Show save prompt when exiting editor if there are unsaved changes

To check if there are unsaved changes, the current text is compared to the original text.
If user uses the "Saved as" button to modify this file, the original text is updated.

When there are unsaved changes:
- If user clicks "Discard", the editor is exited without saving.
- If user clicks "Save" and successfully saves the file, the editor is automatically closed afterward.
- If user clicks "Save" but then fails to save or closes the save dialog, the editor is not closed.

app/src/main/kotlin/com/simplemobiletools/filemanager/pro/activities/ReadTextActivity.kt

@@ -15,9 +15,11 @@ import android.webkit.WebView
 import android.webkit.WebViewClient
 import android.widget.ImageView
 import android.widget.TextView
+import com.simplemobiletools.commons.dialogs.ConfirmationAdvancedDialog
 import com.simplemobiletools.commons.extensions.*
 import com.simplemobiletools.commons.helpers.PERMISSION_WRITE_STORAGE
 import com.simplemobiletools.commons.helpers.REAL_FILE_PATH
+import com.simplemobiletools.commons.helpers.SAVE_DISCARD_PROMPT_INTERVAL
 import com.simplemobiletools.commons.helpers.ensureBackgroundThread
 import com.simplemobiletools.commons.views.MyEditText
 import com.simplemobiletools.filemanager.pro.R
@@ -31,10 +33,12 @@ import java.io.OutputStream
 
 class ReadTextActivity : SimpleActivity() {
     private val SELECT_SAVE_FILE_INTENT = 1
+    private val SELECT_SAVE_FILE_AND_EXIT_INTENT = 2
 
     private var filePath = ""
     private var originalText = ""
     private var searchIndex = 0
+    private var lastSavePromptTS = 0L
     private var searchMatches = emptyList<Int>()
     private var isSearchActive = false
 
@@ -83,15 +87,30 @@ class ReadTextActivity : SimpleActivity() {
         super.onActivityResult(requestCode, resultCode, resultData)
         if (requestCode == SELECT_SAVE_FILE_INTENT && resultCode == Activity.RESULT_OK && resultData != null && resultData.data != null) {
             val outputStream = contentResolver.openOutputStream(resultData.data!!)
-            saveTextContent(outputStream)
+            saveTextContent(outputStream, shouldExitAfterSaving = requestCode == SELECT_SAVE_FILE_AND_EXIT_INTENT,
+                shouldOverwriteOriginalText = getRealPathFromURI(intent.data!!) == filePath)
         }
     }
 
     override fun onBackPressed() {
-        if (isSearchActive) {
-            closeSearch()
-        } else {
-            super.onBackPressed()
+        val hasUnsavedChanges = originalText != read_text_view.text.toString()
+        when {
+            isSearchActive -> {
+                closeSearch()
+            }
+            hasUnsavedChanges && System.currentTimeMillis() - lastSavePromptTS > SAVE_DISCARD_PROMPT_INTERVAL -> {
+                lastSavePromptTS = System.currentTimeMillis()
+                ConfirmationAdvancedDialog(this, "", R.string.save_before_closing, R.string.save, R.string.discard) {
+                    if (it) {
+                        saveText(shouldExitAfterSaving = true)
+                    } else {
+                        super.onBackPressed()
+                    }
+                }
+            }
+            else -> {
+                super.onBackPressed()
+            }
         }
     }
 
@@ -108,7 +127,7 @@ class ReadTextActivity : SimpleActivity() {
         }, 250)
     }
 
-    private fun saveText() {
+    private fun saveText(shouldExitAfterSaving: Boolean = false) {
         if (filePath.isEmpty()) {
             filePath = getRealPathFromURI(intent.data!!) ?: ""
         }
@@ -120,7 +139,12 @@ class ReadTextActivity : SimpleActivity() {
                     putExtra(Intent.EXTRA_TITLE, filename)
                     addCategory(Intent.CATEGORY_OPENABLE)
 
-                    startActivityForResult(this, SELECT_SAVE_FILE_INTENT)
+                    val requestCode = if (shouldExitAfterSaving) {
+                        SELECT_SAVE_FILE_AND_EXIT_INTENT
+                    } else {
+                        SELECT_SAVE_FILE_INTENT
+                    }
+                    startActivityForResult(this, requestCode)
                 }
             }
         } else {
@@ -129,7 +153,7 @@ class ReadTextActivity : SimpleActivity() {
                     if (it) {
                         val file = File(path)
                         getFileOutputStream(file.toFileDirItem(this), true) {
-                            saveTextContent(it)
+                            saveTextContent(it, shouldExitAfterSaving, shouldOverwriteOriginalText = path == filePath)
                         }
                     }
                 }
@@ -137,11 +161,20 @@ class ReadTextActivity : SimpleActivity() {
         }
     }
 
-    private fun saveTextContent(outputStream: OutputStream?) {
+    private fun saveTextContent(outputStream: OutputStream?, shouldExitAfterSaving: Boolean, shouldOverwriteOriginalText: Boolean) {
         if (outputStream != null) {
-            outputStream.bufferedWriter().use { it.write(read_text_view.text.toString()) }
+            val currentText = read_text_view.text.toString()
+            outputStream.bufferedWriter().use { it.write(currentText) }
             toast(R.string.file_saved)
             hideKeyboard()
+
+            if (shouldOverwriteOriginalText) {
+                originalText = currentText
+            }
+
+            if (shouldExitAfterSaving)  {
+                super.onBackPressed()
+            }
         } else {
             toast(R.string.unknown_error_occurred)
         }