fix(mobile): the iOS composer reopens where you left a long draft

apps/mobile/modules/t3-composer-editor/ios/T3ComposerEditorView.swift

@@ -13,7 +13,7 @@ private struct ComposerTokenPayload: Decodable {
   let end: Int
 }
 
-private struct ComposerSelectionPayload: Decodable {
+private struct ComposerSelectionPayload: Decodable, Equatable {
   let start: Int
   let end: Int
 }
@@ -449,6 +449,9 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
   private var tokensNeedRebuild = false
   private var chipsNeedMeasuredWidth = false
   private var hasDeferredForcedRebuild = false
+  private var pendingContentOffset: CGPoint?
+  private var needsSelectionReveal = false
+  private var selectionBeforeFocusingTap: (selection: ComposerSelectionPayload, value: String)?
 
   let onComposerChange = EventDispatcher()
   let onComposerSelectionChange = EventDispatcher()
@@ -520,6 +523,12 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
   @objc private func openContext(_ recognizer: UITapGestureRecognizer) {
     guard let (index, attachment) = contextAttachment(at: recognizer.location(in: textView)) else {
       textView.becomeFirstResponder()
+      if selectionBeforeFocusingTap != nil {
+        // UIKit places the caret from its own tap recognizer during this same touch.
+        DispatchQueue.main.async { [weak self] in
+          self?.restoreSelectionBeforeFocusingTap()
+        }
+      }
       return
     }
     openContext(index: index, attachment: attachment)
@@ -558,7 +567,11 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
   }
 
   public func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldReceive touch: UITouch) -> Bool {
-    true
+    // The collapsed editor only shows the draft's first line, so a tap that expands an
+    // overflowing draft returns to the caret it was left at instead of moving it there.
+    let collapsedOverflow = !textView.isFirstResponder && !textView.isScrollEnabled && draftOverflowsBounds()
+    selectionBeforeFocusingTap = collapsedOverflow ? (sourceSelection(), value) : nil
+    return true
   }
 
   public func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
@@ -583,11 +596,27 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
 
   public override func layoutSubviews() {
     super.layoutSubviews()
+    let previousSize = textView.bounds.size
     textView.frame = bounds
     if chipsNeedMeasuredWidth, bounds.width > 0 {
       chipsNeedMeasuredWidth = false
       applyControlledDocument(force: true)
     }
+    if textView.isScrollEnabled, bounds.width > 0, bounds.height > 0 {
+      textView.layoutIfNeeded()
+      if let offset = pendingContentOffset {
+        let minY = -textView.adjustedContentInset.top
+        let maxY = max(minY, textView.contentSize.height - bounds.height + textView.adjustedContentInset.bottom)
+        textView.setContentOffset(CGPoint(x: offset.x, y: min(maxY, max(minY, offset.y))), animated: false)
+        pendingContentOffset = nil
+      }
+      if needsSelectionReveal || (previousSize != bounds.size && textView.isFirstResponder) {
+        needsSelectionReveal = false
+        if let selection = textView.selectedTextRange {
+          textView.scrollRectToVisible(textView.caretRect(for: selection.end), animated: false)
+        }
+      }
+    }
     let placeholderX = textView.textContainerInset.left + textView.textContainer.lineFragmentPadding
     let placeholderY = textView.textContainerInset.top
     let placeholderWidth = max(
@@ -632,10 +661,12 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
       tokens = decode([ComposerTokenPayload].self, from: document.tokensJson) ?? []
       tokensNeedRebuild = true
     }
+    let previousSelection = sourceSelection()
     value = document.value
     requestedSelection = document.selection
     applyControlledDocument(force: tokensNeedRebuild)
     applyRequestedSelection()
+    cancelFocusingTapRestoreIfSelectionMoved(from: previousSelection)
     if tokensMatchCurrentValue() {
       tokensNeedRebuild = false
     }
@@ -694,7 +725,16 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
   }
 
   func setScrollEnabled(_ scrollEnabled: Bool) {
+    guard textView.isScrollEnabled != scrollEnabled else { return }
+    if !scrollEnabled {
+      // Disabling scrolling discards UITextView's offset. Restore it after
+      // expansion has laid out the text, regardless of prop update order.
+      pendingContentOffset = pendingContentOffset ?? textView.contentOffset
+    }
     textView.isScrollEnabled = scrollEnabled
+    if scrollEnabled {
+      revealSelectionAfterLayout()
+    }
   }
 
   func setAutoFocus(_ autoFocus: Bool) {
@@ -738,8 +778,10 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
   }
 
   func setSelection(start: Int, end: Int) {
+    let previousSelection = sourceSelection()
     requestedSelection = ComposerSelectionPayload(start: start, end: end)
     applyRequestedSelection()
+    cancelFocusingTapRestoreIfSelectionMoved(from: previousSelection)
   }
 
   public func textViewDidChange(_ textView: UITextView) {
@@ -811,6 +853,7 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
   }
 
   public func textViewDidBeginEditing(_ textView: UITextView) {
+    revealSelectionAfterLayout()
     onComposerFocus()
   }
 
@@ -836,13 +879,21 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
     hasDeferredForcedRebuild = false
 
     let previousSelection = sourceSelection()
+    if textView.isScrollEnabled {
+      pendingContentOffset = pendingContentOffset ?? textView.contentOffset
+    }
     isApplyingControlledValue = true
     textView.attributedText = makeAttributedDocument()
     let targetSelection = requestedSelection ?? previousSelection
     requestedSelection = nil
     textView.selectedRange = displayRange(for: targetSelection)
     restoreBaseTypingAttributes()
     isApplyingControlledValue = false
+    if currentSource != value || previousSelection.start != targetSelection.start || previousSelection.end != targetSelection.end {
+      revealSelectionAfterLayout()
+    } else {
+      setNeedsLayout()
+    }
     updatePlaceholderVisibility()
     emitContentSizeIfNeeded()
   }
@@ -1053,6 +1104,7 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
       return
     }
     value = textView.serializedText()
+    revealSelectionAfterLayout()
     let selection = sourceSelection()
     nativeEventCount += 1
     onComposerChange([
@@ -1122,6 +1174,40 @@ public final class T3ComposerEditorView: ExpoView, UITextViewDelegate, UITextDro
     isApplyingControlledValue = true
     textView.selectedRange = nextRange
     isApplyingControlledValue = false
+    revealSelectionAfterLayout()
+  }
+
+  private func restoreSelectionBeforeFocusingTap() {
+    guard let snapshot = selectionBeforeFocusingTap else {
+      return
+    }
+    selectionBeforeFocusingTap = nil
+    // A draft that changed during the touch, such as a transcript landing, owns the caret now.
+    guard textView.isFirstResponder, textView.markedTextRange == nil, value == snapshot.value else {
+      return
+    }
+    let range = displayRange(for: snapshot.selection)
+    guard !NSEqualRanges(range, textView.selectedRange) else {
+      return
+    }
+    textView.selectedRange = range
+    revealSelectionAfterLayout()
+  }
+
+  private func cancelFocusingTapRestoreIfSelectionMoved(from previousSelection: ComposerSelectionPayload) {
+    if sourceSelection() != previousSelection {
+      selectionBeforeFocusingTap = nil
+    }
+  }
+
+  private func draftOverflowsBounds() -> Bool {
+    let size = textView.sizeThatFits(CGSize(width: textView.bounds.width, height: .greatestFiniteMagnitude))
+    return size.height > textView.bounds.height + 1
+  }
+
+  private func revealSelectionAfterLayout() {
+    needsSelectionReveal = true
+    setNeedsLayout()
   }
 
   private func updatePlaceholderVisibility() {