50 lines
1.3 KiB
Swift
50 lines
1.3 KiB
Swift
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// Rotor.swift
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// Enigma
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//
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// Created by Eryn Wells on 2015-07-18.
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// Copyright © 2015 Eryn Wells. All rights reserved.
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//
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import Foundation
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class Rotor {
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enum Error: ErrorType {
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/** Thrown when the initializer is given an invalid series. */
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case InvalidSeries
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case InvalidCharacter
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}
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static let alphabet: [Character] = Array("ABCDEFGHIJKLMNOPQRSTUVWXYZ".characters)
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/** The position of first letter in `series` in the `alphabet`. */
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var position: Int
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/** The series of characters that this rotor cycles through. */
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let series: [Character]!
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convenience init(series: String) throws {
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try self.init(series: Array(series.characters))
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}
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init(series: [Character]) throws {
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self.position = 0
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guard series.count == Rotor.alphabet.count else {
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self.series = nil
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throw Error.InvalidSeries
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}
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self.series = series
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}
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func advance() {
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position = position.successor() % Rotor.alphabet.count
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}
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func encode(c: Character) throws -> Character {
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let offset: Int! = Rotor.alphabet.indexOf(c)
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guard offset != nil else {
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throw Error.InvalidCharacter
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}
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return series[(offset + position) % series.count]
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}
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}
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