allow changing the filename of the file where events will be exported

app/src/main/kotlin/com/simplemobiletools/calendar/activities/MainActivity.kt

@@ -39,7 +39,6 @@ import com.simplemobiletools.commons.models.RadioItem
 import com.simplemobiletools.commons.models.Release
 import kotlinx.android.synthetic.main.activity_main.*
 import org.joda.time.DateTime
-import java.io.File
 import java.io.FileOutputStream
 import java.util.*
 
@@ -309,16 +308,14 @@ class MainActivity : SimpleActivity(), NavigationListener {
     private fun exportEvents() {
         FilePickerDialog(this, pickFile = false) {
             val path = it
-            ExportEventsDialog(this, path) {
+            ExportEventsDialog(this, path) { exportPastEvents, file ->
                 Thread({
-                    val events = dbHelper.getEventsToExport(it)
+                    val events = dbHelper.getEventsToExport(exportPastEvents)
                     if (events.isEmpty()) {
                         runOnUiThread {
                             toast(R.string.no_events_for_exporting)
                         }
                     } else {
-                        val filename = "events_${System.currentTimeMillis() / 1000}.ics"
-                        val file = File(path, filename)
                         IcsExporter().exportEvents(this, file, events) {
                             runOnUiThread {
                                 toast(when (it) {

app/src/main/kotlin/com/simplemobiletools/calendar/dialogs/ExportEventsDialog.kt

@@ -4,21 +4,39 @@ import android.app.Activity
 import android.support.v7.app.AlertDialog
 import android.view.ViewGroup
 import com.simplemobiletools.calendar.R
-import com.simplemobiletools.commons.extensions.humanizePath
+import com.simplemobiletools.commons.extensions.*
-import com.simplemobiletools.commons.extensions.setupDialogStuff
 import kotlinx.android.synthetic.main.dialog_export_events.view.*
+import java.io.File
 
-class ExportEventsDialog(val activity: Activity, val path: String, val callback: (exportPastEvents: Boolean) -> Unit) : AlertDialog.Builder(activity) {
+class ExportEventsDialog(val activity: Activity, val path: String, val callback: (exportPastEvents: Boolean, file: File) -> Unit) : AlertDialog.Builder(activity) {
     init {
         val view = (activity.layoutInflater.inflate(R.layout.dialog_export_events, null) as ViewGroup).apply {
             export_events_folder.text = activity.humanizePath(path)
+            export_events_filename.setText("events_${System.currentTimeMillis() / 1000}")
         }
 
         AlertDialog.Builder(activity)
-                .setPositiveButton(R.string.ok, { dialog, which -> callback(view.export_events_checkbox.isChecked) })
+                .setPositiveButton(R.string.ok, null)
                 .setNegativeButton(R.string.cancel, null)
                 .create().apply {
             activity.setupDialogStuff(view, this, R.string.export_events)
+            getButton(AlertDialog.BUTTON_POSITIVE).setOnClickListener({
+                val filename = view.export_events_filename.value
+                if (filename.isEmpty()) {
+                    context.toast(R.string.empty_name)
+                } else if (filename.isAValidFilename()) {
+                    val file = File(path, "$filename.ics")
+                    if (file.exists()) {
+                        context.toast(R.string.name_taken)
+                        return@setOnClickListener
+                    }
+
+                    callback(view.export_events_checkbox.isChecked, file)
+                    dismiss()
+                } else {
+                    context.toast(R.string.invalid_name)
+                }
+            })
         }
     }
 }