fix(cardano-blockchain-types): txn index conversion

Signed-off-by: bkioshn <[email protected]>

Author: bkioshn

rust/cardano-blockchain-types/src/txn_index.rs

@@ -8,7 +8,7 @@ pub struct TxnIndex(u16);
 
 impl TxnIndex {
     /// Convert an `<T>` to transaction index (saturate if out of range).
-    pub fn from_saturating<
+    pub(crate) fn from_saturating<
         T: Copy
             + TryInto<u16>
             + std::ops::Sub<Output = T>
@@ -21,3 +21,80 @@ impl TxnIndex {
         Self(value)
     }
 }
+
+impl<
+        T: Copy
+            + TryInto<u16>
+            + std::ops::Sub<Output = T>
+            + std::cmp::PartialOrd<T>
+            + num_traits::identities::Zero,
+    > From<T> for TxnIndex
+{
+    fn from(value: T) -> Self {
+        TxnIndex::from_saturating(value)
+    }
+}
+
+impl From<TxnIndex> for i16 {
+    fn from(val: TxnIndex) -> Self {
+        i16::try_from(val.0).unwrap_or(i16::MAX)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // Test for `From<T>` conversion to `TxnIndex`
+    #[test]
+    fn test_from_u8_to_txn_index() {
+        let txn_index: TxnIndex = 100u8.into(); // u8 is a valid type for conversion
+        assert_eq!(txn_index.0, 100);
+    }
+
+    #[test]
+    fn test_from_u16_to_txn_index() {
+        let txn_index: TxnIndex = 500u16.into(); // u16 is valid and within range for `TxnIndex`
+        assert_eq!(txn_index.0, 500);
+    }
+
+    #[test]
+    fn test_from_i32_to_txn_index() {
+        let txn_index: TxnIndex = 1234i32.into(); // i32 can be converted into `TxnIndex`
+        assert_eq!(txn_index.0, 1234);
+    }
+
+    #[test]
+    fn test_from_u32_to_txn_index() {
+        let txn_index: TxnIndex = 500_000u32.into(); // u32 is larger but should be saturated to `u16::MAX`
+        assert_eq!(txn_index.0, u16::MAX);
+    }
+
+    #[test]
+    fn test_from_large_i32_to_txn_index() {
+        let txn_index: TxnIndex = 70000i32.into(); // i32 too large for u16, should saturate to `u16::MAX`
+        assert_eq!(txn_index.0, u16::MAX);
+    }
+
+    // Test for `From<TxnIndex>` conversion to `i16`
+    #[test]
+    fn test_txn_index_to_i16_within_range() {
+        let txn_index = TxnIndex(100);
+        let result: i16 = txn_index.into(); // Should successfully convert to i16
+        assert_eq!(result, 100);
+    }
+
+    #[test]
+    fn test_txn_index_to_i16_with_saturation() {
+        let txn_index = TxnIndex(u16::MAX); // u16::MAX = 65535, which is too large for i16
+        let result: i16 = txn_index.into(); // Should saturate to i16::MAX
+        assert_eq!(result, i16::MAX);
+    }
+
+    #[test]
+    fn test_txn_index_to_i16_with_zero() {
+        let txn_index = TxnIndex(0); // Should be able to convert to i16 without issue
+        let result: i16 = txn_index.into();
+        assert_eq!(result, 0);
+    }
+}