import AppKit

/// A line-number gutter for an NSTextView, themed to match the editor.
/// Highlights the line containing the insertion point.
final class LineNumberRulerView: NSRulerView {
    private weak var textView: NSTextView?
    private var theme: EditorTheme = .system

    init(textView: NSTextView) {
        self.textView = textView
        super.init(scrollView: textView.enclosingScrollView, orientation: .verticalRuler)
        clientView = textView
        ruleThickness = 44

        let center = NotificationCenter.default
        center.addObserver(self, selector: #selector(needsRedraw),
                           name: NSText.didChangeNotification, object: textView)
        center.addObserver(self, selector: #selector(needsRedraw),
                           name: NSTextView.didChangeSelectionNotification, object: textView)
        if let clip = textView.enclosingScrollView?.contentView {
            clip.postsBoundsChangedNotifications = true
            center.addObserver(self, selector: #selector(needsRedraw),
                               name: NSView.boundsDidChangeNotification, object: clip)
        }
    }

    required init(coder: NSCoder) { fatalError("init(coder:) has not been implemented") }

    deinit { NotificationCenter.default.removeObserver(self) }

    func apply(theme: EditorTheme) {
        self.theme = theme
        needsDisplay = true
    }

    /// Point the gutter at a different text view (used when the editor switches
    /// which board page it is showing).
    func retarget(to tv: NSTextView) {
        NotificationCenter.default.removeObserver(self)
        textView = tv
        clientView = tv
        let center = NotificationCenter.default
        center.addObserver(self, selector: #selector(needsRedraw),
                           name: NSText.didChangeNotification, object: tv)
        center.addObserver(self, selector: #selector(needsRedraw),
                           name: NSTextView.didChangeSelectionNotification, object: tv)
        if let clip = tv.enclosingScrollView?.contentView {
            clip.postsBoundsChangedNotifications = true
            center.addObserver(self, selector: #selector(needsRedraw),
                               name: NSView.boundsDidChangeNotification, object: clip)
        }
        needsDisplay = true
    }

    @objc private func needsRedraw() { needsDisplay = true }

    /// Widen the gutter as the line count grows so 4- and 5-digit files fit.
    func updateThickness() {
        guard let lineCount = textView?.string.reduce(into: 1, { c, ch in if ch == "\n" { c += 1 } }) else { return }
        let digits = max(2, String(lineCount).count)
        let font = gutterFont
        let sample = String(repeating: "8", count: digits)
        let width = (sample as NSString).size(withAttributes: [.font: font]).width
        let thickness = ceil(width) + 16
        if abs(thickness - ruleThickness) > 0.5 { ruleThickness = thickness }
    }

    private var gutterFont: NSFont {
        let base = (textView?.font?.pointSize ?? 13) - 2
        return NSFont.monospacedDigitSystemFont(ofSize: max(9, base), weight: .regular)
    }

    override func drawHashMarksAndLabels(in rect: NSRect) {
        guard let textView,
              let layoutManager = textView.layoutManager,
              let container = textView.textContainer,
              let scrollView = scrollView else { return }

        theme.gutterBackground.setFill()
        bounds.fill()

        // Subtle separator line on the gutter's trailing edge.
        theme.gutterText.withAlphaComponent(0.25).setStroke()
        let sep = NSBezierPath()
        sep.move(to: NSPoint(x: bounds.maxX - 0.5, y: bounds.minY))
        sep.line(to: NSPoint(x: bounds.maxX - 0.5, y: bounds.maxY))
        sep.lineWidth = 1
        sep.stroke()

        let content = scrollView.contentView
        let visibleRect = content.bounds
        let inset = textView.textContainerInset
        let nsString = textView.string as NSString

        let font = gutterFont
        let normalAttrs: [NSAttributedString.Key: Any] = [.font: font, .foregroundColor: theme.gutterText]
        let activeAttrs: [NSAttributedString.Key: Any] = [.font: font, .foregroundColor: theme.accent]

        // Which line holds the insertion point?
        let selectedLine = currentLineNumber(in: nsString, selection: textView.selectedRange())

        let glyphRange = layoutManager.glyphRange(forBoundingRect: visibleRect, in: container)
        let charRange = layoutManager.characterRange(forGlyphRange: glyphRange, actualGlyphRange: nil)

        var lineNumber = lineCount(in: nsString, upTo: charRange.location)
        var index = charRange.location

        while index <= NSMaxRange(charRange) {
            let lineRange = nsString.lineRange(for: NSRange(location: index, length: 0))
            let glyphLineRange = layoutManager.glyphRange(forCharacterRange: lineRange, actualCharacterRange: nil)
            var lineRect = layoutManager.boundingRect(forGlyphRange: glyphLineRange, in: container)
            lineRect.origin.y += inset.height

            // Convert text Y into ruler Y.
            let y = lineRect.minY - visibleRect.minY
            let isActive = lineNumber == selectedLine
            if isActive {
                theme.currentLine.setFill()
                NSRect(x: 0, y: y, width: bounds.width, height: lineRect.height).fill()
            }
            let label = "\(lineNumber)" as NSString
            let attrs = isActive ? activeAttrs : normalAttrs
            let size = label.size(withAttributes: attrs)
            let drawY = y + (lineRect.height - size.height) / 2
            label.draw(at: NSPoint(x: bounds.width - size.width - 8, y: drawY), withAttributes: attrs)

            if NSMaxRange(lineRange) <= index { break }
            index = NSMaxRange(lineRange)
            lineNumber += 1
            if index > nsString.length { break }
        }
    }

    private func lineCount(in s: NSString, upTo location: Int) -> Int {
        var count = 1
        var i = 0
        let end = min(location, s.length)
        while i < end {
            if s.character(at: i) == 10 { count += 1 }
            i += 1
        }
        return count
    }

    private func currentLineNumber(in s: NSString, selection: NSRange) -> Int {
        lineCount(in: s, upTo: selection.location)
    }
}