From b65bc063d98c2ddb1dc4cc9b4dbcdc1aef23d5aa Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 3 Aug 2025 08:05:02 +0100
Subject: Ignore style definitions using a style ID that has already been used

---
 NEWS                                               |  4 +++
 .../zwobble/mammoth/internal/docx/StylesXml.java   |  7 ++--
 .../org/zwobble/mammoth/internal/util/Maps.java    | 16 +++++++++
 .../zwobble/mammoth/tests/docx/StylesXmlTests.java | 40 ++++++++++++++++++++++
 4 files changed, 63 insertions(+), 4 deletions(-)

diff --git a/NEWS b/NEWS
index 6224299..ed883f1 100644
--- a/NEWS
+++ b/NEWS
@@ -1,3 +1,7 @@
+# 1.11.0
+
+* Ignore style definitions using a style ID that has already been used.
+
 # 1.10.0
 
 * Add "Heading" and "Body" styles, as found in documents created by Apple Pages,
diff --git a/src/main/java/org/zwobble/mammoth/internal/docx/StylesXml.java b/src/main/java/org/zwobble/mammoth/internal/docx/StylesXml.java
index 656b0dd..31d55b7 100644
--- a/src/main/java/org/zwobble/mammoth/internal/docx/StylesXml.java
+++ b/src/main/java/org/zwobble/mammoth/internal/docx/StylesXml.java
@@ -9,8 +9,7 @@ import java.util.Map;
 import java.util.Optional;
 
 import static org.zwobble.mammoth.internal.util.Iterables.lazyFilter;
-import static org.zwobble.mammoth.internal.util.Maps.entry;
-import static org.zwobble.mammoth.internal.util.Maps.toMap;
+import static org.zwobble.mammoth.internal.util.Maps.*;
 
 public class StylesXml {
     public static Styles readStylesXmlElement(XmlElement element) {
@@ -24,7 +23,7 @@ public class StylesXml {
     }
 
     private static Map<String, Style> readStyles(XmlElementList styleElements, String styleType) {
-        return toMap(
+        return toMapPreferFirst(
             styleElementsOfType(styleElements, styleType),
             StylesXml::readStyle
         );
@@ -37,7 +36,7 @@ public class StylesXml {
     }
 
     private static Map<String, NumberingStyle> readNumberingStyles(XmlElementList styleElements) {
-        return toMap(
+        return toMapPreferFirst(
             styleElementsOfType(styleElements, "numbering"),
             StylesXml::readNumberingStyle
         );
diff --git a/src/main/java/org/zwobble/mammoth/internal/util/Maps.java b/src/main/java/org/zwobble/mammoth/internal/util/Maps.java
index e053c90..72d9fd5 100644
--- a/src/main/java/org/zwobble/mammoth/internal/util/Maps.java
+++ b/src/main/java/org/zwobble/mammoth/internal/util/Maps.java
@@ -63,6 +63,22 @@ public class Maps {
         return map;
     }
 
+    /**
+     * Convert an iterable to map using the given mapping function. If the
+     * mapping function generates entries with the same key, only the first
+     * entry will be used, and subsequent entries will be ignored.
+     */
+    public static <T, K, V> Map<K, V> toMapPreferFirst(Iterable<T> iterable, Function<T, Map.Entry<K, V>> function) {
+        Map<K, V> map = new HashMap<>();
+        for (T element : iterable) {
+            Map.Entry<K, V> entry = function.apply(element);
+            if (!map.containsKey(entry.getKey())) {
+                map.put(entry.getKey(), entry.getValue());
+            }
+        }
+        return map;
+    }
+
     public static <T, K> Map<K, List<T>> toMultiMapWithKey(Iterable<T> iterable, Function<T, K> function) {
         return toMultiMap(iterable, element -> entry(function.apply(element), element));
     }
diff --git a/src/test/java/org/zwobble/mammoth/tests/docx/StylesXmlTests.java b/src/test/java/org/zwobble/mammoth/tests/docx/StylesXmlTests.java
index 89a7d1a..c6ccc82 100644
--- a/src/test/java/org/zwobble/mammoth/tests/docx/StylesXmlTests.java
+++ b/src/test/java/org/zwobble/mammoth/tests/docx/StylesXmlTests.java
@@ -118,6 +118,46 @@ public class StylesXmlTests {
         assertEquals(Optional.of("42"), styles.findNumberingStyleById("List1").get().getNumId());
     }
 
+    @Test
+    public void whenMultipleNonNumberingStyleElementsHaveSameStyleIdThenOnlyFirstElementIsUsed() {
+        XmlElement element = element("w:styles", list(
+            element("w:style", map("w:type", "table", "w:styleId", "TableNormal"), list(
+                nameElement("Normal Table")
+            )),
+            element("w:style", map("w:type", "table", "w:styleId", "TableNormal"), list(
+                nameElement("Table Normal")
+            ))
+        ));
+
+        Styles styles = readStylesXmlElement(element);
+
+        assertEquals(Optional.of("Normal Table"), styles.findTableStyleById("TableNormal").get().getName());
+    }
+
+    @Test
+    public void whenMultipleNumberingStyleElementsHaveSameStyleIdThenOnlyFirstElementIsUsed() {
+        XmlElement element = element("w:styles", list(
+            element("w:style", map("w:type", "numbering", "w:styleId", "List1"), list(
+                element("w:pPr", list(
+                    element("w:numPr", list(
+                        element("w:numId", map("w:val", "42"))
+                    ))
+                ))
+            )),
+            element("w:style", map("w:type", "numbering", "w:styleId", "List1"), list(
+                element("w:pPr", list(
+                    element("w:numPr", list(
+                        element("w:numId", map("w:val", "43"))
+                    ))
+                ))
+            ))
+        ));
+
+        Styles styles = readStylesXmlElement(element);
+
+        assertEquals(Optional.of("42"), styles.findNumberingStyleById("List1").get().getNumId());
+    }
+
     private XmlElement nameElement(String name) {
         return element("w:name", map("w:val", name));
     }
-- 
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