rfq: refactor mock price calculation

The variable name was incorrect in the first place, so we fix that to
properly represent how the mock price is currently interpreted.
And to allow for different ways of specifying a mock price, we move the
static calculation to the constructor.

Author: guggero

rfq/oracle.go

@@ -368,15 +368,18 @@ var _ PriceOracle = (*RpcPriceOracle)(nil)
 // MockPriceOracle is a mock implementation of the PriceOracle interface.
 // It returns the suggested rate as the exchange rate.
 type MockPriceOracle struct {
-	expiryDelay uint64
-	usdPerBTC   uint64
+	expiryDelay  uint64
+	mSatPerAsset lnwire.MilliSatoshi
 }
 
 // NewMockPriceOracle creates a new mock price oracle.
-func NewMockPriceOracle(expiryDelay, usdPerBTC uint64) *MockPriceOracle {
+func NewMockPriceOracle(expiryDelay, assetsPerBTC uint64) *MockPriceOracle {
+	mSatPerAsset := lnwire.NewMSatFromSatoshis(btcutil.SatoshiPerBitcoin) /
+		lnwire.MilliSatoshi(assetsPerBTC)
+
 	return &MockPriceOracle{
-		expiryDelay: expiryDelay,
-		usdPerBTC:   usdPerBTC,
+		expiryDelay:  expiryDelay,
+		mSatPerAsset: mSatPerAsset,
 	}
 }
 
@@ -388,11 +391,8 @@ func (m *MockPriceOracle) QueryAskPrice(_ context.Context,
 	// Calculate the rate expiryDelay lifetime.
 	expiry := uint64(time.Now().Unix()) + m.expiryDelay
 
-	mSatPerUsd := lnwire.NewMSatFromSatoshis(btcutil.SatoshiPerBitcoin) /
-		lnwire.MilliSatoshi(m.usdPerBTC)
-
 	return &OracleAskResponse{
-		AskPrice: &mSatPerUsd,
+		AskPrice: &m.mSatPerAsset,
 		Expiry:   expiry,
 	}, nil
 }
@@ -404,11 +404,8 @@ func (m *MockPriceOracle) QueryBidPrice(_ context.Context, _ *asset.ID,
 	// Calculate the rate expiryDelay lifetime.
 	expiry := uint64(time.Now().Unix()) + m.expiryDelay
 
-	mSatPerUsd := lnwire.NewMSatFromSatoshis(btcutil.SatoshiPerBitcoin) /
-		lnwire.MilliSatoshi(m.usdPerBTC)
-
 	return &OracleBidResponse{
-		BidPrice: &mSatPerUsd,
+		BidPrice: &m.mSatPerAsset,
 		Expiry:   expiry,
 	}, nil
 }