Recipe backtracking

src/main/kotlin/ru/dbotthepony/mc/otm/matter/RecipeResolverManager.kt

@@ -65,7 +65,19 @@ object RecipeResolverManager : SimpleJsonResourceReloadListener(GsonBuilder().se
 		 * if we can't resolve one of ingredient's matter value - consider output also having no matter value
 		 */
 		val isCritical: Boolean = true,
-		val name: ResourceLocation? = null
+		val name: ResourceLocation? = null,
+
+		/**
+		 * Whenever to allow "backtracking" recipe ingredients to recipe outputs.
+		 *
+		 * When an item has no recipes, but takes part in recipes with output of already determined matter value
+		 * (e.g. 4 rabbit hides -> 1 leather), we can assume that we can determine matter value of ingredients based on matter value of output
+		 *
+		 * "Backtrack" can happen if everything of the next holds true:
+		 * * All recipes with item in question contains only that item; and
+		 * * All recipes allow backtracking
+		 */
+		val allowBacktrack: Boolean = true,
 	) {
 		val inputs: List<List<ImmutableStack>> = inputs
 			.map { it.filter { it.multiplier > 0.0 }.collect(ImmutableList.toImmutableList()) }
@@ -92,6 +104,8 @@ object RecipeResolverManager : SimpleJsonResourceReloadListener(GsonBuilder().se
 		 *
 		 * Internally, OTM separate parallel streams from sequential so sequential streams happen strictly on server thread
 		 * (if you can't avoid side effects, or don't bother with synchronization).
+		 *
+		 * You can safely call [MatterManager.getDirect] inside returned stream, both parallel and sequential.
 		 */
 		fun find(server: MinecraftServer, json: JsonObject): Stream<ResolvedRecipe>
 	}
@@ -118,6 +132,7 @@ object RecipeResolverManager : SimpleJsonResourceReloadListener(GsonBuilder().se
 
 				val isCritical = data["is_critical"]?.asBoolean ?: true
 				val ignoreDamageables = data["ignore_damageables"]?.asBoolean ?: false
+				val allowBacktrack = data["allow_backtrack"]?.asBoolean ?: true
 
 				server.recipeManager.byType(findRecipeType).values.parallelStream()
 					.filter { !it.isIncomplete && !it.ingredients.stream().anyMatch { it.isActuallyEmpty } } // get rid of invalid recipes, second "isActuallyEmpty" is required because we do care about ingredients being "missing"
@@ -129,7 +144,8 @@ object RecipeResolverManager : SimpleJsonResourceReloadListener(GsonBuilder().se
 							it.ingredients.stream().map { Arrays.stream(it.items).map { ImmutableStack(it) } },
 							ImmutableStack(it.resultItem),
 							isCritical = isCritical,
-							name = it.id
+							name = it.id,
+							allowBacktrack = allowBacktrack
 						)
 					}
 					.filter { it.inputs.isNotEmpty() }
@@ -291,11 +307,47 @@ object RecipeResolverManager : SimpleJsonResourceReloadListener(GsonBuilder().se
 
 		val recipes = output2Recipes[item]
 
-		if (recipes == null) {
+		if (recipes == null || recipes.isEmpty()) {
+			val recipes2 = input2Recipes[item]
+
+			if (recipes2 == null || recipes2.isEmpty() || !recipes2.all { it.allowBacktrack } || !recipes2.all { it.inputs.all { it.all { it.item == item } } }) {
 				commentary[item] = TextComponent("Item '${item.registryName}' has no recipes")
 				return Result.MISSING
 			}
 
+			var minimal: IMatterValue? = null
+			var minimalMultiplier = 0.0
+			var foundRecipe: ResolvedRecipe? = null
+
+			for (recipe in recipes2) {
+				val value = MatterManager.getDirect(recipe.output.item)
+
+				if (value.hasMatterValue) {
+					if (minimal == null || minimal < value) {
+						minimal = value
+						minimalMultiplier = recipe.output.multiplier / recipe.inputs.size
+						foundRecipe = recipe
+					}
+				} else {
+					minimal = null
+					break
+				}
+			}
+
+			if (minimal == null) {
+				commentary[item] = TextComponent("Item '${item.registryName}' has no valid backtracking recipes, and no output recipes")
+				return Result.MISSING
+			}
+
+			val result = MatterValue(minimal.matter * minimalMultiplier, minimal.complexity * minimalMultiplier)
+
+			changes = true
+			determinedValues[item] = result
+			commentary[item] = TextComponent("Matter value backtracked from ${foundRecipe!!.formattedName}")
+
+			return Result(result)
+		}
+
 		var hadSkips = false
 
 		recipesLoop@ for (recipe in recipes) {