compact_uint_size_marker.swift

/** Compact size uint marker byte
 */
enum CompactSizeMarker: Byte {
  case uint8, uint16 = 253, uint32, uint64
  
  /** Byte length of discriminant
   */
  static let discriminantByteLength = 1
  
  /** Hex byte length
   */
  static let hexByteLength = 2
  
  /** Init from discriminator byte
   */
  init(from discriminator: Byte) throws {
    switch discriminator {
    case type(of: self).uint8.marker..<type(of: self).uint16.marker:
      self = .uint8
      
    case type(of: self).uint16.marker:
      self = .uint16
      
    case type(of: self).uint32.marker:
      self = .uint32
      
    case type(of: self).uint64.marker:
      self = .uint64
      
    default:
      throw MarkerError.unexpectedDiscriminatorValue
    }
  }
  
  /** Marker that indicates type
   */
  var marker: Byte { return rawValue }
  
  /** Compact size errors
   */
  enum MarkerError: String, Error {
    case unexpectedDiscriminatorValue
  }
  
  /** Value byte length
   */
  var valueByteLength: Int {
    switch self {
    case .uint8:
      return 0
      
    case .uint16:
      return 2
      
    case .uint32:
      return 4
      
    case .uint64:
      return 8
    }
  }
  
  /** In a hex, length of characters for the value
   */
  var valueHexOffset: String.IndexDistance {
    return String.IndexDistance(valueByteLength * type(of: self).hexByteLength)
  }
  
  /** Byte length required for the compact size representation
   */
  var variableByteLength: Int {
    return type(of: self).discriminantByteLength + valueByteLength
  }
}