conditionals yes

src/main/java/org/violetmoon/zeta/annotation/ConditionalMixin.java

@@ -0,0 +1,23 @@
+package org.violetmoon.zeta.annotation;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Make a mixin depend on conditions to work
+ */
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface ConditionalMixin {
+    /**
+     * Only load mixin if requirements are fulfilled
+     */
+    Requirement[] require() default {};
+
+    /**
+     * Don't load mixin if any of the requirements are fulfilled, higher priority then require
+     */
+    Requirement[] conflict() default {};
+}

src/main/java/org/violetmoon/zeta/annotation/Requirement.java

@@ -0,0 +1,22 @@
+package org.violetmoon.zeta.annotation;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Requirement {
+    /**
+     * List of mod-id's
+     */
+    String[] value();
+
+    /**
+     * Versions | Doesnt work yet
+     */
+    String[] versionPredicates() default {};
+
+    /**
+     * if true, then mixin is applied when x mod is present otherwise not
+     */
+    boolean applyIfPresent() default true;
+}

src/main/java/org/violetmoon/zeta/api/ConditionalMixinManager.java

@@ -0,0 +1,50 @@
+package org.violetmoon.zeta.api;
+
+import org.objectweb.asm.Type;
+import org.objectweb.asm.tree.AnnotationNode;
+import org.spongepowered.asm.service.MixinService;
+import org.spongepowered.asm.util.Annotations;
+import org.violetmoon.zeta.Zeta;
+import org.violetmoon.zeta.annotation.ConditionalMixin;
+import org.violetmoon.zeta.annotation.Requirement;
+
+import java.io.IOException;
+import java.util.List;
+
+public class ConditionalMixinManager {
+    public static boolean shouldApply(Zeta zeta, String targetClassName, String mixinClassName) {
+        try {
+            List<AnnotationNode> annotationNodes = MixinService.getService().getBytecodeProvider().getClassNode(targetClassName).visibleAnnotations;
+            if (annotationNodes == null) return true;
+
+            boolean shouldApply = true;
+            for (AnnotationNode node : annotationNodes) {
+                if (node.desc.equals(Type.getDescriptor(ConditionalMixin.class))) {
+                    List<Requirement> requirements = Annotations.getValue(node, "require", Requirement.class);
+                    for (Requirement req : requirements) {
+                        String[] modids = req.value();
+                        boolean applyIfPresent = req.applyIfPresent();
+
+                        boolean areModsLoaded = areModsLoaded(zeta, modids);
+
+                        shouldApply = areModsLoaded == applyIfPresent;
+                        Zeta.GLOBAL_LOG.info("{}: {} is{}being applied because the mod(s) {} are{}loaded", zeta.modid, targetClassName, shouldApply ? " " : " not ", modids, areModsLoaded ? " " : " not ");
+                    }
+                }
+            }
+
+            return shouldApply;
+        } catch (IOException | ClassNotFoundException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private static boolean areModsLoaded(Zeta zeta, String[] modids) {
+        for (String mod : modids) {
+            if (zeta.isModLoaded(mod)) {
+                return true;
+            }
+        }
+        return false;
+    }
+}