StorageHelper can save Tracks as JSON to storage

app/build.gradle

@@ -8,8 +8,8 @@ android {
         applicationId "org.y20k.trackbook"
         minSdkVersion 22
         targetSdkVersion 24
-        versionCode 4
-        versionName "0.9.3 (The Great Gig in the Sky)"
+        versionCode 5
+        versionName "0.9.4 (The Great Gig in the Sky)"
         vectorDrawables.useSupportLibrary = true
     }
     buildTypes {
@@ -26,4 +26,5 @@ dependencies {
     compile 'com.android.support:appcompat-v7:24.2.1'
     compile 'com.android.support:design:24.2.1'
     compile 'org.osmdroid:osmdroid-android:5.2@aar'
+    compile 'com.google.code.gson:gson:2.4'
 }

app/src/main/java/org/y20k/trackbook/helpers/LogHelper.java

@@ -26,7 +26,7 @@ import android.util.Log;
  */
 public final class LogHelper {
 
-    private final static boolean mTesting = false;
+    private final static boolean mTesting = true;
 
     public static void d(final String tag, String message) {
         // include logging only in debug versions

app/src/main/java/org/y20k/trackbook/helpers/StorageHelper.java

@@ -0,0 +1,159 @@
+/**
+ * StorageHelper.java
+ * Implements the StorageHelper class
+ * A StorageHelper deals with saving and loading recorded tracks
+ *
+ * This file is part of
+ * TRACKBOOK - Movement Recorder for Android
+ *
+ * Copyright (c) 2016 - Y20K.org
+ * Licensed under the MIT-License
+ * http://opensource.org/licenses/MIT
+ *
+ * Trackbook uses osmdroid - OpenStreetMap-Tools for Android
+ * https://github.com/osmdroid/osmdroid
+ */
+
+package org.y20k.trackbook.helpers;
+
+import android.app.Activity;
+import android.os.Environment;
+import android.support.v4.os.EnvironmentCompat;
+import android.widget.Toast;
+
+import com.google.gson.Gson;
+
+import org.y20k.trackbook.R;
+import org.y20k.trackbook.core.Track;
+
+import java.io.BufferedReader;
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileReader;
+import java.io.FileWriter;
+import java.io.IOException;
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.Locale;
+
+
+/**
+ * StorageHelper class
+ */
+public class StorageHelper implements TrackbookKeys {
+
+    /* Define log tag */
+    private static final String LOG_TAG = StorageHelper.class.getSimpleName();
+
+    /* Main class variables */
+    private final Activity mActivity;
+    private File mFolder;
+
+
+    /* Constructor */
+    public StorageHelper(Activity activity) {
+        mActivity = activity;
+        mFolder  = mActivity.getExternalFilesDir("Tracks");
+        // mFolder = getTracksDirectory();
+
+        // create folder if necessary
+        if (mFolder != null && !mFolder.exists()) {
+            LogHelper.v(LOG_TAG, "Creating new folder: " + mFolder.toString());
+            mFolder.mkdir();
+        }
+    }
+
+
+    /* Saves track object to file */
+    public boolean saveTrack(Track track) {
+
+        Date recordingStart = track.getRecordingStart();
+
+        if (mFolder.exists() && mFolder.isDirectory() && mFolder.canWrite() && recordingStart != null) {
+            // construct filename from track recording date
+            DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss", Locale.US);
+            String fileName = dateFormat.format(recordingStart) + ".trackbook";
+            File file = new File(mFolder.toString() + "/" +  fileName);
+
+            // convert to JSON
+            Gson gson = new Gson();
+            String json = gson.toJson(track);
+
+            // write track
+            try (BufferedWriter bw = new BufferedWriter(new FileWriter(file))) {
+                LogHelper.v(LOG_TAG, "Saving track to external storage: " + file.toString());
+                bw.write(json);
+            } catch (IOException e) {
+                LogHelper.e(LOG_TAG, "Unable to saving track to external storage (IOException): " + file.toString());
+            }
+
+            return true;
+
+        } else {
+            LogHelper.e(LOG_TAG, "Unable to save track to external storage.");
+            return false;
+        }
+
+    }
+
+
+    /* Loads given file into memory */
+    public Track loadTrack (File file) {
+
+        try (BufferedReader br = new BufferedReader(new FileReader(file))) {
+            LogHelper.v(LOG_TAG, "Loading track to external storage: " + file.toString());
+
+            String line;
+            StringBuilder sb = new StringBuilder("");
+
+            // read until last line reached
+            while ((line = br.readLine()) != null) {
+                sb.append(line);
+                sb.append("\n");
+            }
+
+            // get track from JSON
+            Gson gson = new Gson();
+            return gson.fromJson(sb.toString(), Track.class);
+
+        } catch (IOException e) {
+            LogHelper.e(LOG_TAG, "Unable to read file from external storage: " + file.toString());
+            return null;
+        }
+
+    }
+
+
+    /* Gets the last track from directory */
+    public File getLastTrack() {
+        if (mFolder != null && mFolder.isDirectory()) {
+            File[] files = mFolder.listFiles();
+            // TODO
+            return files[0];
+        }
+        // TODO
+        return null;
+    }
+
+
+    /* Return a write-able sub-directory from external storage  */
+    private File getTracksDirectory() {
+        String subDirectory = "Tracks";
+        File[] storage = mActivity.getExternalFilesDirs(subDirectory);
+        for (File file : storage) {
+            if (file != null) {
+                String state = EnvironmentCompat.getStorageState(file);
+                if (Environment.MEDIA_MOUNTED.equals(state)) {
+                    LogHelper.i(LOG_TAG, "External storage: " + file.toString());
+                    return file;
+                }
+            }
+        }
+        Toast.makeText(mActivity, R.string.toast_message_no_external_storage, Toast.LENGTH_LONG).show();
+        LogHelper.e(LOG_TAG, "Unable to access external storage.");
+
+        return null;
+    }
+
+}