1 files changed, 102 insertions, 0 deletions
diff --git a/src/eu/equalparts/cardbase/comparators/CardComparator.java b/src/eu/equalparts/cardbase/comparators/CardComparator.java
new file mode 100644
index 0000000..3640c8b
--- /dev/null
+++ b/src/eu/equalparts/cardbase/comparators/CardComparator.java
@@ -0,0 +1,102 @@
+package eu.equalparts.cardbase.comparators;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.ParameterizedType;
+import java.lang.reflect.Type;
+import java.util.Comparator;
+
+import eu.equalparts.cardbase.Cardbase;
+import eu.equalparts.cardbase.data.Card;
+
+/**
+ * I'm new to this reflection business, so bear with me.
+ * <br><br>
+ * The idea here is to avoid having to write one class
+ * for each comparable field in {@code Card}. The program
+ * can dynamically instantiate them as cards are compared 
+ * by different fields.
+ * <br><br>
+ * This class uses reflection to determine if the specified
+ * field is comparable with itself upon construction, and throws
+ * an {@code IllegalArgumentException} if that is not the case.
+ * 
+ * @author Eduardo Pedroni
+ *
+ */
+@SuppressWarnings({"rawtypes", "unchecked"})
+public class CardComparator implements Comparator<Card> {
+
+	/**
+	 * The field being compared.
+	 */
+	private Field fieldToCompare;
+
+	/**
+	 * Creates a new comparator for the specified field only. This class
+	 * will only be constructed successfully if the field comes from
+	 * {@code Card} and can be compared to itself (i.e. implements
+	 * {@code Comparable<T>} where T is its own type.
+	 * <br>
+	 * For reference, {@code String} and {@code Integer} are both self comparable.
+	 * 
+	 * @param fieldToCompare the field this comparator will use to compare cards, as declared in {@code Card}.
+	 */
+	public CardComparator(Field fieldToCompare) {
+		if (fieldToCompare.getDeclaringClass().equals(Card.class) &&
+				isSelfComparable(fieldToCompare.getType())) {
+
+			this.fieldToCompare = fieldToCompare;
+		} else {
+			System.out.println(fieldToCompare.isAccessible());
+			System.out.println(fieldToCompare.getDeclaringClass().equals(Card.class));
+			System.out.println(isSelfComparable(fieldToCompare.getType()));
+			throw new IllegalArgumentException("The field provided is not valid.");
+		}
+	}
+
+	@Override
+	public int compare(Card o1, Card o2) {
+		try {
+			/*
+			 * we've already checked that the field is self comparable,
+			 * so we are now free to cast to whatever type it is and compare.
+			 */
+			Comparable field1 = (Comparable) fieldToCompare.get(o1);
+			Comparable field2 = (Comparable) fieldToCompare.get(o2);
+			
+			return field1.compareTo(field2);
+
+		} catch (IllegalArgumentException e) {
+			System.out.println("Error: class Card does not define field" + fieldToCompare.getName() + ".");
+			if (Cardbase.DEBUG) e.printStackTrace();
+		} catch (IllegalAccessException e) {
+			System.out.println("Error: field " + fieldToCompare.getName() + " in Card is not visible.");
+			if (Cardbase.DEBUG) e.printStackTrace();
+		}
+		
+		// not comparable, this should never happen
+		return 0;
+	}
+
+	/**
+	 * Use reflection to determine if the specified class can be compared with itself.
+	 * 
+	 * @param type the type to analyse.
+	 * @return true if the type can be compared to itself using {@code compareTo()}, false otherwise.
+	 */
+	private boolean isSelfComparable(Class<?> type) {
+
+		// go through all interfaces implemented by this class
+		for (Type implementedInterface : type.getGenericInterfaces()) {
+			// check if any parameterised interface found is "Comparable"
+			if (implementedInterface instanceof ParameterizedType) {
+				ParameterizedType genericInterface = (ParameterizedType) implementedInterface;
+				if (genericInterface.getRawType().equals(Comparable.class)) {
+					// check that the type argument of comparable is the same as the field type itself
+					return genericInterface.getActualTypeArguments()[0].equals(type);
+				}
+			}
+		}
+		return false;
+	}
+}