Use okhttp caching for feed

app/src/main/AndroidManifest.xml

@@ -3,6 +3,7 @@
 
     package="app.insti">
 
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
     <uses-permission android:name="android.permission.WAKE_LOCK" />
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
     <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />

app/src/main/java/app/insti/activity/MainActivity.java

@@ -87,6 +87,11 @@ public class MainActivity extends AppCompatActivity implements NavigationView.On
     private boolean showNotifications = false;
     private BackHandledFragment selectedFragment;
     private Menu menu;
+    private RetrofitInterface retrofitInterface;
+
+    public RetrofitInterface getRetrofitInterface() {
+        return retrofitInterface;
+    }
 
     public static void hideKeyboard(Activity activity) {
         InputMethodManager imm = (InputMethodManager) activity.getSystemService(Activity.INPUT_METHOD_SERVICE);
@@ -107,6 +112,9 @@ public class MainActivity extends AppCompatActivity implements NavigationView.On
         } catch (IllegalStateException ignored) {
         }
 
+        ServiceGenerator serviceGenerator = new ServiceGenerator(getApplicationContext());
+        this.retrofitInterface = serviceGenerator.getRetrofitInterface();
+
         /* Make notification channel on oreo */
         if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
             createNotificationChannel();

app/src/main/java/app/insti/api/ServiceGenerator.java

 package app.insti.api;
 
+import android.content.Context;
+import android.net.NetworkInfo;
+import android.util.Log;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.concurrent.TimeUnit;
+
+import app.insti.Constants;
+import butterknife.internal.Utils;
+import okhttp3.Cache;
+import okhttp3.CacheControl;
+import okhttp3.Interceptor;
 import okhttp3.OkHttpClient;
+import okhttp3.Request;
+import okhttp3.Response;
 import okhttp3.logging.HttpLoggingInterceptor;
 import retrofit2.Retrofit;
 import retrofit2.converter.gson.GsonConverterFactory;
 
 public class ServiceGenerator {
+    public static final String HEADER_CACHE_CONTROL = "Cache-Control";
+    public static final String HEADER_PRAGMA = "Pragma";
     private static final String BASE_URL = "https://api.insti.app/api/";
+
+    private Context context;
+
+    private Interceptor provideCacheInterceptor = new Interceptor() {
+        @Override
+        public Response intercept(Chain chain) throws IOException {
+            Response response = chain.proceed(chain.request());
+
+            CacheControl cacheControl;
+
+            if (isConnected()) {
+                cacheControl = new CacheControl.Builder()
+                        .maxAge(80, TimeUnit.SECONDS)
+                        .build();
+            } else {
+                cacheControl = new CacheControl.Builder()
+                        .maxStale(7, TimeUnit.DAYS)
+                        .build();
+            }
+
+            return response.newBuilder()
+                    .removeHeader(HEADER_PRAGMA)
+                    .removeHeader(HEADER_CACHE_CONTROL)
+                    .header(HEADER_CACHE_CONTROL, cacheControl.toString())
+                    .build();
+        }
+    };
+
+    private Interceptor provideOfflineCacheInterceptor = new Interceptor() {
+        @Override
+        public Response intercept(Chain chain) throws IOException {
+            Request request = chain.request();
+
+            if (!isConnected()) {
+                CacheControl cacheControl = new CacheControl.Builder()
+                        .maxStale(7, TimeUnit.DAYS)
+                        .build();
+
+                request = request.newBuilder()
+                        .removeHeader(HEADER_PRAGMA)
+                        .removeHeader(HEADER_CACHE_CONTROL)
+                        .cacheControl(cacheControl)
+                        .build();
+            }
+
+            return chain.proceed(request);
+        }
+    };
+
+    private Cache provideCache() {
+        Cache cache = null;
+
+        try {
+            cache = new Cache(new File(context.getCacheDir(), "api-cache"),
+                    50 * 1024 * 1024); // 50 MB
+        } catch (Exception e) {
+            Log.e("cache", "Could not create Cache!");
+        }
+
+        return cache;
+    }
+
+    public boolean isConnected() {
+        Log.wtf("cache", "MEOW");
+        try {
+            android.net.ConnectivityManager e = (android.net.ConnectivityManager) context.getSystemService(
+                    Context.CONNECTIVITY_SERVICE);
+            NetworkInfo activeNetwork = e.getActiveNetworkInfo();
+            Log.wtf("cache", Boolean.toString(activeNetwork != null && activeNetwork.isConnectedOrConnecting()));
+            return activeNetwork != null && activeNetwork.isConnectedOrConnecting();
+        } catch (Exception e) {
+            Log.w("cache", e.toString());
+        }
+
+        return false;
+    }
+
     private static OkHttpClient.Builder clientBuilder = new OkHttpClient.Builder();
+
     private static Retrofit.Builder retrofitBuilder = new Retrofit.Builder()
             .baseUrl(BASE_URL)
             .addConverterFactory(GsonConverterFactory.create());
@@ -17,4 +112,21 @@ public class ServiceGenerator {
         retrofit = retrofitBuilder.client(clientBuilder.build()).build();
         return retrofit.create(serviceClass);
     }
+
+    public RetrofitInterface retrofitInterface;
+    public ServiceGenerator(Context mContext) {
+        context = mContext;
+        retrofit = retrofitBuilder.client(
+                clientBuilder
+                        .addInterceptor(provideOfflineCacheInterceptor)
+                        .addNetworkInterceptor(provideCacheInterceptor)
+                        .cache(provideCache())
+                        .build()
+        ).build();
+        retrofitInterface = retrofit.create(RetrofitInterface.class);
+    }
+
+    public RetrofitInterface getRetrofitInterface() {
+        return retrofitInterface;
+    }
 }

app/src/main/java/app/insti/fragment/FeedFragment.java

@@ -31,9 +31,12 @@ import app.insti.api.ServiceGenerator;
 import app.insti.api.model.NewsFeedResponse;
 import app.insti.data.AppDatabase;
 import app.insti.data.Event;
+import okhttp3.OkHttpClient;
 import retrofit2.Call;
 import retrofit2.Callback;
 import retrofit2.Response;
+import retrofit2.Retrofit;
+import retrofit2.converter.gson.GsonConverterFactory;
 
 /**
  * A simple {@link Fragment} subclass.
@@ -79,7 +82,7 @@ public class FeedFragment extends BaseFragment {
     public void onStart() {
         super.onStart();
         appDatabase = AppDatabase.getAppDatabase(getContext());
-        new showEventsFromDB().execute();
+        //new showEventsFromDB().execute();
         fab = (FloatingActionButton) getView().findViewById(R.id.fab);
         updateFeed();
     }
@@ -104,9 +107,9 @@ public class FeedFragment extends BaseFragment {
         }
     }
 
-
     private void updateFeed() {
-        RetrofitInterface retrofitInterface = ServiceGenerator.createService(RetrofitInterface.class);
+
+        RetrofitInterface retrofitInterface = ((MainActivity) getActivity()).getRetrofitInterface();
         retrofitInterface.getNewsFeed("sessionid=" + getArguments().getString(Constants.SESSION_ID)).enqueue(new Callback<NewsFeedResponse>() {
             @Override
             public void onResponse(Call<NewsFeedResponse> call, Response<NewsFeedResponse> response) {