Correctly check for 'suggestedApk' in app details.

Take into account the preferred/installed signature instead of just the
version code.

app/src/main/java/org/fdroid/fdroid/data/ApkProvider.java

@@ -8,7 +8,6 @@ import android.database.Cursor;
 import android.net.Uri;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
-import android.text.TextUtils;
 import android.util.Log;
 
 import org.fdroid.fdroid.data.Schema.ApkTable;
@@ -84,14 +83,7 @@ public class ApkProvider extends FDroidProvider {
          * </ul>
          */
         public static Apk findSuggestedApk(Context context, App app) {
-            String preferredSignature = null;
+            return findApkFromAnyRepo(context, app.packageName, app.suggestedVersionCode, app.getMostAppropriateSignature());
-            if (!TextUtils.isEmpty(app.installedSig)) {
-                preferredSignature = app.installedSig;
-            } else if (!TextUtils.isEmpty(app.preferredSigner)) {
-                preferredSignature = app.preferredSigner;
-            }
-
-            return findApkFromAnyRepo(context, app.packageName, app.suggestedVersionCode, preferredSignature);
         }
 
         public static Apk findApkFromAnyRepo(Context context, String packageName, int versionCode) {

app/src/main/java/org/fdroid/fdroid/data/App.java

@@ -1098,4 +1098,24 @@ public class App extends ValueObject implements Comparable<App>, Parcelable {
             return new App[size];
         }
     };
+
+    /**
+     * Choose the signature which we should encourage the user to install.
+     * Usually, we want the {@link #preferredSigner} rather than any random signature.
+     * However, if the app is installed, then we override this and instead want to only encourage
+     * the user to try and install versions with that signature (because thats all the OS will let
+     * them do).
+     * TODO: I don't think preferredSigner should ever be null, because if an app has apks then
+     * we should have chosen the first and used that. If so, then we should change to @NonNull and
+     * throw an exception if it is null.
+     */
+    @Nullable
+    public String getMostAppropriateSignature() {
+        if (!TextUtils.isEmpty(installedSig)) {
+            return installedSig;
+        } else if (!TextUtils.isEmpty(preferredSigner)) {
+            return preferredSigner;
+        }
+        return null;
+    }
 }

app/src/main/java/org/fdroid/fdroid/views/AppDetailsRecyclerViewAdapter.java

@@ -178,9 +178,10 @@ public class AppDetailsRecyclerViewAdapter
 
     private Apk getSuggestedApk() {
         Apk curApk = null;
+        String appropriateSig = app.getMostAppropriateSignature();
         for (int i = 0; i < versions.size(); i++) {
             final Apk apk = versions.get(i);
-            if (apk.versionCode == app.suggestedVersionCode) {
+            if (apk.versionCode == app.suggestedVersionCode && TextUtils.equals(apk.sig, appropriateSig)) {
                 curApk = apk;
                 break;
             }