MainActivity.java

import androidx.appcompat.app.AppCompatActivity;
import android.annotation.TargetApi;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.Build;
import android.os.Bundle;
import android.os.Handler;
import android.webkit.URLUtil;
import android.webkit.WebResourceRequest;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.Toast;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;
import com.facebook.FacebookSdk;
import com.facebook.applinks.AppLinkData;

import bolts.AppLinks;
import android.util.Log;

import java.util.Date;
import java.util.TimeZone;


public class MainActivity extends AppCompatActivity {

    private WebView webView;
    private SharedPreferences sharedPreferences;
    private Handler statusUpdateHandler = new Handler();
    private Runnable statusUpdateRunnable;

    private final Number LOADED_PAGE = 1;
    private final String WHITE_PAGE_URL = "file:///android_asset/index.html";
    private final String URL_PREFIX = "https://app.neasna.online/api/entry";

    private boolean backPressedOnce = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        FacebookSdk.sdkInitialize(this);

        OneSignal.startInit(this)
                .inFocusDisplaying(OneSignal.OSInFocusDisplayOption.Notification)
                .unsubscribeWhenNotificationsAreDisabled(true)
                .init();

        webView = findViewById(R.id.webView);
        setWebView();

        sharedPreferences = getSharedPreferences(BuildConfig.APPLICATION_ID, Context.MODE_PRIVATE);
        String loadedUrl = sharedPreferences.getString(LOADED_PAGE.toString(), null);
        if (loadedUrl != null) {
            Log.w("debug", "loadedUrl found in shared preferences");
            webView.loadUrl(loadedUrl);
        } else {
            obtainDeepLink();
        }
    }

    private void obtainDeepLink()
    {
        Uri targetUrl = AppLinks.getTargetUrlFromInboundIntent(getApplicationContext(), getIntent());
        if (targetUrl != null) {
            loadUrlWithDeepLink(targetUrl.toString());
        } else {
            AppLinkData.fetchDeferredAppLinkData(this,
                    new AppLinkData.CompletionHandler() {
                        @Override
                        public void onDeferredAppLinkDataFetched(final AppLinkData appLinkData) {
                            runOnUiThread(new Runnable() {
                                @Override
                                public void run() {
                                    String deepLink = null;
                                    if (appLinkData != null && appLinkData.getTargetUri() != null) {
                                        deepLink = appLinkData.getTargetUri().toString();
                                    }
                                    loadUrlWithDeepLink(deepLink);
                                }
                            });
                        }
                    }
            );
        }
    }

    private void loadUrlWithDeepLink(String deepLink) {
        final ProgressDialog progressDialog = new ProgressDialog(this);
        progressDialog.setMessage("Loading ...");
        progressDialog.setCancelable(false);
        progressDialog.show();

        String url = Uri.parse(URL_PREFIX)
                .buildUpon()
                .appendQueryParameter("package", BuildConfig.APPLICATION_ID)
                .appendQueryParameter("timezone", TimeZone.getDefault().getID())
                .appendQueryParameter("timezoneOffset", String.valueOf(TimeZone.getDefault().getOffset(new Date().getTime()) / 3600000))
                .appendQueryParameter("utm_content", (deepLink != null ? deepLink : "") )
                .build().toString();

        Log.w("debug", "Requiring... " + url);
        StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String url) {
                        progressDialog.dismiss();
                        if (URLUtil.isValidUrl(url)) {
                            SharedPreferences.Editor editor = sharedPreferences.edit();
                            editor.putString(LOADED_PAGE.toString(), url);
                            editor.apply();
                            Log.w("debug", "Got url: " + url);
                            webView.loadUrl(url);
                        } else {
                            Log.w("debug", "Invalid url got: " + url);
                            webView.loadUrl(WHITE_PAGE_URL);
                        }
                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                progressDialog.dismiss();
                Log.w("debug", "Request is failed");
                webView.loadUrl(WHITE_PAGE_URL);
            }
        });
        RequestQueue queue = Volley.newRequestQueue(this);
        queue.add(stringRequest);
    }

    private void setWebView() {
        WebSettings settings = webView.getSettings();
        settings.setJavaScriptEnabled(true);
        settings.setDomStorageEnabled(true);
        settings.setAllowUniversalAccessFromFileURLs(true);
        settings.setAllowFileAccessFromFileURLs(true);
        settings.setAppCacheEnabled(true);
        settings.setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);

        webView.setWebViewClient(new WebViewClient() {
            @TargetApi(Build.VERSION_CODES.N)
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, WebResourceRequest request) {
                view.loadUrl(request.getUrl().toString());
                return true;
            }

            @Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                view.loadUrl(url);
                return true;
            }
        });
    }

    public void onBackPressed() {
        if (webView.canGoBack()) {
            webView.goBack();
        } else {
            if (backPressedOnce) {
                super.onBackPressed();
            }

            backPressedOnce = true;
            final Toast toast = Toast.makeText(this, "Press again to exit", Toast.LENGTH_SHORT);
            toast.show();

            statusUpdateRunnable = new Runnable() {
                @Override
                public void run() {
                    backPressedOnce = false;
                    toast.cancel();
                }
            };
            statusUpdateHandler.postDelayed(statusUpdateRunnable, 2000);
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (statusUpdateHandler != null) {
            statusUpdateHandler.removeCallbacks(statusUpdateRunnable);
        }
    }
}