Font+Util.swift

import Foundation
import CoreText

struct FontUtils {

    enum Error: Swift.Error {

        case dataProviderConstructionFailed
        case cgFontConstructionFailed
        case postScriptNameUnavailable
    }

    static func loadFont(at url: URL) throws -> String {
        let fontData = try Data(contentsOf: url)
        guard let dataProvider = CGDataProvider(data: fontData as CFData) else {
            throw Error.dataProviderConstructionFailed
        }
        guard let font = CGFont(dataProvider) else {
            throw Error.cgFontConstructionFailed
        }
        var unmanagedError: Unmanaged<CFError>?
        CTFontManagerRegisterGraphicsFont(font, &unmanagedError)
        if let unmanagedError = unmanagedError {
            throw unmanagedError.takeRetainedValue()
        }
        guard let fontName = font.postScriptName as String? else {
            throw Error.postScriptNameUnavailable
        }
        return fontName
    }

    private init() { }
}