add circular-buffer, part of 48 in 24

config.json

@@ -822,6 +822,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 5
+      },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "d2eaa3fa-42b3-4287-9b87-714a73ac0c65",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
       }
     ]
   },

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+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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": [
+    "kmarker1101"
+  ],
+  "files": {
+    "solution": [
+      "circular-buffer.el"
+    ],
+    "test": [
+      "circular-buffer-test.el"
+    ],
+    "example": [
+      ".meta/example.el"
+    ]
+  },
+  "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/example.el

@@ -0,0 +1,74 @@
+;;; circular-buffer.el --- Circular Buffer (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(define-error 'empty-buffer-error "buffer is empty")
+
+(define-error 'full-buffer-error "buffer is full")
+
+(defclass circular-buffer ()
+  ((capacity :initarg :capacity :initform 10)
+   (buf-modulus :initform 20)
+   (data :initform nil)
+   (front :initform 0)
+   (back :initform 0))
+  :documentation "Circular buffer class")
+
+
+(cl-defmethod initialize-instance :after ((buf circular-buffer) &rest _)
+  (with-slots (capacity buf-modulus data) buf
+    (setf buf-modulus (* 2 capacity)
+          data (make-vector capacity nil))))
+
+(cl-defmethod buf-empty-p ((buf circular-buffer))
+  (with-slots (front back) buf
+    (= front back)))
+
+(cl-defmethod buf-full-p ((buf circular-buffer))
+  (with-slots (front back buf-modulus capacity) buf
+    (= (mod (- back front) buf-modulus) capacity)))
+
+(cl-defmethod next-spot ((buf circular-buffer) s)
+  (with-slots (buf-modulus) buf
+    (mod (1+ s) buf-modulus)))
+
+(cl-defmethod advance-front ((buf circular-buffer))
+  (with-slots (front) buf
+    (setf front (next-spot buf front))))
+
+(cl-defmethod advance-back ((buf circular-buffer))
+  (with-slots (back) buf
+    (setf back (next-spot buf back))))
+
+(cl-defmethod clear ((buf circular-buffer))
+  (with-slots (front back) buf
+    (setf front back)))
+
+(cl-defmethod read-buff ((buf circular-buffer))
+  (with-slots (front data capacity) buf
+    (if (buf-empty-p buf)
+        (signal 'empty-buffer-error nil)
+      (let ((v (aref data (mod front capacity))))
+        (advance-front buf)
+        v))))
+
+(cl-defmethod write ((buf circular-buffer) v)
+  (with-slots (back data capacity) buf
+    (if (buf-full-p buf)
+        (signal 'full-buffer-error nil)
+      (progn
+        (aset data (mod back capacity) v)
+        (advance-back buf)))))
+
+(cl-defmethod overwrite ((buf circular-buffer) v)
+  (with-slots (front) buf
+    (when (buf-full-p buf)
+      (advance-front buf))
+    (write buf v)))
+
+(provide 'circular-buffer)
+;;; circular-buffer.el ends here
+

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/circular-buffer-test.el

@@ -0,0 +1,132 @@
+;;; circular-buffer-test.el --- Circular Buffer (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(require 'eieio)
+
+(load-file "circular-buffer.el")
+
+(defun create-test-buffer (capacity)
+  "Helper function to create a circular buffer with the given capacity."
+  (circular-buffer :capacity capacity))
+
+(ert-deftest reading-empty-buffer-should-fail ()
+  (let ((buf (create-test-buffer 1)))
+    (should-error (read-buff buf) :type 'empty-buffer-error)))
+
+
+(ert-deftest can-read-an-item-just-written ()
+  (let ((buf (create-test-buffer 1)))
+    (write buf 1)
+    (should (equal (read-buff buf) 1))))
+
+
+(ert-deftest each-item-may-only-be-read-once ()
+  (let ((buf (create-test-buffer 1)))
+    (write buf 1)
+    (should (equal (read-buff buf) 1))
+    (should-error (read-buff buf) :type 'empty-buffer-error)))
+
+
+(ert-deftest items-are-read-in-the-order-they-are-written ()
+  (let ((buf (create-test-buffer 2)))
+    (write buf 1)
+    (write buf 2)
+    (should (equal (read-buff buf) 1))
+    (should (equal (read-buff buf) 2))))
+
+
+(ert-deftest full-buffer-cant-be-written-to ()
+  (let ((buf (create-test-buffer 1)))
+    (write buf 1)
+    (should-error (write buf 2) :type 'full-buffer-error)))
+
+
+(ert-deftest a-read-frees-up-capacity-for-another-write ()
+  (let ((buf (create-test-buffer 1)))
+    (write buf 1)
+    (should (equal (read-buff buf) 1))
+    (write buf 2)
+    (should (equal (read-buff buf) 2))))
+
+
+(ert-deftest read-position-is-maintained-even-across-multiple-writes ()
+  (let ((buf (create-test-buffer 3)))
+    (write buf 1)
+    (write buf 2)
+    (should (equal (read-buff buf) 1))
+    (write buf 3)
+    (should (equal (read-buff buf) 2))
+    (should (equal (read-buff buf) 3))))
+
+
+(ert-deftest items-cleared-out-of-buffer-cant-be-read ()
+  (let ((buf (create-test-buffer 1)))
+    (write buf 1)
+    (clear buf)
+    (should-error (read-buff buf) :type 'empty-buffer-error)))
+
+
+(ert-deftest clear-frees-up-capacity-for-another-write ()
+  (let ((buf (create-test-buffer 1)))
+    (write buf 1)
+    (clear buf)
+    (write buf 2)
+    (should (equal (read-buff buf) 2))))
+
+
+(ert-deftest clear-does-nothing-on-empty-buffer ()
+  (let ((buf (create-test-buffer 1)))
+    (clear buf)
+    (write buf 1)
+    (should (equal (read-buff buf) 1))))
+
+
+(ert-deftest overwrite-acts-like-write-on-non-full-buffer ()
+  (let ((buf (create-test-buffer 2)))
+    (write buf 1)
+    (overwrite buf 2)
+    (should (equal (read-buff buf) 1))
+    (should (equal (read-buff buf) 2))))
+
+
+(ert-deftest overwrite-replaces-the-oldest-item-on-full-buffer ()
+  (let ((buf (create-test-buffer 2)))
+    (write buf 1)
+    (write buf 2)
+    (overwrite buf 3)
+    (should (equal (read-buff buf) 2))
+    (should (equal (read-buff buf) 3))))
+
+
+(ert-deftest overwrite-replaces-the-oldest-item-remaining-in-buffer-following-a-read ()
+  (let ((buf (create-test-buffer 3)))
+    (write buf 1)
+    (write buf 2)
+    (write buf 3)
+    (should (equal (read-buff buf) 1))
+    (write buf 4)
+    (overwrite buf 5)
+    (should (equal (read-buff buf) 3))
+    (should (equal (read-buff buf) 4))
+    (should (equal (read-buff buf) 5))))
+
+
+(ert-deftest initial-clear-does-not-affect-wrapping-around ()
+  (let ((buf (create-test-buffer 2)))
+    (clear buf)
+    (write buf 1)
+    (write buf 2)
+    (overwrite buf 3)
+    (overwrite buf 4)
+    (should (equal (read-buff buf) 3))
+    (should (equal (read-buff buf) 4))
+    (should-error (read-buff buf) :type 'empty-buffer-error)))
+
+
+(provide 'circular-buffer-test)
+;;; circular-buffer-test.el ends here
+

exercises/practice/circular-buffer/circular-buffer.el

@@ -0,0 +1,19 @@
+;;; circular-buffer.el --- Circular Buffer (exercism)  -*- lexical-binding: t; -*-
+
+;;; Commentary:
+
+;;; Code:
+
+
+(define-error 'empty-buffer-error
+              (error "Delete this S-Expression and write your own implementation"))
+
+(define-error 'full-buffer-error
+              (error "Delete this S-Expression and write your own implementation"))
+
+(defclass circular-buffer ()
+  (error "Delete this S-Expression and write your own implementation"))
+
+(provide 'circular-buffer)
+;;; circular-buffer.el ends here
+