calctext/calcpad-macos/Sources/CalcPad/Views/EditorTextView.swift

import AppKit
import SwiftUI

/// A SwiftUI wrapper around NSTextView for the editor pane.
/// Uses NSViewRepresentable to bridge AppKit's NSTextView into SwiftUI,
/// providing line-level control, scroll position access, and performance
/// that SwiftUI's TextEditor cannot match.
struct EditorTextView: NSViewRepresentable {
    @Binding var text: String
    @Binding var scrollOffset: CGFloat
    var font: NSFont

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

    func makeNSView(context: Context) -> NSScrollView {
        let scrollView = NSScrollView()
        scrollView.hasVerticalScroller = true
        scrollView.hasHorizontalScroller = false
        scrollView.autohidesScrollers = true
        scrollView.borderType = .noBorder
        scrollView.drawsBackground = false

        let textView = NSTextView()
        textView.isEditable = true
        textView.isSelectable = true
        textView.allowsUndo = true
        textView.isRichText = false
        textView.usesFontPanel = false
        textView.isAutomaticQuoteSubstitutionEnabled = false
        textView.isAutomaticDashSubstitutionEnabled = false
        textView.isAutomaticTextReplacementEnabled = false
        textView.isAutomaticSpellingCorrectionEnabled = false

        // Disable line wrapping — horizontal scroll instead
        textView.isHorizontallyResizable = true
        textView.textContainer?.widthTracksTextView = false
        textView.textContainer?.containerSize = NSSize(
            width: CGFloat.greatestFiniteMagnitude,
            height: CGFloat.greatestFiniteMagnitude
        )
        textView.maxSize = NSSize(
            width: CGFloat.greatestFiniteMagnitude,
            height: CGFloat.greatestFiniteMagnitude
        )

        // Configure font and text color
        textView.font = font
        textView.textColor = .textColor
        textView.backgroundColor = .clear
        textView.drawsBackground = false
        textView.insertionPointColor = .textColor

        // Set the text
        textView.string = text

        // Configure the text container for consistent line spacing
        textView.textContainer?.lineFragmentPadding = 4
        textView.textContainerInset = NSSize(width: 8, height: 8)

        scrollView.documentView = textView
        context.coordinator.textView = textView
        context.coordinator.scrollView = scrollView

        // Observe text changes
        textView.delegate = context.coordinator

        // Observe scroll changes
        scrollView.contentView.postsBoundsChangedNotifications = true
        NotificationCenter.default.addObserver(
            context.coordinator,
            selector: #selector(Coordinator.scrollViewDidScroll(_:)),
            name: NSView.boundsDidChangeNotification,
            object: scrollView.contentView
        )

        return scrollView
    }

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

        // Update font if changed
        if textView.font != font {
            textView.font = font
            // Reapply font to entire text storage
            let range = NSRange(location: 0, length: textView.textStorage?.length ?? 0)
            textView.textStorage?.addAttribute(.font, value: font, range: range)
        }

        // Update text only if it actually changed (avoid feedback loops)
        if textView.string != text {
            let selectedRanges = textView.selectedRanges
            textView.string = text
            textView.selectedRanges = selectedRanges
        }

        // Update scroll position if driven externally
        context.coordinator.isUpdatingScroll = true
        let currentOffset = scrollView.contentView.bounds.origin.y
        if abs(currentOffset - scrollOffset) > 0.5 {
            scrollView.contentView.scroll(to: NSPoint(x: 0, y: scrollOffset))
            scrollView.reflectScrolledClipView(scrollView.contentView)
        }
        context.coordinator.isUpdatingScroll = false
    }

    final class Coordinator: NSObject, NSTextViewDelegate {
        var parent: EditorTextView
        weak var textView: NSTextView?
        weak var scrollView: NSScrollView?
        var isUpdatingScroll = false

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

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

        @objc func scrollViewDidScroll(_ notification: Notification) {
            guard !isUpdatingScroll,
                  let scrollView = scrollView else { return }
            let offset = scrollView.contentView.bounds.origin.y
            DispatchQueue.main.async { [weak self] in
                self?.parent.scrollOffset = offset
            }
        }

        deinit {
            NotificationCenter.default.removeObserver(self)
        }
    }
}