LNATextField.swift

//
//  LNATextField.swift
//  LonaStudio
//
//  Created by Devin Abbott on 11/1/18.
//  Copyright © 2018 Devin Abbott. All rights reserved.
//

import AppKit
import Foundation

// This NSTextField subclass draws strings with a .baselineOffset attribute correctly.
//
// OSX 10.14 fixes a layout issue when using the .baselineOffset attribute, but we use
// this subclass in order to support 10.12 and 10.13. This isn't a general-purpose replacement
// for NSTextField; it should only be used for non-editable labels. Whenever we drop support
// for pre-10.14 we can remove this and use NSTextField directly instead.
public class LNATextField: NSTextField {
    public init() {
        super.init(frame: .zero)

        self.cell = LNATextFieldCell()
    }

    public convenience init(labelWithAttributedString attributedString: NSAttributedString) {
        self.init()

        self.isBordered = false
        self.drawsBackground = false
        self.isBezeled = false
        self.bezelStyle = .squareBezel
        self.isEnabled = true
        self.isEditable = false
        self.isSelectable = false

        self.attributedStringValue = attributedString
    }

    public convenience init(labelWithString string: String) {
        self.init(labelWithAttributedString: NSAttributedString(string: string))
    }

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

    // Determine the baseline offset from the attributed string value. We store it as a member variable,
    // then we remove it from the attributed string.
    override public var attributedStringValue: NSAttributedString {
        get { return super.attributedStringValue }
        set {
            baselineOffset = newValue.baselineOffset

            let string = NSMutableAttributedString(attributedString: newValue)
            string.removeAttribute(.baselineOffset, range: NSRange(location: 0, length: string.length))
            super.attributedStringValue = string
        }
    }

    var baselineOffset: CGFloat?
}

private class LNATextFieldCell: NSTextFieldCell {
    override func drawInterior(withFrame cellFrame: NSRect, in controlView: NSView) {
        if let textView = controlView as? LNATextField,
            let baselineOffset = textView.baselineOffset,
            let lineHeight = attributedStringValue.lineHeight {

            var rect = cellFrame.insetBy(dx: 2, dy: 0)

            rect.origin.y -= baselineOffset

            let truncatesLastVisibleLine = textView.maximumNumberOfLines > 0 &&
                cellFrame.height / lineHeight >= CGFloat(textView.maximumNumberOfLines)

            let options: NSString.DrawingOptions = truncatesLastVisibleLine
                ? [.usesLineFragmentOrigin, .truncatesLastVisibleLine]
                : [.usesLineFragmentOrigin]

            attributedStringValue.draw(with: rect, options: options)
        } else {
            super.drawInterior(withFrame: cellFrame, in: controlView)
        }
    }
}

private extension NSAttributedString {
    var lineHeight: CGFloat? {
        guard
            length > 0,
            let paragraphStyle = attribute(.paragraphStyle, at: 0, effectiveRange: nil) as? NSParagraphStyle
        else { return nil }

        let lineHeight = paragraphStyle.minimumLineHeight

        if lineHeight <= 0 { return nil }

        return lineHeight
    }

    var baselineOffset: CGFloat? {
        guard
            length > 0,
            let lineHeight = lineHeight,
            let font = attribute(.font, at: 0, effectiveRange: nil) as? NSFont
        else { return nil }

        return (lineHeight - font.ascender + font.descender) / 2
    }
}