Export data as CSV

A file called `prepaid-balance-<timestamp>.csv` will be created in the
downloads folder when the action bar icon is pressed.

Fixes #156

app/src/main/java/com/github/muellerma/prepaidbalance/ui/MainActivity.kt

@@ -4,7 +4,9 @@ import android.Manifest.permission.CALL_PHONE
 import android.Manifest.permission.READ_PHONE_STATE
 import android.annotation.SuppressLint
 import android.content.Intent
+import android.net.Uri
 import android.os.Bundle
+import android.os.Environment
 import android.os.Handler
 import android.os.Looper
 import android.telephony.SubscriptionManager
@@ -23,10 +25,12 @@ import com.github.muellerma.prepaidbalance.databinding.ActivityMainBinding
 import com.github.muellerma.prepaidbalance.room.AppDatabase
 import com.github.muellerma.prepaidbalance.utils.hasPermissions
 import com.github.muellerma.prepaidbalance.utils.prefs
+import com.github.muellerma.prepaidbalance.utils.timestampForUi
 import com.github.muellerma.prepaidbalance.work.CheckBalanceWorker
 import com.github.muellerma.prepaidbalance.work.CheckBalanceWorker.Companion.CheckResult
 import com.google.android.material.snackbar.Snackbar
 import kotlinx.coroutines.launch
+import java.io.File
 
 
 class MainActivity : AbstractBaseActivity(), SwipeRefreshLayout.OnRefreshListener {
@@ -99,6 +103,10 @@ class MainActivity : AbstractBaseActivity(), SwipeRefreshLayout.OnRefreshListene
                 }
                 true
             }
+            R.id.export -> {
+                exportAsCsv()
+                true
+            }
             android.R.id.home -> {
                 onBackPressedDispatcher.onBackPressed()
                 true
@@ -107,6 +115,45 @@ class MainActivity : AbstractBaseActivity(), SwipeRefreshLayout.OnRefreshListene
         }
     }
 
+    private fun exportAsCsv() {
+        launch {
+            val content = buildCsv()
+
+            try {
+                val filename = "prepaid-balance-${System.currentTimeMillis()}.csv"
+                writeToFileInDownloads(content, filename)
+                showSnackbar(getString(R.string.export_saved_file, filename))
+                return@launch
+            } catch (e: Exception) {
+                Log.e(TAG, "Error saving file", e)
+            }
+
+            showSnackbar(R.string.export_error_saving_file)
+        }
+    }
+
+    private fun buildCsv(): String {
+        val entries = database.balanceDao().getAll()
+        val csv = StringBuilder()
+        csv.appendLine("${getString(R.string.export_csv_header_balance)};${getString(R.string.export_csv_header_data)}")
+        entries.forEach {
+            csv.appendLine("${it.balance};${it.timestamp.timestampForUi(this@MainActivity)}")
+        }
+        return csv.toString()
+    }
+
+    private fun writeToFileInDownloads(content: String, fileName: String) {
+        val dir = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)
+        dir.mkdirs()
+        val file = Uri.fromFile(File(dir, fileName))
+
+        contentResolver.openOutputStream(file)?.use { outputStream ->
+            outputStream.write(content.toByteArray())
+            outputStream.flush()
+            outputStream.close()
+        }
+    }
+
     override fun onRefresh() {
         Log.d(TAG, "onRefresh()")
 

app/src/main/res/drawable/ic_outline_table_rows_24.xml

@@ -0,0 +1,5 @@
+<vector android:height="24dp" android:tint="#000000"
+    android:viewportHeight="24" android:viewportWidth="24"
+    android:width="24dp" xmlns:android="http://schemas.android.com/apk/res/android">
+    <path android:fillColor="@android:color/white" android:pathData="M19,3H5C3.9,3 3,3.9 3,5v14c0,1.1 0.9,2 2,2h14c1.1,0 2,-0.9 2,-2V5C21,3.9 20.1,3 19,3zM19,5v3H5V5H19zM19,10v4H5v-4H19zM5,19v-3h14v3H5z"/>
+</vector>

app/src/main/res/menu/main_menu.xml

@@ -1,6 +1,12 @@
 <?xml version="1.0" encoding="utf-8"?>
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:app="http://schemas.android.com/apk/res-auto">
+    <item
+        android:id="@+id/export"
+        android:title="@string/export"
+        app:showAsAction="ifRoom"
+        android:icon="@drawable/ic_outline_table_rows_24"
+        app:iconTint="?android:textColorSecondary" />
     <item
         android:id="@+id/preferences"
         android:title="@string/preferences"

app/src/main/res/values/strings.xml

@@ -48,6 +48,13 @@
     <string name="close">Close</string>
     <string name="no_response_saved">No response saved</string>
 
+    <!-- Export as CSV -->
+    <string name="export">Export as CSV</string>
+    <string name="export_saved_file">Exported as \"%s\" to downloads folder</string>
+    <string name="export_error_saving_file">Export failed</string>
+    <string name="export_csv_header_balance">Balance</string>
+    <string name="export_csv_header_data">Date</string>
+
     <!-- About menu -->
     <string name="about">About Prepaid Balance</string>
     <string name="error_no_browser_found">No browser found</string>