add bar charts

pdb-api/src/main/java/org/lucares/pdb/api/GroupResult.java

@@ -33,4 +33,9 @@ public class GroupResult {
 
         return result;
     }
+
+    @Override
+    public String toString() {
+        return groupedBy.toString();
+    }
 }

pdb-api/src/main/java/org/lucares/pdb/api/Result.java

@@ -27,4 +27,9 @@ public class Result {
     public List<GroupResult> getGroups() {
         return new ArrayList<>(groupResults);
     }
+
+    @Override
+    public String toString() {
+        return groupResults.toString();
+    }
 }

pdb-api/src/main/java/org/lucares/pdb/api/Tags.java

@@ -14,11 +14,13 @@ import org.lucares.utils.byteencoder.VariableByteEncoder;
 
 public class Tags implements Comparable<Tags> {
 
+    private static final String DEFAULT_GROUP = "<none>";
     public static StringCompressor STRING_COMPRESSOR = null;
     private static final byte[] EMPTY_BYTES = new byte[0];
     public static final Tags EMPTY = new Tags();
 
     private final List<Tag> tags;
+    private int hashCode = 0;
 
     public Tags() {
         tags = new ArrayList<>();
@@ -216,10 +218,12 @@ public class Tags implements Comparable<Tags> {
 
     @Override
     public int hashCode() {
-        final int prime = 31;
-        int result = 1;
-        result = prime * result + ((tags == null) ? 0 : tags.hashCode());
-        return result;
+        if (hashCode == 0) {
+            final int prime = 31;
+            final int result = 1;
+            hashCode = prime * result + ((tags == null) ? 0 : tags.hashCode());
+        }
+        return hashCode;
     }
 
     @Override
@@ -278,4 +282,19 @@ public class Tags implements Comparable<Tags> {
 
         return result.toString();
     }
+
+    public String asValueString() {
+        final StringBuilder result = new StringBuilder();
+        if (isEmpty()) {
+            result.append(DEFAULT_GROUP);
+        } else {
+            forEach((k, v) -> {
+                if (result.length() > 0) {
+                    result.append(" / ");
+                }
+                result.append(v);
+            });
+        }
+        return result.toString();
+    }
 }