FileURL.swift

//
//  FileURL.swift
//  Created by Chris Dzombak on 11/16/16.
//

import Validated

public typealias FileURL = Validated<URL, FileURLValidator>

public struct FileURLValidator: Validator, _FileURL_Validating {
    public static func validate(_ value: URL) -> Bool {
        return value.isFileURL
    }
}

public protocol _FileURL_Validating {}

public protocol _FileURL_URLConformer {
    var path: String { get }
    var pathComponents: [String] { get }

    func appendingPathComponent(_ pathComponent: String) -> URL
    func appendingPathComponent(_ pathComponent: String, isDirectory: Bool) -> URL
}
extension URL: _FileURL_URLConformer {}

// Wrap NSURL API that will never return `nil` for `file://` URLs:

public extension Validated where WrapperType: _FileURL_URLConformer, V: _FileURL_Validating {
    var path: String {
        return value.path
    }

    var pathComponents: [String] {
        return value.pathComponents
    }

    func fileURLByAppendingPathComponent(_ pathComponent: String) -> FileURL {
        let result = value.appendingPathComponent(pathComponent)

        guard let validResult = try? FileURL(result) else {
            fatalError("Appending to a file URL should always result in another file URL")
        }

        return validResult
    }

    func fileURLByAppendingPathComponent(_ pathComponent: String, isDirectory: Bool) -> FileURL {
        let result = value.appendingPathComponent(pathComponent, isDirectory: isDirectory)

        guard let validResult = try? FileURL(result) else {
            fatalError("Appending to a file URL should always result in another file URL")
        }

        return validResult
    }
}