TSK-354: added abstract report structure

lib/taskana-core/src/main/java/pro/taskana/impl/report/QueryItem.java

@@ -0,0 +1,9 @@
+package pro.taskana.impl.report;
+
+public interface QueryItem {
+
+    String getKey();
+
+    int getValue();
+
+}

lib/taskana-core/src/main/java/pro/taskana/impl/report/Report.java

@@ -0,0 +1,48 @@
+package pro.taskana.impl.report;
+
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+public abstract class Report<Item extends QueryItem, Column extends ReportColumnHeader<? super Item>> {
+
+    protected List<Column> columns = new ArrayList<>(); //this can be done as an array
+    private Map<String, ReportRow<Item>> reportLines = new LinkedHashMap<>();
+    private ReportRow<Item> sumLine;
+
+    public Report(List<Column> columns) {
+        sumLine = new ReportRow<>(columns.size());
+        this.columns.addAll(columns);
+    }
+
+    protected final void addItem(Item item) {
+        ReportRow<Item> row = reportLines.computeIfAbsent(item.getKey(), (s) -> createReportRow(columns.size()));
+        for (int i = 0; i < columns.size(); i++) {
+            if (columns.get(i).fits(item)) {
+                row.addItem(item, i);
+                sumLine.addItem(item, i);
+            }
+        }
+    }
+
+    public ReportRow<Item> getRow(String key) {
+        return reportLines.get(key);
+    }
+
+    public void addItems(List<Item> items) {
+        items.forEach(this::addItem);
+    }
+
+    public final ReportRow<Item> getSumLine() {
+        return sumLine;
+    }
+
+    public Map<String, ReportRow<Item>> getReportLines() {
+        return reportLines;
+    }
+
+    protected ReportRow<Item> createReportRow(int columnSize) {
+        return new ReportRow<>(columnSize);
+    }
+}

lib/taskana-core/src/main/java/pro/taskana/impl/report/ReportColumnHeader.java

@@ -0,0 +1,9 @@
+package pro.taskana.impl.report;
+
+public interface ReportColumnHeader<Item extends QueryItem> {
+
+    String displayName();
+
+    boolean fits(Item item);
+
+}

lib/taskana-core/src/main/java/pro/taskana/impl/report/ReportRow.java

@@ -0,0 +1,25 @@
+package pro.taskana.impl.report;
+
+public class ReportRow<Item extends QueryItem> {
+
+    private final int[] lineItems;
+    private int totalValue = 0;
+
+    public ReportRow(int columnCount) {
+        //TODO: do you use an assert / throw an exception?
+        lineItems = new int[columnCount];
+    }
+
+    public int[] getLineItems() {
+        return lineItems;
+    }
+
+    public int getTotalValue() {
+        return totalValue;
+    }
+
+    public void addItem(Item item, int index) throws IndexOutOfBoundsException {
+        totalValue += item.getValue();
+        lineItems[index] += item.getValue();
+    }
+}