feat: increase precision for average tft price #435 (#438)

Author: renauter

substrate-node/pallets/pallet-tft-price/src/lib.rs

@@ -400,6 +400,9 @@ impl<T: Config> Pallet<T> {
     fn calc_avg() -> u32 {
         let queue = Self::queue_transient();
         let items = queue.get_all_values();
-        items.iter().fold(0_u32, |a, b| a.saturating_add(*b)) / items.len() as u32
+        let sum = items.iter().fold(0_u32, |a, b| a.saturating_add(*b));
+        (U32F32::from_num(sum) / U32F32::from_num(items.len()))
+            .round()
+            .to_num::<u32>()
     }
 }

substrate-node/pallets/pallet-tft-price/src/tests.rs

@@ -28,6 +28,28 @@ fn test_set_allowed_origin_by_wrong_origin_fails() {
     })
 }
 
+#[test]
+fn test_calc_avg_rounding_works() {
+    let mut t = ExternalityBuilder::build();
+    t.execute_with(|| {
+        let mut queue = TFTPriceModule::queue_transient();
+        queue.push(499); // avg = 499.0
+        assert_eq!(TFTPriceModule::calc_avg(), 499);
+        queue.push(500); // avg = 499.5
+        assert_eq!(TFTPriceModule::calc_avg(), 500);
+        queue.push(500); // avg = 499.66
+        assert_eq!(TFTPriceModule::calc_avg(), 500);
+        queue.push(500); // avg = 499.75
+        assert_eq!(TFTPriceModule::calc_avg(), 500);
+        queue.push(499); // avg = 499.66
+        assert_eq!(TFTPriceModule::calc_avg(), 500);
+        queue.push(499); // avg = 499.5
+        assert_eq!(TFTPriceModule::calc_avg(), 500);
+        queue.push(499); // avg = 499.25
+        assert_eq!(TFTPriceModule::calc_avg(), 499);
+    })
+}
+
 #[test]
 fn test_set_prices_works() {
     let mut t = ExternalityBuilder::build();