import Foundation

/// A type which can be converted to an URL string.
public protocol URLConvertible {
  var urlValue: URL? { get }
  var urlStringValue: String { get }

  /// Returns URL query parameters. For convenience, this property will never return `nil` even if
  /// there's no query string in the URL. This property doesn't take care of the duplicated keys.
  /// For checking duplicated keys, use `queryItems` instead.
  ///
  /// - seealso: `queryItems`
  var queryParameters: [String: String] { get }

  /// Returns `queryItems` property of `URLComponents` instance.
  ///
  /// - seealso: `queryParameters`
  @available(iOS 8, *)
  var queryItems: [URLQueryItem]? { get }
}

extension URLConvertible {
  public var queryParameters: [String: String] {
    var parameters = [String: String]()
    self.urlValue?.query?.components(separatedBy: "&").forEach { component in
      guard let separatorIndex = component.firstIndex(of: "=") else { return }
      let keyRange = component.startIndex..<separatorIndex
      let valueRange = component.index(after: separatorIndex)..<component.endIndex
      let key = String(component[keyRange])
      let value = component[valueRange].removingPercentEncoding ?? String(component[valueRange])
      parameters[key] = value
    }
    return parameters
  }

  @available(iOS 8, *)
  public var queryItems: [URLQueryItem]? {
    return URLComponents(string: self.urlStringValue)?.queryItems
  }
}

extension String: URLConvertible {
  public var urlValue: URL? {
    if let url = URL(string: self) {
      return url
    }
    var set = CharacterSet()
    set.formUnion(.urlHostAllowed)
    set.formUnion(.urlPathAllowed)
    set.formUnion(.urlQueryAllowed)
    set.formUnion(.urlFragmentAllowed)
    return self.addingPercentEncoding(withAllowedCharacters: set).flatMap { URL(string: $0) }
  }

  public var urlStringValue: String {
    return self
  }
}

extension URL: URLConvertible {
  public var urlValue: URL? {
    return self
  }

  public var urlStringValue: String {
    return self.absoluteString
  }
}