Add atbash-cipher (#147)

config.json

@@ -307,6 +307,14 @@
         "prerequisites": [],
         "difficulty": 3
       },
+      {
+        "slug": "atbash-cipher",
+        "name": "Atbash Cipher",
+        "uuid": "57e5a257-9afd-46f1-8c43-6fbd6f371ca3",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
+      },
       {
         "slug": "binary-search",
         "name": "Binary Search",

exercises/practice/atbash-cipher/.docs/instructions.md

@@ -0,0 +1,27 @@
+# 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`

exercises/practice/atbash-cipher/.meta/Example.roc

@@ -0,0 +1,34 @@
+module [encode, decode]
+
+invert : U8 -> U8
+invert = \char ->
+    if char >= 'a' && char <= 'z' then
+        'z' - char + 'a'
+    else
+        char
+
+encode : Str -> Result Str _
+encode = \phrase ->
+    phrase
+    |> Str.toUtf8
+    |> List.joinMap \char ->
+        if char >= 'A' && char <= 'Z' then
+            [invert (char - 'A' + 'a')]
+        else if char >= 'a' && char <= 'z' then
+            [invert char]
+        else if char >= '0' && char <= '9' then
+            [char]
+        else
+            []
+    |> List.chunksOf 5
+    |> List.intersperse [' ']
+    |> List.join
+    |> Str.fromUtf8
+
+decode : Str -> Result Str _
+decode = \phrase ->
+    phrase
+    |> Str.toUtf8
+    |> List.dropIf \c -> c == ' '
+    |> List.map invert
+    |> Str.fromUtf8

exercises/practice/atbash-cipher/.meta/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "ageron"
+  ],
+  "files": {
+    "solution": [
+      "AtbashCipher.roc"
+    ],
+    "test": [
+      "atbash-cipher-test.roc"
+    ],
+    "example": [
+      ".meta/Example.roc"
+    ]
+  },
+  "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"
+}

exercises/practice/atbash-cipher/.meta/template.j2

@@ -0,0 +1,21 @@
+{%- import "generator_macros.j2" as macros with context -%}
+{{ macros.canonical_ref() }}
+{{ macros.header() }}
+
+import {{ exercise | to_pascal }} exposing [encode, decode]
+
+{% for supercase in cases %}
+##
+## {{ supercase["description"] }}
+##
+
+{% for case in supercase["cases"] -%}
+# {{ case["description"] }}
+expect
+    phrase = {{ case["input"]["phrase"] | to_roc }} 
+    result = phrase |> {{ case["property"] | to_camel }}
+    expected = {{ case["expected"] | to_roc }} 
+    result == Ok expected
+
+{% endfor %}
+{% endfor %}

exercises/practice/atbash-cipher/.meta/tests.toml

@@ -0,0 +1,52 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+
+[2f47ebe1-eab9-4d6b-b3c6-627562a31c77]
+description = "encode -> encode yes"
+
+[b4ffe781-ea81-4b74-b268-cc58ba21c739]
+description = "encode -> encode no"
+
+[10e48927-24ab-4c4d-9d3f-3067724ace00]
+description = "encode -> encode OMG"
+
+[d59b8bc3-509a-4a9a-834c-6f501b98750b]
+description = "encode -> encode spaces"
+
+[31d44b11-81b7-4a94-8b43-4af6a2449429]
+description = "encode -> encode mindblowingly"
+
+[d503361a-1433-48c0-aae0-d41b5baa33ff]
+description = "encode -> encode numbers"
+
+[79c8a2d5-0772-42d4-b41b-531d0b5da926]
+description = "encode -> encode deep thought"
+
+[9ca13d23-d32a-4967-a1fd-6100b8742bab]
+description = "encode -> encode all the letters"
+
+[bb50e087-7fdf-48e7-9223-284fe7e69851]
+description = "decode -> decode exercism"
+
+[ac021097-cd5d-4717-8907-b0814b9e292c]
+description = "decode -> decode a sentence"
+
+[18729de3-de74-49b8-b68c-025eaf77f851]
+description = "decode -> decode numbers"
+
+[0f30325f-f53b-415d-ad3e-a7a4f63de034]
+description = "decode -> decode all the letters"
+
+[39640287-30c6-4c8c-9bac-9d613d1a5674]
+description = "decode -> decode with too many spaces"
+
+[b34edf13-34c0-49b5-aa21-0768928000d5]
+description = "decode -> decode with no spaces"

exercises/practice/atbash-cipher/AtbashCipher.roc

@@ -0,0 +1,9 @@
+module [encode, decode]
+
+encode : Str -> Result Str _
+encode = \phrase ->
+    crash "Please implement the 'encode' function"
+
+decode : Str -> Result Str _
+decode = \phrase ->
+    crash "Please implement the 'decode' function"

exercises/practice/atbash-cipher/atbash-cipher-test.roc

@@ -0,0 +1,118 @@
+# These tests are auto-generated with test data from:
+# https://github.com/exercism/problem-specifications/tree/main/exercises/atbash-cipher/canonical-data.json
+# File last updated on 2024-10-10
+app [main] {
+    pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.15.0/SlwdbJ-3GR7uBWQo6zlmYWNYOxnvo8r6YABXD-45UOw.tar.br",
+}
+
+main =
+    Task.ok {}
+
+import AtbashCipher exposing [encode, decode]
+
+##
+## encode
+##
+
+# encode yes
+expect
+    phrase = "yes"
+    result = phrase |> encode
+    expected = "bvh"
+    result == Ok expected
+
+# encode no
+expect
+    phrase = "no"
+    result = phrase |> encode
+    expected = "ml"
+    result == Ok expected
+
+# encode OMG
+expect
+    phrase = "OMG"
+    result = phrase |> encode
+    expected = "lnt"
+    result == Ok expected
+
+# encode spaces
+expect
+    phrase = "O M G"
+    result = phrase |> encode
+    expected = "lnt"
+    result == Ok expected
+
+# encode mindblowingly
+expect
+    phrase = "mindblowingly"
+    result = phrase |> encode
+    expected = "nrmwy oldrm tob"
+    result == Ok expected
+
+# encode numbers
+expect
+    phrase = "Testing,1 2 3, testing."
+    result = phrase |> encode
+    expected = "gvhgr mt123 gvhgr mt"
+    result == Ok expected
+
+# encode deep thought
+expect
+    phrase = "Truth is fiction."
+    result = phrase |> encode
+    expected = "gifgs rhurx grlm"
+    result == Ok expected
+
+# encode all the letters
+expect
+    phrase = "The quick brown fox jumps over the lazy dog."
+    result = phrase |> encode
+    expected = "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"
+    result == Ok expected
+
+##
+## decode
+##
+
+# decode exercism
+expect
+    phrase = "vcvix rhn"
+    result = phrase |> decode
+    expected = "exercism"
+    result == Ok expected
+
+# decode a sentence
+expect
+    phrase = "zmlyh gzxov rhlug vmzhg vkkrm thglm v"
+    result = phrase |> decode
+    expected = "anobstacleisoftenasteppingstone"
+    result == Ok expected
+
+# decode numbers
+expect
+    phrase = "gvhgr mt123 gvhgr mt"
+    result = phrase |> decode
+    expected = "testing123testing"
+    result == Ok expected
+
+# decode all the letters
+expect
+    phrase = "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"
+    result = phrase |> decode
+    expected = "thequickbrownfoxjumpsoverthelazydog"
+    result == Ok expected
+
+# decode with too many spaces
+expect
+    phrase = "vc vix    r hn"
+    result = phrase |> decode
+    expected = "exercism"
+    result == Ok expected
+
+# decode with no spaces
+expect
+    phrase = "zmlyhgzxovrhlugvmzhgvkkrmthglmv"
+    result = phrase |> decode
+    expected = "anobstacleisoftenasteppingstone"
+    result == Ok expected
+