[#12048] Add UsageStatistics entity and db (#12076)

src/main/java/teammates/storage/sqlapi/UsageStatisticsDb.java

@@ -0,0 +1,47 @@
+package teammates.storage.sqlapi;
+
+import java.time.Instant;
+import java.util.List;
+
+import org.hibernate.Session;
+
+import teammates.common.util.HibernateUtil;
+import teammates.storage.sqlentity.UsageStatistics;
+
+import jakarta.persistence.criteria.CriteriaBuilder;
+import jakarta.persistence.criteria.CriteriaQuery;
+import jakarta.persistence.criteria.Root;
+
+/**
+ * Handles CRUD operations for usage statistics.
+ *
+ * @see UsageStatistics
+ */
+public final class UsageStatisticsDb extends EntitiesDb<UsageStatistics> {
+
+    private static final UsageStatisticsDb instance = new UsageStatisticsDb();
+
+    private UsageStatisticsDb() {
+        // prevent initialization
+    }
+
+    public static UsageStatisticsDb inst() {
+        return instance;
+    }
+
+    /**
+     * Gets a list of statistics objects between start time and end time.
+     */
+    public List<UsageStatistics> getUsageStatisticsForTimeRange(Instant startTime, Instant endTime) {
+        Session session = HibernateUtil.getSessionFactory().getCurrentSession();
+        CriteriaBuilder cb = session.getCriteriaBuilder();
+        CriteriaQuery<UsageStatistics> cr = cb.createQuery(UsageStatistics.class);
+        Root<UsageStatistics> root = cr.from(UsageStatistics.class);
+
+        cr.select(root).where(cb.and(
+                cb.greaterThanOrEqualTo(root.get("startTime"), startTime),
+                cb.lessThan(root.get("startTime"), endTime)));
+
+        return session.createQuery(cr).getResultList();
+    }
+}

src/main/java/teammates/storage/sqlentity/UsageStatistics.java

@@ -0,0 +1,140 @@
+package teammates.storage.sqlentity;
+
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.hibernate.annotations.CreationTimestamp;
+import org.hibernate.annotations.UpdateTimestamp;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+
+/**
+ * Represents a system usage statistics for a specified period of time.
+ *
+ * <p>Note that "system usage" here is defined as user-facing usages, such as number of entities created
+ * and number of actions, as opposed to system resources such as hardware and network.
+ */
+@Entity
+@Table(name = "UsageStatistics")
+public class UsageStatistics extends BaseEntity {
+    @Id
+    @GeneratedValue
+    private int id;
+
+    @Column(nullable = false)
+    private Instant startTime;
+
+    @Column(nullable = false)
+    private int timePeriod;
+    @Column(nullable = false)
+    private int numResponses;
+    @Column(nullable = false)
+    private int numCourses;
+    @Column(nullable = false)
+    private int numStudents;
+    @Column(nullable = false)
+    private int numInstructors;
+    @Column(nullable = false)
+    private int numAccountRequests;
+    @Column(nullable = false)
+    private int numEmails;
+    @Column(nullable = false)
+    private int numSubmissions;
+
+    @CreationTimestamp
+    @Column(updatable = false)
+    private Instant createdAt;
+
+    @UpdateTimestamp
+    @Column
+    private Instant updatedAt;
+
+    protected UsageStatistics() {
+        // required by Hibernate
+    }
+
+    private UsageStatistics(
+            Instant startTime, int timePeriod, int numResponses, int numCourses,
+            int numStudents, int numInstructors, int numAccountRequests, int numEmails, int numSubmissions) {
+        this.startTime = startTime;
+        this.timePeriod = timePeriod;
+        this.numResponses = numResponses;
+        this.numCourses = numCourses;
+        this.numStudents = numStudents;
+        this.numInstructors = numInstructors;
+        this.numAccountRequests = numAccountRequests;
+        this.numEmails = numEmails;
+        this.numSubmissions = numSubmissions;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public Instant getStartTime() {
+        return startTime;
+    }
+
+    public int getTimePeriod() {
+        return timePeriod;
+    }
+
+    public int getNumResponses() {
+        return numResponses;
+    }
+
+    public int getNumCourses() {
+        return numCourses;
+    }
+
+    public int getNumStudents() {
+        return numStudents;
+    }
+
+    public int getNumInstructors() {
+        return numInstructors;
+    }
+
+    public int getNumAccountRequests() {
+        return numAccountRequests;
+    }
+
+    public int getNumEmails() {
+        return numEmails;
+    }
+
+    public int getNumSubmissions() {
+        return numSubmissions;
+    }
+
+    public Instant getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(Instant createdAt) {
+        this.createdAt = createdAt;
+    }
+
+    public Instant getUpdatedAt() {
+        return updatedAt;
+    }
+
+    public void setUpdatedAt(Instant updatedAt) {
+        this.updatedAt = updatedAt;
+    }
+
+    @Override
+    public void sanitizeForSaving() {
+        // required by BaseEntity
+    }
+
+    @Override
+    public List<String> getInvalidityInfo() {
+        return new ArrayList<>();
+    }
+}