refactor: move BidiMap to another file to be shared

Also introduces a put method to ensure no duplicates, as well as a
merge method.

Author: benbellick

core/src/main/java/io/substrait/extension/BidiMap.java

@@ -0,0 +1,65 @@
+package io.substrait.extension;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+/** We don't depend on guava... */
+class BidiMap<T1, T2> {
+  private final Map<T1, T2> forwardMap;
+  private final Map<T2, T1> reverseMap;
+
+  BidiMap(Map<T1, T2> forwardMap) {
+    this.forwardMap = forwardMap;
+    this.reverseMap = new HashMap<>();
+    for (Map.Entry<T1, T2> entry : forwardMap.entrySet()) {
+      reverseMap.put(entry.getValue(), entry.getKey());
+    }
+  }
+
+  BidiMap() {
+    this.forwardMap = new HashMap<>();
+    this.reverseMap = new HashMap<>();
+  }
+
+  T2 get(T1 t1) {
+    return forwardMap.get(t1);
+  }
+
+  T1 reverseGet(T2 t2) {
+    return reverseMap.get(t2);
+  }
+
+  /**
+   * Associates the specified values in both directions. Throws if either value is already mapped to
+   * a different value.
+   */
+  void put(T1 t1, T2 t2) {
+    T2 existingForward = forwardMap.get(t1);
+    T1 existingReverse = reverseMap.get(t2);
+
+    if (existingForward != null && !existingForward.equals(t2)) {
+      throw new IllegalArgumentException("Key already exists in map with different value");
+    }
+    if (existingReverse != null && !existingReverse.equals(t1)) {
+      throw new IllegalArgumentException("Key already exists in map with different value");
+    }
+
+    forwardMap.put(t1, t2);
+    reverseMap.put(t2, t1);
+  }
+
+  void merge(BidiMap<T1, T2> other) {
+    for (Map.Entry<T1, T2> entry : other.forwardEntrySet()) {
+      put(entry.getKey(), entry.getValue());
+    }
+  }
+
+  Set<Map.Entry<T1, T2>> forwardEntrySet() {
+    return forwardMap.entrySet();
+  }
+
+  Set<Map.Entry<T2, T1>> reverseEntrySet() {
+    return reverseMap.entrySet();
+  }
+}

core/src/main/java/io/substrait/extension/ExtensionCollector.java

@@ -68,7 +68,7 @@ private SimpleExtensions getExtensions() {
     HashMap<String, SimpleExtensionURN> urns = new HashMap<>();
 
     ArrayList<SimpleExtensionDeclaration> extensionList = new ArrayList<>();
-    for (Map.Entry<Integer, SimpleExtension.FunctionAnchor> e : funcMap.forwardMap.entrySet()) {
+    for (Map.Entry<Integer, SimpleExtension.FunctionAnchor> e : funcMap.forwardEntrySet()) {
       SimpleExtensionURN urn =
           urns.computeIfAbsent(
               e.getValue().urn(),
@@ -87,7 +87,7 @@ private SimpleExtensions getExtensions() {
               .build();
       extensionList.add(decl);
     }
-    for (Map.Entry<Integer, SimpleExtension.TypeAnchor> e : typeMap.forwardMap.entrySet()) {
+    for (Map.Entry<Integer, SimpleExtension.TypeAnchor> e : typeMap.forwardEntrySet()) {
       SimpleExtensionURN urn =
           urns.computeIfAbsent(
               e.getValue().urn(),
@@ -120,28 +120,4 @@ private static final class SimpleExtensions {
       this.extensionList = extensionList;
     }
   }
-
-  /** We don't depend on guava... */
-  private static class BidiMap<T1, T2> {
-    private final Map<T1, T2> forwardMap;
-    private final Map<T2, T1> reverseMap;
-
-    public BidiMap(Map<T1, T2> forwardMap) {
-      this.forwardMap = forwardMap;
-      this.reverseMap = new HashMap<>();
-    }
-
-    public T2 get(T1 t1) {
-      return forwardMap.get(t1);
-    }
-
-    public T1 reverseGet(T2 t2) {
-      return reverseMap.get(t2);
-    }
-
-    public void put(T1 t1, T2 t2) {
-      forwardMap.put(t1, t2);
-      reverseMap.put(t2, t1);
-    }
-  }
 }