: f64 = products
+            .iter()
+            .map(|p| p.volume.parse::<f64>().unwrap())
+            .sum();
+
+        let summary = Summary {
+            total_volume: fmt(total_volume),
+            grand_total: fmt(grand_total),
+            products,
+        };
+
         PreparedCustomer {
             customer_number: customer.customer_number,
             cards,
-            grand_total: fmt(grand_total),
+            summary,
         }
     }
 }