fixed edge cases about balance, neg and zero

interpreter/interpreter.go

@@ -687,12 +687,16 @@ func (s *programState) receiveFrom(destination parser.Destination, amount *big.I
 			case *parser.DestinationTo:
 				var remainingAmount big.Int
 				remainingAmount.Sub(&amountToReceive, receivedTotal)
-				// receivedTotal += destination.receive(monetary-receivedTotal, ctx)
-				received, err := s.receiveFrom(destinationTarget.Destination, &remainingAmount)
-				if err != nil {
-					return err
+
+				if remainingAmount.Cmp(big.NewInt(0)) != 0 {
+					// receivedTotal += destination.receive(monetary-receivedTotal, ctx)
+					received, err := s.receiveFrom(destinationTarget.Destination, &remainingAmount)
+					if err != nil {
+						return err
+					}
+					receivedTotal.Add(receivedTotal, received)
 				}
-				receivedTotal.Add(receivedTotal, received)
+
 				return nil
 
 			default:
@@ -815,6 +819,13 @@ func balance(
 
 	// body
 	balance := s.getBalance(*account, *asset)
+	if balance.Cmp(big.NewInt(0)) == -1 {
+		return nil, NegativeBalanceError{
+			Account: *account,
+			Amount:  *balance,
+		}
+	}
+
 	var balanceCopy big.Int
 	balanceCopy.Set(balance)
 

interpreter/interpreter_error.go

@@ -64,6 +64,15 @@ func (e InvalidTypeErr) Error() string {
 	return fmt.Sprintf("This type does not exist: %s", e.Name)
 }
 
+type NegativeBalanceError struct {
+	Account string
+	Amount  big.Int
+}
+
+func (e NegativeBalanceError) Error() string {
+	return fmt.Sprintf("Cannot fetch negative balance from account @%s", e.Account)
+}
+
 type NegativeAmountErr struct{ Amount MonetaryInt }
 
 func (e NegativeAmountErr) Error() string {

interpreter/interpreter_test.go

@@ -1459,6 +1459,27 @@ func TestDestinationComplex(t *testing.T) {
 
 // TODO TestNeededBalances, TestSetTxMeta, TestSetAccountMeta
 
+func TestSendZero(t *testing.T) {
+	tc := NewTestCase()
+	tc.compile(t, `
+	send [COIN 0] (
+		source = @src
+		destination = @dest
+	)`)
+	tc.expected = CaseResult{
+		Postings: []Posting{
+			{
+				Asset:       "COIN",
+				Amount:      big.NewInt(0),
+				Source:      "src",
+				Destination: "dest",
+			},
+		},
+		Error: nil,
+	}
+	test(t, tc)
+}
+
 func TestBalance(t *testing.T) {
 	tc := NewTestCase()
 	tc.compile(t, `
@@ -1485,6 +1506,52 @@ func TestBalance(t *testing.T) {
 	test(t, tc)
 }
 
+func TestNegativeBalance(t *testing.T) {
+	tc := NewTestCase()
+	tc.compile(t, `
+	vars {
+		monetary $balance = balance(@a, EUR/2)
+	}
+
+	send $balance (
+		source = @world
+		destination = @dest
+	)`)
+	tc.setBalance("a", "EUR/2", -100)
+	tc.expected = CaseResult{
+		Error: machine.NegativeBalanceError{
+			Account: "a",
+			Amount:  *big.NewInt(-100),
+		},
+	}
+	test(t, tc)
+}
+
+func TestBalanceNotFound(t *testing.T) {
+	tc := NewTestCase()
+	tc.compile(t, `
+	vars {
+		monetary $balance = balance(@a, EUR/2)
+	}
+
+	send $balance (
+		source = @world
+		destination = @dest
+	)`)
+	tc.expected = CaseResult{
+		Postings: []Posting{
+			{
+				Asset:       "EUR/2",
+				Amount:      big.NewInt(0),
+				Source:      "world",
+				Destination: "dest",
+			},
+		},
+		Error: nil,
+	}
+	test(t, tc)
+}
+
 func TestInoderDestination(t *testing.T) {
 	tc := NewTestCase()
 	tc.compile(t, `send [COIN 100] (
@@ -1695,16 +1762,19 @@ func TestVariableBalance(t *testing.T) {
 		tc := NewTestCase()
 		script = `
 		vars {
-		  monetary $amount = balance(@world, USD/2)
+		  monetary $amount = balance(@src, USD/2)
 		}
 		send $amount (
 		  source = @A
 		  destination = @B
 		)`
 		tc.compile(t, script)
-		tc.setBalance("world", "USD/2", -40)
+		tc.setBalance("src", "USD/2", -40)
 		tc.expected = CaseResult{
-			Error: machine.NegativeAmountErr{Amount: machine.NewMonetaryInt(-40)},
+			Error: machine.NegativeBalanceError{
+				Account: "src",
+				Amount:  *big.NewInt(-40),
+			},
 		}
 		test(t, tc)
 	})

interpreter/reconciler.go

@@ -105,10 +105,6 @@ func Reconcile(asset string, senders []Sender, receivers []Receiver) ([]Posting,
 			postingAmount = *receiver.Monetary
 		}
 
-		if postingAmt := big.Int(postingAmount); postingAmt.BitLen() == 0 {
-			continue
-		}
-
 		var postingToMerge *Posting
 		if len(postings) != 0 {
 			posting := &postings[len(postings)-1]

interpreter/reconciler_test.go

@@ -41,6 +41,15 @@ func TestReconcileSingletonExactMatch(t *testing.T) {
 	})
 }
 
+func TestReconcileZero(t *testing.T) {
+	runReconcileTestCase(t, ReconcileTestCase{
+		Currency:  "COIN",
+		Senders:   []Sender{{"src", big.NewInt(0)}},
+		Receivers: []Receiver{{"dest", big.NewInt(0)}},
+		Expected:  []Posting{{"src", "dest", big.NewInt(0), "COIN"}},
+	})
+}
+
 func TestNoReceiversLeft(t *testing.T) {
 	runReconcileTestCase(t, ReconcileTestCase{
 		Senders: []Sender{{