Add circular-buffer exercise (#701)

config.json

@@ -239,6 +239,14 @@
         "prerequisites": [],
         "difficulty": 1
       },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "2135af8f-5849-4611-8492-29a8c5b63629",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 4
+      },
       {
         "slug": "clock",
         "name": "Clock",

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+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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 +1,19 @@
+{
+  "authors": [
+    "glennj"
+  ],
+  "files": {
+    "solution": [
+      "lib/CircularBuffer.pm"
+    ],
+    "test": [
+      "t/circular-buffer.t"
+    ],
+    "example": [
+      ".meta/solutions/lib/CircularBuffer.pm"
+    ]
+  },
+  "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/solutions/lib/CircularBuffer.pm

@@ -0,0 +1,33 @@
+use strict;
+use warnings;
+use experimental qw<signatures postderef postderef_qq>;
+use Feature::Compat::Class;
+
+class CircularBuffer;
+
+field $capacity :reader :param;
+field @data = (); # kind of cheating to use a non-fixed size array.
+
+method _isFull  { scalar @data == $capacity; }
+method _isEmpty { scalar @data == 0; }
+
+method write ($item) {
+    die 'buffer full' if $self->_isFull;
+    push @data, $item;
+}
+
+method read () {
+    die 'buffer empty' if $self->_isEmpty;
+    return shift @data;
+}
+
+method clear () {
+    @data = ();
+}
+
+method overwrite ($item) {
+    $self->read() if $self->_isFull;
+    $self->write($item);
+}
+
+1;

exercises/practice/circular-buffer/.meta/solutions/t/circular-buffer.t

@@ -0,0 +1 @@
+../../../t/circular-buffer.t

exercises/practice/circular-buffer/.meta/template-data.yaml

@@ -0,0 +1,109 @@
+class: true
+
+properties:
+  run:
+    test: |-
+      use Data::Dmp;
+      (my $_t_name = $case->{description}) =~ s/'//g;
+      $_t_name =~ s/\W+/_/g;
+      my $_t = sprintf(<<'END1', $_t_name, $case->{input}{capacity});
+      subtest %s => sub {
+        my $buff = CircularBuffer->new(capacity => %s);
+      END1
+
+      my $n = 1;
+      foreach my $_op (@{$case->{input}{operations}}) {
+        if ($_op->{operation} eq 'clear') {
+          $_t .= sprintf(<<'END2', $n);
+        ok(lives { $buff->clear() }, "check %d");
+      END2
+        }
+
+        elsif ($_op->{operation} eq 'write') {
+          if ($_op->{should_succeed}) {
+            $_t .= sprintf(<<'END3', $_op->{item}, $n);
+        ok(lives { $buff->write(%s) }, "check %d");
+      END3
+          }
+          else {
+            $_t .= sprintf(<<'END4', $_op->{item}, $n);
+        like(
+          dies { $buff->write(%s) }, 
+          qr/buffer full/,
+          "check %d"
+        );
+      END4
+          }
+        }
+
+        elsif ($_op->{operation} eq 'read') {
+          if ($_op->{should_succeed}) {
+            $_t .= sprintf(<<'END5', $_op->{expected}, $n);
+        is($buff->read(), %s, "check %d");
+      END5
+          }
+          else {
+            $_t .= sprintf(<<'END6', $n);
+        like(
+          dies { $buff->read() }, 
+          qr/buffer empty/,
+          "check %d"
+        );
+      END6
+          }
+        }
+
+        elsif ($_op->{operation} eq 'overwrite') {
+          $_t .= sprintf(<<'END7', $_op->{item}, $n);
+        ok(lives { $buff->overwrite(%s) }, "check %d");
+      END7
+        }
+
+        ++$n;
+      }
+      $_t . "};\n"
+
+stub: |-
+  field $capacity :reader :param;
+
+  method write ($item) {
+    return undef;
+  }
+
+  method read () {
+    return undef;
+  }
+
+  method clear () {
+    return undef;
+  }
+
+  method overwrite ($item) {
+    return undef;
+  }
+
+example: |-
+  field $capacity :reader :param;
+  field @data = (); # kind of cheating to use a non-fixed size array.
+
+  method _isFull { scalar @data == $capacity; }
+  method _isEmpty { scalar @data == 0; }
+
+  method write ($item) {
+    die 'buffer full' if $self->_isFull;
+    push @data, $item;
+  }
+
+  method read () {
+    die 'buffer empty' if $self->_isEmpty;
+    return shift @data;
+  }
+
+  method clear () {
+    @data = ();
+  }
+
+  method overwrite ($item) {
+    $self->read() if $self->_isFull;
+    $self->write($item);
+  }

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/lib/CircularBuffer.pm

@@ -0,0 +1,24 @@
+use v5.40;
+use experimental qw<class>;
+
+class CircularBuffer;
+
+field $capacity :reader :param;
+
+method write ($item) {
+    return undef;
+}
+
+method read () {
+    return undef;
+}
+
+method clear () {
+    return undef;
+}
+
+method overwrite ($item) {
+    return undef;
+}
+
+1;