compact_size_uint.swift

/** Compact Size UInt
 */
enum CompactSizeUInt {
  case uint8(UInt8), uint16(UInt16), uint32(UInt32), uint64(UInt64)
  
  // MARK: - Init
  
  /** Create from hex string
   */
  init(from hex: String) throws {
    let bytes = [Byte](try Data(hex: hex))
    let hexByteLength = CompactSizeMarker.hexByteLength
    
    // Confirm that the hex has a discriminant
    guard let discriminant = bytes.first else { throw CompactSizeUIntError.expectedDiscriminant }
    
    let compactSizeMarker = try CompactSizeMarker(from: discriminant)
    let valueStartIndex = hex.index(hex.startIndex, offsetBy: CompactSizeMarker.discriminantByteLength * hexByteLength)
    
    // Confirm that there are enough bytes in the hex
    guard bytes.count >= compactSizeMarker.variableByteLength else { throw CompactSizeUIntError.insufficientBytes }
    
    let range = valueStartIndex..<hex.index(valueStartIndex, offsetBy: compactSizeMarker.valueHexOffset)
    
    let valueData = try Data(hex: hex.substring(with: range))
    
    switch compactSizeMarker {
    case .uint8:
      self = CompactSizeUInt.uint8(discriminant)
      
    case .uint16: // fd
      self = CompactSizeUInt.uint16(UInt16(fromLittleEndian: valueData))
      
    case .uint32: // fe
      self = CompactSizeUInt.uint32(UInt32(fromLittleEndian: valueData))
      
    case .uint64: // ff
      self = CompactSizeUInt.uint64(UInt64(fromLittleEndian: valueData))
    }
  }
  
  // MARK: - Error
  
  /** Errors
   */
  enum CompactSizeUIntError: String, Error {
    case expectedDiscriminant
    case insufficientBytes
  }
  
  // MARK: - Value Information
  
  /** Get the size marker for this uint
   */
  var marker: CompactSizeMarker {
    switch self {
    case .uint8(_):
      return .uint8
      
    case .uint16(_):
      return .uint16
      
    case .uint32(_):
      return .uint32
      
    case .uint64(_):
      return .uint64
    }
  }
  
  /** Determine the uint64 value
   */
  var uint64Value: UInt64 {
    switch self {
    case .uint8(let val):
      return UInt64(val)
      
    case .uint16(let val):
      return UInt64(val)
      
    case .uint32(let val):
      return UInt64(val)
      
    case .uint64(let val):
      return UInt64(val)
    }
  }
}