fix: extending paragraph style on paste (#472)

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# Summary

This PR fixes applying styles for pasted text at the end of paragraph.
It was mentioned here: #409 

## Test Plan
1. Create Heading with text "Hello"
2. Copy some text
3. paste it at the end of "Hello"
4. Heading styles should extend on pasted text

## Screenshots / Videos
Before:


https://github.com/user-attachments/assets/cad248b8-1674-477f-af45-fae8c0a63538


After:


https://github.com/user-attachments/assets/e67b861e-8394-41da-9305-71799ccca072


## Compatibility

| OS      | Implemented |
| ------- | :---------: |
| iOS     |    ❌     |
| Android |    ✅     |

---------

Author: kacperzolkiewski

.maestro/flows/extending_paragraph_style_on_paste_after_copy.yaml

@@ -0,0 +1,45 @@
+appId: swmansion.enriched.example
+tags:
+    - android-only
+---
+- launchApp
+- tapOn:
+    id: "toggle-screen-button"
+
+- tapOn:
+    id: "focus-button"
+
+- inputText: "EADING"
+- doubleTapOn:
+    id: "editor-input"
+    point: "10%, 50%"
+
+- tapOn:
+    id: "android:id/floating_toolbar_menu_item_text"
+    text: "Copy"
+
+# Dismiss toolbar with Copy/Cut etc. options
+- tapOn:
+    id: "editor-input"
+- tapOn:
+    id: "clear-button"
+- tapOn:
+    id: "focus-button"
+
+- tapOn:
+    id: "toolbar-heading-1"
+
+- inputText: "H"
+
+- longPressOn:
+    id: "editor-input"
+    point: "50%, 50%"
+
+- tapOn:
+    id: "android:id/floating_toolbar_menu_item_text"
+    text: "Paste"
+
+- runFlow:
+    file: "../subflows/capture_or_assert_screenshot.yaml"
+    env:
+       SCREENSHOT_NAME: "extending_paragraph_style_on_paste_after_copy"

.maestro/flows/extending_paragraph_style_on_paste_after_cut.yaml

@@ -0,0 +1,37 @@
+appId: swmansion.enriched.example
+tags:
+    - android-only
+---
+- launchApp
+- tapOn:
+    id: "toggle-screen-button"
+
+- tapOn:
+    id: "focus-button"
+
+- inputText: "EADING"
+- doubleTapOn:
+    id: "editor-input"
+    point: "10%, 50%"
+
+- tapOn:
+    id: "android:id/floating_toolbar_menu_item_text"
+    text: "Cut"
+
+- tapOn:
+    id: "toolbar-heading-1"
+
+- inputText: "H"
+
+- longPressOn:
+    id: "editor-input"
+    point: "50%, 50%"
+
+- tapOn:
+    id: "android:id/floating_toolbar_menu_item_text"
+    text: "Paste"
+
+- runFlow:
+    file: "../subflows/capture_or_assert_screenshot.yaml"
+    env:
+       SCREENSHOT_NAME: "extending_paragraph_style_on_paste_after_cut"

.maestro/screenshots/android/extending_paragraph_style_on_paste_after_copy.png

@@ -12,6 +12,7 @@ import android.os.Build
 import android.text.Editable
 import android.text.InputType
 import android.text.Spannable
+import android.text.SpannableString
 import android.util.AttributeSet
 import android.util.Log
 import android.util.Patterns
@@ -338,28 +339,37 @@ class EnrichedTextInputView :
   }
 
   fun handleTextPaste(item: ClipData.Item) {
-    val htmlText = item.htmlText
     val currentText = text as Spannable
     val start = selectionStart.coerceAtLeast(0)
     val end = selectionEnd.coerceAtLeast(0)
+    val lengthBefore = currentText.length
+
+    val pastedSpannable: Spannable =
+      when {
+        item.htmlText != null -> {
+          val parsed = parseText(item.htmlText)
+          (parsed as? Spannable) ?: return
+        }
+
+        item.text != null -> {
+          SpannableString(item.text.toString())
+        }
 
-    if (htmlText != null) {
-      val parsedText = parseText(htmlText)
-      if (parsedText is Spannable) {
-        val finalText = currentText.mergeSpannables(start, end, parsedText)
-        setValue(finalText, false)
-        return
+        else -> {
+          return
+        }
       }
-    }
 
-    if (item.text == null) return
-    val lengthBefore = currentText.length
-    val finalText = currentText.mergeSpannables(start, end, item.text.toString())
-    setValue(finalText)
+    val finalText = currentText.mergeSpannables(start, end, pastedSpannable)
+    setValue(finalText, false)
+
+    // replacement-safe: oldLength - removed + inserted
+    val insertedLength = finalText.length - (lengthBefore - (end - start))
+    val pasteEnd = (start + insertedLength).coerceIn(0, finalText.length)
+    setSelection(pasteEnd)
 
     // Detect links in the newly pasted range
-    val finalEndIndex = start + finalText.length - lengthBefore
-    parametrizedStyles?.detectLinksInRange(finalText, start, finalEndIndex)
+    parametrizedStyles?.detectLinksInRange(finalText, start.coerceAtMost(pasteEnd), pasteEnd)
   }
 
   fun requestFocusProgrammatically() {

.maestro/screenshots/android/extending_paragraph_style_on_paste_after_cut.png

@@ -100,9 +100,14 @@ class ParametrizedStyles(
     end: Int,
   ) {
     val regex = view.linkRegex ?: return
-    val contextText = spannable.subSequence(start, end).toString()
+    val textLength = spannable.length
+    val safeStart = minOf(start, end).coerceIn(0, textLength)
+    val safeEnd = maxOf(start, end).coerceIn(0, textLength)
+    if (safeStart >= safeEnd) return
 
-    val spans = spannable.getSpans(start, end, EnrichedInputLinkSpan::class.java)
+    val contextText = spannable.subSequence(safeStart, safeEnd).toString()
+
+    val spans = spannable.getSpans(safeStart, safeEnd, EnrichedInputLinkSpan::class.java)
     for (span in spans) {
       spannable.removeSpan(span)
     }

android/src/main/java/com/swmansion/enriched/textinput/EnrichedTextInputView.kt

@@ -66,6 +66,10 @@ fun Spannable.mergeSpannables(
   val isNewLineStart = startBlockSpans.isNotEmpty() || startParagraphSpans.isNotEmpty()
   val isNewLineEnd = endBlockSpans.isNotEmpty() || endParagraphSpans.isNotEmpty()
 
+  val pastedHasOwnStyles =
+    spannable.getSpans(0, spannable.length, EnrichedBlockSpan::class.java).isNotEmpty() ||
+      spannable.getSpans(0, spannable.length, EnrichedParagraphSpan::class.java).isNotEmpty()
+
   if (isNewLineStart && start != paragraphStart) {
     builder.insert(start, "\n")
     finalStart = start + 1
@@ -78,5 +82,25 @@ fun Spannable.mergeSpannables(
 
   builder.replace(finalStart, finalEnd, spannable)
 
+  // Manually extend existing paragraph/block spans to cover the pasted text.
+  if (!pastedHasOwnStyles) {
+    val pasteEnd = finalStart + spannable.length
+
+    val affectedParagraphSpans = builder.getSpans(finalStart, finalStart, EnrichedParagraphSpan::class.java)
+    val affectedBlockSpans = builder.getSpans(finalStart, finalStart, EnrichedBlockSpan::class.java)
+    val affectedSpans = affectedBlockSpans.toList() + affectedParagraphSpans.toList()
+
+    for (span in affectedSpans) {
+      val spanStart = builder.getSpanStart(span)
+      val spanEnd = builder.getSpanEnd(span)
+      if (spanStart == -1 || spanEnd >= pasteEnd) continue
+
+      val (_, newParagraphEnd) = builder.getParagraphBounds(spanStart, pasteEnd)
+      val flags = builder.getSpanFlags(span)
+      builder.removeSpan(span)
+      builder.setSpan(span, spanStart, newParagraphEnd, flags)
+    }
+  }
+
   return builder
 }