Transform Morse code data model to on/off states with relative durations

TransmissionState.swift

enum TransmissionState {
    typealias RelativeDuration = Int
    case On(RelativeDuration)
    case Off(RelativeDuration)
    
    static func createStates(from encodedMessage: EncodedMessage) 
        -> [TransmissionState] {
        let transformation = MorseTransformation(
            dot:             TransmissionState.On(1),
            dash:            TransmissionState.On(3),
            markSeparator:   TransmissionState.Off(1),
            symbolSeparator: TransmissionState.Off(3),
            termSeparator:   TransmissionState.Off(7))
        return transformation.apply(to: encodedMessage)
    }
}