simplify the editing callback hell

By wrapping the `Mutable` part in `CustomTextStorageBase` in
begin/end editing calls, now deletions will be wrapped in an endEditing
call, making the custom callback dance obsolete.

Author: DivineDominion

Typewriter/TypewriterTextStorage.swift

@@ -34,50 +34,24 @@ fileprivate extension String {
 }
 
 protocol TypewriterTextStorageDelegate: class {
-    /// Like `textStorage(_:willProcessEditing:range:changeInLength:)` called
-    /// before the actual processing begins.
-    func typewriterTextStorageWillProcessEditing(_ typewriterTextStorage: TypewriterTextStorage)
-
-    /// Called after `typewriterTextStorageDidEndEditing`, if `processEditing()`
-    /// does emit that message.
-    func typewriterTextStorageDidProcessEditing(_ typewriterTextStorage: TypewriterTextStorage)
-
-    /// Called to notify about the end of `endEditing()`, or in case of an edit
-    /// outside of a begin/end editing block, at the end of `processEditing()`
-    /// but before `typewriterTextStorageDidProcessEditing(_:)`.
-    func typewriterTextStorageDidEndEditing(
-        _ typewriterTextStorage: TypewriterTextStorage,
-        butItReallyOnlyProcessedTheEdit endingAfterProcessing: Bool)
+    /// Called to notify about the end of `endEditing()`.
+    func typewriterTextStorageDidEndEditing(_ typewriterTextStorage: TypewriterTextStorage)
 }
 
 class TypewriterTextStorage: CustomTextStorageBase {
 
     weak var typewriterDelegate: TypewriterTextStorageDelegate?
 
-    private var isBlockEditing = false
-    private var wasBlockEditing = false
-
     override func beginEditing() {
-        isBlockEditing = true
         super.beginEditing()
     }
 
     override func processEditing() {
-        typewriterDelegate?.typewriterTextStorageWillProcessEditing(self)
-
         super.processEditing()
-
-        if !wasBlockEditing { typewriterDelegate?.typewriterTextStorageDidEndEditing(self, butItReallyOnlyProcessedTheEdit: true) }
-        wasBlockEditing = false
-
-        typewriterDelegate?.typewriterTextStorageDidProcessEditing(self)
     }
 
     override func endEditing() {
-        // `super.endEditing()` triggers `processEditing`, so `wasBlockEditing` needs to be set first
-        wasBlockEditing = isBlockEditing
-        isBlockEditing = false
         super.endEditing()
-        typewriterDelegate?.typewriterTextStorageDidEndEditing(self, butItReallyOnlyProcessedTheEdit: false)
+        typewriterDelegate?.typewriterTextStorageDidEndEditing(self)
     }
 }

Typewriter/ViewController.swift

@@ -87,12 +87,10 @@ class ViewController: NSViewController, NSTextStorageDelegate, TypewriterTextSto
 
     // MARK: Preparation
 
-    func typewriterTextStorageWillProcessEditing(_ typewriterTextStorage: TypewriterTextStorage) {
-        isProcessingEdit = true
-    }
+    func textStorage(_ textStorage: NSTextStorage, willProcessEditing editedMask: NSTextStorageEditActions, range editedRange: NSRange, changeInLength delta: Int) {
 
-    func typewriterTextStorageDidProcessEditing(_ typewriterTextStorage: TypewriterTextStorage) {
-        isProcessingEdit = false
+        guard isInTypewriterMode else { return }
+        isProcessingEdit = true
     }
 
     func textStorage(_ textStorage: NSTextStorage, didProcessEditing editedMask: NSTextStorageEditActions, range editedRange: NSRange, changeInLength delta: Int) {
@@ -133,16 +131,14 @@ class ViewController: NSViewController, NSTextStorageDelegate, TypewriterTextSto
     private(set) var pendingPreparation: TypewriterScrollPreparation?
 
     func prepareScroll(_ preparation: TypewriterScrollPreparation) {
+        
         self.pendingPreparation = preparation
     }
 
-    func typewriterTextStorageDidEndEditing(_ typewriterTextStorage: TypewriterTextStorage, butItReallyOnlyProcessedTheEdit endingAfterProcessing: Bool) {
+    func typewriterTextStorageDidEndEditing(_ typewriterTextStorage: TypewriterTextStorage) {
 
-        // If we would not schedule for later here, the layout manager would not be in
-        // a valid state for querying and the app crashes. So we schedule the command for later.
-        // Affects deletion only, it seems, so the tradeoff (making it an async problem) isn't that bad.
-        guard !endingAfterProcessing else { RunLoop.current.perform(processScrollPreparation); return }
         processScrollPreparation()
+        isProcessingEdit = false
     }
 
     fileprivate func processScrollPreparation() {