Aprs heard list

codec2talkie/src/main/java/com/radio/codec2talkie/protocol/aprs/tools/AprsHeardList.java

@@ -1,4 +1,69 @@
 package com.radio.codec2talkie.protocol.aprs.tools;
 
+import java.util.Map;
+
+import java.util.Timer;
+import java.util.TimerTask;
+import java.util.TreeMap;
+
 public class AprsHeardList {
+
+    private final int CLEANUP_PERIOD_MS = 30000;
+
+    private static class AprsHeardListItem {
+        public long timestamp;
+        public String callsign;
+
+        public AprsHeardListItem(long timestamp, String callsign) {
+            this.timestamp = timestamp;
+            this.callsign = callsign;
+        }
+    }
+
+    private final int _keepSeconds;
+    private final TreeMap<String, AprsHeardListItem> _data = new TreeMap<>();
+
+    public AprsHeardList(int keepSeconds) {
+        _keepSeconds = keepSeconds;
+        scheduleCleanup();
+    }
+
+    public void add(String callsign) {
+        synchronized (_data) {
+            AprsHeardListItem heardItem = _data.get(callsign);
+            if (heardItem == null) {
+                AprsHeardListItem newHeardItem = new AprsHeardListItem(System.currentTimeMillis(), callsign);
+                _data.put(callsign, newHeardItem);
+            } else {
+                heardItem.timestamp = System.currentTimeMillis();
+            }
+        }
+    }
+
+    public boolean contains(String callsign) {
+        synchronized (_data) {
+            return _data.containsKey(callsign);
+        }
+    }
+
+    private void scheduleCleanup() {
+        Timer cleanupTimer = new Timer();
+        cleanupTimer.schedule(new TimerTask() {
+            @Override
+            public void run() {
+                cleanup();
+            }
+        }, CLEANUP_PERIOD_MS, CLEANUP_PERIOD_MS);
+    }
+
+    private void cleanup() {
+        long removeOlderThan = System.currentTimeMillis() - _keepSeconds * 1000L;
+        synchronized (_data) {
+            for (Map.Entry<String, AprsHeardListItem> entryElement : _data.entrySet()) {
+                if (entryElement.getValue().timestamp < removeOlderThan) {
+                    _data.remove(entryElement.getKey());
+                }
+            }
+        }
+    }
 }