#if canImport(UIKit) || canImport(AppKit)
  import SwiftUI

  /// A SwiftUI source editor for `.norg` documents with syntax highlighting
  /// and context-aware indentation.
  ///
  /// ```swift
  /// NorgEditor(text: $draft)
  ///     .norgEditorTheme(myTheme)
  /// ```
  public struct NorgEditor {

    @Binding private var text: String
    @Environment(\.norgEditorTheme) private var theme

    public init(text: Binding<String>) {
      self._text = text
    }
  }
#endif

#if canImport(UIKit)
  import UIKit
  import NorgKeyboardToolbar

  extension NorgEditor: UIViewRepresentable {

    public func makeUIView(context: Context) -> UITextView {
      let textView = UITextView()
      textView.delegate = context.coordinator
      textView.backgroundColor = .clear
      textView.textContainerInset = UIEdgeInsets(top: 8, left: 0, bottom: 8, right: 0)
      textView.textContainer.lineFragmentPadding = 0
      textView.alwaysBounceVertical = true
      textView.contentInsetAdjustmentBehavior = .never

      textView.installNorgKeyboardAccessory()

      textView.smartQuotesType = .yes
      textView.smartDashesType = .no
      textView.smartInsertDeleteType = .no
      textView.dataDetectorTypes = []
      textView.autocorrectionType = .default
      textView.spellCheckingType = .default
      textView.autocapitalizationType = .sentences

      #if os(iOS)
        context.coordinator.observeKeyboard(for: textView)
      #endif
      textView.text = text
      context.coordinator.apply(theme, to: textView)
      return textView
    }

    public func updateUIView(_ textView: UITextView, context: Context) {
      context.coordinator.parent = self

      if textView.text != text {
        textView.text = text
        context.coordinator.highlight(textView)
      }
    }

    public func makeCoordinator() -> Coordinator { Coordinator(self) }

    public final class Coordinator: NSObject, UITextViewDelegate {
      fileprivate var parent: NorgEditor
      private var theme: EditorTheme = .default
      private var isAutoIndenting = false

      init(_ parent: NorgEditor) { self.parent = parent }

      deinit { NotificationCenter.default.removeObserver(self) }

      // MARK: - Auto-indentation

      public func textView(
        _ textView: UITextView,
        shouldChangeTextIn range: NSRange,
        replacementText text: String
      ) -> Bool {
        guard !isAutoIndenting, text == "\n" else { return true }

        let indent = NorgAutoIndent.indentation(
          for: textView.text, newlineAt: range.location)
        guard !indent.isEmpty else { return true }

        guard
          let start = textView.position(
            from: textView.beginningOfDocument, offset: range.location),
          let end = textView.position(from: start, offset: range.length),
          let textRange = textView.textRange(from: start, to: end)
        else { return true }

        isAutoIndenting = true
        textView.replace(textRange, withText: "\n" + indent)
        isAutoIndenting = false
        return false
      }

      // MARK: - Highlighting

      func apply(_ theme: EditorTheme, to textView: UITextView) {
        self.theme = theme
        textView.font = theme.font
        textView.typingAttributes = [
          .font: theme.font,
          .foregroundColor: theme.textColor,
        ]
        highlight(textView)
      }

      func highlight(_ textView: UITextView) {
        guard textView.markedTextRange == nil else { return }
        let storage = textView.textStorage
        let selection = textView.selectedRange
        storage.beginEditing()
        theme.applyHighlighting(to: storage)
        storage.endEditing()
        textView.selectedRange = selection
      }

      public func textViewDidChange(_ textView: UITextView) {
        parent.text = textView.text
        highlight(textView)
      }

      // MARK: - Keyboard avoidance

      #if os(iOS)
        private weak var textView: UITextView?

        func observeKeyboard(for textView: UITextView) {
          self.textView = textView
          NotificationCenter.default.addObserver(
            self,
            selector: #selector(keyboardFrameChanged(_:)),
            name: UIResponder.keyboardWillChangeFrameNotification,
            object: nil
          )
        }

        @objc private func keyboardFrameChanged(_ note: Notification) {
          guard let textView, let window = textView.window,
            let endFrame = note.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? CGRect
          else { return }

          let keyboardInWindow = window.convert(endFrame, from: window.screen.fixedCoordinateSpace)
          let textViewInWindow = textView.convert(textView.bounds, to: window)
          let overlap = max(0, textViewInWindow.maxY - keyboardInWindow.minY)

          textView.contentInset.bottom = overlap
          textView.verticalScrollIndicatorInsets.bottom = overlap
        }
      #endif
    }
  }
#elseif canImport(AppKit)
  import AppKit

  extension NorgEditor: NSViewRepresentable {

    public func makeNSView(context: Context) -> NSScrollView {
      let scrollView = NSTextView.scrollableTextView()
      scrollView.drawsBackground = false
      guard let textView = scrollView.documentView as? NSTextView else { return scrollView }

      textView.delegate = context.coordinator
      textView.drawsBackground = false
      textView.isRichText = false
      textView.allowsUndo = true
      textView.textContainerInset = NSSize(width: 0, height: 8)
      textView.textContainer?.lineFragmentPadding = 0

      textView.isAutomaticQuoteSubstitutionEnabled = true
      textView.isAutomaticDashSubstitutionEnabled = false
      textView.isAutomaticTextReplacementEnabled = false
      textView.isAutomaticLinkDetectionEnabled = false

      textView.string = text
      context.coordinator.apply(theme, to: textView)
      return scrollView
    }

    public func updateNSView(_ scrollView: NSScrollView, context: Context) {
      context.coordinator.parent = self
      guard let textView = scrollView.documentView as? NSTextView else { return }

      if textView.string != text {
        textView.string = text
        context.coordinator.highlight(textView)
      }
    }

    public func makeCoordinator() -> Coordinator { Coordinator(self) }

    // AppKit's `NSTextViewDelegate` isn't `@MainActor`-annotated (UIKit's is),
    // so isolation isn't inferred for these callbacks even though the text view
    // only ever calls them on the main thread; state the isolation explicitly.
    @MainActor
    public final class Coordinator: NSObject, NSTextViewDelegate {
      fileprivate var parent: NorgEditor
      private var theme: EditorTheme = .default
      private var isAutoIndenting = false

      init(_ parent: NorgEditor) { self.parent = parent }

      // MARK: - Auto-indentation

      public func textView(
        _ textView: NSTextView,
        shouldChangeTextIn affectedCharRange: NSRange,
        replacementString: String?
      ) -> Bool {
        guard !isAutoIndenting, replacementString == "\n" else { return true }

        let indent = NorgAutoIndent.indentation(
          for: textView.string, newlineAt: affectedCharRange.location)
        guard !indent.isEmpty else { return true }

        isAutoIndenting = true
        textView.insertText("\n" + indent, replacementRange: affectedCharRange)
        isAutoIndenting = false
        return false
      }

      // MARK: - Highlighting

      func apply(_ theme: EditorTheme, to textView: NSTextView) {
        self.theme = theme
        textView.font = theme.font
        textView.typingAttributes = [
          .font: theme.font,
          .foregroundColor: theme.textColor,
        ]
        highlight(textView)
      }

      func highlight(_ textView: NSTextView) {
        guard !textView.hasMarkedText(), let storage = textView.textStorage else { return }
        let selection = textView.selectedRange()
        storage.beginEditing()
        theme.applyHighlighting(to: storage)
        storage.endEditing()
        textView.setSelectedRange(selection)
      }

      public func textDidChange(_ notification: Notification) {
        guard let textView = notification.object as? NSTextView else { return }
        parent.text = textView.string
        highlight(textView)
      }
    }
  }
#endif