Extensions to make attributed strings composable

NSMutableAttributedString+Extensions.swift

import Foundation

public func + (lhs: NSAttributedString, rhs: NSAttributedString) -> NSMutableAttributedString {
    let mutable = NSMutableAttributedString(attributedString: lhs)
    mutable.append(rhs)
    return mutable
}

extension String {
    public var attributedString: NSMutableAttributedString {
        return NSMutableAttributedString(string: self)
    }
}

extension NSMutableAttributedString {
    public var range: NSRange {
        return NSRange(location: 0, length: length)
    }
    
    @discardableResult
    public func add(color: UIColor, to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        addAttribute(NSAttributedString.Key.foregroundColor, value: color, range: textRage)
        return self
    }

    @discardableResult
    public func add(font: UIFont, to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        addAttribute(NSAttributedString.Key.font, value: font, range: textRage)
        return self
    }

    @discardableResult
    public func add(paragraph: NSMutableParagraphStyle, to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        addAttribute(NSAttributedString.Key.paragraphStyle, value: paragraph, range: textRage)
        return self
    }

    @discardableResult
    public func addStrike(to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        addAttribute(NSAttributedString.Key.strikethroughStyle, value: NSNumber(value: NSUnderlineStyle.single.rawValue), range: textRage)
        return self
    }

    @discardableResult
    public func addUnderline(to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        addAttribute(NSAttributedString.Key.underlineStyle, value: NSNumber(value: NSUnderlineStyle.single.rawValue), range: textRage)
        return self
    }

    @discardableResult
    public func add(alignment: NSTextAlignment, to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        let paragraphStyle = currentParagraphStyle()
        paragraphStyle.alignment = alignment
        addAttribute(NSAttributedString.Key.paragraphStyle, value: paragraphStyle, range: textRage)
        return self
    }

    @discardableResult
    public func add(lineSpacing: CGFloat, to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        let paragraphStyle = currentParagraphStyle()
        paragraphStyle.lineSpacing = lineSpacing
        addAttribute(NSAttributedString.Key.paragraphStyle, value: paragraphStyle, range: textRage)
        return self
    }

    @discardableResult
    public func add(lineBreakMode: NSLineBreakMode, to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        let paragraphStyle = currentParagraphStyle()
        paragraphStyle.lineBreakMode = lineBreakMode
        addAttribute(NSAttributedString.Key.paragraphStyle, value: paragraphStyle, range: textRage)
        return self
    }

    @discardableResult
    public func add(lineHeightMultiple: CGFloat, to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        let paragraphStyle = currentParagraphStyle()
        paragraphStyle.lineHeightMultiple = lineHeightMultiple
        addAttribute(NSAttributedString.Key.paragraphStyle, value: paragraphStyle, range: textRage)
        return self
    }

    @discardableResult
    public func add(letterSpacing: Float, to range: NSRange? = nil) -> NSMutableAttributedString {
        let textRage = range ?? self.range
        guard textRage.length != 0 else { return self }
        addAttribute(NSAttributedString.Key.kern, value: NSNumber(value: letterSpacing), range: textRage)
        return self
    }

    @discardableResult
    private func currentParagraphStyle(to range: NSRange? = nil) -> NSMutableParagraphStyle {
        let textRage = range ?? self.range
        guard length != 0 else { return NSMutableParagraphStyle() }
        guard let paragraphStyle = attribute(NSAttributedString.Key.paragraphStyle, at: 0, longestEffectiveRange: nil, in: textRage) as? NSParagraphStyle else {
            return NSMutableParagraphStyle()
        }

        guard let mutableParagraphStyle = paragraphStyle.mutableCopy() as? NSMutableParagraphStyle else {
            return NSMutableParagraphStyle()
        }

        return mutableParagraphStyle
    }
}