1 files changed, 120 insertions, 0 deletions
diff --git a/BJC-Utils2/src/main/java/bjc/utils/esodata/PushdownMap.java b/BJC-Utils2/src/main/java/bjc/utils/esodata/PushdownMap.java
new file mode 100644
index 0000000..4b758e3
--- /dev/null
+++ b/BJC-Utils2/src/main/java/bjc/utils/esodata/PushdownMap.java
@@ -0,0 +1,120 @@
+package bjc.utils.esodata;
+
+import bjc.utils.funcdata.FunctionalMap;
+import bjc.utils.funcdata.IList;
+import bjc.utils.funcdata.IMap;
+
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+import java.util.function.Function;
+
+/**
+ * A variant of a map where inserting a duplicate key shadows the existing value
+ * instead of replacing it.
+ * 
+ * @author EVE
+ *
+ * @param <KeyType>
+ *                The key of the map.
+ * @param <ValueType>
+ *                The values in the map.
+ */
+public class PushdownMap<KeyType, ValueType> implements IMap<KeyType, ValueType> {
+	private IMap<KeyType, Stack<ValueType>> backing;
+
+	/**
+	 * Create a new empty stack-based map.
+	 */
+	public PushdownMap() {
+		backing = new FunctionalMap<>();
+	}
+
+	private PushdownMap(IMap<KeyType, Stack<ValueType>> back) {
+		backing = back;
+	}
+
+	@Override
+	public void clear() {
+		backing.clear();
+	}
+
+	@Override
+	public boolean containsKey(KeyType key) {
+		return backing.containsKey(key);
+	}
+
+	@Override
+	public IMap<KeyType, ValueType> extend() {
+		return new PushdownMap<>(backing.extend());
+	}
+
+	@Override
+	public void forEach(BiConsumer<KeyType, ValueType> action) {
+		backing.forEach((key, stk) -> action.accept(key, stk.top()));
+	}
+
+	@Override
+	public void forEachKey(Consumer<KeyType> action) {
+		backing.forEachKey(action);
+	}
+
+	@Override
+	public void forEachValue(Consumer<ValueType> action) {
+		backing.forEachValue(stk -> action.accept(stk.top()));
+	}
+
+	@Override
+	public ValueType get(KeyType key) {
+		return backing.get(key).top();
+	}
+
+	@Override
+	public int getSize() {
+		return backing.getSize();
+	}
+
+	@Override
+	public IList<KeyType> keyList() {
+		return backing.keyList();
+	}
+
+	@Override
+	public <V2> IMap<KeyType, V2> mapValues(Function<ValueType, V2> transformer) {
+		throw new UnsupportedOperationException("Cannot transform pushdown maps.");
+	}
+
+	@Override
+	public ValueType put(KeyType key, ValueType val) {
+		if(backing.containsKey(key)) {
+			Stack<ValueType> stk = backing.get(key);
+
+			ValueType vl = stk.top();
+
+			stk.push(val);
+
+			return vl;
+		} else {
+			Stack<ValueType> stk = new SimpleStack<>();
+
+			stk.push(val);
+
+			return null;
+		}
+	}
+
+	@Override
+	public ValueType remove(KeyType key) {
+		Stack<ValueType> stk = backing.get(key);
+
+		if(stk.size() > 1) {
+			return stk.pop();
+		} else {
+			return backing.remove(key).top();
+		}
+	}
+
+	@Override
+	public IList<ValueType> valueList() {
+		return backing.valueList().map(stk -> stk.top());
+	}
+}