fix: NbpService cache & tests fixes

src/main/java/eu/ztsh/wymiana/service/NbpService.java

@@ -13,6 +13,8 @@ import java.time.DayOfWeek;
 import java.time.LocalDate;
 import java.time.format.DateTimeFormatter;
 import java.time.temporal.TemporalAdjusters;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
 
 /**
  * NBP exchange rates service
@@ -26,12 +28,30 @@ public class NbpService {
     private static final String URI_PATTERN = "/api/exchangerates/rates/c/{code}/{date}/";
     private final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
 
+    private final ConcurrentMap<String, RatesCache> cache = new ConcurrentHashMap<>(1);
+
     public double getSellRate(String currency) {
-        return fetchData(currency, dtf.format(getFetchDate())).getRates().get(0).getAsk();
+        return getCurrency(currency).sell();
     }
 
     public double getBuyRate(String currency) {
-        return fetchData(currency, dtf.format(getFetchDate())).getRates().get(0).getBid();
+        return getCurrency(currency).buy();
+    }
+
+    private synchronized RatesCache getCurrency(String currency) {
+        var today = getFetchDate();
+        var cacheObject = cache.get(currency);
+        if (cacheObject == null || cacheObject.date().isBefore(today)) {
+            var fresh = fetchData(currency, dtf.format(today));
+            var rate = fresh.getRates().get(0);
+            cacheObject = new RatesCache(
+                LocalDate.parse(rate.getEffectiveDate(), dtf),
+                rate.getBid(),
+                rate.getAsk()
+            );
+            cache.put(fresh.getCode(), cacheObject);
+        }
+        return cacheObject;
     }
 
     /**

src/test/java/eu/ztsh/wymiana/service/NbpServiceTest.java

@@ -2,7 +2,6 @@ package eu.ztsh.wymiana.service;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
-import com.github.tomakehurst.wiremock.client.WireMock;
 import eu.ztsh.wymiana.EntityCreator;
 import eu.ztsh.wymiana.WireMockExtension;
 import eu.ztsh.wymiana.exception.NoDataException;
@@ -81,20 +80,22 @@ class NbpServiceTest {
         WireMockExtension.response(url, 200, new ObjectMapper().writeValueAsString(EntityCreator.rates(date)));
         try {
             assertThat(nbpService.getSellRate(EntityCreator.Constants.USD_SYMBOL)).isEqualTo(EntityCreator.Constants.SELL_RATE);
-            assertThat(nbpService.getBuyRate(EntityCreator.Constants.USD_SYMBOL)).isEqualTo(EntityCreator.Constants.BUY_RATE);
         } finally {
-            WireMockExtension.verifyGet(2, url);
+            WireMockExtension.verifyGet(1, url);
         }
     }
 
     @DisplayName("Fetch rates from cache")
     @Test
-    void getWithCacheTest() {
+    void getWithCacheTest() throws JsonProcessingException {
         var date = dtf.format(updateClock(DayOfWeek.FRIDAY));
         var url = "/api/exchangerates/rates/c/usd/%s/".formatted(date);
+        WireMockExtension.response(url, 200, new ObjectMapper().writeValueAsString(EntityCreator.rates(date)));
+        // save to cache
         assertThat(nbpService.getSellRate(EntityCreator.Constants.USD_SYMBOL)).isEqualTo(EntityCreator.Constants.SELL_RATE);
+        // get from cache
         assertThat(nbpService.getBuyRate(EntityCreator.Constants.USD_SYMBOL)).isEqualTo(EntityCreator.Constants.BUY_RATE);
-        WireMockExtension.verifyGet(0, url);
+        WireMockExtension.verifyGet(1, url);
     }
 
     @DisplayName("Support 404: invalid currency or no data")