4-rot13-feature.js

import { fakeStdin, fakeStdout } from "../helpers/fake-process.js";
import { run } from "../../app.js";

// https://en.wikipedia.org/wiki/ROT13
Feature("Rot 13", () => {
  Scenario("Rot 13 on a long user input", () => {
    let stdout, stdin;
    Given("we have a fake stdout and stdin", () => {
      stdout = fakeStdout();
      stdin = fakeStdin();
    });

    When("Running the Rot 13 program with a long user input", async () => {
      const program = `
,                Read one character
----- -----      Remove 10 to check if it was the newline character
[                Skip loop if it was the newline
  +++++ +++++    Add 10 to get the input character back
    [                       Skip forward if character is 0
        >>++++[>++++++++<-]  Set up divisor (32) for division loop
                               (MEMORY LAYOUT: dividend copy remainder divisor quotient zero zero)
        <+<-[                Set up dividend (x minus 1) and enter division loop
            >+>+>-[>>>]      Increase copy and remainder / reduce divisor / Normal case: skip forward
            <[[>+<-]>>+>]    Special case: move remainder back to divisor and increase quotient
            <<<<<-           Decrement dividend
        ]                    End division loop
    ]>>>[-]+                 End skip loop; zero former divisor and reuse space for a flag
    >--[-[<->+++[-]]]<[         Zero that flag unless quotient was 2 or 3; zero quotient; check flag
        ++++++++++++<[       If flag then set up divisor (13) for second division loop
                               (MEMORY LAYOUT: zero copy dividend divisor remainder quotient zero zero)
            >-[>+>>]         Reduce divisor; Normal case: increase remainder
            >[+[<+>-]>+>>]   Special case: increase remainder / move it back to divisor / increase quotient
            <<<<<-           Decrease dividend
        ]                    End division loop
        >>[<+>-]             Add remainder back to divisor to get a useful 13
        >[                   Skip forward if quotient was 0
            -[               Decrement quotient and skip forward if quotient was 1
                -<<[-]>>     Zero quotient and divisor if quotient was 2
            ]<<[<<->>-]>>    Zero divisor and subtract 13 from copy if quotient was 1
        ]<<[<<+>>-]          Zero divisor and add 13 to copy if quotient was 0
    ]                        End outer skip loop (jump to here if ((character minus 1)/32) was not 2 or 3)
    <[-]                     Clear remainder from first division if second division was skipped
    <.[-]                    Output ROT13ed character from copy and clear it
    <,                     Read next character
    ----- -----            Remove 10 to check if it was the newline character
]                            End character reading loop
      `;
      stdin.write("Gur Dhvpx Oebja Sbk Whzcf Bire Gur Ynml Qbt\n");
      await run(program, stdin, stdout);
    });

    Then("The output should be the exected", () => {
      expect(stdout.getData()).to.eql("The Quick Brown Fox Jumps Over The Lazy Dog");
    });
  });
});