reflectorD

immutable pbCI = plugboard("ABIDEFGHCJKLMNOPQRSTUVWXYZ"); // C <-> I
immutable enWh = entryWheel("ABCDEFGHIJKLMNOPQRSTUVWXYZ");
immutable refB = reflector("YRUHQSLDPXNGOKMIEBFZCWVJAT");
immutable rot1 = rotor("EKMFLGDQVZNTOWYHXUSPAIBRCJ", 'Q', 'A');
immutable rot2 = rotor("AJDKSIRUXBLHWTMCQGZNPYFVOE", 'E', 'B');
immutable rot3 = rotor("BDFHJLCPRTXVZNYEIWGAKMUSQO", 'V', 'A');

auto e3 = Enigma!(3, EnigmaType.plugboard)(pbCI, enWh, rot1, rot2, rot3, refB, ['X', 'Q', 'E']);
assert(e3('A') == 'K');
assert(e3('a') == 'T'); // A lowercase is automatically converted to an uppercase.
assert(e3('5') == '5'); // A non-alphabetical character does not changes
assert(e3('Ü') == 'Ü'); // the machine state and will be output as it is.
assert(e3('A') == 'Q');

// These have the same settings.
auto encipherer = Enigma!2(entryWheelABC, rotorVI, rotorVII, reflectorC, "PY");
auto decipherer = Enigma!2(entryWheelABC, rotorVI, rotorVII, reflectorC, "PY");

foreach (dchar c; "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
{
    auto enciphered = encipherer(c);
    auto deciphered = decipherer(enciphered);
}

// These have the equivalent settings.
auto m3 = EnigmaM3(entryWheelABC, rotorIII, rotorII, rotorI, reflectorB /*!*/ ,
    "FOO");
auto m4 = EnigmaM4(entryWheelABC, rotorIII, rotorII, rotorI,
    rotorBeta('A') /*!*/ , reflectorBThin /*!*/ , "FOOA" /*!*/ ); // FOO*A*

// If each machine has just one movable rotor...
auto e1 = Enigma!1(entryWheelABC, rotorI, reflectorC /*!*/ , "X");
auto e2fixed = Enigma!(2, EnigmaType.fixedFinalRotor  /*!*/ )(entryWheelABC, rotorI,
    rotorGamma('A') /*!*/ , reflectorCThin /*!*/ , "XA" /*!*/ ); // X*A*

foreach (dchar c; "ABCDEFGHIJKLMNOPQRSTUVWXYZ")
{
    assert(m3(c) == m4(c));
    assert(e1(c) == e2fixed(c));
}

import std.algorithm.comparison : equal;
import std.algorithm.iteration : each, map;
import std.array : appender;

// These have the equivalent settings.
auto m4 = EnigmaM4(plugboard("SBCDEGFHIJKLMNOPQRATUVWXYZ"), entryWheelABC, rotorIII('Y'),
    rotorII('V'), rotorI('R'), rotorBeta, reflectorBThin, "UEQA");
auto m3 = EnigmaM3(plugboard("SBCDEGFHIJKLMNOPQRATUVWXYZ"), entryWheelABC, rotorIII('Y'),
    rotorII('V'), rotorI('R'), reflectorB, "UEQ");

auto enciphered = appender!dstring;
"ABCDEFGHIJKLMNOPQRSTUVWXYZ".map!m4.each!(c => enciphered.put(c));
assert(enciphered.data == "RIIGSIBEBIZKCTZSSDGQMLSVUX");

auto deciphered = enciphered.data.map!m3;
assert(deciphered.equal("ABCDEFGHIJKLMNOPQRSTUVWXYZ"));