Add events relating to falling blocks

src/main/java/xyz/nucleoid/stimuli/event/block/BlockFallEvent.java

@@ -0,0 +1,36 @@
+package xyz.nucleoid.stimuli.event.block;
+
+import net.minecraft.block.BlockState;
+import net.minecraft.server.world.ServerWorld;
+import net.minecraft.util.ActionResult;
+import net.minecraft.util.math.BlockPos;
+import xyz.nucleoid.stimuli.event.StimulusEvent;
+
+/**
+ * Called when a gravity-affected block attempts to fall.
+ *
+ * <p>Upon return:
+ * <ul>
+ * <li>{@link ActionResult#SUCCESS} cancels further processing and allows the block to fall.
+ * <li>{@link ActionResult#FAIL} cancels further processing and prevents the block from falling.
+ * <li>{@link ActionResult#PASS} moves on to the next listener.</ul>
+ * <p>
+ * If all listeners return {@link ActionResult#PASS}, the block successfully falls.
+ */
+public interface BlockFallEvent {
+    StimulusEvent<BlockFallEvent> EVENT = StimulusEvent.create(BlockFallEvent.class, ctx -> (world, pos, state) -> {
+        try {
+            for (BlockFallEvent listener : ctx.getListeners()) {
+                ActionResult result = listener.onBlockFall(world, pos, state);
+                if (result != ActionResult.PASS) {
+                    return result;
+                }
+            }
+        } catch (Throwable t) {
+            ctx.handleException(t);
+        }
+        return ActionResult.PASS;
+    });
+
+    ActionResult onBlockFall(ServerWorld world, BlockPos pos, BlockState state);
+}

src/main/java/xyz/nucleoid/stimuli/mixin/block/FallingBlockMixin.java

@@ -0,0 +1,30 @@
+package xyz.nucleoid.stimuli.mixin.block;
+
+import java.util.Random;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import net.minecraft.block.BlockState;
+import net.minecraft.block.FallingBlock;
+import net.minecraft.server.world.ServerWorld;
+import net.minecraft.util.ActionResult;
+import net.minecraft.util.math.BlockPos;
+import xyz.nucleoid.stimuli.EventInvokers;
+import xyz.nucleoid.stimuli.Stimuli;
+import xyz.nucleoid.stimuli.event.block.BlockFallEvent;
+
+@Mixin(FallingBlock.class)
+public class FallingBlockMixin {
+    @Inject(method = "scheduledTick", at = @At("HEAD"), cancellable = true)
+    private void scheduledTick(BlockState state, ServerWorld world, BlockPos pos, Random random, CallbackInfo ci) {
+        try (EventInvokers invokers = Stimuli.select().at(world, pos)) {
+            ActionResult result = invokers.get(BlockFallEvent.EVENT).onBlockFall(world, pos, state);
+            if (result == ActionResult.FAIL) {
+                ci.cancel();
+            }
+        }
+    }
+}

src/main/resources/stimuli.mixins.json

@@ -6,6 +6,7 @@
   "mixins": [
     "block.BlockItemMixin",
     "block.BlockMixin",
+    "block.FallingBlockMixin",
     "block.FarmlandBlockMixin",
     "entity.LivingEntityMixin",
     "player.CraftingResultInventoryMixin",