fix: surface the inventory error when the stock check fails

OrderService reported every failed stock check as insufficient stock, which hid the real reason, for example a non-positive quantity. It now forwards the inventory message and only reports insufficient stock when the check itself succeeded.

Author: ylcn91

service-oriented-architecture/README.md

@@ -203,7 +203,10 @@ public class OrderService implements Service {
     }
     var stock = bus.send(new ServiceRequest(INVENTORY_SERVICE, "checkStock",
         Map.of("sku", sku, "quantity", quantity), credential));
-    if (!stock.success() || !Boolean.TRUE.equals(stock.body())) {
+    if (!stock.success()) {
+      return ServiceResponse.error("Order rejected: " + stock.message());
+    }
+    if (!Boolean.TRUE.equals(stock.body())) {
       return ServiceResponse.error("Order rejected: insufficient stock for " + sku);
     }
     var reservation = bus.send(new ServiceRequest(INVENTORY_SERVICE, "reserve",

service-oriented-architecture/src/main/java/com/iluwatar/soa/OrderService.java

@@ -115,7 +115,10 @@ private ServiceResponse placeOrder(ServiceRequest request) {
                 "checkStock",
                 Map.of("sku", sku, "quantity", quantity),
                 credential));
-    if (!stock.success() || !Boolean.TRUE.equals(stock.body())) {
+    if (!stock.success()) {
+      return ServiceResponse.error("Order rejected: " + stock.message());
+    }
+    if (!Boolean.TRUE.equals(stock.body())) {
       return ServiceResponse.error("Order rejected: insufficient stock for " + sku);
     }
 

service-oriented-architecture/src/test/java/com/iluwatar/soa/OrderServiceTest.java

@@ -147,10 +147,19 @@ void shouldRejectOrderWhenStockCheckFails() {
     var response = placeOrder(stubBus, "C-1", "LAPTOP", 1, 899.0, CREDENTIAL);
 
     assertFalse(response.success());
-    assertEquals("Order rejected: insufficient stock for LAPTOP", response.message());
+    assertEquals("Order rejected: inventory unavailable", response.message());
     assertEquals(0, charges.get());
   }
 
+  @Test
+  void shouldRejectNonPositiveQuantityWithTheInventoryReason() {
+    var response = placeOrder("C-1", "LAPTOP", -5, 899.0, CREDENTIAL);
+
+    assertFalse(response.success());
+    assertEquals("Order rejected: Quantity must be positive: -5", response.message());
+    assertEquals(true, checkStock("LAPTOP", 2));
+  }
+
   @Test
   void shouldFailForUnknownOperation() {
     var response = bus.send(new ServiceRequest(OrderService.NAME, "cancelOrder", Map.of()));