Add exercise Circular Buffer

config.json

@@ -33,7 +33,6 @@
     ]
   },
   "exercises": {
-    "concept": [],
     "practice": [
       {
         "slug": "hello-world",
@@ -1172,10 +1171,17 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 3
+      },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "c423440e-d374-462e-baa9-e81dcbc085f3",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 7
       }
     ]
   },
-  "concepts": [],
   "key_features": [
     {
       "title": "Automation",
@@ -1209,12 +1215,12 @@
     }
   ],
   "tags": [
-    "used_for/scripts",
-    "paradigm/procedural",
     "execution_mode/interpreted",
-    "typing/weak",
+    "paradigm/procedural",
     "platform/linux",
     "platform/mac",
-    "platform/windows"
+    "platform/windows",
+    "typing/weak",
+    "used_for/scripts"
   ]
 }

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+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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": [
+      "circular_buffer.sh"
+    ],
+    "test": [
+      "circular_buffer.bats"
+    ],
+    "example": [
+      ".meta/example.sh"
+    ]
+  },
+  "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.sh

@@ -0,0 +1,102 @@
+#!/usr/bin/env bash
+
+# Namerefs require bash version 4.3 or greater
+bash_version=$((10 * BASH_VERSINFO[0] + BASH_VERSINFO[1]))
+if (( bash_version < 43 )); then
+    echo "This library requires at least bash version 4.3" >&2
+    return 4
+fi
+
+# I'm storing all the data for all circular buffers in a single global
+# associative array.
+# Empty cells are denoted by empty strings.
+# Therefore, an empty string cannot be stored in this circular buffer
+
+declare -gA _buffer_data=()
+
+buffer::new() {
+    local name=$1
+    local size=$2
+    _buffer_data[size,$name]=$size
+    buffer::clear "$name"
+}
+
+buffer::destroy() {
+    local name=$1
+    for ((idx = 0; idx < _buffer_data[size,$name]; idx++)); do
+        unset "_buffer_data[$idx,$name]"
+    done
+    unset "_buffer_data[read,$name]"
+    unset "_buffer_data[write,$name]"
+    unset "_buffer_data[size,$name]"
+}
+
+buffer::clear() {
+    local name=$1
+    _buffer_data[read,$name]=0
+    _buffer_data[write,$name]=0
+    for ((idx = 0; idx < _buffer_data[size,$name]; idx++)); do
+        _buffer_data[$idx,$name]=''
+    done
+}
+
+buffer::is_empty() {
+    local name=$1
+    local idx=${_buffer_data[read,$name]}
+    [[ -z ${_buffer_data[$idx,$name]} ]]
+}
+
+buffer::is_full() {
+    local name=$1
+    local idx=${_buffer_data[write,$name]}
+    [[ -n ${_buffer_data[$idx,$name]} ]]
+}
+
+buffer::read() {
+    local name=$1
+    local -n _read_value=$2
+    if buffer::is_empty "$name"; then
+        return 1
+    fi
+
+    local idx=${_buffer_data[read,$name]}
+    _read_value=${_buffer_data[$idx,$name]}
+    _buffer_data[$idx,$name]=''
+
+    buffer::incr_pointer "$name" read
+}
+
+buffer::write() {
+    local overwrite=false
+    # To use `getopts` in a function, these vars must be local.
+    local OPTIND OPTARG
+    while getopts :f opt; do
+        case $opt in
+            f) overwrite=true ;;
+            '?') return 2 ;;
+        esac
+    done
+    shift $((OPTIND - 1))
+
+    local name=$1 item=$2
+    if buffer::is_full "$name"; then
+        if $overwrite; then 
+            # Read to free up a cell.
+            # shellcheck disable=SC2034
+            local tmp
+            buffer::read "$name" tmp
+        else
+            return 1
+        fi
+    fi
+
+    local idx=${_buffer_data[write,$name]}
+    _buffer_data[$idx,$name]=$item
+
+    buffer::incr_pointer "$name" write
+}
+
+buffer::incr_pointer() {
+    local name=$1 p=$2
+    _buffer_data[$p,$name]=$(( (_buffer_data[$p,$name] + 1) % _buffer_data[size,$name] ))
+}

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"