Add atbash-cipher (#78)

* add `atbash-cipher`

* encode and then decode

Author: BNAndras

config.json

@@ -50,6 +50,14 @@
         "prerequisites": [],
         "difficulty": 2
       },
+      {
+        "slug": "atbash-cipher",
+        "name": "Atbash Cipher",
+        "uuid": "dc112a08-5969-490e-8108-833f6f927cb2",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "collatz-conjecture",
         "name": "Collatz Conjecture",

exercises/practice/atbash-cipher/.busted

@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}

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/config.json

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "BNAndras"
+  ],
+  "files": {
+    "solution": [
+      "atbash_cipher.moon"
+    ],
+    "test": [
+      "atbash_cipher_spec.moon"
+    ],
+    "example": [
+      ".meta/example.moon"
+    ]
+  },
+  "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/example.moon

@@ -0,0 +1,13 @@
+{
+    encode: (phrase) ->
+        clean = phrase\lower!\gsub "[^a-z0-9]", ""
+        decoded = clean\gsub "[a-z]", (letter) ->
+            string.char 219 - letter\byte!
+        spaced = decoded\gsub(".....", "%0 ")
+        spaced\match("^%s*(.-)%s*$") or spaced
+
+    decode: (phrase) ->
+        clean = phrase\lower!\gsub "[^a-z0-9]", ""
+        clean\gsub "[a-z]", (letter) ->
+            string.char 219 - letter\byte!
+}

exercises/practice/atbash-cipher/.meta/spec_generator.moon

@@ -0,0 +1,12 @@
+{
+  module_name: 'AtbashCipher',
+
+  generate_test: (case, level) ->
+    lines = {
+      "result = AtbashCipher.#{case.property} #{quote case.input.phrase}"
+      "expected = #{quote case.expected}"
+      "assert.are.equal expected, result"
+    }
+
+    table.concat [indent line, level for line in *lines], '\n'
+}

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/atbash_cipher.moon

@@ -0,0 +1,7 @@
+{
+  encode: (phrase) ->
+    error 'Implement me'
+
+  decode: (phrase) ->
+    error 'Implement me'
+}

exercises/practice/atbash-cipher/atbash_cipher_spec.moon

@@ -0,0 +1,74 @@
+AtbashCipher = require 'atbash_cipher'
+
+describe 'atbash-cipher', ->
+  describe 'encode', ->
+    it 'encode yes', ->
+      result = AtbashCipher.encode 'yes'
+      expected = 'bvh'
+      assert.are.equal expected, result
+
+    pending 'encode no', ->
+      result = AtbashCipher.encode 'no'
+      expected = 'ml'
+      assert.are.equal expected, result
+
+    pending 'encode OMG', ->
+      result = AtbashCipher.encode 'OMG'
+      expected = 'lnt'
+      assert.are.equal expected, result
+
+    pending 'encode spaces', ->
+      result = AtbashCipher.encode 'O M G'
+      expected = 'lnt'
+      assert.are.equal expected, result
+
+    pending 'encode mindblowingly', ->
+      result = AtbashCipher.encode 'mindblowingly'
+      expected = 'nrmwy oldrm tob'
+      assert.are.equal expected, result
+
+    pending 'encode numbers', ->
+      result = AtbashCipher.encode 'Testing,1 2 3, testing.'
+      expected = 'gvhgr mt123 gvhgr mt'
+      assert.are.equal expected, result
+
+    pending 'encode deep thought', ->
+      result = AtbashCipher.encode 'Truth is fiction.'
+      expected = 'gifgs rhurx grlm'
+      assert.are.equal expected, result
+
+    pending 'encode all the letters', ->
+      result = AtbashCipher.encode 'The quick brown fox jumps over the lazy dog.'
+      expected = 'gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt'
+      assert.are.equal expected, result
+
+  describe 'decode', ->
+    pending 'decode exercism', ->
+      result = AtbashCipher.decode 'vcvix rhn'
+      expected = 'exercism'
+      assert.are.equal expected, result
+
+    pending 'decode a sentence', ->
+      result = AtbashCipher.decode 'zmlyh gzxov rhlug vmzhg vkkrm thglm v'
+      expected = 'anobstacleisoftenasteppingstone'
+      assert.are.equal expected, result
+
+    pending 'decode numbers', ->
+      result = AtbashCipher.decode 'gvhgr mt123 gvhgr mt'
+      expected = 'testing123testing'
+      assert.are.equal expected, result
+
+    pending 'decode all the letters', ->
+      result = AtbashCipher.decode 'gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt'
+      expected = 'thequickbrownfoxjumpsoverthelazydog'
+      assert.are.equal expected, result
+
+    pending 'decode with too many spaces', ->
+      result = AtbashCipher.decode 'vc vix    r hn'
+      expected = 'exercism'
+      assert.are.equal expected, result
+
+    pending 'decode with no spaces', ->
+      result = AtbashCipher.decode 'zmlyhgzxovrhlugvmzhgvkkrmthglmv'
+      expected = 'anobstacleisoftenasteppingstone'
+      assert.are.equal expected, result