Trigger chunk load when remove_spawn_chunks is enabled and end portal…

… teleportation occurs

Related: #404

common/src/main/java/org/embeddedt/modernfix/common/mixin/perf/remove_spawn_chunks/EntityMixin.java

@@ -0,0 +1,37 @@
+package org.embeddedt.modernfix.common.mixin.perf.remove_spawn_chunks;
+
+import com.llamalad7.mixinextras.injector.ModifyExpressionValue;
+import net.minecraft.core.BlockPos;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.server.level.TicketType;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.level.ChunkPos;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+
+@Mixin(Entity.class)
+public class EntityMixin {
+    /**
+     * @author embeddedt
+     * @reason If the spawn chunks are not loaded, end portals linking to the overworld will teleport entities into
+     * the void at the spawn position, which is not ideal. To solve this, we create a PORTAL ticket if the expected
+     * overworld chunk is missing.
+     */
+    @ModifyExpressionValue(method = "findDimensionEntryPoint", at = @At(value = "INVOKE", target = "Lnet/minecraft/server/level/ServerLevel;getSharedSpawnPos()Lnet/minecraft/core/BlockPos;"), require = 0)
+    private BlockPos mfix$triggerChunkloadAtSpawnPos(BlockPos spawnPos, ServerLevel destination) {
+        // Only apply this change if the overworld is the destination
+        if (destination.dimension() == ServerLevel.OVERWORLD) {
+            // No ticket is required if the chunk happens to already be loaded
+            if(!destination.hasChunk(spawnPos.getX() >> 4, spawnPos.getZ() >> 4)) {
+                // Create a portal ticket. While we could just load the chunk once, it would immediately unload on the
+                // next tick, causing churn. The ticket will keep it loaded for a few seconds which should give high
+                // performance for farms pumping things through portals frequently.
+                BlockPos key = spawnPos.immutable();
+                destination.getChunkSource().addRegionTicket(TicketType.PORTAL, new ChunkPos(key), 3, key);
+                // Wait for the chunk to be loaded, as adding the ticket is asynchronous
+                destination.getChunk(key);
+            }
+        }
+        return spawnPos;
+    }
+}