refactor

README.md

@@ -2,11 +2,17 @@
 
 ### Introduction
 
-- Reactive CQRS application with matching engine as it core
-- Matching engine implemented using Max-Heap and Min-Heap
-- Supports backpressure and event streaming
+This project demonstrates reactive implementation of simple stock exchange platform.
+Originally assigment is given to Senior Software Engineers as a technical code interview in stock/crypto exchange companies.
+See original [system requirements](system_requirements.pdf)
 
-### Reasoning
+Takeaways of implementation:
+- Spring Boot application with matching engine as it core
+- Custom Reactive CQRS framework
+- Matching engine implemented using Max-Heap and Min-Heap
+- Application supports backpressure and event streaming
+
+### Implementation
 
 - **Matching engine**
     + Matching engine uses Max-Heap and Min-Heap
@@ -17,7 +23,6 @@
     + Sell tree - The collection of orders in the descending order, that is, lower sell prices have priority to be matched over higher.
     + Each state transition is the consequence of an event. Events are played sequentially and therefore engine is single-threaded. Thread synchronisation is handled outside of engine.
 
-
 - **Reactive**
     + Asynchronous, event driven, non-blocking programming perfectly fits for given problem. We want to subscribe to engine updates instead of blocking the threads.
     + Business logic can be broken down into a pipeline of steps where each of the steps can be executed asynchronously
@@ -46,16 +51,6 @@
 - [x] Integration tests
 - [x] Load test (stress test)
 
-**Coverage:**
-
-| Classes | Lines |
-|----|-----------|
-| 100%  |   96%         | 
-
-### Bonus
-- [x] Order cancellation
-- [ ] Reactive Book UI
-
 ### How to run
 
 Execute `mvn clean install` to build project and generate protobuf classes.

src/main/java/com/github/schananas/reactivestockexchange/cqrs/QueryRepository.java

@@ -17,10 +17,10 @@ public interface QueryRepository<T> {
     Mono<Void> updateProjection(Event e);
 
     /**
-     * Returns current order projection
+     * Returns materialized projection
      *
-     * @param orderId - order identifier
+     * @param projectionId - order identifier
      * @return - materialized projection
      */
-    Mono<T> getOrder(long orderId);
+    Mono<T> getProjection(long projectionId);
 }

src/main/java/com/github/schananas/reactivestockexchange/domain/BookAggregateRepository.java

@@ -35,7 +35,7 @@ public class BookAggregateRepository implements AggregateRepository<Book> {
         return Mono.fromCallable(() -> aggregates.computeIfAbsent(aggregateId, (k) -> {
             Book book = new Book(aggregateId);
             //subscribe query projection for book events
-            book.aggregateEvents().flatMap(bookQueryRepository::updateProjection).subscribe();
+            book.aggregateEvents().concatMap(bookQueryRepository::updateProjection).subscribe();
             return book;
         }));
     }

src/main/java/com/github/schananas/reactivestockexchange/domain/query/BookQueryRepository.java

@@ -30,7 +30,7 @@ public class BookQueryRepository implements QueryRepository<OrderEntry> {
      * @return - materialized projection
      */
     @Override
-    public Mono<OrderEntry> getOrder(long orderId) {
+    public Mono<OrderEntry> getProjection(long orderId) {
         return Mono.fromCallable(() -> projection.get(orderId));
     }
 

src/main/java/com/github/schananas/reactivestockexchange/web/MarketController.java

@@ -65,7 +65,7 @@ public class MarketController {
 
     /**
      * Not used - POC
-     * Intended to UI or client applications to mantain their own projection
+     * Intended to UI or client applications to maintain their own projection
      *
      * @param asset
      * @return streams all events from aggregate
@@ -84,7 +84,7 @@ public class MarketController {
      */
     @GetMapping("/orders/{orderId}")
     public Mono<OrderStatusResponse> getOrder(@PathVariable Long orderId) {
-        return bookQueryRepository.getOrder(orderId)
+        return bookQueryRepository.getProjection(orderId)
                                   .map(this::toOrderStatus);
     }
 
@@ -96,7 +96,7 @@ public class MarketController {
      */
     @PostMapping("/orders/{orderId}/cancel")
     public Mono<ResponseEntity<String>> cancelOrder(@PathVariable Long orderId) {
-        return bookQueryRepository.getOrder(orderId)
+        return bookQueryRepository.getProjection(orderId)
                                   .flatMap(MarketController::validateOrderAmount)
                                   .flatMap(this::sendCancelCommand)
                                   .switchIfEmpty(Mono.error(new IllegalStateException(
@@ -114,7 +114,7 @@ public class MarketController {
     }
 
     private Mono<? extends OrderEntry> getOrderProjection(OrderAcceptedEvent ev) {
-        return bookQueryRepository.getOrder(ev.orderId())
+        return bookQueryRepository.getProjection(ev.orderId())
                                   .repeatWhenEmpty(5, o -> o.delayElements(
                                           Duration.ofMillis(50)));
     }

src/test/java/com/github/schananas/reactivestockexchange/domain/BookQueryRepositoryTest.java

@@ -30,7 +30,7 @@ class BookQueryRepositoryTest {
                                                                               OrderType.SELL,
                                                                               BigDecimal.valueOf(10),
                                                                               BigDecimal.valueOf(100)))
-                                       .then(testSubject.getOrder(1L)))
+                                       .then(testSubject.getProjection(1L)))
                     .expectNextMatches(orderEntry -> orderEntry.orderId() == 1L
                             && orderEntry.entryTimestamp().equals(Instant.MIN)
                             && orderEntry.direction() == OrderType.SELL
@@ -51,7 +51,7 @@ class BookQueryRepositoryTest {
                                                                                       43251.00),
                                                                               BigDecimal.valueOf(
                                                                                       1.0)))
-                                       .then(testSubject.getOrder(0L)))
+                                       .then(testSubject.getProjection(0L)))
                     .expectNextMatches(orderEntry -> orderEntry.orderId() == 0L
                             && orderEntry.entryTimestamp().equals(Instant.MIN)
                             && orderEntry.direction() == OrderType.SELL
@@ -74,7 +74,7 @@ class BookQueryRepositoryTest {
                                                                               BigDecimal.valueOf(
                                                                                       0.25)
                                        ))
-                                       .then(testSubject.getOrder(1L)))
+                                       .then(testSubject.getProjection(1L)))
                     .expectNextMatches(orderEntry -> orderEntry.orderId() == 1L
                             && orderEntry.entryTimestamp().equals(Instant.MIN)
                             && orderEntry.direction() == OrderType.BUY
@@ -103,7 +103,7 @@ class BookQueryRepositoryTest {
                                                                                BigDecimal.valueOf(
                                                                                        0.65)
                                        ))
-                                       .then(testSubject.getOrder(0L)))
+                                       .then(testSubject.getProjection(0L)))
                     .expectNextMatches(orderEntry -> orderEntry.orderId() == 0L
                             && orderEntry.entryTimestamp().equals(Instant.MIN)
                             && orderEntry.direction() == OrderType.SELL
@@ -136,7 +136,7 @@ class BookQueryRepositoryTest {
                                                                                BigDecimal.valueOf(
                                                                                        0.0)
                                        ))
-                                       .then(testSubject.getOrder(0L)))
+                                       .then(testSubject.getProjection(0L)))
                     .expectNextMatches(orderEntry -> orderEntry.orderId() == 0L
                             && orderEntry.entryTimestamp().equals(Instant.MIN)
                             && orderEntry.direction() == OrderType.SELL