2 files changed, 76 insertions, 0 deletions
diff --git a/src/main/java/com/keuin/crosslink/messaging/history/HistoricMessageRecorder.java b/src/main/java/com/keuin/crosslink/messaging/history/HistoricMessageRecorder.java
new file mode 100644
index 0000000..2412bb4
--- /dev/null
+++ b/src/main/java/com/keuin/crosslink/messaging/history/HistoricMessageRecorder.java
@@ -0,0 +1,51 @@
+package com.keuin.crosslink.messaging.history;
+
+import com.keuin.crosslink.messaging.message.IMessage;
+import com.keuin.crosslink.util.Pair;
+
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Objects;
+import java.util.stream.Collectors;
+
+public class HistoricMessageRecorder implements IHistoricMessageRecorder {
+    private final long ttlMillis;
+    private final LinkedList<Pair<Long, IMessage>> que = new LinkedList<>();
+    private final Object lock = new Object();
+
+    public HistoricMessageRecorder(long ttlMillis) {
+        this.ttlMillis = ttlMillis;
+    }
+
+    private void clean() {
+        for (var head = que.peek();
+             head != null &&
+                     Math.abs(System.currentTimeMillis() - head.getK()) > ttlMillis;
+             head = que.peek()
+        ) {
+            // head has expired, remove it
+            que.removeFirst();
+        }
+    }
+    /**
+     * Add and memorize a message.
+     * Note: this implementation is synchronized. Be caution if you requires a high performance.
+     * @param message the message to save.
+     */
+    @Override
+    public void addMessage(IMessage message) {
+        Objects.requireNonNull(message);
+        synchronized (lock) {
+            que.add(new Pair<>(System.currentTimeMillis(), message));
+            clean();
+        }
+    }
+
+    @Override
+    public List<IMessage> getMessages() {
+        synchronized (lock) {
+            clean();
+            return que.stream().map(Pair::getV).collect(Collectors.toList());
+        }
+    }
+}
diff --git a/src/main/java/com/keuin/crosslink/messaging/history/IHistoricMessageRecorder.java b/src/main/java/com/keuin/crosslink/messaging/history/IHistoricMessageRecorder.java
new file mode 100644
index 0000000..f5f245d
--- /dev/null
+++ b/src/main/java/com/keuin/crosslink/messaging/history/IHistoricMessageRecorder.java
@@ -0,0 +1,25 @@
+package com.keuin.crosslink.messaging.history;
+
+import com.keuin.crosslink.messaging.message.IMessage;
+
+import java.util.List;
+
+/**
+ * Save and keep messages with a TTL.
+ * The recorder behaves like an unlimited queue which features TTL on the messages.
+ * Messages can be appended and traverse at any time.
+ * Outdated messages will be removed from the internal storage.
+ */
+public interface IHistoricMessageRecorder {
+    /**
+     * Add and memorize a message.
+     * @param message the message to save.
+     */
+    void addMessage(IMessage message);
+
+    /**
+     * Get recent messages.
+     * @return an {@link List} containing all recent messages in the time scope.
+     */
+    List<IMessage> getMessages();
+}