Add circular-buffer (#103)

* Add circular-buffer

* implement overwrite with an argument to write

Author: glennj

config.json

@@ -538,6 +538,14 @@
         "prerequisites": [],
         "difficulty": 5
       },
+      {
+        "slug": "circular-buffer",
+        "name": "Circular Buffer",
+        "uuid": "1ef26e0a-c4de-4250-999e-0ab72c57f3cf",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 5
+      },
       {
         "slug": "flower-field",
         "name": "Flower Field",

exercises/practice/circular-buffer/.busted

@@ -0,0 +1,5 @@
+return {
+  default = {
+    ROOT = { '.' }
+  }
+}

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+3 & 4 have been replaced by A & B making 5 now the oldest data in the buffer.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

@@ -0,0 +1,31 @@
+class CircularBuffer
+  new: (@size) =>
+    @buff = [0 for _ = 1, @size]
+    @idx = r: 1, w: 1
+    @count = 0
+
+  read: =>
+    return nil, false if @count == 0
+    item = @buff[@idx.r]
+    @idx.r = @idx.r == @size and 1 or @idx.r + 1
+    @count -= 1
+    item, true
+
+  write: (item, options={}) =>
+    if @count == @size
+      if options.overwrite
+        @read!
+      else
+        return false
+
+    @buff[@idx.w] = item
+    @idx.w = @idx.w == @size and 1 or @idx.w + 1
+    @count += 1
+    true
+
+  clear: =>
+    @count = 0
+    @idx.r = @idx.w
+
+
+CircularBuffer

exercises/practice/circular-buffer/.meta/spec_generator.moon

@@ -0,0 +1,25 @@
+{
+  module_name: 'CircularBuffer',
+
+  generate_test: (case, level) ->
+    lines = { "buffer = CircularBuffer #{case.input.capacity}" }
+    for op in *case.input.operations
+      switch op.operation
+        when 'read'
+          table.insert lines, 'value, ok = buffer\\read!'
+          table.insert lines, "assert.is_#{op.should_succeed} ok"
+          if op.should_succeed
+            table.insert lines, "assert.are.equal #{op.expected}, value"
+
+        when 'write'
+          table.insert lines, "ok = buffer\\write #{op.item}"
+          table.insert lines, "assert.is_#{op.should_succeed} ok"
+
+        when 'clear'
+          table.insert lines, 'buffer\\clear!'
+
+        when 'overwrite'
+          table.insert lines, "buffer\\write #{op.item}, overwrite: true"
+
+    table.concat [indent line, level for line in *lines], '\n'
+}

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.moon

@@ -0,0 +1,15 @@
+class CircularBuffer
+  new: (size) =>
+    error 'Implement the constructor'
+
+  read: =>
+    error 'Implement the read method'
+
+  write: (item) =>
+    error 'Implement the write method'
+
+  clear: =>
+    error 'Implement the clear method'
+
+
+CircularBuffer

exercises/practice/circular-buffer/circular_buffer_spec.moon

@@ -0,0 +1,172 @@
+CircularBuffer = require 'circular_buffer'
+
+describe 'circular-buffer', ->
+  it 'reading empty buffer should fail', ->
+    buffer = CircularBuffer 1
+    value, ok = buffer\read!
+    assert.is_false ok
+
+  pending 'can read an item just written', ->
+    buffer = CircularBuffer 1
+    ok = buffer\write 1
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 1, value
+
+  pending 'each item may only be read once', ->
+    buffer = CircularBuffer 1
+    ok = buffer\write 1
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 1, value
+    value, ok = buffer\read!
+    assert.is_false ok
+
+  pending 'items are read in the order they are written', ->
+    buffer = CircularBuffer 2
+    ok = buffer\write 1
+    assert.is_true ok
+    ok = buffer\write 2
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 1, value
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 2, value
+
+  pending "full buffer can't be written to", ->
+    buffer = CircularBuffer 1
+    ok = buffer\write 1
+    assert.is_true ok
+    ok = buffer\write 2
+    assert.is_false ok
+
+  pending 'a read frees up capacity for another write', ->
+    buffer = CircularBuffer 1
+    ok = buffer\write 1
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 1, value
+    ok = buffer\write 2
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 2, value
+
+  pending 'read position is maintained even across multiple writes', ->
+    buffer = CircularBuffer 3
+    ok = buffer\write 1
+    assert.is_true ok
+    ok = buffer\write 2
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 1, value
+    ok = buffer\write 3
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 2, value
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 3, value
+
+  pending "items cleared out of buffer can't be read", ->
+    buffer = CircularBuffer 1
+    ok = buffer\write 1
+    assert.is_true ok
+    buffer\clear!
+    value, ok = buffer\read!
+    assert.is_false ok
+
+  pending 'clear frees up capacity for another write', ->
+    buffer = CircularBuffer 1
+    ok = buffer\write 1
+    assert.is_true ok
+    buffer\clear!
+    ok = buffer\write 2
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 2, value
+
+  pending 'clear does nothing on empty buffer', ->
+    buffer = CircularBuffer 1
+    buffer\clear!
+    ok = buffer\write 1
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 1, value
+
+  pending 'overwrite acts like write on non-full buffer', ->
+    buffer = CircularBuffer 2
+    ok = buffer\write 1
+    assert.is_true ok
+    buffer\write 2, overwrite: true
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 1, value
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 2, value
+
+  pending 'overwrite replaces the oldest item on full buffer', ->
+    buffer = CircularBuffer 2
+    ok = buffer\write 1
+    assert.is_true ok
+    ok = buffer\write 2
+    assert.is_true ok
+    buffer\write 3, overwrite: true
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 2, value
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 3, value
+
+  pending 'overwrite replaces the oldest item remaining in buffer following a read', ->
+    buffer = CircularBuffer 3
+    ok = buffer\write 1
+    assert.is_true ok
+    ok = buffer\write 2
+    assert.is_true ok
+    ok = buffer\write 3
+    assert.is_true ok
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 1, value
+    ok = buffer\write 4
+    assert.is_true ok
+    buffer\write 5, overwrite: true
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 3, value
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 4, value
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 5, value
+
+  pending 'initial clear does not affect wrapping around', ->
+    buffer = CircularBuffer 2
+    buffer\clear!
+    ok = buffer\write 1
+    assert.is_true ok
+    ok = buffer\write 2
+    assert.is_true ok
+    buffer\write 3, overwrite: true
+    buffer\write 4, overwrite: true
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 3, value
+    value, ok = buffer\read!
+    assert.is_true ok
+    assert.are.equal 4, value
+    value, ok = buffer\read!
+    assert.is_false ok