Add missed messages util

app/src/main/java/com/github/gotify/MissedMessageUtil.java

@@ -0,0 +1,75 @@
+package com.github.gotify;
+
+import com.github.gotify.api.Api;
+import com.github.gotify.api.Callback;
+import com.github.gotify.client.ApiClient;
+import com.github.gotify.client.ApiException;
+import com.github.gotify.client.api.MessageApi;
+import com.github.gotify.client.model.Message;
+import com.github.gotify.client.model.PagedMessages;
+import com.github.gotify.log.Log;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class MissedMessageUtil {
+    static final int NO_MESSAGES = 0;
+
+    private final MessageApi api;
+
+    public MissedMessageUtil(ApiClient client) {
+        api = new MessageApi(client);
+    }
+
+    public void lastReceivedMessage(Callback.SuccessCallback<Integer> successCallback) {
+        Api.<PagedMessages>withLogging((cb) -> api.getMessagesAsync(1, 0, cb))
+                .handle(
+                        (messages) -> {
+                            if (messages.getMessages().size() == 1) {
+                                successCallback.onSuccess(messages.getMessages().get(0).getId());
+                            } else {
+                                successCallback.onSuccess(NO_MESSAGES);
+                            }
+                        },
+                        (e) -> {});
+    }
+
+    public List<Message> missingMessages(int till) {
+        List<Message> result = new ArrayList<>();
+        try {
+
+            Integer since = null;
+            while (true) {
+                PagedMessages pagedMessages = api.getMessages(10, since);
+                List<Message> messages = pagedMessages.getMessages();
+                List<Message> filtered = filter(messages, till);
+                result.addAll(filtered);
+                if (messages.size() != filtered.size()
+                        || messages.size() == 0
+                        || pagedMessages.getPaging().getNext() == null) {
+                    break;
+                }
+                since = pagedMessages.getPaging().getSince();
+            }
+        } catch (ApiException e) {
+            Log.e("cannot retrieve missing messages", e);
+        }
+        Collections.reverse(result);
+        return result;
+    }
+
+    private List<Message> filter(List<Message> messages, int till) {
+        List<Message> result = new ArrayList<>();
+
+        for (Message message : messages) {
+            if (message.getId() > till) {
+                result.add(message);
+            } else {
+                break;
+            }
+        }
+
+        return result;
+    }
+}