1 files changed, 30 insertions, 0 deletions
diff --git a/src/main/java/moe/nea/zwirn/Index.java b/src/main/java/moe/nea/zwirn/Index.java
new file mode 100644
index 0000000..a27344e
--- /dev/null
+++ b/src/main/java/moe/nea/zwirn/Index.java
@@ -0,0 +1,30 @@
+package moe.nea.zwirn;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Function;
+
+public class Index<K, V> {
+    Map<K, Set<V>> map = new HashMap<>();
+
+    public void addToIndex(K k, V v) {
+        find(k).add(v);
+    }
+
+    public Set<K> keys() {
+        return map.keySet();
+    }
+
+    public <T> void loadFrom(Iterable<T> it, Function<T, K> keyExtractor, Function<T, V> valueExtractor) {
+        for (T t : it) {
+            addToIndex(keyExtractor.apply(t), valueExtractor.apply(t));
+        }
+    }
+
+    public Set<V> find(K k) {
+        return map.computeIfAbsent(k, ignored -> new HashSet<>());
+    }
+
+}
+\ No newline at end of file