Add atbash-cipher

config.json

@@ -129,6 +129,14 @@
           "strings"
         ]
       },
+      {
+        "slug": "atbash-cipher",
+        "name": "Atbash Cipher",
+        "uuid": "7093ae21-54ce-4cc8-87a8-777fae080b57",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
+      },
       {
         "slug": "eliuds-eggs",
         "name": "Eliud's Eggs",

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": [
+      "lib/atbash_cipher.dart"
+    ],
+    "test": [
+      "test/atbash_cipher_test.dart"
+    ],
+    "example": [
+      ".meta/lib/example.dart"
+    ]
+  },
+  "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/lib/example.dart

@@ -0,0 +1,59 @@
+class AtbashCipher {
+  final lowercaseA = 'a'.codeUnitAt(0);
+  final lowercaseZ = 'z'.codeUnitAt(0);
+  final uppercaseA = 'A'.codeUnitAt(0);
+  final uppercaseZ = 'Z'.codeUnitAt(0);
+
+  String encode(String input) {
+    final encoded = StringBuffer();
+    int count = 0;
+    input.split('').where((elt) => elt.isAlphanumeric()).forEach((elt) {
+      int char = elt.codeUnitAt(0);
+      if (count == 5) {
+        encoded.write(" ");
+        count = 0;
+      }
+
+      if (char.isAlphabetic()) {
+        char = char.isLowercase() ? char : char.toLowercase();
+        char = lowercaseA + lowercaseZ - char;
+      }
+
+      encoded.write(String.fromCharCode(char));
+      count += 1;
+    });
+
+    return encoded.toString();
+  }
+
+  String decode(String input) {
+    final encoded = StringBuffer();
+    input.split('').where((elt) => elt.isAlphanumeric()).forEach((elt) {
+      int char = elt.codeUnitAt(0);
+      if (char.isAlphabetic()) {
+        char = char.isLowercase() ? char : char.toLowercase();
+        char = lowercaseA + lowercaseZ - char;
+      }
+
+      encoded.write(String.fromCharCode(char));
+    });
+    return encoded.toString();
+  }
+}
+
+extension IntNum on int {
+  bool inRange(int lower, int upper) => this >= lower && this <= upper;
+  bool isUppercase() => inRange('A'.codeUnitAt(0), 'Z'.codeUnitAt(0));
+  bool isLowercase() => inRange('a'.codeUnitAt(0), 'z'.codeUnitAt(0));
+  bool isAlphabetic() => isUppercase() || isLowercase();
+  bool isNumeric() => this >= '0'.codeUnitAt(0) && this <= '9'.codeUnitAt(0);
+  bool isAlphanumeric() => isAlphabetic() || isNumeric();
+  bool isWhitespace() => this == ' '.codeUnitAt(0);
+  int toLowercase() => this + 'a'.codeUnitAt(0) - 'A'.codeUnitAt(0);
+}
+
+extension StringExt on String {
+  bool isWhitespace() => this.codeUnitAt(0).isWhitespace();
+  bool isNotWhitespace() => !isWhitespace();
+  bool isAlphanumeric() => this.codeUnitAt(0).isAlphanumeric();
+}

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/analysis_options.yaml

@@ -0,0 +1,18 @@
+analyzer:
+  strong-mode:
+    implicit-casts: false
+    implicit-dynamic: false
+  errors:
+    unused_element:        error
+    unused_import:         error
+    unused_local_variable: error
+    dead_code:             error
+
+linter:
+  rules:
+    # Error Rules
+    - avoid_relative_lib_imports
+    - avoid_types_as_parameter_names
+    - literal_only_boolean_expressions
+    - no_adjacent_strings_in_list
+    - valid_regexps

exercises/practice/atbash-cipher/lib/atbash_cipher.dart

@@ -0,0 +1,3 @@
+class AtbashCipher {
+  // Put your code here
+}

exercises/practice/atbash-cipher/pubspec.yaml

@@ -0,0 +1,5 @@
+name: 'atbash_cipher'
+environment:
+  sdk: '>=3.2.0 <4.0.0'
+dev_dependencies:
+  test: '<2.0.0'

exercises/practice/atbash-cipher/test/atbash_cipher_test.dart

@@ -0,0 +1,85 @@
+import 'package:atbash_cipher/atbash_cipher.dart';
+import 'package:test/test.dart';
+
+void main() {
+  final atbashCipher = AtbashCipher();
+
+  group('AtbashCipher', () {
+    group('encode', () {
+      test('encode yes', () {
+        final result = atbashCipher.encode("yes");
+        expect(result, equals("bvh"));
+      }, skip: false);
+
+      test('encode no', () {
+        final result = atbashCipher.encode("no");
+        expect(result, equals("ml"));
+      }, skip: true);
+
+      test('encode OMG', () {
+        final result = atbashCipher.encode("OMG");
+        expect(result, equals("lnt"));
+      }, skip: true);
+
+      test('encode spaces', () {
+        final result = atbashCipher.encode("O M G");
+        expect(result, equals("lnt"));
+      }, skip: true);
+
+      test('encode mindblowingly', () {
+        final result = atbashCipher.encode("mindblowingly");
+        expect(result, equals("nrmwy oldrm tob"));
+      }, skip: true);
+
+      test('encode numbers', () {
+        final result = atbashCipher.encode("Testing,1 2 3, testing.");
+        expect(result, equals("gvhgr mt123 gvhgr mt"));
+      }, skip: true);
+
+      test('encode deep thought', () {
+        final result = atbashCipher.encode("Truth is fiction.");
+        expect(result, equals("gifgs rhurx grlm"));
+      }, skip: true);
+
+      test('encode all the letters', () {
+        final result =
+            atbashCipher.encode("The quick brown fox jumps over the lazy dog.");
+        expect(result, equals("gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt"));
+      }, skip: true);
+    });
+
+    group('decode', () {
+      test('decode exercism', () {
+        final result = atbashCipher.decode("vcvix rhn");
+        expect(result, equals("exercism"));
+      }, skip: true);
+
+      test('decode a sentence', () {
+        final result =
+            atbashCipher.decode("zmlyh gzxov rhlug vmzhg vkkrm thglm v");
+        expect(result, equals("anobstacleisoftenasteppingstone"));
+      }, skip: true);
+
+      test('decode numbers', () {
+        final result = atbashCipher.decode("gvhgr mt123 gvhgr mt");
+        expect(result, equals("testing123testing"));
+      }, skip: true);
+
+      test('decode all the letters', () {
+        final result =
+            atbashCipher.decode("gsvjf rxpyi ldmul cqfnk hlevi gsvoz abwlt");
+        expect(result, equals("thequickbrownfoxjumpsoverthelazydog"));
+      }, skip: true);
+
+      test('decode with too many spaces', () {
+        final result = atbashCipher.decode("vc vix    r hn");
+        expect(result, equals("exercism"));
+      }, skip: true);
+
+      test('decode with no spaces', () {
+        final result = atbashCipher.decode("zmlyhgzxovrhlugvmzhgvkkrmthglmv");
+        expect(result, equals("anobstacleisoftenasteppingstone"));
+      }, skip: true);
+    });
+  });
+}