Add support for timestamp field for Balance Candlesticks

src/main/java/nl/utwente/ing/misc/date/IntervalHelper.java

@@ -23,7 +23,7 @@ public class IntervalHelper {
      *
      * @param intervalPeriod The size of the intervals to be generated.
      * @param amount         The amount of intervals to be generated.
-     * @return An array containing (amount
+     * @return An array containing LocalDateTime objects representing the requested intervals.
      */
     public static LocalDateTime[] getIntervals(IntervalPeriod intervalPeriod, int amount) {
         LocalDateTime[] intervals = new LocalDateTime[amount + 1];

src/main/java/nl/utwente/ing/model/bean/BalanceCandlestick.java

@@ -9,21 +9,23 @@
 public class BalanceCandlestick {
 
     private float open, close, high, low, volume;
+    private long timestamp;
 
     /**
      * The constructor of BalanceCandlestick.
-     * Initially, only the opening balance is specified, after which this balance can be modified by using the mutate
-     * method. Along the way, this bean keeps track of the opening balance, the closing balance, the highest balance,
-     * the lowest balance and the volume of all the mutations combined.
+     * Initially, only the opening balance and the opening timestamp are specified, after which this balance can be
+     * modified by using the mutate method. Along the way, this bean keeps track of the opening balance, the closing
+     * balance, the highest balance, the lowest balance and the volume of all the mutations combined.
      *
      * @param open The opening balance of this BalanceCandlestick.
      */
-    public BalanceCandlestick(float open) {
+    public BalanceCandlestick(float open, long timestamp) {
         this.open = open;
         this.close = open;
         this.high = open;
         this.low = open;
         this.volume = 0;
+        this.timestamp = timestamp;
     }
 
     /**
@@ -71,6 +73,16 @@ public float getVolume() {
         return volume;
     }
 
+    /**
+     * Method used to retrieve the unix (seconds) timestamp indicating the beginning of the period of the
+     * BalanceCandlestick.
+     *
+     * @return The unix (seconds) timestamp indicating the beginning of the period of the BalanceCandlestick.
+     */
+    public long getTimestamp() {
+        return timestamp;
+    }
+
     /**
      * Method used to indicate a mutation of the balance of BalanceCandlestick.
      * Along the way, this method updates the closing balance, the highest balance, the lowest balance

src/main/java/nl/utwente/ing/model/persistentmodel/PersistentModel.java

@@ -10,6 +10,7 @@
 import java.sql.Connection;
 import java.sql.SQLException;
 import java.time.LocalDateTime;
+import java.time.ZoneOffset;
 import java.util.ArrayList;
 import java.util.UUID;
 
@@ -466,10 +467,12 @@ public ArrayList<BalanceCandlestick> getBalanceHistory(String sessionID, Interva
         ArrayList<BalanceCandlestick> candlesticks = new ArrayList<>();
         int index = 0;
         for (int i = 1; i <= amount; i++) {
-            LocalDateTime interval = intervals[i];
-            BalanceCandlestick candlestick = new BalanceCandlestick(balance);
+            LocalDateTime startInterval = intervals[i - 1];
+            LocalDateTime endInterval = intervals[i];
+            long startUnixTime =  startInterval.toEpochSecond(ZoneOffset.UTC); // Convert start of interval to UNIX time
+            BalanceCandlestick candlestick = new BalanceCandlestick(balance, startUnixTime);
             while (index < transactions.size() &&
-                    !IntervalHelper.isSmallerThan(interval, transactions.get(index).getDate())) {
+                    !IntervalHelper.isSmallerThan(endInterval, transactions.get(index).getDate())) {
                 if (transactions.get(index).getType().equals("deposit")) {
                     candlestick.mutation(transactions.get(index).getAmount());
                 } else {