feat: add AggregateCommits use case

src/main/java/io/pakland/mdas/githubstats/application/AggregateCommits.java

@@ -0,0 +1,17 @@
+package io.pakland.mdas.githubstats.application;
+
+import io.pakland.mdas.githubstats.domain.Commit;
+import io.pakland.mdas.githubstats.domain.CommitAggregation;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+
+@Service
+public class AggregateCommits {
+
+    public AggregateCommits() {}
+
+    public CommitAggregation execute(List<Commit> commits) {
+        return CommitAggregation.aggregate(commits);
+    }
+}

src/main/java/io/pakland/mdas/githubstats/domain/CommitAggregation.java

@@ -0,0 +1,30 @@
+package io.pakland.mdas.githubstats.domain;
+
+import java.util.List;
+
+public class CommitAggregation {
+
+    private int numCommits;
+    private int linesAdded;
+    private int linesRemoved;
+
+    public static CommitAggregation aggregate(List<Commit> commits) {
+        CommitAggregation commitAggregation = new CommitAggregation();
+        commitAggregation.numCommits = (int) commits.stream().distinct().count();
+        commitAggregation.linesAdded = commits.stream().mapToInt(Commit::getAdditions).sum();
+        commitAggregation.linesRemoved = commits.stream().mapToInt(Commit::getDeletions).sum();
+        return commitAggregation;
+    }
+
+    public int getNumCommits() {
+        return numCommits;
+    }
+
+    public int getLinesAdded() {
+        return linesAdded;
+    }
+
+    public int getLinesRemoved() {
+        return linesRemoved;
+    }
+}

src/test/java/io/pakland/mdas/githubstats/application/AggregateCommitsTest.java

@@ -0,0 +1,67 @@
+package io.pakland.mdas.githubstats.application;
+
+import io.pakland.mdas.githubstats.domain.Commit;
+import io.pakland.mdas.githubstats.domain.CommitAggregation;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Random;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class AggregateCommitsTest {
+
+    @Test
+    public void aggregatingCommits_shouldGiveValidNumCommits() {
+        List<Commit> commits = new ArrayList<>();
+
+        int numCommits = new Random().nextInt(10);
+
+        for (int i = 0; i < numCommits; i++) {
+            commits.add(mock(Commit.class));
+        }
+
+        CommitAggregation commitAggregation = CommitAggregation.aggregate(commits);
+        assertEquals(commitAggregation.getNumCommits(), numCommits);
+    }
+
+    @Test
+    public void aggregatingCommits_shouldGiveValidLinesAdded() {
+        List<Commit> commits = new ArrayList<>();
+
+        int totalLines = 0;
+
+        for (int i = 0; i < 10; i++) {
+            int numLines = new Random().nextInt(1000);
+            Commit commit = mock(Commit.class);
+            when(commit.getAdditions()).thenReturn(numLines);
+            commits.add(commit);
+            totalLines += numLines;
+        }
+
+        CommitAggregation commitAggregation = CommitAggregation.aggregate(commits);
+        assertEquals(commitAggregation.getLinesAdded(), totalLines);
+    }
+
+    @Test
+    public void aggregatingCommits_shouldGiveValidLinesRemoved() {
+        List<Commit> commits = new ArrayList<>();
+
+        int totalLines = 0;
+
+        for (int i = 0; i < 10; i++) {
+            int numLines = new Random().nextInt(1000);
+            Commit commit = mock(Commit.class);
+            when(commit.getDeletions()).thenReturn(numLines);
+            commits.add(commit);
+            totalLines += numLines;
+        }
+
+        CommitAggregation commitAggregation = CommitAggregation.aggregate(commits);
+        assertEquals(commitAggregation.getLinesRemoved(), totalLines);
+    }
+
+}