add: Helper#teleportSafely

also fix: /back incorrectly teleports player

src/main/java/io/ib67/sfcraft/module/command/BackModule.java

@@ -42,10 +42,10 @@ public class BackModule extends ServerModule {
         var nearby = wld.getClosestPlayer(_pos.getX(), _pos.getY(), _pos.getZ(), 20, true);
         if (nearby != null) {
             _pos = nearby.getBlockPos();
-            player.teleport(wld, _pos.getX(), _pos.getY(), _pos.getZ(), 0, 0);
+            Helper.teleportSafely(player, wld, _pos.getX(), _pos.getY(), _pos.getZ());
         } else {
             if (SFConsts.UNLIMITED_COMMAND_BACK.hasPermission(player)) {
-                player.teleport(wld, _pos.getX(), _pos.getY(), _pos.getZ(), 0, 0);
+                Helper.teleportSafely(player, wld, _pos.getX(), _pos.getY(), _pos.getZ());
                 return 0;
             }
             player.sendMessage(Text.of("周围没有玩家。").copy().withColor(Colors.RED));

src/main/java/io/ib67/sfcraft/util/Helper.java

@@ -5,7 +5,16 @@ import io.ib67.sfcraft.SFCraft;
 import io.ib67.sfcraft.config.SFConfig;
 import io.ib67.sfcraft.geoip.GeoIPService;
 import lombok.SneakyThrows;
+import net.minecraft.fluid.EmptyFluid;
+import net.minecraft.fluid.LavaFluid;
+import net.minecraft.fluid.WaterFluid;
 import net.minecraft.server.network.ServerPlayerEntity;
+import net.minecraft.server.world.ServerWorld;
+import net.minecraft.text.Text;
+import net.minecraft.util.Colors;
+import net.minecraft.util.math.BlockPos;
+import net.minecraft.util.math.Direction;
+import net.minecraft.world.World;
 
 import java.net.InetSocketAddress;
 import java.nio.file.Files;
@@ -13,6 +22,8 @@ import java.nio.file.Path;
 import java.util.Optional;
 
 public class Helper {
+    public static final char COLOR = '§';
+
     public static boolean canBack(ServerPlayerEntity player) {
         if (!SFConsts.COMMAND_BACK.hasPermission(player)) return false;
         var pos = player.getLastDeathPos().get();
@@ -23,6 +34,41 @@ public class Helper {
         return nearby != null;
     }
 
+    public static boolean teleportSafely(ServerPlayerEntity player, ServerWorld world, int x, int y, int z) {
+        var pos = new BlockPos(x, y, z);
+        var stand = world.getBlockState(pos);
+        if (!stand.isAir() && !stand.isSolidBlock(world, pos)) {
+            // check block type
+            var fluid = stand.getFluidState().getFluid();
+            if (!(fluid instanceof EmptyFluid) && !(fluid instanceof WaterFluid)) {
+                player.sendMessage(Text.literal("§c传送目的地具有非水流体, 因此拒绝传送。"));
+                return false;
+            }
+        }
+        var groundPos = new BlockPos(x, y - 1, z);
+        var ground = world.getBlockState(groundPos);
+        if (!ground.hasSolidTopSurface(world, groundPos, player)
+                && !stand.isSolidSurface(world, pos, player, Direction.DOWN)) {
+            player.sendMessage(Text.literal("§c传送目的地没有可靠落地点，且为非空气方块, 因此拒绝传送。"));
+            return false;
+        } else {
+            var deltaY = 0.0;
+            var deltaX = 0.5;
+            var deltaZ = 0.5;
+            var fluid = stand.getFluidState().getFluid();
+            if (!stand.isAir()) {
+                deltaY = stand.getCollisionShape(world, pos).getMax(Direction.Axis.Y);
+                deltaY = Double.isFinite(deltaY) ? deltaY + 0.1 : 0;
+                deltaX = stand.getCollisionShape(world, pos).getMax(Direction.Axis.X);
+                deltaX = Double.isFinite(deltaX) ? deltaX / 2 : 0.5;
+                deltaZ = stand.getCollisionShape(world, pos).getMax(Direction.Axis.X);
+                deltaZ = Double.isFinite(deltaZ) ? deltaZ / 2 : 0.5;
+            }
+            player.teleport(world, x + deltaX, y + deltaY, z + deltaZ, 0, 0);
+        }
+        return true;
+    }
+
     public static String getVersionString(InetSocketAddress address) {
         var geoIp = SFCraft.getInjector().getInstance(GeoIPService.class);
         var config = SFCraft.getInjector().getInstance(SFConfig.class);
@@ -36,6 +82,7 @@ public class Helper {
         }
         return null;
     }
+
     @SneakyThrows
     public static Optional<String> getConfigResource(Path root, String resource) {
         if (Files.exists(root)) {