#6 DMR Decoder (#947)

* #6 DMR decoder feature - work in progress

* #6 DMR Decoder.

* #6 DMR Decoder.  Code review updates.

Co-authored-by: Zhenyu Mao <maozhenyu@foxmail.com>
Co-authored-by: Denny <denny@denny-desktop>

src/main/java/io/github/dsheirer/module/HistoryModule.java

@@ -0,0 +1,101 @@
+/*
+ * *****************************************************************************
+ *  Copyright (C) 2014-2020 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.module;
+
+import io.github.dsheirer.sample.Broadcaster;
+import io.github.dsheirer.sample.Listener;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Abstract base history module.  Maintains a history of items and constrains the total history size.  Adds support
+ * for registering a listener to receive a copy of new items as they arrive.
+ *
+ * Note: internal history items are de-duplicated.  However, all items are passed through to the listener.
+ */
+public abstract class HistoryModule<T> extends Module implements Listener<T>
+{
+    private List<T> mItems = new ArrayList<>();
+    private Broadcaster<T> mBroadcaster = new Broadcaster<>();
+    private int mMaximumHistorySize;
+
+    /**
+     * Constructs an instance
+     */
+    public HistoryModule(int maximumHistorySize)
+    {
+        mMaximumHistorySize = maximumHistorySize;
+    }
+
+    /**
+     * Access a copy of the events from this event history
+     */
+    public List<T> getItems()
+    {
+    return new ArrayList<>(mItems);
+    }
+
+    @Override
+    public void reset()
+    {
+        mItems.clear();
+    }
+
+    @Override
+    public void start()
+    {
+    }
+
+    @Override
+    public void stop()
+    {
+        mItems.clear();
+        mBroadcaster.clear();
+    }
+
+    /**
+     * Adds the listener to receive a copy of all items received by this history.
+     * @param listener to receive items, or pass null to clear existing listener.
+     */
+    public void addListener(Listener<T> listener)
+    {
+        mBroadcaster.addListener(listener);
+    }
+
+    /**
+     * Primary item receiver method.
+     */
+    @Override
+    public void receive(T item)
+    {
+        while(mItems.size() > mMaximumHistorySize)
+        {
+            mItems.remove(0);
+        }
+
+        if(!mItems.contains(item))
+        {
+            mItems.add(item);
+        }
+
+        mBroadcaster.broadcast(item);
+    }
+}