Always Zip files when exporting to QIF

When having transactions with multiple commodities, a QIF file for each
commodity is created. With Android's Storage Access Framework we are
limited to one file, so now we always pack QIFs into a single ZIP file.

Fixes codinguser#696

app/src/main/java/org/gnucash/android/export/qif/QifExporter.java

@@ -19,12 +19,14 @@
 import android.content.ContentValues;
 import android.database.Cursor;
 import android.database.sqlite.SQLiteDatabase;
+import android.support.annotation.NonNull;
 
 import org.gnucash.android.db.adapter.AccountsDbAdapter;
 import org.gnucash.android.db.adapter.TransactionsDbAdapter;
 import org.gnucash.android.export.ExportParams;
 import org.gnucash.android.export.Exporter;
 import org.gnucash.android.model.Commodity;
+import org.gnucash.android.util.FileUtils;
 import org.gnucash.android.util.PreferencesHelper;
 import org.gnucash.android.util.TimestampHelper;
 
@@ -38,6 +40,7 @@
 import java.io.OutputStreamWriter;
 import java.math.BigDecimal;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
 
@@ -52,6 +55,8 @@
  * @author Yongxin Wang <fefe.wyx@gmail.com>
  */
 public class QifExporter extends Exporter{
+    private static final String TAG = "QifExporter";
+
     /**
      * Initialize the exporter
      * @param params Export options
@@ -232,12 +237,20 @@ public List<String> generateExport() throws ExporterException {
 
             /// export successful
             PreferencesHelper.setLastExportTime(TimestampHelper.getTimestampFromNow());
-            return splitQIF(file);
+            List<String> exportedFiles = splitQIF(file);
+            return zipQifs(exportedFiles);
         } catch (IOException e) {
             throw new ExporterException(mExportParams, e);
         }
     }
 
+    @NonNull
+    private List<String> zipQifs(List<String> exportedFiles) throws IOException {
+        String zipFileName = getExportCacheFilePath() + ".zip";
+        FileUtils.zipFiles(exportedFiles, zipFileName);
+        return Collections.singletonList(zipFileName);
+    }
+
     /**
      * Splits a Qif file into several ones for each currency.
      *

app/src/main/java/org/gnucash/android/util/FileUtils.java

@@ -0,0 +1,34 @@
+package org.gnucash.android.util;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.List;
+import java.util.zip.ZipEntry;
+import java.util.zip.ZipOutputStream;
+
+/**
+ * Misc methods for dealing with files.
+ */
+public final class FileUtils {
+    public static void zipFiles(List<String> files, String zipFileName) throws IOException {
+        OutputStream outputStream = new FileOutputStream(zipFileName);
+        ZipOutputStream zipOutputStream = new ZipOutputStream(outputStream);
+        byte[] buffer = new byte[1024];
+        for (String fileName : files) {
+            File file = new File(fileName);
+            FileInputStream fileInputStream = new FileInputStream(file);
+            zipOutputStream.putNextEntry(new ZipEntry(file.getName()));
+
+            int length;
+            while ((length = fileInputStream.read(buffer)) > 0) {
+                zipOutputStream.write(buffer, 0, length);
+            }
+            zipOutputStream.closeEntry();
+            fileInputStream.close();
+        }
+        zipOutputStream.close();
+    }
+}