Add the concept of "available peripherals" to IComputerAccess

This provides a mechanism for peripherals to see what else a computer is
connected to - and then interact with those peripherals.

We also add the ability to query what block or tile a peripheral
targets. This allows one to interact with the original block of adjacent
peripherals instead.

src/main/java/dan200/computercraft/api/peripheral/IComputerAccess.java

@@ -13,6 +13,8 @@ import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
+import java.util.Collections;
+import java.util.Map;
 
 /**
  * The interface passed to peripherals by computers or turtles, providing methods
@@ -154,4 +156,33 @@ public interface IComputerAccess
      */
     @Nonnull
     String getAttachmentName();
+
+    /**
+     * Get a set of peripherals that this computer access can "see", along with their attachment name.
+     *
+     * This may include other peripherals on the wired network or peripherals on other sides of the computer.
+     *
+     * @return All reachable peripherals
+     * @see #getAttachmentName()
+     * @see #getAvailablePeripheral(String)
+     */
+    @Nonnull
+    default Map<String, IPeripheral> getAvailablePeripherals()
+    {
+        return Collections.emptyMap();
+    }
+
+    /**
+     * Get a reachable peripheral with the given attachement name. This is a equivalent to
+     * {@link #getAvailablePeripherals()}{@code .get(name)}, though may be more performant.
+     *
+     * @param name The peripheral's attached name
+     * @return The reachable peripheral, or {@code null} if none can be found.
+     * @see #getAvailablePeripherals()
+     */
+    @Nullable
+    default IPeripheral getAvailablePeripheral( @Nonnull String name )
+    {
+        return null;
+    }
 }

src/main/java/dan200/computercraft/api/peripheral/IPeripheral.java

@@ -114,6 +114,18 @@ public interface IPeripheral
     {
     }
 
+    /**
+     * Get the object that this peripheral provides methods for. This will generally be the tile entity
+     * or block, but may be an inventory, entity, etc...
+     *
+     * @return The object this peripheral targets
+     */
+    @Nonnull
+    default Object getTarget()
+    {
+        return this;
+    }
+
     /**
      * Determine whether this peripheral is equivalent to another one.
      *

src/main/java/dan200/computercraft/core/apis/PeripheralAPI.java

@@ -15,10 +15,11 @@ import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.core.computer.Computer;
 import dan200.computercraft.core.computer.ComputerThread;
 import dan200.computercraft.core.computer.ITask;
-import dan200.computercraft.core.filesystem.FileSystem;
 
 import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -180,10 +181,49 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
             }
             return m_side;
         }
+
+        @Nonnull
+        @Override
+        public Map<String, IPeripheral> getAvailablePeripherals()
+        {
+            if( !m_attached )
+            {
+                throw new RuntimeException( "You are not attached to this Computer" );
+            }
+
+            Map<String, IPeripheral> peripherals = new HashMap<>();
+            for( PeripheralWrapper wrapper : m_peripherals )
+            {
+                if( wrapper != null && wrapper.isAttached() )
+                {
+                    peripherals.put( wrapper.getAttachmentName(), wrapper.getPeripheral() );
+                }
+            }
+
+            return Collections.unmodifiableMap( peripherals );
+        }
+
+        @Nullable
+        @Override
+        public IPeripheral getAvailablePeripheral( @Nonnull String name )
+        {
+            if( !m_attached )
+            {
+                throw new RuntimeException( "You are not attached to this Computer" );
+            }
+
+            for( PeripheralWrapper wrapper : m_peripherals )
+            {
+                if( wrapper != null && wrapper.isAttached() && wrapper.getAttachmentName().equals( name ) )
+                {
+                    return wrapper.getPeripheral();
+                }
+            }
+            return null;
+        }
     }
 
     private final IAPIEnvironment m_environment;
-    private FileSystem m_fileSystem;
     private final PeripheralWrapper[] m_peripherals;
     private boolean m_running;
 
@@ -285,7 +325,6 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
     {
         synchronized( m_peripherals )
         {
-            m_fileSystem = m_environment.getFileSystem();
             m_running = true;
             for( int i=0; i<6; ++i )
             {
@@ -312,7 +351,6 @@ public class PeripheralAPI implements ILuaAPI, IAPIEnvironment.IPeripheralChange
                     wrapper.detach();
                 }
             }
-            m_fileSystem = null;
         }
     }
 

src/main/java/dan200/computercraft/shared/computer/blocks/ComputerPeripheral.java

@@ -97,4 +97,11 @@ public class ComputerPeripheral
     {
         return (other != null && other.getClass() == this.getClass());
     }
+
+    @Nonnull
+    @Override
+    public Object getTarget()
+    {
+        return m_computer.getTile();
+    }
 }

src/main/java/dan200/computercraft/shared/peripheral/diskdrive/DiskDrivePeripheral.java

@@ -196,4 +196,11 @@ public class DiskDrivePeripheral implements IPeripheral
         }
         return false;
     }
+
+    @Nonnull
+    @Override
+    public Object getTarget()
+    {
+        return m_diskDrive;
+    }
 }

src/main/java/dan200/computercraft/shared/peripheral/printer/PrinterPeripheral.java

@@ -145,6 +145,13 @@ public class PrinterPeripheral implements IPeripheral
         return false;
     }
 
+    @Nonnull
+    @Override
+    public Object getTarget()
+    {
+        return m_printer;
+    }
+
     private Terminal getCurrentPage() throws LuaException
     {
         Terminal currentPage = m_printer.getCurrentPage();