diff --git a/pom.xml b/pom.xml
index bb6d9b8a..f30e7d03 100644
--- a/pom.xml
+++ b/pom.xml
@@ -63,6 +63,11 @@
                     </annotationProcessorPaths>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-surefire-plugin</artifactId>
+                <version>3.2.5</version>
+            </plugin>
         </plugins>
     </build>
 
diff --git a/src/main/java/hse/java/lectures/lesson7/dau/DauServiceImpl.java b/src/main/java/hse/java/lectures/lesson7/dau/DauServiceImpl.java
new file mode 100644
index 00000000..60e8d564
--- /dev/null
+++ b/src/main/java/hse/java/lectures/lesson7/dau/DauServiceImpl.java
@@ -0,0 +1,52 @@
+package hse.java.lectures.lesson7.dau;
+ 
+import java.time.LocalDate;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+ 
+public class DauServiceImpl implements DauService {
+ 
+    private Map<Integer, Set<Integer>> yesterday = new HashMap<>();
+    private Map<Integer, Set<Integer>> today = new HashMap<>();
+    private LocalDate currentDate = LocalDate.now();
+ 
+    @Override
+    public synchronized void postEvent(Event event) {
+        valiDate();
+        today.computeIfAbsent(event.authorId(), id -> new HashSet<>())
+             .add(event.userId());
+    }
+ 
+    @Override
+    public synchronized Map<Integer, Long> getDauStatistics(List<Integer> authorIds) {
+        valiDate();
+        Map<Integer, Long> result = new HashMap<>();
+        for (int authorId : authorIds) {
+            result.put(authorId, getAuthorDauStatistics(authorId));
+        }
+        return result;
+    }
+ 
+    @Override
+    public synchronized Long getAuthorDauStatistics(int authorId) {
+        valiDate();
+        Set<Integer> users = yesterday.get(authorId);
+        return users == null ? 0L : (long) users.size();
+    }
+    void nextDay() {
+        yesterday = today;
+        today = new HashMap<>();
+    }
+ 
+    private void valiDate() {
+        LocalDate now = LocalDate.now();
+        if (now.isAfter(currentDate)) {
+            yesterday = today;
+            today = new HashMap<>();
+            currentDate = now;
+        }
+    }
+}
diff --git a/src/test/java/hse/java/lectures/lesson7/dau/DauServiceTest.java b/src/test/java/hse/java/lectures/lesson7/dau/DauServiceTest.java
new file mode 100644
index 00000000..c1800d16
--- /dev/null
+++ b/src/test/java/hse/java/lectures/lesson7/dau/DauServiceTest.java
@@ -0,0 +1,73 @@
+package hse.java.lectures.lesson7.dau;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.Map;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@Tag("dau")
+class DauServiceTest {
+
+    private DauServiceImpl service;
+
+    @BeforeEach
+    void setUp() {
+        service = new DauServiceImpl();
+        service.postEvent(new Event(1, 10));
+        service.postEvent(new Event(2, 10));
+        service.postEvent(new Event(3, 20));
+        service.nextDay();
+    }
+
+    @Test
+    void sameUserClickedTwice_countedOnce() {
+        service.postEvent(new Event(5, 10));
+        service.postEvent(new Event(5, 10));
+        service.nextDay();
+
+        assertEquals(1L, service.getAuthorDauStatistics(10));
+    }
+
+    @Test
+    void twoUniqueUsers_countedCorrectly() {
+        assertEquals(2L, service.getAuthorDauStatistics(10));
+    }
+
+    @Test
+    void authorWithNoClicks_returnsZero() {
+        assertEquals(0L, service.getAuthorDauStatistics(99));
+    }
+
+    @Test
+    void differentAuthors_countedIndependently() {
+        Map<Integer, Long> stats = service.getDauStatistics(List.of(10, 20));
+        assertEquals(2L, stats.get(10));
+        assertEquals(1L, stats.get(20));
+    }
+
+    @Test
+    void getDauStatistics_unknownAuthorReturnsZero() {
+        Map<Integer, Long> stats = service.getDauStatistics(List.of(999));
+        assertEquals(0L, stats.get(999));
+    }
+
+    @Test
+    void eventsPostedToday_notVisibleUntilTomorrow() {
+        service.postEvent(new Event(100, 10));
+        assertEquals(2L, service.getAuthorDauStatistics(10));
+    }
+
+    @Test
+    void afterNewDay_previousDataReplaced() {
+        service.postEvent(new Event(7, 10));
+        service.postEvent(new Event(8, 10));
+        service.postEvent(new Event(9, 10));
+        service.nextDay();
+
+        assertEquals(3L, service.getAuthorDauStatistics(10));
+    }
+}