it is done

core/src/mindustry/world/DirectionalItemBuffer.java

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+package mindustry.world;
+
+import mindustry.annotations.Annotations.Struct;
+import arc.util.Time;
+import mindustry.gen.BufferItem;
+import mindustry.type.Item;
+
+import java.io.*;
+
+import static mindustry.Vars.content;
+
+public class DirectionalItemBuffer{
+    public final long[][] buffers;
+    public final int[] indexes;
+    private final float speed;
+
+    public DirectionalItemBuffer(int capacity, float speed){
+        this.buffers = new long[4][capacity];
+        this.indexes = new int[5];
+        this.speed = speed;
+    }
+
+    public boolean accepts(int buffer){
+        return indexes[buffer] < buffers[buffer].length;
+    }
+
+    public void accept(int buffer, Item item){
+        if(!accepts(buffer)) return;
+        buffers[buffer][indexes[buffer]++] = BufferItem.get((byte)item.id, Time.time());
+    }
+
+    public Item poll(int buffer){
+        if(indexes[buffer] > 0){
+            long l = buffers[buffer][0];
+            float time = BufferItem.time(l);
+
+            if(Time.time() >= time + speed || Time.time() < time){
+                return content.item(BufferItem.item(l));
+            }
+        }
+        return null;
+    }
+
+    public void remove(int buffer){
+        System.arraycopy(buffers[buffer], 1, buffers[buffer], 0, indexes[buffer] - 1);
+        indexes[buffer] --;
+    }
+
+    public void write(DataOutput stream) throws IOException{
+        for(int i = 0; i < 4; i++){
+            stream.writeByte(indexes[i]);
+            stream.writeByte(buffers[i].length);
+            for(long l : buffers[i]){
+                stream.writeLong(l);
+            }
+        }
+    }
+
+    public void read(DataInput stream) throws IOException{
+        for(int i = 0; i < 4; i++){
+            indexes[i] = stream.readByte();
+            byte length = stream.readByte();
+            for(int j = 0; j < length; j++){
+                long value = stream.readLong();
+                if(j < buffers[i].length){
+                    buffers[i][j] = value;
+                }
+            }
+        }
+    }
+
+    @Struct
+    class BufferItemStruct{
+        byte item;
+        float time;
+    }
+}