add export/import of my list

fixes #39

app/src/main/java/org/mosad/teapod/util/StorageController.kt

@@ -1,12 +1,18 @@
 package org.mosad.teapod.util
 
 import android.content.Context
+import android.net.Uri
 import android.util.Log
+import android.widget.Toast
 import com.google.gson.Gson
 import com.google.gson.JsonParser
 import kotlinx.coroutines.*
+import org.mosad.teapod.R
 import java.io.File
+import java.io.FileReader
+import java.io.FileWriter
 import java.lang.Exception
+import java.net.URI
 
 /**
  * This controller contains the logic for permanently saved data.
@@ -19,6 +25,10 @@ object StorageController {
     val myList = ArrayList<Int>() // a list of saved mediaIds
 
     fun load(context: Context) {
+        loadMyList(context)
+    }
+
+    fun loadMyList(context: Context) {
         val file = File(context.filesDir, fileNameMyList)
 
         if (!file.exists()) runBlocking { saveMyList(context).join() }
@@ -30,7 +40,6 @@ object StorageController {
             myList.clear()
             Log.e(javaClass.name, "Parsing of My-List failed.")
         }
-
     }
 
     fun saveMyList(context: Context): Job {
@@ -41,4 +50,44 @@ object StorageController {
         }
     }
 
+    fun exportMyList(context: Context, uri: Uri) {
+        try {
+            context.contentResolver.openFileDescriptor(uri, "w")?.use {
+                FileWriter(it.fileDescriptor).use { writer ->
+                    writer.write(Gson().toJson(myList.distinct()))
+                }
+            }
+        } catch (ex: Exception) {
+            Log.e(javaClass.name, "Exporting my list failed.", ex)
+        }
+    }
+
+    /**
+     * import my list from a (previously exported) json file
+     * @param context the current context
+     * @param uri the uri of the selected file
+     * @return 0 if import was successfull, else 1
+     */
+    fun importMyList(context: Context, uri: Uri): Int {
+        try {
+            val text = context.contentResolver.openFileDescriptor(uri, "r")?.use {
+                FileReader(it.fileDescriptor).use { reader ->
+                    reader.readText()
+                }
+            }
+
+            myList.clear()
+            myList.addAll(JsonParser.parseString(text).asJsonArray.map { it.asInt }.distinct())
+
+            // after the list has been imported also save it
+            saveMyList(context)
+        } catch (ex: Exception) {
+            myList.clear()
+            Log.e(javaClass.name, "Importing my list failed.", ex)
+            return 1
+        }
+
+        return 0
+    }
+
 }