Refactor fee computation and validation functions

contracts/src/fee.rs

@@ -1,15 +1,26 @@
 use crate::errors::TrustFlowError;
 
-pub const DEFAULT_FEE_BPS: u32 = 50; // 0.5%
-pub const MAX_FEE_BPS: u32 = 1_000;  // 10%
+pub const DEFAULT_FEE_BPS: u32 = 50;
+pub const MAX_FEE_BPS: u32 = 1_000;
+pub const BASIS_POINTS: i128 = 10_000;
 
-pub fn compute_fee(amount: i128, fee_bps: u32) -> Result<(i128, i128), TrustFlowError> {
-    let fee = amount.checked_mul(fee_bps as i128).ok_or(TrustFlowError::ArithmeticOverflow)?
-        .checked_div(10_000).ok_or(TrustFlowError::ArithmeticOverflow)?;
-    let payout = amount.checked_sub(fee).ok_or(TrustFlowError::ArithmeticOverflow)?;
-    Ok((fee, payout))
+pub fn validate_fee_bps(fee_bps: u32) -> Result<(), TrustFlowError> {
+    if fee_bps > MAX_FEE_BPS {
+        Err(TrustFlowError::InvalidAmount)
+    } else {
+        Ok(())
+    }
 }
 
-pub fn validate_fee_bps(fee_bps: u32) -> Result<(), TrustFlowError> {
-    if fee_bps > MAX_FEE_BPS { Err(TrustFlowError::InvalidAmount) } else { Ok(()) }
+pub fn compute_fee(amount: i128, fee_bps: u32) -> Result<(i128, i128), TrustFlowError> {
+    let fee = amount
+        .checked_mul(fee_bps as i128)
+        .and_then(|v| v.checked_div(BASIS_POINTS))
+        .ok_or(TrustFlowError::ArithmeticOverflow)?;
+
+    let payout = amount
+        .checked_sub(fee)
+        .ok_or(TrustFlowError::ArithmeticOverflow)?;
+
+    Ok((fee, payout))
 }