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{
"authors": [
"rubysolo"
],
"contributors": [
"andrewsardone",
"angelikatyborska",
"Br1ght0ne",
"Cohen-Carlisle",
"dalexj",
"devonestes",
"jinyeow",
"kytrinyx",
"lpil",
"mhinz",
"neenjaw",
"parkerl",
"sotojuan",
"Teapane",
"waiting-for-dev"
],
"files": {
"solution": [
"lib/atbash.ex"
],
"test": [
"test/atbash_test.exs"
],
"example": [
".meta/example.ex"
]
},
"blurb": "Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.",
"source": "Wikipedia",
"source_url": "https://en.wikipedia.org/wiki/Atbash"
}

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{"track":"elixir","exercise":"atbash-cipher","id":"156913b0379c4b8886dff7de48ab370e","url":"https://exercism.org/tracks/elixir/exercises/atbash-cipher","handle":"negrienko","is_requester":true,"auto_approve":false}

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# Used by "mix format"
[
inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
]

24
elixir/atbash-cipher/.gitignore vendored Normal file
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# The directory Mix will write compiled artifacts to.
/_build/
# If you run "mix test --cover", coverage assets end up here.
/cover/
# The directory Mix downloads your dependencies sources to.
/deps/
# Where third-party dependencies like ExDoc output generated docs.
/doc/
# Ignore .fetch files in case you like to edit your project deps locally.
/.fetch
# If the VM crashes, it generates a dump, let's ignore it too.
erl_crash.dump
# Also ignore archive artifacts (built via "mix archive.build").
*.ez
# Ignore package tarball (built via "mix hex.build").
atbash_cipher-*.tar

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# Help
## Running the tests
From the terminal, change to the base directory of the exercise then execute the tests with:
```bash
$ mix test
```
This will execute the test file found in the `test` subfolder -- a file ending in `_test.exs`
Documentation:
* [`mix test` - Elixir's test execution tool](https://hexdocs.pm/mix/Mix.Tasks.Test.html)
* [`ExUnit` - Elixir's unit test library](https://hexdocs.pm/ex_unit/ExUnit.html)
## Pending tests
In test suites of practice exercises, all but the first test have been tagged to be skipped.
Once you get a test passing, you can unskip the next one by commenting out the relevant `@tag :pending` with a `#` symbol.
For example:
```elixir
# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
```
If you wish to run all tests at once, you can include all skipped test by using the `--include` flag on the `mix test` command:
```bash
$ mix test --include pending
```
Or, you can enable all the tests by commenting out the `ExUnit.configure` line in the file `test/test_helper.exs`.
```elixir
# ExUnit.configure(exclude: :pending, trace: true)
```
## Useful `mix test` options
* `test/<FILE>.exs:LINENUM` - runs only a single test, the test from `<FILE>.exs` whose definition is on line `LINENUM`
* `--failed` - runs only tests that failed the last time they ran
* `--max-failures` - the suite stops evaluating tests when this number of test failures
is reached
* `--seed 0` - disables randomization so the tests in a single file will always be ran
in the same order they were defined in
## Submitting your solution
You can submit your solution using the `exercism submit lib/atbash.ex` command.
This command will upload your solution to the Exercism website and print the solution page's URL.
It's possible to submit an incomplete solution which allows you to:
- See how others have completed the exercise
- Request help from a mentor
## Need to get help?
If you'd like help solving the exercise, check the following pages:
- The [Elixir track's documentation](https://exercism.org/docs/tracks/elixir)
- The [Elixir track's programming category on the forum](https://forum.exercism.org/c/programming/elixir)
- [Exercism's programming category on the forum](https://forum.exercism.org/c/programming/5)
- The [Frequently Asked Questions](https://exercism.org/docs/using/faqs)
Should those resources not suffice, you could submit your (incomplete) solution to request mentoring.
If you're stuck on something, it may help to look at some of the [available resources](https://exercism.org/docs/tracks/elixir/resources) out there where answers might be found.

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# Atbash Cipher
Welcome to Atbash Cipher on Exercism's Elixir Track.
If you need help running the tests or submitting your code, check out `HELP.md`.
## Instructions
Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
The Atbash cipher is a simple substitution cipher that relies on transposing all the letters in the alphabet such that the resulting alphabet is backwards.
The first letter is replaced with the last letter, the second with the second-last, and so on.
An Atbash cipher for the Latin alphabet would be as follows:
```text
Plain: abcdefghijklmnopqrstuvwxyz
Cipher: zyxwvutsrqponmlkjihgfedcba
```
It is a very weak cipher because it only has one possible key, and it is a simple mono-alphabetic substitution cipher.
However, this may not have been an issue in the cipher's time.
Ciphertext is written out in groups of fixed length, the traditional group size being 5 letters, leaving numbers unchanged, and punctuation is excluded.
This is to make it harder to guess things based on word boundaries.
All text will be encoded as lowercase letters.
## Examples
- Encoding `test` gives `gvhg`
- Encoding `x123 yes` gives `c123b vh`
- Decoding `gvhg` gives `test`
- Decoding `gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt` gives `thequickbrownfoxjumpsoverthelazydog`
## Source
### Created by
- @rubysolo
### Contributed to by
- @andrewsardone
- @angelikatyborska
- @Br1ght0ne
- @Cohen-Carlisle
- @dalexj
- @devonestes
- @jinyeow
- @kytrinyx
- @lpil
- @mhinz
- @neenjaw
- @parkerl
- @sotojuan
- @Teapane
- @waiting-for-dev
### Based on
Wikipedia - https://en.wikipedia.org/wiki/Atbash

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defmodule Atbash do
@letters ?a..?z
|> Enum.to_list
|> to_string
|> String.graphemes()
@digits ?0..?9
|> Enum.to_list
|> to_string
|> String.graphemes()
@table Map.new(Enum.zip(@letters, Enum.reverse(@letters)))
defguardp is_letter(char) when char in @letters
defguardp is_digit(char) when char in @digits
@doc """
Encode a given plaintext to the corresponding ciphertext
## Examples
iex> Atbash.encode("completely insecure")
"xlnko vgvob rmhvx fiv"
"""
@spec encode(String.t()) :: String.t()
def encode(plaintext) do
plaintext
|> transpose()
|> String.graphemes()
|> Enum.chunk_every(5)
|> Enum.join(" ")
end
@spec decode(String.t()) :: String.t()
def decode(cipher), do: transpose(cipher)
defp transpose(string) do
string
|> String.downcase()
|> String.graphemes()
|> Enum.map(&code/1)
|> Enum.join()
end
defp code(char) when is_digit(char), do: char
defp code(char) when is_letter(char), do: @table[char]
defp code(_char), do: nil
end

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defmodule Atbash.MixProject do
use Mix.Project
def project do
[
app: :atbash,
version: "0.1.0",
# elixir: "~> 1.8",
start_permanent: Mix.env() == :prod,
deps: deps()
]
end
# Run "mix help compile.app" to learn about applications.
def application do
[
extra_applications: [:logger]
]
end
# Run "mix help deps" to learn about dependencies.
defp deps do
[
# {:dep_from_hexpm, "~> 0.3.0"},
# {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
]
end
end

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defmodule AtbashTest do
use ExUnit.Case
describe "encode" do
test "yes" do
assert Atbash.encode("yes") == "bvh"
end
test "no" do
assert Atbash.encode("no") == "ml"
end
test "OMG" do
assert Atbash.encode("OMG") == "lnt"
end
test "O M G" do
assert Atbash.encode("O M G") == "lnt"
end
test "mindblowingly" do
assert Atbash.encode("mindblowingly") == "nrmwy oldrm tob"
end
test "numbers" do
assert Atbash.encode("Testing, 1 2 3, testing.") == "gvhgr mt123 gvhgr mt"
end
test "deep thought" do
assert Atbash.encode("Truth is fiction.") == "gifgs rhurx grlm"
end
test "all the letters" do
plaintext = "The quick brown fox jumps over the lazy dog."
cipher = "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"
assert Atbash.encode(plaintext) == cipher
end
end
describe "decode" do
test "exercism" do
cipher = "vcvix rhn"
plaintext = "exercism"
assert Atbash.decode(cipher) == plaintext
end
test "a sentence" do
cipher = "zmlyh gzxov rhlug vmzhg vkkrm thglm v"
plaintext = "anobstacleisoftenasteppingstone"
assert Atbash.decode(cipher) == plaintext
end
test "numbers" do
cipher = "gvhgr mt123 gvhgr mt"
plaintext = "testing123testing"
assert Atbash.decode(cipher) == plaintext
end
test "all the letters" do
cipher = "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"
plaintext = "thequickbrownfoxjumpsoverthelazydog"
assert Atbash.decode(cipher) == plaintext
end
test "with too many spaces" do
cipher = "vc vix r hn"
plaintext = "exercism"
assert Atbash.decode(cipher) == plaintext
end
test "with no spaces" do
cipher = "zmlyhgzxovrhlugvmzhgvkkrmthglmv"
plaintext = "anobstacleisoftenasteppingstone"
assert Atbash.decode(cipher) == plaintext
end
end
end

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ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)