Set up tests & clean up

.gitignore

@@ -19,5 +19,6 @@ build
 .gradle
 
 # other
+*.log
 eclipse
 run

Common/build.gradle.kts

@@ -45,6 +45,12 @@ dependencies {
      * DON'T USE THIS! NEEDED TO COMPILE THIS PROJECT
      */
     modCompileOnly("net.fabricmc:fabric-loader:${fabricLoaderVersion}")
+
+    /**
+     * Test dependencies
+     */
+    testImplementation ("org.junit.jupiter:junit-jupiter-api:5.8.1")
+    testRuntimeOnly ("org.junit.jupiter:junit-jupiter-engine:5.8.1")
 }
 
 tasks.processResources {
@@ -75,3 +81,7 @@ buildConfig {
 
     packageName(project.group as String)
 }
+
+tasks.withType<Test> {
+    useJUnitPlatform()
+}

Common/src/main/java/com/almostreliable/unified/AlmostUnifiedRuntime.java

@@ -6,12 +6,12 @@ import com.almostreliable.unified.utils.ReplacementMap;
 import com.almostreliable.unified.utils.TagMap;
 import com.google.gson.JsonElement;
 import net.minecraft.resources.ResourceLocation;
-import net.minecraft.tags.TagKey;
 import net.minecraft.tags.TagManager;
-import net.minecraft.world.item.Item;
 
 import javax.annotation.Nullable;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
 
 public abstract class AlmostUnifiedRuntime {
 
@@ -29,7 +29,8 @@ public abstract class AlmostUnifiedRuntime {
         config.load();
         modPriorities = config.getModPriorities();
         onRun();
-        ReplacementMap replacementMap = createContext(config.getAllowedTags(), modPriorities);
+        TagMap tagMap = createTagMap();
+        ReplacementMap replacementMap = new ReplacementMap(tagMap, config.getAllowedTags(), modPriorities);
         RecipeTransformer transformer = new RecipeTransformer(recipeHandlerFactory, replacementMap);
         transformer.transformRecipes(recipes);
     }
@@ -46,26 +47,5 @@ public abstract class AlmostUnifiedRuntime {
         return TagMap.create(tagManager);
     }
 
-    protected ReplacementMap createContext(List<TagKey<Item>> allowedTags, List<String> modPriorities) {
-        TagMap tagMap = createTagMap();
-        Map<ResourceLocation, TagKey<Item>> itemToTagMapping = new HashMap<>(allowedTags.size());
-
-        for (TagKey<Item> tag : allowedTags) {
-            Collection<ResourceLocation> items = tagMap.getItems(tag);
-            for (ResourceLocation item : items) {
-                if (itemToTagMapping.containsKey(item)) {
-                    AlmostUnified.LOG.warn("Item '{}' already has a tag '{}' for recipe replacement. Skipping this tag",
-                            item,
-                            tag);
-                    continue;
-                }
-
-                itemToTagMapping.put(item, tag);
-            }
-        }
-
-        return new ReplacementMap(tagMap, itemToTagMapping, modPriorities);
-    }
-
     protected abstract void onRun();
 }

Common/src/main/java/com/almostreliable/unified/ModConfig.java

@@ -1,14 +1,13 @@
 package com.almostreliable.unified;
 
+import com.almostreliable.unified.utils.UnifyTag;
 import com.electronwill.nightconfig.core.Config;
 import com.electronwill.nightconfig.core.ConfigSpec;
 import com.electronwill.nightconfig.core.file.CommentedFileConfig;
 import com.electronwill.nightconfig.core.file.FileConfig;
 import com.google.common.collect.HashMultimap;
 import com.google.common.collect.Multimap;
-import net.minecraft.core.Registry;
 import net.minecraft.resources.ResourceLocation;
-import net.minecraft.tags.TagKey;
 import net.minecraft.world.item.Item;
 
 import javax.annotation.Nullable;
@@ -164,13 +163,13 @@ public class ModConfig {
         return currentConfig.get(UNIFICATION_MOD_PRIORITIES);
     }
 
-    public List<TagKey<Item>> getAllowedTags() {
+    public List<UnifyTag<Item>> getAllowedTags() {
         if (currentConfig == null) {
             throw new IllegalStateException("Config is not loaded");
         }
 
         Multimap<String, String> variables = compileVariables();
-        List<TagKey<Item>> collectedPattern = new ArrayList<>();
+        List<UnifyTag<Item>> collectedPattern = new ArrayList<>();
 
         Collection<String> patterns = currentConfig.get(UNIFICATION_PATTERN);
         for (String pattern : patterns) {
@@ -183,7 +182,7 @@ public class ModConfig {
                     if (rl == null) {
                         AlmostUnified.LOG.warn("Invalid pattern: " + s);
                     } else {
-                        TagKey<Item> tag = TagKey.create(Registry.ITEM_REGISTRY, rl);
+                        UnifyTag<Item> tag = UnifyTag.item(rl);
                         collectedPattern.add(tag);
                     }
                 }

Common/src/main/java/com/almostreliable/unified/api/recipe/RecipeConstants.java

@@ -10,4 +10,5 @@ public class RecipeConstants {
     public static final String OUTPUT = "output";
     public static final String RESULT = "result";
     public static final String RESULTS = "results";
+    public static final String VALUE = "value";
 }

Common/src/main/java/com/almostreliable/unified/api/recipe/RecipeContext.java

@@ -1,11 +1,13 @@
 package com.almostreliable.unified.api.recipe;
 
+import com.almostreliable.unified.utils.UnifyTag;
 import com.google.gson.JsonElement;
+import com.google.gson.JsonPrimitive;
 import net.minecraft.resources.ResourceLocation;
-import net.minecraft.tags.TagKey;
 import net.minecraft.world.item.Item;
 
 import javax.annotation.Nullable;
+import java.util.function.UnaryOperator;
 
 public interface RecipeContext {
 
@@ -13,19 +15,18 @@ public interface RecipeContext {
     ResourceLocation getReplacementForItem(@Nullable ResourceLocation item);
 
     @Nullable
-    ResourceLocation getPreferredItemByTag(TagKey<Item> tag);
+    ResourceLocation getPreferredItemByTag(@Nullable UnifyTag<Item> tag);
 
     @Nullable
-    TagKey<Item> getPreferredTagByItem(@Nullable ResourceLocation item);
+    UnifyTag<Item> getPreferredTagByItem(@Nullable ResourceLocation item);
 
-    JsonElement replaceIngredient(JsonElement element);
+    JsonElement createIngredientReplacement(@Nullable JsonElement element);
 
-    JsonElement replaceResult(JsonElement element);
+    @Nullable
+    JsonElement createResultReplacement(@Nullable JsonElement element);
 
     ResourceLocation getType();
 
-    ResourceLocation getId();
-
     boolean hasProperty(String property);
 
     default String getModId() {

Common/src/main/java/com/almostreliable/unified/api/recipe/RecipeTransformations.java

@@ -9,10 +9,6 @@ public interface RecipeTransformations {
 
     void forEachObject(String property, BiFunction<JsonObject, RecipeContext, JsonObject> consumer);
 
-    void replaceIngredient(String property);
-
-    void replaceResult(String property);
-
     void put(String property, BiFunction<JsonElement, RecipeContext, JsonElement> consumer);
 
     <T extends JsonElement> void put(String property, Class<T> type, BiFunction<T, RecipeContext, T> consumer);

Common/src/main/java/com/almostreliable/unified/api/recipe/ReplacementFallbackStrategy.java

@@ -1,6 +1,7 @@
 package com.almostreliable.unified.api.recipe;
 
 import com.almostreliable.unified.utils.TagMap;
+import com.almostreliable.unified.utils.UnifyTag;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.tags.TagKey;
 import net.minecraft.world.item.Item;
@@ -19,5 +20,5 @@ public interface ReplacementFallbackStrategy {
      * @throws IllegalStateException if returning the lookupItem
      */
     @Nullable
-    ResourceLocation getFallback(TagKey<Item> tag, Collection<ResourceLocation> potentialItems, TagMap tags);
+    ResourceLocation getFallback(UnifyTag<Item> tag, Collection<ResourceLocation> potentialItems, TagMap tags);
 }

Common/src/main/java/com/almostreliable/unified/recipe/RecipeContextImpl.java

@@ -2,28 +2,26 @@ package com.almostreliable.unified.recipe;
 
 import com.almostreliable.unified.api.recipe.RecipeConstants;
 import com.almostreliable.unified.api.recipe.RecipeContext;
+import com.almostreliable.unified.utils.JsonUtils;
 import com.almostreliable.unified.utils.ReplacementMap;
+import com.almostreliable.unified.utils.UnifyTag;
 import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonPrimitive;
 import net.minecraft.resources.ResourceLocation;
-import net.minecraft.tags.TagKey;
 import net.minecraft.world.item.Item;
 
 import javax.annotation.Nullable;
-import java.util.function.UnaryOperator;
 
 @SuppressWarnings("SameParameterValue")
 public class RecipeContextImpl implements RecipeContext {
     private final ResourceLocation type;
-    private final ResourceLocation id;
     private final JsonObject currentRecipe;
     private final ReplacementMap replacementMap;
 
-    public RecipeContextImpl(ResourceLocation type, ResourceLocation id, JsonObject currentRecipe, ReplacementMap replacementMap) {
+    public RecipeContextImpl(ResourceLocation type, JsonObject currentRecipe, ReplacementMap replacementMap) {
         this.type = type;
-        this.id = id;
         this.currentRecipe = currentRecipe;
         this.replacementMap = replacementMap;
     }
@@ -40,13 +38,17 @@ public class RecipeContextImpl implements RecipeContext {
 
     @Nullable
     @Override
-    public ResourceLocation getPreferredItemByTag(TagKey<Item> tag) {
+    public ResourceLocation getPreferredItemByTag(@Nullable UnifyTag<Item> tag) {
+        if (tag == null) {
+            return null;
+        }
+
         return replacementMap.getPreferredItemByTag(tag);
     }
 
     @Nullable
     @Override
-    public TagKey<Item> getPreferredTagByItem(@Nullable ResourceLocation item) {
+    public UnifyTag<Item> getPreferredTagByItem(@Nullable ResourceLocation item) {
         if (item == null) {
             return null;
         }
@@ -54,58 +56,74 @@ public class RecipeContextImpl implements RecipeContext {
         return replacementMap.getPreferredTag(item);
     }
 
+    @Override
     @Nullable
-    protected JsonElement depthReplace(JsonElement element, String potentialFrom, String potentialTo, UnaryOperator<JsonPrimitive> primitiveCallback) {
+    public JsonElement createIngredientReplacement(@Nullable JsonElement element) {
-        if (element instanceof JsonPrimitive primitive) {
+        if (element == null) {
-            return primitiveCallback.apply(primitive);
+            return null;
+        }
+        JsonElement copy = element.deepCopy();
+        tryReplacingItemInIngredient(copy);
+        return element.equals(copy) ? null : copy;
+    }
+
+    private void tryReplacingItemInIngredient(@Nullable JsonElement element) {
+        if (element instanceof JsonArray array) {
+            for (JsonElement e : array) {
+                tryReplacingItemInIngredient(e);
+            }
         }
 
         if (element instanceof JsonObject object) {
-            JsonElement replace = depthReplace(object.get(potentialFrom),
+            tryReplacingItemInIngredient(object.get(RecipeConstants.VALUE));
-                    potentialFrom,
+            tryReplacingItemInIngredient(object.get(RecipeConstants.INGREDIENT));
-                    potentialTo,
-                    primitiveCallback);
-            if (replace != null) {
-                object.remove(potentialFrom);
-                object.add(potentialTo, replace);
-            }
-        }
 
-        if (element instanceof JsonArray array) {
+            if (object.get(RecipeConstants.ITEM) instanceof JsonPrimitive primitive) {
-            for (int i = 0; i < array.size(); i++) {
+                ResourceLocation item = ResourceLocation.tryParse(primitive.getAsString());
-                JsonElement replace = depthReplace(array.get(i), potentialFrom, potentialTo, primitiveCallback);
+                UnifyTag<Item> tag = getPreferredTagByItem(item);
-                if (replace != null) {
+                if (tag != null) {
-                    array.set(i, replace);
+                    object.remove(RecipeConstants.ITEM);
+                    object.add(RecipeConstants.TAG, new JsonPrimitive(tag.location().toString()));
                 }
             }
         }
-
-        return null;
     }
 
     @Override
     @Nullable
-    public JsonElement replaceIngredient(JsonElement element) {
+    public JsonElement createResultReplacement(@Nullable JsonElement element) {
-        return depthReplace(element, RecipeConstants.ITEM, RecipeConstants.TAG, primitive -> {
+        if (element == null) {
-            ResourceLocation item = ResourceLocation.tryParse(primitive.getAsString());
-            TagKey<Item> tag = getPreferredTagByItem(item);
-            if (tag != null) {
-                return new JsonPrimitive(tag.location().toString());
-            }
             return null;
-        });
+        }
+        JsonElement copy = element.deepCopy();
+        JsonElement result = tryCreateResultReplacement(copy);
+        return element.equals(result) ? null : result;
     }
 
-    @Override
+    @Nullable
-    public JsonElement replaceResult(JsonElement element) {
+    private JsonElement tryCreateResultReplacement(JsonElement element) {
-        return depthReplace(element, RecipeConstants.ITEM, RecipeConstants.ITEM, primitive -> {
+        if (element instanceof JsonPrimitive primitive) {
             ResourceLocation item = ResourceLocation.tryParse(primitive.getAsString());
             ResourceLocation replacement = getReplacementForItem(item);
             if (replacement != null) {
                 return new JsonPrimitive(replacement.toString());
             }
             return null;
-        });
+        }
+
+        if (element instanceof JsonArray array) {
+            if (JsonUtils.replaceOn(array, this::tryCreateResultReplacement)) {
+                return element;
+            }
+        }
+
+        if (element instanceof JsonObject object) {
+            if (JsonUtils.replaceOn(object, RecipeConstants.ITEM, this::tryCreateResultReplacement)) {
+                return element;
+            }
+        }
+
+        return null;
     }
 
     @Override
@@ -113,11 +131,6 @@ public class RecipeContextImpl implements RecipeContext {
         return type;
     }
 
-    @Override
-    public ResourceLocation getId() {
-        return id;
-    }
-
     @Override
     public boolean hasProperty(String property) {
         return currentRecipe.has(property);

Common/src/main/java/com/almostreliable/unified/recipe/RecipeTransformationsImpl.java

@@ -32,16 +32,6 @@ public class RecipeTransformationsImpl implements RecipeTransformations {
         put(property, JsonArray.class, arrayConsumer);
     }
 
-    @Override
-    public void replaceIngredient(String property) {
-        put(property, JsonElement.class, (jsonElement, context) -> context.replaceIngredient(jsonElement));
-    }
-
-    @Override
-    public void replaceResult(String property) {
-        put(property, JsonElement.class, (jsonElement, context) -> context.replaceResult(jsonElement));
-    }
-
     @Override
     public void put(String property, BiFunction<JsonElement, RecipeContext, JsonElement> consumer) {
         consumers.put(property, new Entry<>(JsonElement.class, consumer));
@@ -52,16 +42,37 @@ public class RecipeTransformationsImpl implements RecipeTransformations {
         consumers.put(property, new Entry<>(type, consumer));
     }
 
-    public void transform(JsonObject json, RecipeContext context) {
+    @Nullable
+    public JsonObject transform(JsonObject json, RecipeContext context) {
+        JsonObject changedValues = new JsonObject();
+
         for (var e : json.entrySet()) {
             Entry<?> consumer = consumers.get(e.getKey());
             if (consumer != null) {
-                JsonElement result = consumer.apply(e.getValue(), context);
+                JsonElement currentElement = e.getValue();
-                if (result != null) {
+                JsonElement transformedElement = consumer.apply(currentElement.deepCopy(), context);
-                    e.setValue(result);
+                if (transformedElement != null && !transformedElement.equals(currentElement)) {
+                    changedValues.add(e.getKey(), transformedElement);
                 }
             }
         }
+
+        if (changedValues.size() == 0) {
+            return null;
+        }
+
+        // helps to preserve the order of the elements
+        JsonObject result = new JsonObject();
+        for (var entry : json.entrySet()) {
+            JsonElement changedValue = changedValues.get(entry.getKey());
+            if (changedValue != null) {
+                result.add(entry.getKey(), changedValue);
+            } else {
+                result.add(entry.getKey(), entry.getValue());
+            }
+        }
+
+        return result;
     }
 
     private record Entry<T extends JsonElement>(Class<T> expectedType,

Common/src/main/java/com/almostreliable/unified/recipe/RecipeTransformer.java

@@ -32,7 +32,7 @@ public class RecipeTransformer {
         long start = System.nanoTime();
         for (var entry : recipes.entrySet()) {
             if (entry.getValue() instanceof JsonObject json) {
-                JsonObject transformedJson = transformRecipe(entry.getKey(), json);
+                JsonObject transformedJson = transformRecipe(json);
                 if (transformedJson != null) {
                     transformedRecipes++;
                     entry.setValue(transformedJson);
@@ -54,25 +54,24 @@ public class RecipeTransformer {
             AlmostUnified.LOG.info("{}: {} | {}",
                     StringUtils.leftPad(e.getKey().toString(), 40),
                     StringUtils.leftPad(String.valueOf(e.getValue().size()), 4),
-                    e.getValue().toString());
+                    e.getValue().stream().map(rl -> "\"" + rl.toString() + "\"").toList().toString());
         });
     }
 
     @Nullable
-    public JsonObject transformRecipe(ResourceLocation id, JsonObject json) {
+    public JsonObject transformRecipe(JsonObject json) {
         ResourceLocation recipeType = getRecipeType(json);
         if (recipeType == null) {
             return null;
         }
 
         try {
-            RecipeContextImpl ctx = new RecipeContextImpl(recipeType, id, json, replacementMap);
+            RecipeContextImpl ctx = new RecipeContextImpl(recipeType, json, replacementMap);
             RecipeTransformationsImpl builder = new RecipeTransformationsImpl();
             factory.create(builder, ctx);
-            JsonObject copy = json.deepCopy();
+            JsonObject result = builder.transform(json, ctx);
-            builder.transform(copy, ctx);
+            if (result != null) {
-            if (!json.equals(copy)) {
+                return result;
-                return copy;
             }
         } catch (Exception e) {
             AlmostUnified.LOG.warn("Error transforming recipe type '{}': {}",

Common/src/main/java/com/almostreliable/unified/recipe/fallbacks/StoneStrataFallbackStrategy.java

@@ -2,6 +2,7 @@ package com.almostreliable.unified.recipe.fallbacks;
 
 import com.almostreliable.unified.api.recipe.ReplacementFallbackStrategy;
 import com.almostreliable.unified.utils.TagMap;
+import com.almostreliable.unified.utils.UnifyTag;
 import net.minecraft.resources.ResourceLocation;
 import net.minecraft.tags.TagKey;
 import net.minecraft.world.item.Item;
@@ -12,7 +13,7 @@ import java.util.Comparator;
 // TODO use config and not this :D
 public class StoneStrataFallbackStrategy implements ReplacementFallbackStrategy {
     @Override
-    public ResourceLocation getFallback(TagKey<Item> tag, Collection<ResourceLocation> potentialItems, TagMap tags) {
+    public ResourceLocation getFallback(UnifyTag<Item> tag, Collection<ResourceLocation> potentialItems, TagMap tags) {
         if (tag.location().getPath().contains("ores")) {
             return potentialItems
                     .stream()

Common/src/main/java/com/almostreliable/unified/recipe/handler/GenericRecipeHandler.java

@@ -18,11 +18,11 @@ public class GenericRecipeHandler implements RecipeHandler {
     @Override
     public void collectTransformations(RecipeTransformations builder) {
         for (String inputKey : inputKeys) {
-            builder.replaceIngredient(inputKey);
+            builder.put(inputKey, (json, ctx) -> ctx.createIngredientReplacement(json));
         }
 
         for (String outputKey : outputKeys) {
-            builder.replaceResult(outputKey);
+            builder.put(outputKey, (json, ctx) -> ctx.createResultReplacement(json));
         }
     }
 }

Common/src/main/java/com/almostreliable/unified/recipe/handler/RecipeHandlerFactory.java

@@ -20,15 +20,15 @@ public class RecipeHandlerFactory {
             ShapedRecipeKeyHandler.INSTANCE.collectTransformations(builder);
         }
 
-        RecipeHandler byType = transformersByType.get(context.getType());
-        if (byType != null) {
-            byType.collectTransformations(builder);
-        }
-
         RecipeHandler byMod = transformersByModId.get(context.getModId());
         if (byMod != null) {
             byMod.collectTransformations(builder);
         }
+
+        RecipeHandler byType = transformersByType.get(context.getType());
+        if (byType != null) {
+            byType.collectTransformations(builder);
+        }
     }
 
     public void registerForType(ResourceLocation type, RecipeHandler transformer) {

Common/src/main/java/com/almostreliable/unified/recipe/handler/ShapedRecipeKeyHandler.java

@@ -14,7 +14,7 @@ public class ShapedRecipeKeyHandler implements RecipeHandler {
     public void collectTransformations(RecipeTransformations builder) {
         builder.put(KEY_PROPERTY, JsonObject.class, (json, context) -> {
             for (var entry : json.entrySet()) {
-                JsonElement result = context.replaceIngredient(entry.getValue());
+                JsonElement result = context.createIngredientReplacement(entry.getValue());
                 if (result != null) {
                     entry.setValue(result);
                 }

Common/src/main/java/com/almostreliable/unified/utils/JsonQuery.java

@@ -0,0 +1,86 @@
+package com.almostreliable.unified.utils;
+
+import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import org.apache.commons.lang3.StringUtils;
+
+public class JsonQuery {
+
+    private final JsonElement element;
+
+    public static JsonQuery of(JsonElement element) {
+        return new JsonQuery(element);
+    }
+
+    public static JsonQuery of(JsonElement element, String path) {
+        String[] parts = path.split("/");
+        JsonQuery current = of(element);
+        for (String part : parts) {
+            if(StringUtils.isNumeric(part)) {
+                current = current.get(Integer.parseInt(part));
+            } else {
+                current = current.get(part);
+            }
+        }
+        return current;
+    }
+
+    JsonQuery(JsonElement element) {
+        this.element = element;
+    }
+
+    public JsonQuery get(String identifier) {
+        if(!element.isJsonObject()) {
+            throw new IllegalArgumentException("Expected JsonObject, got " + element.getClass());
+        }
+
+        JsonElement child = element.getAsJsonObject().get(identifier);
+        if(child == null) {
+            return null;
+        }
+
+        return new JsonQuery(child);
+    }
+
+    public JsonQuery get(int index) {
+        if(!element.isJsonArray()) {
+            throw new IllegalArgumentException("Expected JsonArray, got " + element.getClass());
+        }
+
+        JsonElement child = element.getAsJsonArray().get(index);
+        if(child == null) {
+            return null;
+        }
+
+        return new JsonQuery(child);
+    }
+
+    public JsonQuery get(String identifier, int index) {
+        return get(identifier).get(index);
+    }
+
+    public JsonObject asObject() {
+        return element.getAsJsonObject();
+    }
+
+    public JsonArray asArray() {
+        return element.getAsJsonArray();
+    }
+
+    public String asString() {
+        return element.getAsString();
+    }
+
+    public int asInt() {
+        return element.getAsInt();
+    }
+
+    public boolean asBoolean() {
+        return element.getAsBoolean();
+    }
+
+    public float asFloat() {
+        return element.getAsFloat();
+    }
+}

Common/src/main/java/com/almostreliable/unified/utils/JsonUtils.java

@@ -2,9 +2,11 @@ package com.almostreliable.unified.utils;
 
 import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
 
 import javax.annotation.Nullable;
 import java.util.function.Consumer;
+import java.util.function.UnaryOperator;
 
 public class JsonUtils {
     public static JsonArray arrayOrSelf(@Nullable JsonElement element) {
@@ -28,4 +30,46 @@ public class JsonUtils {
             }
         }
     }
+
+    /**
+     * Loops through the array and applies the given callback to each element.
+     * If the callback returns non-null, the element is replaced with the returned value.
+     *
+     * @param jsonArray The array to loop through.
+     * @param callback  The callback to apply to each element.
+     * @return true if any elements were replaced, false otherwise.
+     */
+    public static boolean replaceOn(JsonArray jsonArray, UnaryOperator<JsonElement> callback) {
+        boolean changed = false;
+        for (int i = 0; i < jsonArray.size(); i++) {
+            JsonElement result = callback.apply(jsonArray.get(i));
+            if (result != null) {
+                jsonArray.set(i, result);
+                changed = true;
+            }
+        }
+        return changed;
+    }
+
+    /**
+     * Replaces the element for the key through given callback.
+     * If the callback returns non-null, the element is replaced with the returned value.
+     *
+     * @param jsonObject The object to loop through.
+     * @param callback   The callback to apply to each element.
+     * @return true if the element was replaced, false otherwise.
+     */
+    public static boolean replaceOn(JsonObject jsonObject, String key, UnaryOperator<JsonElement> callback) {
+        JsonElement element = jsonObject.get(key);
+        if (element == null) {
+            return false;
+        }
+
+        JsonElement result = callback.apply(element);
+        if (result != null) {
+            jsonObject.add(key, result);
+            return true;
+        }
+        return false;
+    }
 }

Common/src/main/java/com/almostreliable/unified/utils/ReplacementMap.java

@@ -1,5 +1,6 @@
 package com.almostreliable.unified.utils;
 
+import com.almostreliable.unified.AlmostUnified;
 import com.almostreliable.unified.api.recipe.ReplacementFallbackStrategy;
 import com.almostreliable.unified.recipe.fallbacks.StoneStrataFallbackStrategy;
 import net.minecraft.resources.ResourceLocation;
@@ -8,6 +9,7 @@ import net.minecraft.world.item.Item;
 
 import javax.annotation.Nullable;
 import java.util.Collection;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -15,24 +17,43 @@ public class ReplacementMap {
 
     private final Collection<String> modPriorities;
     private final TagMap tagMap;
-    private final Map<ResourceLocation, TagKey<Item>> itemToTagMapping;
+    private final Map<ResourceLocation, UnifyTag<Item>> itemToTagMapping;
     // TODO - In the future this may be a list of multiple fallbacks.
     private final ReplacementFallbackStrategy fallbackStrategy = new StoneStrataFallbackStrategy();
 
-    public ReplacementMap(TagMap tagMap, Map<ResourceLocation, TagKey<Item>> itemToTagMapping, List<String> modPriorities) {
+    public ReplacementMap(TagMap tagMap, List<UnifyTag<Item>> allowedTags, List<String> modPriorities) {
         this.tagMap = tagMap;
-        this.itemToTagMapping = itemToTagMapping;
         this.modPriorities = modPriorities;
+        this.itemToTagMapping = createItemMapping(allowedTags);
+    }
+
+    protected Map<ResourceLocation, UnifyTag<Item>> createItemMapping(List<UnifyTag<Item>> allowedTags) {
+        Map<ResourceLocation, UnifyTag<Item>> itemToTagMapping = new HashMap<>(allowedTags.size());
+        for (UnifyTag<Item> tag : allowedTags) {
+            Collection<ResourceLocation> items = tagMap.getItems(tag);
+            for (ResourceLocation item : items) {
+                if (itemToTagMapping.containsKey(item)) {
+                    AlmostUnified.LOG.warn("Item '{}' already has a tag '{}' for recipe replacement. Skipping this tag",
+                            item,
+                            tag);
+                    continue;
+                }
+
+                itemToTagMapping.put(item, tag);
+            }
+        }
+
+        return itemToTagMapping;
     }
 
     @Nullable
-    public TagKey<Item> getPreferredTag(ResourceLocation item) {
+    public UnifyTag<Item> getPreferredTag(ResourceLocation item) {
         return itemToTagMapping.get(item);
     }
 
     @Nullable
     public ResourceLocation getReplacementForItem(ResourceLocation item) {
-        TagKey<Item> tag = getPreferredTag(item);
+        UnifyTag<Item> tag = getPreferredTag(item);
         if (tag == null) {
             return null;
         }
@@ -46,13 +67,17 @@ public class ReplacementMap {
     }
 
     @Nullable
-    public ResourceLocation getPreferredItemByTag(TagKey<Item> tag) {
+    public ResourceLocation getPreferredItemByTag(UnifyTag<Item> tag) {
         return getPreferredItemByTag(tag, null);
     }
 
     @Nullable
-    public ResourceLocation getPreferredItemByTag(TagKey<Item> tag, @Nullable String ignoredNamespace) {
+    public ResourceLocation getPreferredItemByTag(UnifyTag<Item> tag, @Nullable String ignoredNamespace) {
         for (String mod : modPriorities) {
+            if(mod.equals(ignoredNamespace)) {
+                return null;
+            }
+
             List<ResourceLocation> sameModItems = tagMap
                     .getItems(tag)
                     .stream()
@@ -62,7 +87,7 @@ public class ReplacementMap {
                 return sameModItems.get(0);
             }
 
-            if (sameModItems.size() > 1 && !mod.equals(ignoredNamespace)) {
+            if (sameModItems.size() > 1) {
                 ResourceLocation fallback = fallbackStrategy.getFallback(tag, sameModItems, tagMap);
                 if (fallback != null) {
                     return fallback;

Common/src/main/java/com/almostreliable/unified/utils/TagMap.java

@@ -12,8 +12,8 @@ import net.minecraft.world.item.Item;
 import java.util.*;
 
 public class TagMap {
-    private final Map<TagKey<Item>, Set<ResourceLocation>> tagsToItems = new HashMap<>();
+    private final Map<UnifyTag<Item>, Set<ResourceLocation>> tagsToItems = new HashMap<>();
-    private final Map<ResourceLocation, Set<TagKey<Item>>> itemsToTags = new HashMap<>();
+    private final Map<ResourceLocation, Set<UnifyTag<Item>>> itemsToTags = new HashMap<>();
 
     protected TagMap() {}
 
@@ -31,7 +31,7 @@ public class TagMap {
         TagMap tagMap = new TagMap();
 
         for (var entry : tags.entrySet()) {
-            TagKey<Item> tag = TagKey.create(Registry.ITEM_REGISTRY, entry.getKey());
+            UnifyTag<Item> tag = UnifyTag.item(entry.getKey());
             Tag<? extends Holder<?>> holderTag = entry.getValue();
 
             for (Holder<?> holder : holderTag.getValues()) {
@@ -46,16 +46,24 @@ public class TagMap {
         return tagMap;
     }
 
-    protected void put(TagKey<Item> tag, ResourceLocation item) {
+    protected void put(UnifyTag<Item> tag, ResourceLocation item) {
         tagsToItems.computeIfAbsent(tag, k -> new HashSet<>()).add(item);
         itemsToTags.computeIfAbsent(item, k -> new HashSet<>()).add(tag);
     }
 
-    public Collection<ResourceLocation> getItems(TagKey<Item> tag) {
+    public Collection<ResourceLocation> getItems(UnifyTag<Item> tag) {
         return Collections.unmodifiableSet(tagsToItems.getOrDefault(tag, Collections.emptySet()));
     }
 
-    public Collection<TagKey<Item>> getTags(ResourceLocation items) {
+    public Collection<UnifyTag<Item>> getTags(ResourceLocation items) {
         return Collections.unmodifiableSet(itemsToTags.getOrDefault(items, Collections.emptySet()));
     }
+
+    public int tagSize() {
+        return tagsToItems.size();
+    }
+
+    public int itemSize() {
+        return itemsToTags.size();
+    }
 }

Common/src/main/java/com/almostreliable/unified/utils/UnifyTag.java

@@ -0,0 +1,15 @@
+package com.almostreliable.unified.utils;
+
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.item.Item;
+
+public record UnifyTag<T>(Class<T> boundType, ResourceLocation location) {
+    public static UnifyTag<Item> item(ResourceLocation location) {
+        return new UnifyTag<>(Item.class, location);
+    }
+
+    @Override
+    public String toString() {
+        return "UnifyTag[" + boundType.getSimpleName().toLowerCase() + " / " + location + "]";
+    }
+}

Common/src/main/java/com/almostreliable/unified/utils/Utils.java

@@ -10,9 +10,9 @@ import javax.annotation.Nullable;
 
 public class Utils {
     public static final ResourceLocation UNUSED_ID = new ResourceLocation(BuildConfig.MOD_ID, "unused_id");
-    public static final TagKey<Item> UNUSED_TAG = TagKey.create(Registry.ITEM_REGISTRY, UNUSED_ID);
+    public static final UnifyTag<Item> UNUSED_TAG = UnifyTag.item(UNUSED_ID);
 
-    public static TagKey<Item> toItemTag(@Nullable String tag) {
+    public static UnifyTag<Item> toItemTag(@Nullable String tag) {
         if (tag == null) {
             return UNUSED_TAG;
         }
@@ -22,6 +22,6 @@ public class Utils {
             return UNUSED_TAG;
         }
 
-        return TagKey.create(Registry.ITEM_REGISTRY, rl);
+        return UnifyTag.item(rl);
     }
 }

Common/src/test/java/com/almostreliable/unified/FakeResourceKeyRegistry.java

@@ -0,0 +1,23 @@
+package com.almostreliable.unified;
+
+import net.minecraft.core.Registry;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.resources.ResourceLocation;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+
+public class FakeResourceKeyRegistry {
+    @SuppressWarnings("unchecked")
+    public static <T> ResourceKey<Registry<T>> create(String name) {
+        try {
+            Constructor<?> c = ResourceKey.class.getDeclaredConstructor(ResourceLocation.class, ResourceLocation.class);
+            c.setAccessible(true);
+            return (ResourceKey<Registry<T>>) c.newInstance(new ResourceLocation("test_registry"),
+                    new ResourceLocation(name));
+        } catch (NoSuchMethodException | InvocationTargetException | InstantiationException | IllegalAccessException e) {
+            e.printStackTrace();
+            return null;
+        }
+    }
+}

Common/src/test/java/com/almostreliable/unified/TestUtils.java

@@ -0,0 +1,76 @@
+package com.almostreliable.unified;
+
+import com.almostreliable.unified.recipe.RecipeTransformer;
+import com.almostreliable.unified.recipe.handler.RecipeHandlerFactory;
+import com.almostreliable.unified.utils.ReplacementMap;
+import com.almostreliable.unified.utils.TagMapTests;
+import com.almostreliable.unified.utils.UnifyTag;
+import com.google.gson.Gson;
+import net.minecraft.core.Registry;
+import net.minecraft.resources.ResourceKey;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.item.Item;
+
+import java.util.List;
+import java.util.function.Consumer;
+
+public class TestUtils {
+    public static final String TEST_MOD_1 = "test_mod_1";
+    public static final String TEST_MOD_2 = "test_mod_2";
+    public static final String TEST_MOD_3 = "test_mod_3";
+    public static final String TEST_MOD_4 = "test_mod_4";
+    public static final String TEST_MOD_5 = "test_mod_5";
+    public static final List<String> TEST_MOD_PRIORITIES = List.of(TEST_MOD_1,
+            TEST_MOD_2,
+            TEST_MOD_3,
+            TEST_MOD_4,
+            TEST_MOD_5);
+    public static final ResourceKey<Registry<Item>> FAKE_ITEM_REGISTRY = FakeResourceKeyRegistry.create("item");
+    public static final UnifyTag<Item> BRONZE_ORES_TAG = tag("forge:ores/bronze");
+    public static final UnifyTag<Item> INVAR_ORES_TAG = tag("forge:ores/invar");
+    public static final UnifyTag<Item> TIN_ORES_TAG = tag("forge:ores/tin");
+    public static final UnifyTag<Item> SILVER_ORES_TAG = tag("forge:ores/silver");
+    public static final List<UnifyTag<Item>> TEST_ALLOWED_TAGS = List.of(BRONZE_ORES_TAG,
+            INVAR_ORES_TAG,
+            TIN_ORES_TAG,
+            SILVER_ORES_TAG);
+
+    /**
+     * ResourceKey is null because otherwise tests can't run because Minecraft is not bootstrapped ...
+     *
+     * @param name the name of the tag
+     * @return a TagKey for the given name
+     */
+    public static UnifyTag<Item> tag(String name) {
+        return UnifyTag.item(new ResourceLocation(name));
+    }
+
+    public static ResourceLocation mod1RL(String name) {
+        return new ResourceLocation(TEST_MOD_1, name);
+    }
+
+    public static ResourceLocation mod2RL(String name) {
+        return new ResourceLocation(TEST_MOD_2, name);
+    }
+
+    public static ResourceLocation mod3RL(String name) {
+        return new ResourceLocation(TEST_MOD_3, name);
+    }
+
+    public static ResourceLocation mod4RL(String name) {
+        return new ResourceLocation(TEST_MOD_4, name);
+    }
+
+    public static ResourceLocation mod5RL(String name) {
+        return new ResourceLocation(TEST_MOD_5, name);
+    }
+
+    public static RecipeTransformer basicTransformer(Consumer<RecipeHandlerFactory> consumer) {
+        ReplacementMap map = new ReplacementMap(TagMapTests.testTagMap(),
+                TestUtils.TEST_ALLOWED_TAGS,
+                TestUtils.TEST_MOD_PRIORITIES);
+        RecipeHandlerFactory factory = new RecipeHandlerFactory();
+        consumer.accept(factory);
+        return new RecipeTransformer(factory, map);
+    }
+}

Common/src/test/java/com/almostreliable/unified/recipe/RecipeContextImplTest.java

@@ -0,0 +1,97 @@
+package com.almostreliable.unified.recipe;
+
+import com.almostreliable.unified.TestUtils;
+import com.almostreliable.unified.utils.JsonQuery;
+import com.almostreliable.unified.utils.ReplacementMap;
+import com.almostreliable.unified.utils.TagMapTests;
+import com.google.gson.Gson;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonPrimitive;
+import net.minecraft.resources.ResourceLocation;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+
+public class RecipeContextImplTest {
+    private static String testJson = """
+            {
+                "input": [
+                    {
+                        "tag": "tag_replace_me"
+                    },
+                    [
+                        {
+                            "item": "item_replace_me"
+                        },
+                        {
+                            "item": "item_replace_me"
+                        },
+                        [
+                            {
+                                "item": "item_replace_me"
+                            },
+                            {
+                                "tag": "tag_replace_me"
+                            }
+                        ]
+                    ]
+                ],
+                "results": {
+                    "item": "item_replace_me"
+                }
+            }""";
+
+    public static String mekaTest = """
+            {
+                "type": "mekanism:combining",
+                "mainInput": { "amount": 8, "ingredient": { "tag": "forge:raw_materials/tin" } },
+                "extraInput": { "ingredient": { "tag": "forge:cobblestone/normal" } },
+                "output": { "item": "mekanism:tin_ore" }
+            }
+            """;
+
+    @Test
+    public void depthReplace_MekaTest() {
+        JsonObject json = new Gson().fromJson(mekaTest, JsonObject.class);
+        ReplacementMap map = new ReplacementMap(TagMapTests.testTagMap(),
+                TestUtils.TEST_ALLOWED_TAGS,
+                TestUtils.TEST_MOD_PRIORITIES);
+        RecipeContextImpl context = new RecipeContextImpl(new ResourceLocation("test"), json, map);
+        JsonElement result = context.replaceResultOld(json.getAsJsonObject("output"));
+        assertNull(result);
+    }
+
+    @Test
+    public void depthReplace_NothingReplaced() {
+        JsonObject json = new Gson().fromJson(testJson, JsonObject.class);
+        ReplacementMap map = new ReplacementMap(TagMapTests.testTagMap(),
+                TestUtils.TEST_ALLOWED_TAGS,
+                TestUtils.TEST_MOD_PRIORITIES);
+        RecipeContextImpl context = new RecipeContextImpl(new ResourceLocation("test"), json, map);
+        JsonElement result = context.depthReplace(json,
+                "not_existing",
+                "item",
+                primitive -> new JsonPrimitive("dont_find_this"));
+        assertNull(result);
+    }
+
+    @Test
+    public void depthReplace_Items() {
+        JsonObject json = new Gson().fromJson(testJson, JsonObject.class);
+        ReplacementMap map = new ReplacementMap(TagMapTests.testTagMap(),
+                TestUtils.TEST_ALLOWED_TAGS,
+                TestUtils.TEST_MOD_PRIORITIES);
+        RecipeContextImpl context = new RecipeContextImpl(new ResourceLocation("test"), json, map);
+        JsonElement result = context.depthReplace(json,
+                "item",
+                "item",
+                primitive -> new JsonPrimitive("item_was_replaced"));
+        assertNotNull(result);
+        assertEquals(JsonQuery.of(result, "input/0/item").asString(), "item_was_replaced");
+        assertEquals(JsonQuery.of(result, "input/1/1/item").asString(), "item_was_replaced");
+        assertEquals(JsonQuery.of(result, "input/1/2/0/item").asString(), "item_was_replaced");
+        assertEquals(JsonQuery.of(result, "result/item").asString(), "item_was_replaced");
+    }
+}

Common/src/test/java/com/almostreliable/unified/utils/ReplacementMapTests.java

@@ -0,0 +1,49 @@
+package com.almostreliable.unified.utils;
+
+import com.almostreliable.unified.TestUtils;
+import com.google.common.collect.Lists;
+import net.minecraft.resources.ResourceLocation;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class ReplacementMapTests {
+
+    @Test
+    public void getPreferredItemByTag() {
+        ReplacementMap map = new ReplacementMap(TagMapTests.testTagMap(),
+                TestUtils.TEST_ALLOWED_TAGS,
+                TestUtils.TEST_MOD_PRIORITIES);
+        assertEquals(map.getPreferredItemByTag(TestUtils.BRONZE_ORES_TAG), TestUtils.mod1RL("bronze_ore"));
+        assertNotEquals(map.getPreferredItemByTag(TestUtils.BRONZE_ORES_TAG), TestUtils.mod2RL("bronze_ore"));
+        assertEquals(map.getPreferredItemByTag(TestUtils.INVAR_ORES_TAG), TestUtils.mod1RL("invar_ore"));
+        assertNotEquals(map.getPreferredItemByTag(TestUtils.INVAR_ORES_TAG), TestUtils.mod2RL("invar_ore"));
+        assertEquals(map.getPreferredItemByTag(TestUtils.TIN_ORES_TAG), TestUtils.mod3RL("tin_ore"));
+        assertNotEquals(map.getPreferredItemByTag(TestUtils.TIN_ORES_TAG), TestUtils.mod4RL("tin_ore"));
+        assertEquals(map.getPreferredItemByTag(TestUtils.SILVER_ORES_TAG), TestUtils.mod3RL("silver_ore"));
+        assertNotEquals(map.getPreferredItemByTag(TestUtils.SILVER_ORES_TAG), TestUtils.mod4RL("silver_ore"));
+    }
+
+    @Test
+    public void getPreferredItemByTag_ReversePriority() {
+        // We reverse the order. See `testTagMap` for the mapping.
+        List<String> reverse = Lists.reverse(TestUtils.TEST_MOD_PRIORITIES);
+        ReplacementMap reverseMap = new ReplacementMap(TagMapTests.testTagMap(), TestUtils.TEST_ALLOWED_TAGS, reverse);
+        assertEquals(reverseMap.getPreferredItemByTag(TestUtils.BRONZE_ORES_TAG), TestUtils.mod3RL("bronze_ore"));
+        assertEquals(reverseMap.getPreferredItemByTag(TestUtils.INVAR_ORES_TAG), TestUtils.mod4RL("invar_ore"));
+        assertEquals(reverseMap.getPreferredItemByTag(TestUtils.TIN_ORES_TAG), TestUtils.mod4RL("tin_ore"));
+        assertEquals(reverseMap.getPreferredItemByTag(TestUtils.SILVER_ORES_TAG), TestUtils.mod5RL("silver_ore"));
+    }
+
+    @Test
+    public void getPreferredTag() {
+        ReplacementMap map = new ReplacementMap(TagMapTests.testTagMap(),
+                TestUtils.TEST_ALLOWED_TAGS,
+                TestUtils.TEST_MOD_PRIORITIES);
+
+        assertEquals(map.getPreferredTag(TestUtils.mod1RL("bronze_ore")), TestUtils.BRONZE_ORES_TAG);
+        assertNull(map.getPreferredTag(new ResourceLocation("minecraft:diamond")), "We don't have a tag for diamond");
+    }
+}

Common/src/test/java/com/almostreliable/unified/utils/TagMapTests.java

@@ -0,0 +1,59 @@
+package com.almostreliable.unified.utils;
+
+import com.almostreliable.unified.TestUtils;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.item.Item;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class TagMapTests {
+
+    public static TagMap testTagMap() {
+        TagMap tagMap = new TagMap();
+        UnifyTag<Item> bronzeOreTag = UnifyTag.item(new ResourceLocation("forge:ores/bronze"));
+        UnifyTag<Item> invarOreTag = UnifyTag.item(new ResourceLocation("forge:ores/invar"));
+        UnifyTag<Item> tinOreTag = UnifyTag.item(new ResourceLocation("forge:ores/tin"));
+        UnifyTag<Item> silverOreTag = UnifyTag.item(new ResourceLocation("forge:ores/silver"));
+
+        tagMap.put(bronzeOreTag, TestUtils.mod1RL("bronze_ore"));
+        tagMap.put(bronzeOreTag, TestUtils.mod2RL("bronze_ore"));
+        tagMap.put(bronzeOreTag, TestUtils.mod3RL("bronze_ore"));
+
+        tagMap.put(invarOreTag, TestUtils.mod1RL("invar_ore"));
+        tagMap.put(invarOreTag, TestUtils.mod2RL("invar_ore"));
+        tagMap.put(invarOreTag, TestUtils.mod3RL("invar_ore"));
+        tagMap.put(invarOreTag, TestUtils.mod4RL("invar_ore"));
+
+        tagMap.put(tinOreTag, TestUtils.mod3RL("tin_ore"));
+        tagMap.put(tinOreTag, TestUtils.mod4RL("tin_ore"));
+
+        tagMap.put(silverOreTag, TestUtils.mod3RL("silver_ore"));
+        tagMap.put(silverOreTag, TestUtils.mod4RL("silver_ore"));
+        tagMap.put(silverOreTag, TestUtils.mod5RL("silver_ore"));
+        return tagMap;
+    }
+
+    @Test
+    public void simpleCheck() {
+        TagMap tagMap = new TagMap();
+        UnifyTag<Item> bronzeOreTag = UnifyTag.item(new ResourceLocation("forge:ores/bronze"));
+        tagMap.put(bronzeOreTag, TestUtils.mod1RL("bronze_ore"));
+        tagMap.put(bronzeOreTag, TestUtils.mod2RL("bronze_ore"));
+        tagMap.put(bronzeOreTag, TestUtils.mod3RL("bronze_ore"));
+        tagMap.put(bronzeOreTag, TestUtils.mod4RL("bronze_ore"));
+        tagMap.put(bronzeOreTag, TestUtils.mod5RL("bronze_ore"));
+
+        assertEquals(tagMap.getItems(bronzeOreTag).size(), 5);
+        assertEquals(tagMap.getTags(TestUtils.mod1RL("bronze_ore")).size(), 1);
+        assertEquals(tagMap.getTags(TestUtils.mod2RL("bronze_ore")).size(), 1);
+        assertEquals(tagMap.getTags(TestUtils.mod3RL("bronze_ore")).size(), 1);
+        assertEquals(tagMap.getTags(TestUtils.mod4RL("bronze_ore")).size(), 1);
+        assertEquals(tagMap.getTags(TestUtils.mod5RL("bronze_ore")).size(), 1);
+
+        tagMap.put(UnifyTag.item(new ResourceLocation("forge:ores/invar")), TestUtils.mod1RL("invar_ore"));
+
+        assertEquals(tagMap.tagSize(), 2);
+        assertEquals(tagMap.itemSize(), 6);
+    }
+}

Forge/build.gradle.kts

@@ -61,6 +61,9 @@ minecraft {
 
 sourceSets.main.get().resources.srcDir("src/generated/resources")
 
+// from millions of solutions, this is the only one which works... :-)
+val commonTests: SourceSetOutput = project(":Common").sourceSets["test"].output
+
 dependencies {
     minecraft("net.minecraftforge:forge:${minecraftVersion}-${forgeVersion}")
     compileOnly(project(":Common"))
@@ -80,6 +83,14 @@ dependencies {
     runtimeOnly(fg.deobf("curse.maven:nihilo-400012:3810814"))
 
     annotationProcessor("org.spongepowered:mixin:${mixinVersion}:processor")
+
+    /**
+     * Test dependencies
+     */
+    testImplementation(project(":Common"))
+    testImplementation(commonTests)
+    testImplementation ("org.junit.jupiter:junit-jupiter-api:5.8.1")
+    testRuntimeOnly ("org.junit.jupiter:junit-jupiter-engine:5.8.1")
 }
 
 mixin {
@@ -101,6 +112,10 @@ tasks {
     }
 }
 
+tasks.withType<Test> {
+    useJUnitPlatform()
+}
+
 publishing {
     publications {
         register("mavenJava", MavenPublication::class) {

Forge/src/main/java/com/almostreliable/unified/compat/ie/IERecipeHandler.java

@@ -6,6 +6,7 @@ import com.almostreliable.unified.api.recipe.RecipeHandler;
 import com.almostreliable.unified.api.recipe.RecipeTransformations;
 import com.almostreliable.unified.utils.JsonUtils;
 import com.almostreliable.unified.utils.Utils;
+import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import net.minecraft.resources.ResourceLocation;
@@ -20,79 +21,65 @@ public class IERecipeHandler implements RecipeHandler {
     // TODO make it cleaner
     @Override
     public void collectTransformations(RecipeTransformations builder) {
-        builder.put("input0", (json, context) -> {
+        builder.put("input0", this::replaceIEIngredient); // alloy recipes, refinery
-            replaceIEIngredient(json, context);
+        builder.put("input1", this::replaceIEIngredient); // alloy recipes, refinery
-            return json;
+        builder.put(RecipeConstants.INPUT,
-        }); // alloy recipes, refinery
+                this::replaceIEIngredient); // arc furnace, squeezer, cloche, coke oven, fermenter, fertilizer, metal_press
-        builder.put("input1", (json, context) -> {
+        builder.put("additives", this::replaceIEIngredient); // arc furnace
-            replaceIEIngredient(json, context);
+        builder.put(RecipeConstants.INPUTS, this::replaceIEIngredient); // blueprint, mixer
-            return json;
-        }); // alloy recipes, refinery
-        builder.put(RecipeConstants.INPUT, (json, context) -> {
-            replaceIEIngredient(json, context);
-            return json;
-        }); // arc furnace, squeezer, cloche, coke oven, fermenter, fertilizer, metal_press
-        builder.put("additives", (json, context) -> {
-            replaceIEIngredient(json, context);
-            return json;
-        }); // arc furnace
-        builder.put(RecipeConstants.INPUTS, (json, context) -> {
-            replaceIEIngredient(json, context);
-            return json;
-        }); // blueprint, mixer
-
         // alloy recipes, crusher
-        builder.forEachObject("secondaries", (jsonObject, context) -> {
+        builder.forEachObject("secondaries",
-            replaceIEResult(jsonObject.get(RecipeConstants.OUTPUT), context);
+                (jsonObject, context) ->
-            return jsonObject;
+                        replaceIEResult(jsonObject.get(RecipeConstants.OUTPUT), context) instanceof JsonObject
-        });
+                        ? jsonObject : null);
-
+        builder.put(RecipeConstants.RESULT, this::replaceIEResult);
-        builder.put(RecipeConstants.RESULT, (json, context) -> {
+        builder.put(RecipeConstants.RESULTS, this::replaceIEResult);
-            replaceIEResult(json, context);
-            return json;
-        });
-
-        builder.put(RecipeConstants.RESULTS, (json, context) -> {
-            replaceIEResult(json, context);
-            return json;
-        });
     }
 
-    protected void replaceIEResult(@Nullable JsonElement element, RecipeContext context) {
+    @Nullable
-        if (element == null) {
+    protected JsonElement replaceIEResult(@Nullable JsonElement element, RecipeContext context) {
-            return;
+        if (element instanceof JsonArray array) {
+            if (JsonUtils.replaceOn(array, e -> this.replaceIEResult(e, context))) {
+                return array;
+            }
         }
 
-        JsonUtils.arrayForEach(element, JsonObject.class, json -> {
+        if (element instanceof JsonObject object) {
-            if (json.has(RecipeConstants.ITEM)) {
+            JsonElement tag = object.get(RecipeConstants.TAG);
-                context.replaceResult(json);
+            if (tag != null) {
-            } else if (json.has(RecipeConstants.TAG)) {
                 /*
                  * Immersive Engineering allows tags in result and filters them. So we replace the tags with
                  * the preferred item from our config.
                  */
-                ResourceLocation item = context.getPreferredItemByTag(Utils.toItemTag(json
+                ResourceLocation item = context.getPreferredItemByTag(Utils.toItemTag(object
                         .get(RecipeConstants.TAG)
                         .getAsString()));
                 if (item != null) {
-                    json.remove(RecipeConstants.TAG);
+                    object.remove(RecipeConstants.TAG);
-                    json.addProperty(RecipeConstants.ITEM, item.toString());
+                    object.addProperty(RecipeConstants.ITEM, item.toString());
+                    return object;
                 }
-            } else if (json.has(BASE_KEY)) {
-                replaceIEResult(json.get(BASE_KEY), context);
             }
-        });
+
+            JsonElement base = object.get(BASE_KEY);
+            if (base != null) {
+                JsonElement baseResult = replaceIEResult(base, context);
+                if (baseResult != null) {
+                    object.add(BASE_KEY, baseResult);
+                    return object;
+                }
+            }
+        }
+
+        return context.createResultReplacement(element);
     }
 
-    protected void replaceIEIngredient(@Nullable JsonElement element, RecipeContext context) {
+    @Nullable
-        if (element == null) {
+    public JsonElement replaceIEIngredient(@Nullable JsonElement element, RecipeContext context) {
-            return;
+        if (element instanceof JsonObject json && json.has(BASE_KEY)) {
+            return context.createIngredientReplacement(json.get(BASE_KEY));
         }
 
-        if (element instanceof JsonObject json && json.has(BASE_KEY)) {
+        return context.createIngredientReplacement(element);
-            context.replaceIngredient(json.get(BASE_KEY));
-        } else {
-            context.replaceIngredient(element);
-        }
     }
 }

Forge/src/test/java/com/almostreliable/unified/compat/ie/IERecipeHandlerTest.java

@@ -0,0 +1,88 @@
+package com.almostreliable.unified.compat.ie;
+
+import com.almostreliable.unified.TestUtils;
+import com.almostreliable.unified.api.ModConstants;
+import com.almostreliable.unified.recipe.RecipeTransformer;
+import com.almostreliable.unified.utils.JsonQuery;
+import com.google.gson.Gson;
+import com.google.gson.JsonObject;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class IERecipeHandlerTest {
+    public final Gson gson = new Gson();
+
+    private final String simpleAlloyRecipe = """
+            {
+                "type": "immersiveengineering:alloy",
+                "time": 200,
+                "result": { "count": 2, "base_ingredient": { "tag": "forge:ingots/electrum" } },
+                "input0": { "tag": "forge:ingots/gold" },
+                "input1": { "tag": "forge:ingots/silver" }
+            }
+            """;
+
+    @Test
+    public void notMatching() {
+        RecipeTransformer transformer = TestUtils.basicTransformer(f -> f.registerForMod(ModConstants.IE,
+                new IERecipeHandler()));
+        JsonObject alloy = gson.fromJson(simpleAlloyRecipe, JsonObject.class);
+        JsonObject result = transformer.transformRecipe(alloy);
+        assertNull(result, "Nothing to transform, so it should be null");
+    }
+
+    @Test
+    public void resultTagMatches() {
+        RecipeTransformer transformer = TestUtils.basicTransformer(f -> f.registerForMod(ModConstants.IE,
+                new IERecipeHandler()));
+        JsonObject alloy = gson.fromJson(simpleAlloyRecipe, JsonObject.class);
+        alloy
+                .getAsJsonObject("result")
+                .getAsJsonObject("base_ingredient")
+                .addProperty("tag", TestUtils.BRONZE_ORES_TAG.location().toString());
+        JsonObject result = transformer.transformRecipe(alloy);
+        assertNotEquals(result, alloy, "Result should be different");
+        assertNotNull(result, "Result should not be null");
+        assertNull(JsonQuery.of(result, "result/base_ingredient/tag"), "Tag key should be removed");
+        assertEquals(JsonQuery.of(result, "result/base_ingredient/item").asString(),
+                TestUtils.mod1RL("bronze_ore").toString(),
+                "Result should be bronze_ore");
+    }
+
+    @Test
+    public void resultItemMatches() {
+        RecipeTransformer transformer = TestUtils.basicTransformer(f -> f.registerForMod(ModConstants.IE,
+                new IERecipeHandler()));
+        JsonObject alloy = gson.fromJson(simpleAlloyRecipe, JsonObject.class);
+        alloy.getAsJsonObject("result").getAsJsonObject("base_ingredient").remove("tag");
+        alloy
+                .getAsJsonObject("result")
+                .getAsJsonObject("base_ingredient")
+                .addProperty("item", TestUtils.mod3RL("bronze_ore").toString());
+        JsonObject result = transformer.transformRecipe(alloy);
+        assertNotEquals(result, alloy, "Result should be different");
+        assertNotNull(result, "Result should not be null");
+        assertEquals(JsonQuery.of(result, ("result/base_ingredient/item")).asString(),
+                TestUtils.mod1RL("bronze_ore").toString(),
+                "Transformer should replace bronze_ore from mod3 with bronze_ore from mod1");
+    }
+
+    @Test
+    public void inputAlloyItemMatches() {
+        RecipeTransformer transformer = TestUtils.basicTransformer(f -> f.registerForMod(ModConstants.IE,
+                new IERecipeHandler()));
+        JsonObject alloy = gson.fromJson(simpleAlloyRecipe, JsonObject.class);
+        alloy.getAsJsonObject("result").getAsJsonObject("base_ingredient").remove("tag");
+        alloy
+                .getAsJsonObject("result")
+                .getAsJsonObject("base_ingredient")
+                .addProperty("item", TestUtils.mod3RL("bronze_ore").toString());
+        JsonObject result = transformer.transformRecipe(alloy);
+        assertNotEquals(result, alloy, "Result should be different");
+        assertNotNull(result, "Result should not be null");
+        assertEquals(JsonQuery.of(result, ("result/base_ingredient/item")).asString(),
+                TestUtils.mod1RL("bronze_ore").toString(),
+                "Transformer should replace bronze_ore from mod3 with bronze_ore from mod1");
+    }
+}