Feature: Undo function

AnkiDroid/src/main/java/com/ichi2/anki/NoteEditorFragment.kt

@@ -134,6 +134,7 @@ import com.ichi2.anki.multimediacard.impl.MultimediaEditableNote
 import com.ichi2.anki.noteeditor.CustomToolbarButton
 import com.ichi2.anki.noteeditor.FieldState
 import com.ichi2.anki.noteeditor.FieldState.FieldChangeType
+import com.ichi2.anki.noteeditor.NoteEditorActionsListener
 import com.ichi2.anki.noteeditor.NoteEditorLauncher
 import com.ichi2.anki.noteeditor.Toolbar
 import com.ichi2.anki.noteeditor.Toolbar.TextFormatListener
@@ -188,6 +189,7 @@ import timber.log.Timber
 import java.io.File
 import java.util.LinkedList
 import java.util.Locale
+import java.util.Stack
 import java.util.function.Consumer
 import kotlin.math.max
 import kotlin.math.min
@@ -215,7 +217,8 @@ class NoteEditorFragment :
     BaseSnackbarBuilderProvider,
     DispatchKeyEventListener,
     MenuProvider,
-    ShortcutGroupProvider {
+    ShortcutGroupProvider,
+    NoteEditorActionsListener {
     /** Whether any change are saved. E.g. multimedia, new card added, field changed and saved. */
     private var changed = false
     private var isTagsEdited = false
@@ -279,6 +282,12 @@ class NoteEditorFragment :
     private val fieldState = FieldState.fromEditor(this)
     private lateinit var toolbar: Toolbar
 
+    // indicates changes to noteEditorActionListener
+    private val undoStacks: MutableMap<Int, Stack<String>> = mutableMapOf()
+    private val redoStacks: MutableMap<Int, Stack<String>> = mutableMapOf()
+    private var currentActiveFieldIn: Int? = null
+    private var isPerformingUndoRedo = false
+
     // Use the same HTML if the same image is pasted multiple times.
     private var pastedImageCache: HashMap<String, String> = HashMap()
 
@@ -536,8 +545,11 @@ class NoteEditorFragment :
             formatListener =
                 TextFormatListener { formatter: Toolbar.TextFormatter ->
                     val currentFocus = requireActivity().currentFocus as? FieldEditText ?: return@TextFormatListener
+                    saveCurrentTextState(currentFocus.id, currentFocus.text.toString())
                     modifyCurrentSelection(formatter, currentFocus)
+                    redoStacks[currentFocus.id]?.clear()
                 }
+            actionsListener = this@NoteEditorFragment
             // Sets the background and icon color of toolbar respectively.
             setBackgroundColor(
                 MaterialColors.getColor(
@@ -1015,6 +1027,12 @@ class NoteEditorFragment :
         formatter: Toolbar.TextFormatter,
         textBox: FieldEditText,
     ) {
+        val fieldId = textBox.id
+        val currentTextBeforeModification = textBox.text.toString()
+        isPerformingUndoRedo = true
+        saveCurrentTextState(fieldId, currentTextBeforeModification)
+        redoStacks[fieldId]?.clear()
+
         // get the current text and selection locations
         val selectionStart = textBox.selectionStart
         val selectionEnd = textBox.selectionEnd
@@ -1033,9 +1051,14 @@ class NoteEditorFragment :
         // Update text field with updated text and selection
         val length = beforeText.length + newText.length + afterText.length
         val newFieldContent =
-            StringBuilder(length).append(beforeText).append(newText).append(afterText)
-        textBox.setText(newFieldContent)
-        textBox.setSelection(start + newStart, start + newEnd)
+            StringBuilder(length)
+                .append(beforeText)
+                .append(newText) // O resultado FORMATADO da seleção
+                .append(afterText)
+
+        textBox.setText(newFieldContent) // DEFINE O TEXTO MODIFICADO UMA ÚNICA VEZ
+        textBox.setSelection(start + newStart, start + newEnd) // DEFINE A SELEÇÃO CORRETA UMA ÚNICA VEZ
+        isPerformingUndoRedo = false
     }
 
     override fun onStop() {
@@ -1707,6 +1730,8 @@ class NoteEditorFragment :
         showDialogFragment(dialog)
     }
 
+    private fun getEditTextForFieldId(fieldIndex: Int): FieldEditText = editFields!![fieldIndex]
+
     override fun onSelectedTags(
         selectedTags: List<String>,
         indeterminateTags: List<String>,
@@ -1719,6 +1744,39 @@ class NoteEditorFragment :
         updateTags()
     }
 
+    override fun performUndo() {
+        currentActiveFieldIn?.let { fieldId ->
+            val editText = getEditTextForFieldId(fieldId)
+            val undoStack = undoStacks.getOrPut(fieldId) { Stack() }
+            val redoStack = redoStacks.getOrPut(fieldId) { Stack() }
+
+            if (undoStack.isNotEmpty()) {
+                val currentText = editText.text.toString()
+                redoStack.push(currentText)
+
+                isPerformingUndoRedo = true
+                val previousText = undoStack.pop()
+                editText.setText(previousText)
+                editText.setSelection(previousText.length)
+                isPerformingUndoRedo = false
+            }
+        }
+    }
+
+    override fun saveCurrentTextState(
+        fieldId: Int,
+        text: String,
+    ) {
+        val undoStack = undoStacks.getOrPut(fieldId) { Stack() }
+
+        if (undoStack.isNotEmpty() && undoStack.peek() == text) {
+            return
+        }
+
+        undoStack.push(text)
+        redoStacks[fieldId]?.clear()
+    }
+
     private fun showCardTemplateEditor() {
         val intent = Intent(requireContext(), CardTemplateEditor::class.java)
         // Pass the note type ID
@@ -1863,6 +1921,22 @@ class NoteEditorFragment :
                 newEditText.textSize = prefs.getInt(PREF_NOTE_EDITOR_FONT_SIZE, -1).toFloat()
             }
             newEditText.setCapitalize(prefs.getBoolean(PREF_NOTE_EDITOR_CAPITALIZE, true))
+
+            newEditText.onFocusChangeListener =
+                View.OnFocusChangeListener { v, hasFocus ->
+                    if (hasFocus) {
+                        val focusedEditText = v as FieldEditText
+                        val indexInEditFields = editFields?.indexOf(focusedEditText)
+                        if (indexInEditFields != null && indexInEditFields != -1) {
+                            currentActiveFieldIn = indexInEditFields
+                            Timber.d(
+                                "DEBUG_UNDO: Campo com ID ${v.id} (index $indexInEditFields) ganhou foco. currentActiveFieldIn definido para $currentActiveFieldIn",
+                            )
+                        } else {
+                            Timber.e("DEBUG_UNDO: FieldEditText com ID ${v.id} não encontrado em editFields!")
+                        }
+                    }
+                }
             val mediaButton = editLineView.mediaButton
             val toggleStickyButton = editLineView.toggleSticky
             // Make the icon change between media icon and switch field icon depending on whether editing note type
@@ -1875,7 +1949,6 @@ class NoteEditorFragment :
                 mediaButton.setBackgroundResource(0)
                 toggleStickyButton.setBackgroundResource(0)
             } else {
-                // Use media editor button if not changing note type
                 mediaButton.setBackgroundResource(R.drawable.ic_attachment)
 
                 mediaButton.setOnClickListener {
@@ -1884,7 +1957,6 @@ class NoteEditorFragment :
                 }
 
                 if (addNote) {
-                    // toggle sticky button
                     toggleStickyButton.setBackgroundResource(R.drawable.ic_baseline_push_pin_24)
                     setToggleStickyButtonListener(toggleStickyButton, i)
                 } else {
@@ -2240,7 +2312,7 @@ class NoteEditorFragment :
         enabled: Boolean,
     ) {
         // Listen for changes in the first field so we can re-check duplicate status.
-        editText!!.addTextChangedListener(EditFieldTextWatcher(index))
+        editText!!.addTextChangedListener(EditFieldTextWatcher(index, this))
         if (index == 0) {
             editText.onFocusChangeListener =
                 OnFocusChangeListener { _: View?, hasFocus: Boolean ->
@@ -2401,6 +2473,10 @@ class NoteEditorFragment :
         if (selectedTags == null) {
             selectedTags = editorNote!!.tags
         }
+
+        undoStacks.clear()
+        redoStacks.clear()
+
         // nb: setOnItemSelectedListener and populateEditFields need to occur after this
         setNoteTypePosition()
         setDid(note)
@@ -2907,7 +2983,6 @@ class NoteEditorFragment :
     ) {
         val editText = editFields!![i]
         editText.setText(newText)
-        EditFieldTextWatcher(i).afterTextChanged(editText.text!!)
     }
 
     @VisibleForTesting(otherwise = VisibleForTesting.NONE)
@@ -2926,33 +3001,63 @@ class NoteEditorFragment :
     private var loadingStickyFields = false
 
     private inner class EditFieldTextWatcher(
-        private val index: Int,
+        private val fieldId: Int,
+        private val listener: NoteEditorActionsListener,
     ) : TextWatcher {
-        override fun afterTextChanged(arg0: Editable) {
-            if (!loadingStickyFields) {
-                isFieldEdited = true
-            }
-            if (index == 0) {
-                setDuplicateFieldStyles()
-            }
-        }
+        private var lastRecordedText: String = ""
+        private val handler = android.os.Handler(android.os.Looper.getMainLooper())
+        private var runnable: Runnable? = null
 
         override fun beforeTextChanged(
-            arg0: CharSequence,
-            arg1: Int,
-            arg2: Int,
-            arg3: Int,
+            s: CharSequence,
+            start: Int,
+            count: Int,
+            after: Int,
         ) {
-            // do nothing
+            // Capture text before change
+            if (isPerformingUndoRedo) return
+            lastRecordedText = s.toString()
         }
 
         override fun onTextChanged(
-            arg0: CharSequence,
-            arg1: Int,
-            arg2: Int,
-            arg3: Int,
+            s: CharSequence,
+            start: Int,
+            before: Int,
+            count: Int,
         ) {
-            // do nothing
+            if (isPerformingUndoRedo) return
+            runnable?.let { handler.removeCallbacks(it) }
+        }
+
+        override fun afterTextChanged(s: Editable) {
+            if (!loadingStickyFields) {
+                isFieldEdited = true
+            }
+            if (fieldId == 0) {
+                setDuplicateFieldStyles()
+            }
+
+            if (isPerformingUndoRedo) return
+            val textAfterEdit = s.toString()
+
+            if (lastRecordedText != textAfterEdit) {
+                val textToSaveOnUndo = lastRecordedText
+
+                runnable =
+                    Runnable {
+                        val undoStack = undoStacks.getOrPut(fieldId) { Stack() }
+
+                        if (undoStack.isEmpty() || undoStack.peek() != textToSaveOnUndo) {
+                            listener.saveCurrentTextState(fieldId, textToSaveOnUndo)
+                            Timber.d("DEBUG_UNDO: CONSOLIDATED SAVE for fieldId: $fieldId, text: '$textToSaveOnUndo'")
+                        } else {
+                            Timber.d(
+                                "DEBUG_UNDO: SKIPPING CONSOLIDATED SAVE for fieldId: $fieldId, text: '$textToSaveOnUndo' (duplicate or already at top)",
+                            )
+                        }
+                    }
+                handler.postDelayed(runnable!!, 700)
+            }
         }
     }
 

AnkiDroid/src/main/java/com/ichi2/anki/noteeditor/NoteEditorActionsListener.kt

@@ -0,0 +1,26 @@
+/*
+ * Copyright (c) 2025 Guilherme Silva <sgsouza.173@gmail.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it under
+ * the terms of the GNU General Public License as published by the Free Software
+ * Foundation; either version 3 of the License, or (at your option) any later
+ * version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE. See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.ichi2.anki.noteeditor
+
+interface NoteEditorActionsListener {
+    fun performUndo()
+
+    fun saveCurrentTextState(
+        fieldId: Int,
+        text: String,
+    )
+}

AnkiDroid/src/main/java/com/ichi2/anki/noteeditor/Toolbar.kt

@@ -78,6 +78,7 @@ import kotlin.math.ceil
  */
 class Toolbar : FrameLayout {
     var formatListener: TextFormatListener? = null
+    var actionsListener: NoteEditorActionsListener? = null
     private val toolbar: LinearLayout
     private val toolbarLayout: LinearLayout
 
@@ -130,6 +131,7 @@ class Toolbar : FrameLayout {
         setupButtonWrappingText(R.id.note_editor_toolbar_button_underline, "<u>", "</u>")
         setupButtonWrappingText(R.id.note_editor_toolbar_button_insert_mathjax, "\\(", "\\)")
         setupButtonWrappingText(R.id.note_editor_toolbar_button_horizontal_rule, "<hr>", "")
+        findViewById<View>(R.id.note_editor_toolbar_button_undo).setOnClickListener { undoText() }
         findViewById<View>(R.id.note_editor_toolbar_button_font_size).setOnClickListener { displayFontSizeDialog() }
         findViewById<View>(R.id.note_editor_toolbar_button_title).setOnClickListener { displayInsertHeadingDialog() }
         findViewById<View>(R.id.note_editor_toolbar_button_insert_mathjax).setOnLongClickListener {
@@ -343,6 +345,13 @@ class Toolbar : FrameLayout {
         }
     }
 
+    /**
+     * Initiates the undo action by notifying the TextFormatListener
+     */
+    private fun undoText() {
+        actionsListener?.performUndo()
+    }
+
     /** Given a string [text], generates a [Drawable] which can be used as a button icon */
     fun createDrawableForString(text: String): Drawable {
         val baseline = -stringPaint!!.ascent()

AnkiDroid/src/main/res/drawable/ic_undo_black_24dp.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="960"
+    android:viewportHeight="960">
+  <path
+      android:pathData="M280,760v-80h284q63,0 109.5,-40T720,540q0,-60 -46.5,-100T564,400L312,400l104,104 -56,56 -200,-200 200,-200 56,56 -104,104h252q97,0 166.5,63T800,540q0,94 -69.5,157T564,760L280,760Z"
+      android:fillColor="#000000"/>
+</vector>

AnkiDroid/src/main/res/layout/note_editor_toolbar.xml

@@ -74,6 +74,14 @@
             android:tag="u"
             style="@style/note_editor_toolbar_button" />
 
+        <androidx.appcompat.widget.AppCompatImageButton
+            android:id="@+id/note_editor_toolbar_button_undo"
+            app:srcCompat="@drawable/ic_undo_black_24dp"
+            android:contentDescription="@string/undo_text_change"
+            android:tooltipText="@string/undo_text_change"
+            android:tag="g"
+            style="@style/note_editor_toolbar_button" />
+
         <androidx.appcompat.widget.AppCompatImageButton
             android:id="@+id/note_editor_toolbar_button_horizontal_rule"
             app:srcCompat="@drawable/ic_horizontal_rule_black_24dp"

AnkiDroid/src/main/res/values/02-strings.xml

@@ -226,6 +226,7 @@
     <string name="format_insert_bold">Format as Bold</string>
     <string name="format_insert_italic">Format as Italic</string>
     <string name="format_insert_underline">Format as Underline</string>
+    <string name="undo_text_change">Undo Last Change In Text</string>
     <string name="insert_horizontal_line">Insert Horizontal Line</string>
     <string name="insert_heading">Insert Heading</string>
     <string name="format_font_size">Change Font Size</string>