fix: Fix issue where replace does not do a in-place replacement

Bug was that newElement is always added to the back of the collection regardless of the position of existingElement.

Add unit test to check ordering after replace

impl/src/main/java/io/jsonwebtoken/impl/lang/DefaultCollectionMutator.java

@@ -23,6 +23,7 @@
 import io.jsonwebtoken.lang.Strings;
 
 import java.util.Collection;
+import java.util.Iterator;
 import java.util.LinkedHashSet;
 import java.util.NoSuchElementException;
 
@@ -62,10 +63,25 @@ public M replace(E existingElement, E newElement) {
             throw new NoSuchElementException(msg);
         }
 
-        // FIXME: Ordering is not correct
-        if (this.collection.remove(existingElement))
-            if (doAdd(newElement))
-                changed(); // removed and add successfully, notify changed()
+        // Replacement step 1: iterate until element to replace
+        Iterator<E> it = this.collection.iterator();
+        while (it.hasNext())
+            if (it.next().equals(existingElement)) {
+                it.remove(); // step 2: remove existingElement
+                break;
+            }
+
+        // Replacement step 3: collect and remove elements after element to replace
+        Collection<E> elementsAfterExisting = new LinkedHashSet<>();
+        while (it.hasNext()) {
+            elementsAfterExisting.add(it.next());
+            it.remove();
+        }
+
+        this.doAdd(newElement); // step 4: add replacer element (position will be at the existingElement)
+        this.collection.addAll(elementsAfterExisting); // step 5: add back the elemnts found after existingElement
+
+        changed(); // trigger changed()
 
         return self();
     }

impl/src/test/groovy/io/jsonwebtoken/impl/lang/DefaultCollectionMutatorTest.groovy

@@ -177,6 +177,13 @@ class DefaultCollectionMutatorTest {
         m.replace('foo', Strings.EMPTY)
     }
 
+    @Test
+    void replaceMaintainsOrder() {
+        m.add(['1', '2', '3'])
+        m.replace('2', 'B')
+        assertArrayEquals(new Object[] {'1', 'B', '3'}, m.collection.toArray())
+    }
+
     @Test
     void clear() {
         m.add('one').add('two').add(['three', 'four'])