From eb97a2b6cc7d7c5402c04f863f8e482b21a6c1ae Mon Sep 17 00:00:00 2001
From: Michael Williamson <mike@zwobble.org>
Date: Sun, 3 Aug 2025 08:17:47 +0100
Subject: Add toMapPreferFirst()

---
 Mammoth/Couscous/mammoth/internal/util/Maps.cs | 61 +++++++++++++++++---------
 1 file changed, 40 insertions(+), 21 deletions(-)

diff --git a/Mammoth/Couscous/mammoth/internal/util/Maps.cs b/Mammoth/Couscous/mammoth/internal/util/Maps.cs
index 0902fd3..7848f13 100644
--- a/Mammoth/Couscous/mammoth/internal/util/Maps.cs
+++ b/Mammoth/Couscous/mammoth/internal/util/Maps.cs
@@ -3,6 +3,7 @@ using Mammoth.Couscous.java.util;
 using Mammoth.Couscous.java.lang;
 using Mammoth.Couscous.java.util.function;
 using Mammoth.Couscous;
+using System.Collections.Generic;
 
 namespace Mammoth.Couscous.org.zwobble.mammoth.@internal.util
 {
@@ -11,20 +12,20 @@ namespace Mammoth.Couscous.org.zwobble.mammoth.@internal.util
         internal static Map<K, V> map<K, V>() {
             return ToJava.DictionaryToMap(new System.Collections.Generic.Dictionary<K, V>());
         }
-        
+
         internal static Map<K, V> map<K, V>(K key1, V value1) {
             return ToJava.DictionaryToMap(new System.Collections.Generic.Dictionary<K, V> {
                 {key1, value1}
             });
         }
-        
+
         internal static Map<K, V> map<K, V>(K key1, V value1, K key2, V value2) {
             return ToJava.DictionaryToMap(new System.Collections.Generic.Dictionary<K, V> {
                 {key1, value1},
                 {key2, value2}
             });
         }
-        
+
         internal static Map<K, V> map<K, V>(K key1, V value1, K key2, V value2, K key3, V value3) {
             return ToJava.DictionaryToMap(new System.Collections.Generic.Dictionary<K, V> {
                 {key1, value1},
@@ -32,15 +33,33 @@ namespace Mammoth.Couscous.org.zwobble.mammoth.@internal.util
                 {key3, value3}
             });
         }
-        
+
         internal static Map<K, V> toMap<T, K, V>(Iterable<T> iterable, Function<T, Map__Entry<K, V>> function) {
             var dictionary = FromJava.IterableToEnumerable(iterable)
                 .Select(function.apply)
                 .ToDictionary(entry => entry.getKey(), entry => entry.getValue());
             return ToJava.DictionaryToMap(dictionary);
-            
+
+        }
+
+        /// <summary>
+        /// 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.
+        /// </summary>
+        internal static Map<K, V> toMapPreferFirst<T, K, V>(Iterable<T> iterable, Function<T, Map__Entry<K, V>> function) {
+            var dictionary = new Dictionary<K, V>();
+
+            foreach (var element in FromJava.IterableToEnumerable(iterable)) {
+                var entry = function.apply(element);
+                if (!dictionary.ContainsKey(entry.getKey())) {
+                    dictionary[entry.getKey()] = entry.getValue();
+                }
+            }
+
+            return ToJava.DictionaryToMap(dictionary);
         }
-        
+
         internal static Map<K, T> toMapWithKey<T, K>(Iterable<T> iterable, Function<T, K> function) {
             var dictionary = FromJava.IterableToEnumerable(iterable)
                 .ToDictionary(function.apply);
@@ -55,7 +74,7 @@ namespace Mammoth.Couscous.org.zwobble.mammoth.@internal.util
                     grouping => ToJava.ListToList(grouping.ToList()));
             return ToJava.DictionaryToMap(dictionary);
         }
-    
+
         internal static Map<K, java.util.List<V>> toMultiMap<T, K, V>(Iterable<T> iterable, Function<T, Map__Entry<K, V>> function) {
             var dictionary = FromJava.IterableToEnumerable(iterable)
                 .Select(element => function.apply(element))
@@ -65,11 +84,11 @@ namespace Mammoth.Couscous.org.zwobble.mammoth.@internal.util
                     grouping => ToJava.ListToList(grouping.Select(entry => entry.getValue()).ToList()));
             return ToJava.DictionaryToMap(dictionary);
         }
-        
+
         internal static Optional<V> lookup<K, V>(Map<K, V> map, K key) {
             return map._lookup(key);
         }
-        
+
         internal static Map<K2, V> eagerMapKeys<K1, K2, V>(Map<K1, V> map, Function<K1, K2> function) {
             var dictionary = FromJava.MapToDictionary(map)
                 .ToDictionary(
@@ -77,7 +96,7 @@ namespace Mammoth.Couscous.org.zwobble.mammoth.@internal.util
                     entry => entry.Value);
             return ToJava.DictionaryToMap(dictionary);
         }
-        
+
         internal static Map<K, V2> eagerMapValues<K, V1, V2>(Map<K, V1> map, Function<V1, V2> function) {
             var dictionary = FromJava.MapToDictionary(map)
                 .ToDictionary(
@@ -85,28 +104,28 @@ namespace Mammoth.Couscous.org.zwobble.mammoth.@internal.util
                     entry => function.apply(entry.Value));
             return ToJava.DictionaryToMap(dictionary);
         }
-        
+
         internal static Map__Entry<K, V> entry<K, V>(K key, V value) {
             return new Entry<K, V>(key, value);
         }
-        
+
         private class Entry<K, V> : Map__Entry<K, V> {
             private readonly K _key;
             private readonly V _value;
-            
+
             internal Entry(K key, V value) {
                 this._key = key;
                 this._value = value;
             }
-            
+
             public K getKey() {
                 return _key;
             }
-            
+
             public V getValue() {
                 return _value;
             }
-            
+
             public override bool Equals(object otherObj) {
                 var other = otherObj as Entry<K, V>;
                 if (other == null) {
@@ -122,24 +141,24 @@ namespace Mammoth.Couscous.org.zwobble.mammoth.@internal.util
                 return _key.GetHashCode() * 17 + _value.GetHashCode();
             }
         }
-        
+
         internal static Builder<K, V> builder<K, V>() {
             return new Builder<K, V>();
         }
-        
+
         internal class Builder<K, V> {
             private readonly System.Collections.Generic.Dictionary<K, V> _values = new System.Collections.Generic.Dictionary<K, V>();
-            
+
             internal Builder<K, V> put(K key, V value) {
                 _values[key] = value;
                 return this;
             }
-            
+
             internal Map<K, V> build() {
                 return ToJava.DictionaryToMap(_values);
             }
         }
-        
+
         internal static Map<K, V> mutableMap<K, V>(K key1, V value1) {
             var map = new HashMap<K, V>();
             map.put(key1, value1);
-- 
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