import AppKit

/// Selection-aware Markdown insertion used by both the toolbar and the Format
/// menu. Wraps the selection (or inserts a placeholder), keeping the change on
/// the text view's own undo stack.
enum TextMarkup {
    static func wrap(_ textView: NSTextView, prefix: String, suffix: String, placeholder: String) {
        let range = textView.selectedRange()
        let ns = textView.string as NSString
        let selected = ns.substring(with: range)
        let body = selected.isEmpty ? placeholder : selected
        let replacement = prefix + body + suffix
        guard textView.shouldChangeText(in: range, replacementString: replacement) else { return }
        textView.replaceCharacters(in: range, with: replacement)
        textView.didChangeText()
        // Re-select the body so the user can keep typing or toggle again.
        let bodyStart = range.location + (prefix as NSString).length
        textView.setSelectedRange(NSRange(location: bodyStart, length: (body as NSString).length))
    }

    /// Prefix every line touched by the selection (headings, lists, quotes).
    static func linePrefix(_ textView: NSTextView, prefix: String) {
        let ns = textView.string as NSString
        let lineRange = ns.lineRange(for: textView.selectedRange())
        let block = ns.substring(with: lineRange)
        let prefixed = block
            .components(separatedBy: "\n")
            .enumerated()
            .map { idx, line in
                // Don't add a stray prefix to a trailing empty line from the split.
                (line.isEmpty && idx > 0) ? line : prefix + line
            }
            .joined(separator: "\n")
        guard textView.shouldChangeText(in: lineRange, replacementString: prefixed) else { return }
        textView.replaceCharacters(in: lineRange, with: prefixed)
        textView.didChangeText()
        textView.setSelectedRange(NSRange(location: lineRange.location, length: (prefixed as NSString).length))
    }
}