Codereview #2 of 8 from 3

.gitignore

@@ -51,6 +51,7 @@ captures/
 
 # Google Services (e.g. APIs or Firebase)
 google-services.json
+app/google-services.json
 
 # Freeline
 freeline.py

ShowPosts_VM.java

@@ -0,0 +1,206 @@
+package unipd.se18.ocrcamera.forum.viewmodels;
+
+import android.arch.lifecycle.MutableLiveData;
+import android.arch.lifecycle.ViewModel;
+import android.content.Context;
+import android.support.annotation.NonNull;
+import android.util.Log;
+
+import com.google.android.gms.tasks.OnCompleteListener;
+import com.google.android.gms.tasks.OnFailureListener;
+import com.google.android.gms.tasks.OnSuccessListener;
+import com.google.android.gms.tasks.Task;
+import com.google.firebase.firestore.QueryDocumentSnapshot;
+import com.google.firebase.firestore.QuerySnapshot;
+
+import org.json.JSONArray;
+import org.json.JSONException;
+import org.json.JSONObject;
+
+import java.text.ParseException;
+import java.text.SimpleDateFormat;
+import java.util.ArrayList;
+import java.util.Date;
+import java.util.Map;
+
+import unipd.se18.ocrcamera.forum.DatabaseManager;
+import unipd.se18.ocrcamera.forum.R;
+import unipd.se18.ocrcamera.forum.RequestManager;
+import unipd.se18.ocrcamera.forum.models.Post;
+
+
+/**
+ * According to the MVVM (Model-View-ViewModel) architecture this class contains all fragment ShowPosts' logic.
+ * This architecture ensures that the code is more testable and organised than the classic approch to put everything
+ * in the activity or fragment class. 
+ * In particular the methods that are implemented here are used to get posts from forum and to handle users' likes. The
+ * forum's data are stored into a database handle thanks to FirebaseFirestore API
+ * @author Leonardo Rossi g2
+ */
+public class ShowPosts_VM extends ViewModel implements ShowPostsMethods
+{
+
+    /**
+     * ********************
+     * **   LISTENERS    **
+     * ********************
+     */
+
+    /**
+    * This listener is triggered to update the UI with the result of a db interrogation to get posts inside the forum.
+    * If the result is successfull, that is all the posts are correctly downloaded, the ShowPost fragment recevives the
+    * posts list, otherwise it receives an error message that can be shown to the user
+    */
+    public interface GetPostListener
+    {
+        /**
+         * Triggered when, after the db interrogation, all the posts are correctly parsed
+         * @param posts The posts list
+         */
+        void onGetPostsSuccess(ArrayList<Post> posts);
+
+        /**
+         * Triggered when after the db interrogation an error occurs while parsing the posts
+         * @param message The error message
+         */
+        void onGetPostFailure(String message);
+
+    }
+
+    /**
+    * This listener is triggered to update the UI when a user put "like" to a specific post. This operation is
+    * successfull if the like is correctly store to the db, failed otherwise.
+    */
+    public interface AddLikeListener
+    {
+        /**
+         * Triggered when after the db interrogation the like has successfully been added
+         * @param message A message to show to the user
+         */
+        void onAddLikeSuccess(String message);
+
+        /**
+         * Triggered when after the db interrogation an error occurred while adding a like
+         * @param message The error message to show to the user
+         */
+        void onAddLikeFailure(String message);
+    }
+
+    /**
+     * ***************************
+     * **   GLOBAL VARIABLES    **
+     * ***************************
+     */
+    private GetPostListener getPostListener;
+    private AddLikeListener addLikeListener;
+    private final String LOG_TAG = "@@ShowPosts_VM";
+
+    @Override
+    public void getPosts(final Context context)
+    {
+        //Definition of the listener that will be triggered when the db interrogation is finished
+        final DatabaseManager.Listeners listeners = new DatabaseManager.Listeners();
+        listeners.completeListener = new OnCompleteListener<QuerySnapshot>()
+        {
+            @Override
+            public void onComplete(@NonNull Task<QuerySnapshot> task)
+            {
+                //This array will contain the posts downloaded from the db
+                ArrayList<Post> posts = new ArrayList<>();
+
+                //Loopping through the db interrogation's result
+                for (QueryDocumentSnapshot item: task.getResult())
+                {
+                    //Each item inside the db interrogation's result is a map
+                    //where the key identifies the db field to which is associated the corresponding value
+                    Map<String, Object> postData = item.getData();
+
+                    //Post attributes reading
+                    String postID = item.getId();
+                    String postTitle = postData.get(context.getString(R.string.postTitleKey)).toString();
+                    String postMessage = postData.get(context.getString(R.string.postMessageKey)).toString();
+                    String postAuthor = postData.get(context.getString(R.string.postAuthorKey)).toString();
+                    int comments = Integer.valueOf(postData.get(context.getString(R.string.postCommentsKey)).toString());
+                    int likes = Integer.valueOf(postData.get(context.getString(R.string.postLikesKey)).toString());
+
+                    //The date read from the db is converted into a specific format stored in the static variable
+                    //DATE_FORMAT so that in this way it can be directly present in the UI
+                    SimpleDateFormat format = new SimpleDateFormat(Post.DATE_FORMAT);
+                    String postDate = postData.get(context.getString(R.string.postDateKey)).toString();
+
+                    try
+                    {
+                        //At this point, if no exception are thrown, a post object can be built and stored into the
+                        //specific array
+                        posts.add(new Post(postID, postTitle, postMessage, format.parse(postDate), likes, comments, postAuthor));
+                    }
+                    catch (ParseException e)
+                    {
+                        //If an error occurs while converting the post's date an error message is logged to console and 
+                        //the failure UI listener is triggered with a explanation message for the user
+                        Log.d(LOG_TAG, e.getMessage());
+                        if (getPostListener != null){ getPostListener.onGetPostFailure(context.getString(R.string.requestFailedMessage)); }
+                    }
+                }
+
+                //If everithing goes well the success listener can be triggered with the posts list as parameter.
+                //In this way it can be used in the fragment to populate the UI
+                if (getPostListener != null){ getPostListener.onGetPostsSuccess(posts); }
+            }
+        };
+
+        //Calling to the method to get posts from the db passing the previously defined listener as parameter
+        DatabaseManager.getPosts(context, listeners);
+    }
+
+    /**
+     * Adds a like to the specified post
+     * @param context The reference to the activity/fragment that has invoked this method
+     * @param post The ID of the post to which the like will be added
+     * @param user The user that has added the like
+     * @param prevLikes The number of likes before the last addition
+     */
+    public void addLikeToPost(final Context context, String post, String user, int prevLikes)
+    {
+        //Definition of the listeners that will be triggered when the db interrogation is finished.
+        //In particular two listeners are defined: one for a successful db interrogation, the other in case of failure
+        DatabaseManager.Listeners listeners = new DatabaseManager.Listeners();
+
+        listeners.successListener = new OnSuccessListener() {
+            @Override
+            public void onSuccess(Object o) {
+                //If the like has correctly been added to the db the success listener is triggerd
+                //(In this case there's an empty string as parameter because there's no specific message to show to the user)
+                if (addLikeListener != null) { addLikeListener.onAddLikeSuccess(""); }
+            }
+        };
+
+        listeners.failureListener = new OnFailureListener() {
+            @Override
+            public void onFailure(@NonNull Exception e)
+            {
+                //If an error occurrs while storing a like into the db an error message is logged to console and
+                //and the failure UI listener is trigger with an explanation message for the user
+                Log.d(LOG_TAG, "Error: " + e.getMessage());
+                if (addLikeListener != null) { addLikeListener.onAddLikeFailure(context.getString(R.string.addLikeOnFailureMessage)); }
+            }
+        };
+
+        //Calling to the method to store a like into the db passing as parameter:
+        //The context which references to the fragment, the post ID, the user that has put "like" to the post,
+        //the amount of likes before the last one is added and the listeners previously defined
+        DatabaseManager.addLike(context, post, user, prevLikes, listeners);
+    }
+
+    /**
+     * Adds the specified listener to the view model
+     * @param listener The specified listener that has to be added to the view model
+     */
+    public void setGetPostsListener(GetPostListener listener) { this.getPostListener = listener; }
+
+    /**
+     * Adds the specified listener to the view model
+     * @param listener The specified listener that has to be added to the view model
+     */
+    public void setAddLikeListener(AddLikeListener listener) { this.addLikeListener = listener; }
+}