Add atbash-cipher (#87)

config.json

@@ -372,6 +372,14 @@
         "prerequisites": [],
         "difficulty": 4
       },
+      {
+        "slug": "atbash-cipher",
+        "name": "Atbash Cipher",
+        "uuid": "ef527899-03b7-495c-84f6-b681cbb2c57a",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "pascals-triangle",
         "name": "Pascal's Triangle",

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": [
+      "src/atbash-cipher.art"
+    ],
+    "test": [
+      "tests/test-atbash-cipher.art"
+    ],
+    "example": [
+      ".meta/src/example.art"
+    ]
+  },
+  "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/src/example.art

@@ -0,0 +1,56 @@
+encode: function[phrase][
+    count: 0
+    result: ""
+
+    loop phrase 'chr [
+        if equal? chr ' ' -> continue
+        if punctuation? chr -> continue
+
+
+        if equal? count 5 [
+            result: append result ' '
+            count: 0
+        ]
+
+        chr: switch letter? chr -> to :char sub add to :integer 'a' to :integer 'z' to :integer lower chr
+                                -> chr
+
+        result: append result chr
+        count: count + 1
+    ]
+
+
+    result
+]
+
+decode: function[phrase][
+    result: ""
+    loop phrase 'chr [
+        if equal? chr ' ' -> continue
+
+
+        chr: switch letter? chr -> to :char sub add to :integer 'a' to :integer 'z' to :integer lower chr
+                                -> chr
+        result: append result chr
+    ]
+
+    result
+]
+
+
+letter?: function [chr][
+    or? in? chr 'a' .. 'z' in? chr 'A' .. 'Z'
+]
+
+punctuation?: function [chr][
+    case [chr]
+        when? [ caseIn? '!' .. '/' ] -> return true
+        when? [ caseIn? ':' .. '@' ] -> return true
+        when? [ caseIn? '[' .. '`' ] -> return true
+        when? [ caseIn? '{' .. '~' ] -> return true
+        else -> return false
+]
+
+caseIn?: function [range chr][
+    in? chr range
+]

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/src/atbash-cipher.art

@@ -0,0 +1,7 @@
+encode: function[phrase][
+    panic "Please implement the encode function"
+]
+
+decode: function[phrase][
+    panic "Please implement the decode function"
+]

exercises/practice/atbash-cipher/tester.art

@@ -0,0 +1,3 @@
+import {unitt}!
+
+runTests.failFast findTests "tests"

exercises/practice/atbash-cipher/tests/test-atbash-cipher.art

@@ -0,0 +1,79 @@
+import {unitt}!
+import {src/atbash-cipher}!
+
+suite "Atbash Cipher"
+[
+  suite "Atbash Cipher - Encode" [
+    test "encode yes" [
+      result: encode "yes"
+      assert -> "bvh" = result
+    ]
+
+    test.skip "encode no" [
+      result: encode "no"
+      assert -> "ml" = result
+    ]
+
+    test.skip "encode OMG" [
+      result: encode "OMG"
+      assert -> "lnt" = result
+    ]
+
+    test.skip "encode spaces" [
+      result: encode "O M G"
+      assert -> "lnt" = result
+    ]
+
+    test.skip "encode mindblowingly" [
+      result: encode "mindblowingly"
+      assert -> "nrmwy oldrm tob" = result
+    ]
+
+    test.skip "encode numbers" [
+      result: encode "Testing,1 2 3, testing."
+      assert -> "gvhgr mt123 gvhgr mt" = result
+    ]
+
+    test.skip "encode deep thought" [
+      result: encode "Truth is fiction."
+      assert -> "gifgs rhurx grlm" = result
+    ]
+
+    test.skip "encode all the letters" [
+      result: encode "The quick brown fox jumps over the lazy dog."
+      assert -> "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt" = result
+    ]
+  ]
+
+  suite "Atbash Cipher - Decode" [
+    test.skip "decode exercism" [
+      result: decode "vcvix rhn"
+      assert -> "exercism" = result
+    ]
+
+    test.skip "decode a sentence" [
+      result: decode "zmlyh gzxov rhlug vmzhg vkkrm thglm v"
+      assert -> "anobstacleisoftenasteppingstone" = result
+    ]
+
+    test.skip "decode numbers" [
+      result: decode "gvhgr mt123 gvhgr mt"
+      assert -> "testing123testing" = result
+    ]
+
+    test.skip "decode all the letters" [
+      result: decode "gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"
+      assert -> "thequickbrownfoxjumpsoverthelazydog" = result
+    ]
+
+    test.skip "decode with too many spaces" [
+      result: decode "vc vix    r hn"
+      assert -> "exercism" = result
+    ]
+
+    test.skip "decode with no spaces" [
+      result: decode "zmlyhgzxovrhlugvmzhgvkkrmthglmv"
+      assert -> "anobstacleisoftenasteppingstone" = result
+    ]
+  ]
+]