Ignore style definitions using a style ID that has already been used

2 files changed, 19 insertions, 4 deletions

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));
     }