wip implementation of viewmodel/executor/livedata headlines

11 files changed, 401 insertions, 373 deletions

diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiCommon.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiCommon.java
index 75963c96..adc0881d 100644
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiCommon.java
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiCommon.java
@@ -41,13 +41,16 @@ public class ApiCommon {
         void setLastErrorMessage(String message);
     }
 
-    public enum ApiError { NO_ERROR, HTTP_UNAUTHORIZED, HTTP_FORBIDDEN, HTTP_NOT_FOUND,
+    public enum ApiError {
+        SUCCESS, UNKNOWN_ERROR, HTTP_UNAUTHORIZED, HTTP_FORBIDDEN, HTTP_NOT_FOUND,
         HTTP_SERVER_ERROR, HTTP_OTHER_ERROR, SSL_REJECTED, SSL_HOSTNAME_REJECTED, PARSE_ERROR, IO_ERROR, OTHER_ERROR, API_DISABLED,
         API_UNKNOWN, LOGIN_FAILED, INVALID_URL, API_INCORRECT_USAGE, NETWORK_UNAVAILABLE, API_UNKNOWN_METHOD }
 
     public static int getErrorMessage(ApiError error) {
         switch (error) {
-            case NO_ERROR:
+            case SUCCESS:
+                return R.string.error_success;
+            case UNKNOWN_ERROR:
                 return R.string.error_unknown;
             case HTTP_UNAUTHORIZED:
                 return R.string.error_http_unauthorized;
@@ -154,6 +157,7 @@ public class ApiCommon {
 
                 switch (statusCode) {
                     case API_STATUS_OK:
+                        caller.setLastError(ApiError.SUCCESS);
                         return result.getAsJsonObject().get("content");
                     case API_STATUS_ERR:
                         JsonObject contentObj = resultObj.get("content").getAsJsonObject();
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiLoader.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiLoader.java
index 259d7a28..8d83e7bd 100755
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiLoader.java
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiLoader.java
@@ -27,7 +27,7 @@ public class ApiLoader extends AsyncTaskLoader<JsonElement> implements ApiCommon
 		super(context);
 
 		m_context = context;
-		m_lastError = ApiError.NO_ERROR;
+		m_lastError = ApiError.UNKNOWN_ERROR;
 		m_params = params;
 	}
 
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiRequest.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiRequest.java
index 409047f0..ba8dad20 100644
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiRequest.java
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/ApiRequest.java
@@ -21,7 +21,7 @@ public class ApiRequest extends AsyncTask<HashMap<String,String>, Integer, JsonE
 
 	public ApiRequest(Context context) {
 		m_context = context;
-		m_lastError = ApiError.NO_ERROR;
+		m_lastError = ApiError.UNKNOWN_ERROR;
 	}
 
 	@SuppressLint("NewApi")
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/Application.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/Application.java
index 81ae7bdf..08beaa99 100755
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/Application.java
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/Application.java
@@ -19,19 +19,24 @@ public class Application extends android.app.Application {
 
 	// this is the only instance of a (large) object which contains all currently loaded articles and is
 	// used by all fragments and activities concurrently
-	private final ArticleList m_articles = new ArticleList();
+	// private final ArticleList m_articles = new ArticleList();
 
 	private String m_sessionId;
 	private int m_apiLevel;
 	public LinkedHashMap<String, String> m_customSortModes = new LinkedHashMap<>();
 	ConnectivityManager m_cmgr;
+	HeadlinesModel m_headlinesModel;
 
 	public static Application getInstance(){
 		return m_singleton;
 	}
 
 	public static ArticleList getArticles() {
-		return getInstance().m_articles;
+		return getInstance().m_headlinesModel.getArticles();
+	}
+
+	public HeadlinesModel getHeadlinesModel() {
+		return getInstance().m_headlinesModel;
 	}
 
 	@Override
@@ -40,6 +45,7 @@ public class Application extends android.app.Application {
 
 		m_singleton = this;
 		m_cmgr = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
+		m_headlinesModel = new HeadlinesModel(this);
 	}
 
 	public String getSessionId() {
@@ -87,5 +93,4 @@ public class Application extends android.app.Application {
 
 		return false;
 	}
-
 }
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/ArticlePager.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/ArticlePager.java
index f1ff8384..72b873a2 100755
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/ArticlePager.java
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/ArticlePager.java
@@ -35,8 +35,6 @@ public class ArticlePager extends androidx.fragment.app.Fragment {
 
 		public PagerAdapter(@NonNull Fragment fragment) {
 			super(fragment, new HeadlinesDiffItemCallback());
-
-			syncToSharedArticles();
 		}
 
 		private void syncToSharedArticles() {
@@ -88,6 +86,15 @@ public class ArticlePager extends androidx.fragment.app.Fragment {
 		View view = inflater.inflate(R.layout.fragment_article_pager, container, false);
 
 		m_adapter = new PagerAdapter(this);
+		m_adapter.submitList(Application.getArticles());
+
+		HeadlinesModel model = Application.getInstance().getHeadlinesModel();
+
+		// deal with further updates
+		model.getLiveData().observe(getActivity(), articles -> {
+				Log.d(TAG, "observed article list size=" + articles.size());
+				m_adapter.submitList(articles);
+			});
 		
 		m_pager = view.findViewById(R.id.article_pager);
 
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesFragment.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesFragment.java
index a3a1bb46..6ca33b60 100755
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesFragment.java
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesFragment.java
@@ -48,7 +48,6 @@ import androidx.annotation.Nullable;
 import androidx.core.app.ActivityCompat;
 import androidx.core.app.ActivityOptionsCompat;
 import androidx.core.view.ViewCompat;
-import androidx.loader.app.LoaderManager;
 import androidx.loader.content.Loader;
 import androidx.preference.PreferenceManager;
 import androidx.recyclerview.widget.DefaultItemAnimator;
@@ -86,74 +85,10 @@ import java.util.TimeZone;
 
 import jp.wasabeef.glide.transformations.CropCircleTransformation;
 
-public class HeadlinesFragment extends androidx.fragment.app.Fragment implements LoaderManager.LoaderCallbacks<ArticleList> {
+public class HeadlinesFragment extends androidx.fragment.app.Fragment {
 
 	private boolean m_isLazyLoading;
 
-	@NonNull
-	@Override
-	public Loader<ArticleList> onCreateLoader(int id, @Nullable Bundle args) {
-		return new HeadlinesLoader(getContext(), m_feed, m_activity.getResizeWidth(), Application.getArticles());
-	}
-
-	@Override
-	public void onLoadFinished(@NonNull Loader<ArticleList> loader, ArticleList data) {
-		Log.d(TAG, "onLoadFinished loader=" + loader + " size=" + (data != null ? data.size() : "N/A (null)"));
-
-		HeadlinesLoader headlinesLoader = (HeadlinesLoader) loader;
-
-		// successful update
-		if (data != null) {
-
-			// shared article list contains raw returned data without footers
-			ArticleList sharedArticles = Application.getArticles();
-			sharedArticles.clear();
-			sharedArticles.addAll(data);
-
-			ArticleList tmp = new ArticleList();
-
-			tmp.addAll(data);
-
-			if (m_prefs.getBoolean("headlines_mark_read_scroll", false))
-				tmp.add(new Article(Article.TYPE_AMR_FOOTER));
-
-			final boolean appended = headlinesLoader.getAppend();
-
-			m_adapter.submitList(tmp, () -> {
-				if (!appended)
-					m_list.scrollToPosition(0);
-			});
-
-			if (headlinesLoader.getFirstIdChanged())
-				Snackbar.make(getView(), R.string.headlines_row_top_changed, Snackbar.LENGTH_LONG)
-						.setAction(R.string.reload, v -> refresh(false)).show();
-
-			m_listener.onHeadlinesLoaded(headlinesLoader.getAppend());
-
-		} else {
-			if (headlinesLoader.getLastError() == ApiCommon.ApiError.LOGIN_FAILED) {
-				m_activity.login();
-			} else {
-				if (headlinesLoader.getLastErrorMessage() != null) {
-					m_activity.toast(m_activity.getString(headlinesLoader.getErrorMessage()) + "\n" + headlinesLoader.getLastErrorMessage());
-				} else {
-					m_activity.toast(headlinesLoader.getErrorMessage());
-				}
-			}
-		}
-
-		if (m_swipeLayout != null)
-			m_swipeLayout.setRefreshing(false);
-
-		m_isLazyLoading = false;
-	}
-
-	@Override
-	public void onLoaderReset(@NonNull Loader<ArticleList> loader) {
-		if (m_swipeLayout != null)
-			m_swipeLayout.setRefreshing(false);
-	}
-
 	public void notifyItemChanged(int position) {
 		if (m_adapter != null)
 			m_adapter.notifyItemChanged(position);
@@ -169,7 +104,7 @@ public class HeadlinesFragment extends androidx.fragment.app.Fragment implements
 	private Feed m_feed;
 	private int m_activeArticleId;
 	private String m_searchQuery = "";
-	private HeadlinesLoader m_loader;
+	//private HeadlinesLoader m_loader;
 
 	private SharedPreferences m_prefs;
 
@@ -502,7 +437,9 @@ public class HeadlinesFragment extends androidx.fragment.app.Fragment implements
 					}
 				}
 
-				if (dy > 0 && !m_isLazyLoading && (m_loader == null || m_loader.lazyLoadEnabled()) &&
+				HeadlinesModel model = Application.getInstance().getHeadlinesModel();
+
+				if (dy > 0 && !m_isLazyLoading && model.lazyLoadEnabled() &&
 						lastVisibleItem >= Application.getArticles().size() - 5) {
 
 					m_isLazyLoading = true;
@@ -519,6 +456,47 @@ public class HeadlinesFragment extends androidx.fragment.app.Fragment implements
             m_activity.setTitle(m_feed.title);
         }
 
+		HeadlinesModel model = Application.getInstance().getHeadlinesModel();
+
+		model.getLiveData().observe(getActivity(), articles -> {
+			Log.d(TAG, "observed article list size=" + articles.size());
+
+			ArticleList tmp = new ArticleList();
+
+			tmp.addAll(articles);
+
+			if (m_prefs.getBoolean("headlines_mark_read_scroll", false))
+				tmp.add(new Article(Article.TYPE_AMR_FOOTER));
+
+			final boolean appended = model.getAppend();
+
+			m_adapter.submitList(tmp, () -> {
+				if (!appended)
+					m_list.scrollToPosition(0);
+			});
+
+			if (model.getFirstIdChanged())
+				Snackbar.make(getView(), R.string.headlines_row_top_changed, Snackbar.LENGTH_LONG)
+						.setAction(R.string.reload, v -> refresh(false)).show();
+
+			if (m_swipeLayout != null)
+				m_swipeLayout.setRefreshing(false);
+
+			m_isLazyLoading = false;
+
+			if (model.getLastError() == ApiCommon.ApiError.LOGIN_FAILED) {
+				m_activity.login();
+			} else if (model.getLastError() != null && model.getLastError() != ApiCommon.ApiError.SUCCESS) {
+				if (model.getLastErrorMessage() != null) {
+					m_activity.toast(m_activity.getString(model.getErrorMessage()) + "\n" + model.getLastErrorMessage());
+				} else {
+					m_activity.toast(model.getErrorMessage());
+				}
+			}
+
+			m_listener.onHeadlinesLoaded(appended);
+		});
+
 		return view;
 	}
 
@@ -561,17 +539,22 @@ public class HeadlinesFragment extends androidx.fragment.app.Fragment implements
 
 		// if we try to initLoader() all the time, onLoadFinished() might be sent twice
 		// https://stackoverflow.com/questions/11293441/android-loadercallbacks-onloadfinished-called-twice
-		if (m_loader == null) {
+		/* if (m_loader == null) {
 			m_loader = (HeadlinesLoader) LoaderManager.getInstance(this).
 					initLoader(Application.LOADER_HEADLINES, null, this);
 
-		}
+		} */
 
 		if (m_swipeLayout != null)
 			m_swipeLayout.setRefreshing(true);
 
-		m_loader.setSearchQuery(getSearchQuery());
-		m_loader.startLoading(append);
+		HeadlinesModel model = Application.getInstance().getHeadlinesModel();
+
+		model.setSearchQuery(getSearchQuery());
+		model.startLoading(append, m_feed, m_activity.getResizeWidth());
+
+		//m_loader.setSearchQuery(getSearchQuery());
+		//m_loader.startLoading(append);
 	}
 
 	static class ArticleViewHolder extends RecyclerView.ViewHolder {
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesLoader.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesLoader.java
deleted file mode 100755
index 812a745e..00000000
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesLoader.java
+++ /dev/null
@@ -1,289 +0,0 @@
-package org.fox.ttrss;
-
-import android.content.Context;
-import android.content.SharedPreferences;
-import android.util.Log;
-
-import androidx.loader.content.AsyncTaskLoader;
-import androidx.preference.PreferenceManager;
-
-import com.google.gson.Gson;
-import com.google.gson.JsonArray;
-import com.google.gson.JsonElement;
-import com.google.gson.JsonObject;
-import com.google.gson.reflect.TypeToken;
-
-import org.fox.ttrss.ApiCommon.ApiError;
-import org.fox.ttrss.types.Article;
-import org.fox.ttrss.types.ArticleList;
-import org.fox.ttrss.types.Feed;
-
-import java.lang.reflect.Type;
-import java.util.HashMap;
-import java.util.List;
-
-public class HeadlinesLoader extends AsyncTaskLoader<ArticleList> implements ApiCommon.ApiCaller {
-	private final String TAG = this.getClass().getSimpleName();
-
-	private final int m_responseCode = 0;
-	protected String m_responseMessage;
-	private int m_apiStatusCode = 0;
-
-	private Context m_context;
-	private String m_lastErrorMessage;
-	private ApiError m_lastError;
-	private ArticleList m_articles;
-	private Feed m_feed;
-	private SharedPreferences m_prefs;
-	private int m_firstId;
-	private String m_searchQuery = "";
-	private boolean m_firstIdChanged;
-	private int m_offset;
-	private int m_amountLoaded;
-	private int m_resizeWidth;
-	private boolean m_append;
-	private boolean m_lazyLoadEnabled = true;
-	private boolean m_loadingInProgress;
-
-	HeadlinesLoader(Context context, Feed feed, int resizeWidth, ArticleList articles) {
-		super(context);
-
-		Log.d(TAG, "HeadlinesLoader created!");
-
-		m_context = context;
-		m_lastError = ApiError.NO_ERROR;
-		m_feed = feed;
-		m_articles = new ArticleList();
-
-		m_articles.addAll(articles);
-
-		m_resizeWidth = resizeWidth;
-		m_prefs = PreferenceManager.getDefaultSharedPreferences(context);
-	}
-
-	protected void startLoading(boolean append) {
-		Log.d(TAG, this + " startLoading append=" + append + " inProgress=" + m_loadingInProgress + " lazyLoadEnabled=" + m_lazyLoadEnabled + "localSize="+ m_articles.size());
-
-		if (!append) {
-			m_append = false;
-			m_lazyLoadEnabled = true;
-
-			forceLoad();
-		} else if (m_lazyLoadEnabled && !m_loadingInProgress) {
-			m_append = true;
-			forceLoad();
-		} else {
-			deliverResult(m_articles);
-		}
-	}
-
-	@Override
-	public void deliverResult(ArticleList data) {
-		super.deliverResult(data);
-	}
-
-	public int getErrorMessage() {
-		return ApiCommon.getErrorMessage(m_lastError);
-	}
-
-	ApiError getLastError() {
-		return m_lastError;
-	}
-
-	String getLastErrorMessage() {
-		return m_lastErrorMessage;
-	}
-
-	public boolean lazyLoadEnabled() {
-		return m_lazyLoadEnabled;
-	}
-
-	@Override
-	public ArticleList loadInBackground() {
-		Log.d(TAG, this + " loadInBackground append=" + m_append + " offset=" + m_offset);
-
-		m_loadingInProgress = true;
-
-		final int skip = getSkip(m_append);
-		final boolean allowForceUpdate = Application.getInstance().getApiLevel() >= 9 &&
-				!m_feed.is_cat && m_feed.id > 0 && !m_append && skip == 0;
-
-		HashMap<String,String> params = new HashMap<>();
-
-		params.put("op", "getHeadlines");
-		params.put("sid", Application.getInstance().getSessionId());
-		params.put("feed_id", String.valueOf(m_feed.id));
-		params.put("show_excerpt", "true");
-		params.put("excerpt_length", String.valueOf(CommonActivity.EXCERPT_MAX_LENGTH));
-		params.put("show_content", "true");
-		params.put("include_attachments", "true");
-		params.put("view_mode", m_prefs.getString("view_mode", "adaptive"));
-		params.put("limit", m_prefs.getString("headlines_request_size", "15"));
-		params.put("skip", String.valueOf(skip));
-		params.put("include_nested", "true");
-		params.put("has_sandbox", "true");
-		params.put("order_by", m_prefs.getString("headlines_sort_mode", "default"));
-
-		if (m_prefs.getBoolean("enable_image_downsampling", false)) {
-			if (m_prefs.getBoolean("always_downsample_images", false) || !Application.getInstance().isWifiConnected()) {
-				params.put("resize_width", String.valueOf(m_resizeWidth));
-			}
-		}
-
-		if (m_feed.is_cat)
-			params.put("is_cat", "true");
-
-		if (allowForceUpdate) {
-			params.put("force_update", "true");
-		}
-
-		if (m_searchQuery != null && !m_searchQuery.isEmpty()) {
-			params.put("search", m_searchQuery);
-			params.put("search_mode", "");
-			params.put("match_on", "both");
-		}
-
-		if (m_firstId > 0)
-			params.put("check_first_id", String.valueOf(m_firstId));
-
-		if (Application.getInstance().getApiLevel() >= 12) {
-			params.put("include_header", "true");
-		}
-
-		Log.d(TAG, "firstId=" + m_firstId + " append=" + m_append + " skip=" + skip + " localSize=" + m_articles.size());
-
-		JsonElement result = ApiCommon.performRequest(m_context, params, this);
-
-		Log.d(TAG, "got result=" + result);
-
-		if (result != null) {
-			try {
-				JsonArray content = result.getAsJsonArray();
-				if (content != null) {
-					final List<Article> articlesJson;
-					final JsonObject header;
-
-					if (Application.getInstance().getApiLevel() >= 12) {
-						header = content.get(0).getAsJsonObject();
-
-						m_firstIdChanged = header.get("first_id_changed") != null;
-
-						try {
-							m_firstId = header.get("first_id").getAsInt();
-						} catch (NumberFormatException e) {
-							m_firstId = 0;
-						}
-
-						Log.d(TAG, this + " firstID=" + m_firstId + " firstIdChanged=" + m_firstIdChanged);
-
-						Type listType = new TypeToken<List<Article>>() {}.getType();
-						articlesJson = new Gson().fromJson(content.get(1), listType);
-					} else {
-						Type listType = new TypeToken<List<Article>>() {}.getType();
-						articlesJson = new Gson().fromJson(content, listType);
-					}
-
-					if (!m_append)
-						m_articles.clear();
-
-					m_amountLoaded = articlesJson.size();
-
-					for (Article article : articlesJson)
-						if (!m_articles.containsId(article.id)) {
-							article.collectMediaInfo();
-							article.cleanupExcerpt();
-							article.fixNullFields();
-							m_articles.add(article);
-						}
-
-					if (m_firstIdChanged) {
-						Log.d(TAG, "first id changed, disabling lazy load");
-						m_lazyLoadEnabled = false;
-					}
-
-					if (m_amountLoaded < Integer.parseInt(m_prefs.getString("headlines_request_size", "15"))) {
-						Log.d(TAG, this + " amount loaded "+m_amountLoaded+" < request size, disabling lazy load");
-						m_lazyLoadEnabled = false;
-					}
-
-					m_offset += m_amountLoaded;
-					m_loadingInProgress = false;
-
-					Log.d(TAG, this + " loaded headlines=" + m_amountLoaded + " resultingLocalSize=" + m_articles.size());
-
-					return m_articles;
-				}
-
-			} catch (Exception e) {
-				e.printStackTrace();
-			}
-		}
-
-		m_loadingInProgress = false;
-
-		return null;
-	}
-
-	private int getSkip(boolean append) {
-		int skip = 0;
-
-		if (append) {
-			// adaptive, all_articles, marked, published, unread
-			String viewMode = m_prefs.getString("view_mode", "adaptive");
-
-			int numUnread = Math.toIntExact(m_articles.getUnreadCount());
-			int numAll = Math.toIntExact(m_articles.getSizeWithoutFooters());
-
-			if ("marked".equals(viewMode)) {
-				skip = numAll;
-			} else if ("published".equals(viewMode)) {
-				skip = numAll;
-			} else if ("unread".equals(viewMode)) {
-				skip = numUnread;
-			} else if (m_searchQuery != null && !m_searchQuery.isEmpty()) {
-				skip = numAll;
-			} else if ("adaptive".equals(viewMode)) {
-				skip = numUnread > 0 ? numUnread : numAll;
-			} else {
-				skip = numAll;
-			}
-		}
-
-		return skip;
-	}
-
-	@Override
-	public void setStatusCode(int statusCode) {
-		m_apiStatusCode = statusCode;
-	}
-
-	@Override
-	public void setLastError(ApiError lastError) {
-		m_lastError = lastError;
-	}
-
-	@Override
-	public void setLastErrorMessage(String message) {
-		m_lastErrorMessage = message;
-	}
-
-	public boolean getFirstIdChanged() {
-		return m_firstIdChanged;
-	}
-
-	public boolean getAppend() {
-		return m_append;
-	}
-
-	public void setSearchQuery(String searchQuery) {
-		m_searchQuery = searchQuery;
-	}
-
-	public String getSearchQuery() {
-		return m_searchQuery;
-	}
-
-	public int getOffset() {
-		return m_offset;
-	}
-}
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesModel.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesModel.java
new file mode 100644
index 00000000..08adb73b
--- /dev/null
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/HeadlinesModel.java
@@ -0,0 +1,317 @@
+package org.fox.ttrss;
+
+import android.app.Application;
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.os.Handler;
+import android.os.Looper;
+import android.util.Log;
+
+import androidx.annotation.NonNull;
+import androidx.lifecycle.AndroidViewModel;
+import androidx.lifecycle.LiveData;
+import androidx.lifecycle.MutableLiveData;
+import androidx.loader.app.LoaderManager;
+import androidx.preference.PreferenceManager;
+
+import com.google.gson.Gson;
+import com.google.gson.JsonArray;
+import com.google.gson.JsonElement;
+import com.google.gson.JsonObject;
+import com.google.gson.reflect.TypeToken;
+
+import org.fox.ttrss.types.Article;
+import org.fox.ttrss.types.ArticleList;
+import org.fox.ttrss.types.Feed;
+
+import java.lang.reflect.Type;
+import java.util.HashMap;
+import java.util.List;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+public class HeadlinesModel extends AndroidViewModel implements ApiCommon.ApiCaller {
+    private final String TAG = this.getClass().getSimpleName();
+    private final MutableLiveData<ArticleList> m_articles = new MutableLiveData<>(new ArticleList());
+    private SharedPreferences m_prefs;
+    private final int m_responseCode = 0;
+    protected String m_responseMessage;
+    private int m_apiStatusCode = 0;
+
+    private String m_lastErrorMessage;
+    private ApiCommon.ApiError m_lastError;
+    private Feed m_feed;
+    private int m_firstId;
+    private String m_searchQuery = "";
+    private boolean m_firstIdChanged;
+    private int m_offset;
+    private int m_amountLoaded;
+    private int m_resizeWidth;
+    private boolean m_append;
+    private boolean m_lazyLoadEnabled = true;
+    private boolean m_loadingInProgress;
+    private ExecutorService m_executor;
+    private Handler m_mainHandler = new Handler(Looper.getMainLooper());
+
+    public HeadlinesModel(@NonNull Application application) {
+        super(application);
+
+        m_prefs = PreferenceManager.getDefaultSharedPreferences(application);
+
+        // do we need concurrency or not?
+        m_executor = Executors.newSingleThreadExecutor();
+    }
+
+    public LiveData<ArticleList> getLiveData() {
+        return m_articles;
+
+    }
+
+    public ArticleList getArticles() {
+        return m_articles.getValue();
+    }
+
+    public void update(ArticleList articles) {
+        m_articles.postValue(articles);
+    }
+
+    public void startLoading(boolean append, @NonNull Feed feed, int resizeWidth) {
+        Log.d(TAG, "startLoading append=" + append);
+
+        m_resizeWidth = resizeWidth;
+
+        if (!append) {
+            m_append = false;
+            m_lazyLoadEnabled = true;
+            m_feed = feed;
+
+            forceLoad();
+        } else if (feed != m_feed || m_lazyLoadEnabled && !m_loadingInProgress) {
+            m_append = true;
+            m_feed = feed;
+            forceLoad();
+        } else {
+            ArticleList tmp = new ArticleList();
+            tmp.addAll(m_articles.getValue());
+
+            m_articles.postValue(tmp);
+        }
+    }
+
+    public void forceLoad() {
+        Log.d(TAG, "forceLoad");
+
+        m_articles.postValue(loadInBackground());
+    }
+
+    public ArticleList loadInBackground() {
+        Log.d(TAG, this + " loadInBackground append=" + m_append + " offset=" + m_offset);
+
+        ArticleList articlesWork = new ArticleList();
+        articlesWork.addAll(m_articles.getValue());
+
+        m_loadingInProgress = true;
+
+        final int skip = getSkip(m_append, articlesWork);
+        final boolean allowForceUpdate = org.fox.ttrss.Application.getInstance().getApiLevel() >= 9 &&
+                !m_feed.is_cat && m_feed.id > 0 && !m_append && skip == 0;
+
+        HashMap<String,String> params = new HashMap<>();
+
+        params.put("op", "getHeadlines");
+        params.put("sid", org.fox.ttrss.Application.getInstance().getSessionId());
+        params.put("feed_id", String.valueOf(m_feed.id));
+        params.put("show_excerpt", "true");
+        params.put("excerpt_length", String.valueOf(CommonActivity.EXCERPT_MAX_LENGTH));
+        params.put("show_content", "true");
+        params.put("include_attachments", "true");
+        params.put("view_mode", m_prefs.getString("view_mode", "adaptive"));
+        params.put("limit", m_prefs.getString("headlines_request_size", "15"));
+        params.put("skip", String.valueOf(skip));
+        params.put("include_nested", "true");
+        params.put("has_sandbox", "true");
+        params.put("order_by", m_prefs.getString("headlines_sort_mode", "default"));
+
+        if (m_prefs.getBoolean("enable_image_downsampling", false)) {
+            if (m_prefs.getBoolean("always_downsample_images", false) || !org.fox.ttrss.Application.getInstance().isWifiConnected()) {
+                params.put("resize_width", String.valueOf(m_resizeWidth));
+            }
+        }
+
+        if (m_feed.is_cat)
+            params.put("is_cat", "true");
+
+        if (allowForceUpdate) {
+            params.put("force_update", "true");
+        }
+
+        if (m_searchQuery != null && !m_searchQuery.isEmpty()) {
+            params.put("search", m_searchQuery);
+            params.put("search_mode", "");
+            params.put("match_on", "both");
+        }
+
+        if (m_firstId > 0)
+            params.put("check_first_id", String.valueOf(m_firstId));
+
+        if (org.fox.ttrss.Application.getInstance().getApiLevel() >= 12) {
+            params.put("include_header", "true");
+        }
+
+        Log.d(TAG, "firstId=" + m_firstId + " append=" + m_append + " skip=" + skip + " localSize=" + articlesWork.size());
+
+        m_executor.execute(() -> {
+            JsonElement result = ApiCommon.performRequest(getApplication(), params, this);
+
+            Log.d(TAG, "got result=" + result);
+
+            if (result != null) {
+                try {
+                    JsonArray content = result.getAsJsonArray();
+                    if (content != null) {
+                        final List<Article> articlesJson;
+                        final JsonObject header;
+
+                        if (org.fox.ttrss.Application.getInstance().getApiLevel() >= 12) {
+                            header = content.get(0).getAsJsonObject();
+
+                            m_firstIdChanged = header.get("first_id_changed") != null;
+
+                            try {
+                                m_firstId = header.get("first_id").getAsInt();
+                            } catch (NumberFormatException e) {
+                                m_firstId = 0;
+                            }
+
+                            Log.d(TAG, this + " firstID=" + m_firstId + " firstIdChanged=" + m_firstIdChanged);
+
+                            Type listType = new TypeToken<List<Article>>() {}.getType();
+                            articlesJson = new Gson().fromJson(content.get(1), listType);
+                        } else {
+                            Type listType = new TypeToken<List<Article>>() {}.getType();
+                            articlesJson = new Gson().fromJson(content, listType);
+                        }
+
+                        if (!m_append)
+                            articlesWork.clear();
+
+                        m_amountLoaded = articlesJson.size();
+
+                        for (Article article : articlesJson)
+                            if (!articlesWork.containsId(article.id)) {
+                                article.collectMediaInfo();
+                                article.cleanupExcerpt();
+                                article.fixNullFields();
+                                articlesWork.add(article);
+                            }
+
+                        if (m_firstIdChanged) {
+                            Log.d(TAG, "first id changed, disabling lazy load");
+                            m_lazyLoadEnabled = false;
+                        }
+
+                        if (m_amountLoaded < Integer.parseInt(m_prefs.getString("headlines_request_size", "15"))) {
+                            Log.d(TAG, this + " amount loaded "+m_amountLoaded+" < request size, disabling lazy load");
+                            m_lazyLoadEnabled = false;
+                        }
+
+                        m_offset += m_amountLoaded;
+                        m_loadingInProgress = false;
+
+                        Log.d(TAG, this + " loaded headlines=" + m_amountLoaded + " resultingLocalSize=" + articlesWork.size());
+                    }
+                } catch (Exception e) {
+                    e.printStackTrace();
+                }
+            }
+
+            m_mainHandler.post(() -> {
+                m_articles.postValue(articlesWork);
+            });
+        });
+
+        m_loadingInProgress = false;
+
+        return articlesWork;
+    }
+
+    private int getSkip(boolean append, ArticleList articles) {
+        int skip = 0;
+
+        if (append) {
+            // adaptive, all_articles, marked, published, unread
+            String viewMode = m_prefs.getString("view_mode", "adaptive");
+
+            int numUnread = Math.toIntExact(articles.getUnreadCount());
+            int numAll = Math.toIntExact(articles.size());
+
+            if ("marked".equals(viewMode)) {
+                skip = numAll;
+            } else if ("published".equals(viewMode)) {
+                skip = numAll;
+            } else if ("unread".equals(viewMode)) {
+                skip = numUnread;
+            } else if (m_searchQuery != null && !m_searchQuery.isEmpty()) {
+                skip = numAll;
+            } else if ("adaptive".equals(viewMode)) {
+                skip = numUnread > 0 ? numUnread : numAll;
+            } else {
+                skip = numAll;
+            }
+        }
+
+        return skip;
+    }
+
+    @Override
+    public void setStatusCode(int statusCode) {
+        m_apiStatusCode = statusCode;
+    }
+
+    @Override
+    public void setLastError(ApiCommon.ApiError lastError) {
+        m_lastError = lastError;
+    }
+
+    @Override
+    public void setLastErrorMessage(String message) {
+        m_lastErrorMessage = message;
+    }
+
+    public boolean getFirstIdChanged() {
+        return m_firstIdChanged;
+    }
+
+    public boolean getAppend() {
+        return m_append;
+    }
+
+    public void setSearchQuery(String searchQuery) {
+        m_searchQuery = searchQuery;
+    }
+
+    public String getSearchQuery() {
+        return m_searchQuery;
+    }
+
+    public int getOffset() {
+        return m_offset;
+    }
+
+    public boolean lazyLoadEnabled() {
+        return m_lazyLoadEnabled;
+    }
+
+    public int getErrorMessage() {
+        return ApiCommon.getErrorMessage(m_lastError);
+    }
+
+    ApiCommon.ApiError getLastError() {
+        return m_lastError;
+    }
+
+    String getLastErrorMessage() {
+        return m_lastErrorMessage;
+    }
+
+}
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/share/ShareActivity.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/share/ShareActivity.java
index 3a1553b6..66a77aef 100644
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/share/ShareActivity.java
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/share/ShareActivity.java
@@ -86,7 +86,7 @@ public class ShareActivity extends CommonShareActivity {
 			protected void onPostExecute(JsonElement result) {
 				setProgressBarIndeterminateVisibility(false);
 
-				if (m_lastError != ApiCommon.ApiError.NO_ERROR) {
+				if (m_lastError != ApiCommon.ApiError.UNKNOWN_ERROR) {
 					toast(getErrorMessage());
 				} else {
 					toast(R.string.share_article_posted);
diff --git a/org.fox.ttrss/src/main/java/org/fox/ttrss/share/SubscribeActivity.java b/org.fox.ttrss/src/main/java/org/fox/ttrss/share/SubscribeActivity.java
index e71583d3..82e2d52d 100755
--- a/org.fox.ttrss/src/main/java/org/fox/ttrss/share/SubscribeActivity.java
+++ b/org.fox.ttrss/src/main/java/org/fox/ttrss/share/SubscribeActivity.java
@@ -157,7 +157,7 @@ public class SubscribeActivity extends CommonShareActivity {
 			protected void onPostExecute(JsonElement result) {
 				m_progressBar.setVisibility(View.INVISIBLE);
 
-				if (m_lastError != ApiCommon.ApiError.NO_ERROR) {
+				if (m_lastError != ApiCommon.ApiError.UNKNOWN_ERROR) {
 					toast(getErrorMessage());
 				} else {
 					try {
@@ -259,7 +259,7 @@ public class SubscribeActivity extends CommonShareActivity {
 			protected void onPostExecute(JsonElement result) {
 				m_progressBar.setVisibility(View.INVISIBLE);
 
-				if (m_lastError != ApiCommon.ApiError.NO_ERROR) {
+				if (m_lastError != ApiCommon.ApiError.UNKNOWN_ERROR) {
 					toast(getErrorMessage());
 				} else {
 					JsonArray content = result.getAsJsonArray();
diff --git a/org.fox.ttrss/src/main/res/values/strings.xml b/org.fox.ttrss/src/main/res/values/strings.xml
index 6a67013a..fb7e6309 100755
--- a/org.fox.ttrss/src/main/res/values/strings.xml
+++ b/org.fox.ttrss/src/main/res/values/strings.xml
@@ -303,4 +303,5 @@
     <string name="check_for_updates">Check for updates</string>
     <string name="dont_open_anything">Nothing</string>
     <string name="open_on_startup">Open on startup</string>
+    <string name="error_success">Operation completed successfully</string>
 </resources>