feat: circular-buffer exercise

config.json

@@ -664,7 +664,15 @@
           "arrays",
           "lists"
         ]
-      } 
+      },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "c69af85e-f089-4457-a375-63ad29fc266b",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 3
+      }
     ]
   },
   "concepts": [

exercises/practice/circular-buffer/.docs/instructions.md

@@ -0,0 +1,58 @@
+# Instructions
+
+A circular buffer, cyclic buffer or ring buffer is a data structure that uses a single, fixed-size buffer as if it were connected end-to-end.
+
+A circular buffer first starts empty and of some predefined length.
+For example, this is a 7-element buffer:
+
+```text
+[ ][ ][ ][ ][ ][ ][ ]
+```
+
+Assume that a 1 is written into the middle of the buffer (exact starting location does not matter in a circular buffer):
+
+```text
+[ ][ ][ ][1][ ][ ][ ]
+```
+
+Then assume that two more elements are added — 2 & 3 — which get appended after the 1:
+
+```text
+[ ][ ][ ][1][2][3][ ]
+```
+
+If two elements are then removed from the buffer, the oldest values inside the buffer are removed.
+The two elements removed, in this case, are 1 & 2, leaving the buffer with just a 3:
+
+```text
+[ ][ ][ ][ ][ ][3][ ]
+```
+
+If the buffer has 7 elements then it is completely full:
+
+```text
+[5][6][7][8][9][3][4]
+```
+
+When the buffer is full an error will be raised, alerting the client that further writes are blocked until a slot becomes free.
+
+When the buffer is full, the client can opt to overwrite the oldest data with a forced write.
+In this case, two more elements — A & B — are added and they overwrite the 3 & 4:
+
+```text
+[5][6][7][8][9][A][B]
+```
+
+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.
+Finally, if two elements are removed then what would be returned is 5 & 6 yielding the buffer:
+
+```text
+[ ][ ][7][8][9][A][B]
+```
+
+Because there is space available, if the client again uses overwrite to store C & D then the space where 5 & 6 were stored previously will be used not the location of 7 & 8.
+7 is still the oldest element and the buffer is once again full.
+
+```text
+[C][D][7][8][9][A][B]
+```

exercises/practice/circular-buffer/.meta/config.json

@@ -0,0 +1,22 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "lib/circular_buffer.dart"
+    ],
+    "test": [
+      "test/circular_buffer_test.dart"
+    ],
+    "example": [
+      ".meta/lib/example.dart"
+    ],
+    "invalidator": [
+      "pubspec.yaml"
+    ]
+  },
+  "blurb": "A data structure that uses a single, fixed-size buffer as if it were connected end-to-end.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/Circular_buffer"
+}

exercises/practice/circular-buffer/.meta/lib/example.dart

@@ -0,0 +1,29 @@
+class EmptyBufferException implements Exception {}
+
+class FullBufferException implements Exception {}
+
+class CircularBuffer {
+  final int size;
+  final List<int> data = [];
+  CircularBuffer(this.size);
+
+  int read() {
+    if (data.isEmpty) throw EmptyBufferException();
+    return data.removeAt(0);
+  }
+
+  void write(int value, {bool force = false}) {
+    if (size == data.length) {
+      if (force) {
+        read();
+      } else {
+        throw FullBufferException();
+      }
+    }
+    data.add(value);
+  }
+
+  void clear() {
+    data.clear();
+  }
+}

exercises/practice/circular-buffer/.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.
+
+[28268ed4-4ff3-45f3-820e-895b44d53dfa]
+description = "reading empty buffer should fail"
+
+[2e6db04a-58a1-425d-ade8-ac30b5f318f3]
+description = "can read an item just written"
+
+[90741fe8-a448-45ce-be2b-de009a24c144]
+description = "each item may only be read once"
+
+[be0e62d5-da9c-47a8-b037-5db21827baa7]
+description = "items are read in the order they are written"
+
+[2af22046-3e44-4235-bfe6-05ba60439d38]
+description = "full buffer can't be written to"
+
+[547d192c-bbf0-4369-b8fa-fc37e71f2393]
+description = "a read frees up capacity for another write"
+
+[04a56659-3a81-4113-816b-6ecb659b4471]
+description = "read position is maintained even across multiple writes"
+
+[60c3a19a-81a7-43d7-bb0a-f07242b1111f]
+description = "items cleared out of buffer can't be read"
+
+[45f3ae89-3470-49f3-b50e-362e4b330a59]
+description = "clear frees up capacity for another write"
+
+[e1ac5170-a026-4725-bfbe-0cf332eddecd]
+description = "clear does nothing on empty buffer"
+
+[9c2d4f26-3ec7-453f-a895-7e7ff8ae7b5b]
+description = "overwrite acts like write on non-full buffer"
+
+[880f916b-5039-475c-bd5c-83463c36a147]
+description = "overwrite replaces the oldest item on full buffer"
+
+[bfecab5b-aca1-4fab-a2b0-cd4af2b053c3]
+description = "overwrite replaces the oldest item remaining in buffer following a read"
+
+[9cebe63a-c405-437b-8b62-e3fdc1ecec5a]
+description = "initial clear does not affect wrapping around"

exercises/practice/circular-buffer/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/circular-buffer/lib/circular_buffer.dart

@@ -0,0 +1,11 @@
+/* These implementation definitions enable zero-argument contructors:
+ *    throw EmptyBufferException();
+ */
+
+class EmptyBufferException implements Exception {}
+
+class FullBufferException implements Exception {}
+
+class CircularBuffer {
+  // Put your code here
+}

exercises/practice/circular-buffer/pubspec.yaml

@@ -0,0 +1,5 @@
+name: 'circular_buffer'
+environment:
+  sdk: '>=2.18.0 <3.0.0'
+dev_dependencies:
+  test: '<2.0.0'

exercises/practice/circular-buffer/test/circular_buffer_test.dart

@@ -0,0 +1,139 @@
+import 'package:circular_buffer/circular_buffer.dart';
+import 'package:test/test.dart';
+
+void main() {
+  test("reading empty buffer should fail", () {
+    final buff = CircularBuffer(1);
+    expect(() => buff.read(), throwsA(isA<EmptyBufferException>()));
+  }, skip: false);
+
+  test("can read an item just written", () {
+    final buff = CircularBuffer(1);
+    buff.write(1);
+    var value = buff.read();
+    expect(value, 1);
+  }, skip: true);
+
+  test("each item may only be read once", () {
+    final buff = CircularBuffer(1);
+    buff.write(1);
+    var value = buff.read();
+    expect(value, 1);
+    expect(() => buff.read(), throwsA(isA<EmptyBufferException>()));
+  }, skip: true);
+
+  test("items are read in the order they are written", () {
+    final buff = CircularBuffer(2);
+    buff.write(1);
+    buff.write(2);
+    var value = buff.read();
+    expect(value, 1);
+    value = buff.read();
+    expect(value, 2);
+  }, skip: true);
+
+  test("full buffer can't be written to", () {
+    final buff = CircularBuffer(1);
+    buff.write(1);
+    expect(() => buff.write(2), throwsA(isA<FullBufferException>()));
+  }, skip: true);
+
+  test("a read frees up capacity for another write", () {
+    final buff = CircularBuffer(1);
+    buff.write(1);
+    var value = buff.read();
+    expect(value, 1);
+    buff.write(2);
+    value = buff.read();
+    expect(value, 2);
+  }, skip: true);
+
+  test("read position is maintained even across multiple writes", () {
+    final buff = CircularBuffer(3);
+    buff.write(1);
+    buff.write(2);
+    var value = buff.read();
+    expect(value, 1);
+    buff.write(3);
+    value = buff.read();
+    expect(value, 2);
+    value = buff.read();
+    expect(value, 3);
+  }, skip: true);
+
+  test("items cleared out of buffer can't be read", () {
+    final buff = CircularBuffer(1);
+    buff.write(1);
+    buff.clear();
+    expect(() => buff.read(), throwsA(isA<EmptyBufferException>()));
+  }, skip: true);
+
+  test("clear frees up capacity for another write", () {
+    final buff = CircularBuffer(1);
+    buff.write(1);
+    buff.clear();
+    buff.write(2);
+    var value = buff.read();
+    expect(value, 2);
+  }, skip: true);
+
+  test("clear does nothing on empty buffer", () {
+    final buff = CircularBuffer(1);
+    buff.clear();
+    buff.write(1);
+    var value = buff.read();
+    expect(value, 1);
+  }, skip: true);
+
+  test("overwrite acts like write on non-full buffer", () {
+    final buff = CircularBuffer(2);
+    buff.write(1);
+    buff.write(2, force: true);
+    var value = buff.read();
+    expect(value, 1);
+    value = buff.read();
+    expect(value, 2);
+  }, skip: true);
+
+  test("overwrite replaces the oldest item on full buffer", () {
+    final buff = CircularBuffer(2);
+    buff.write(1);
+    buff.write(2);
+    buff.write(3, force: true);
+    var value = buff.read();
+    expect(value, 2);
+    value = buff.read();
+    expect(value, 3);
+  }, skip: true);
+
+  test("overwrite replaces the oldest item remaining in buffer following a read", () {
+    final buff = CircularBuffer(3);
+    buff.write(1);
+    buff.write(2);
+    buff.write(3);
+    var value = buff.read();
+    expect(value, 1);
+    buff.write(4);
+    buff.write(5, force: true);
+    value = buff.read();
+    expect(value, 3);
+    value = buff.read();
+    expect(value, 4);
+    value = buff.read();
+    expect(value, 5);
+  }, skip: true);
+
+  test("initial clear does not affect wrapping around", () {
+    final buff = CircularBuffer(2);
+    buff.clear();
+    buff.write(1);
+    buff.write(2);
+    buff.write(3, force: true);
+    buff.write(4, force: true);
+    var value = buff.read();
+    expect(value, 3);
+    value = buff.read();
+    expect(value, 4);
+    expect(() => buff.read(), throwsA(isA<EmptyBufferException>()));
+  }, skip: true);
+}