ruby - circular-buffer

ruby/circular-buffer/README.md

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+# Circular Buffer
+
+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:
+
+    [ ][ ][ ][ ][ ][ ][ ]
+
+Assume that a 1 is written into the middle of the buffer (exact starting
+location does not matter in a circular buffer):
+
+    [ ][ ][ ][1][ ][ ][ ]
+
+Then assume that two more elements are added — 2 & 3 — which get
+appended after the 1:
+
+    [ ][ ][ ][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:
+
+    [ ][ ][ ][ ][ ][3][ ]
+
+If the buffer has 7 elements then it is completely full:
+
+    [6][7][8][9][3][4][5]
+
+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:
+
+    [6][7][8][9][A][B][5]
+
+3 & 4 have been replaced by A & B making 5 now the oldest data in the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:
+
+    [ ][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.
+
+    [D][7][8][9][A][B][C]
+
+* * * *
+
+For installation and learning resources, refer to the
+[Ruby resources page](http://exercism.io/languages/ruby/resources).
+
+For running the tests provided, you will need the Minitest gem. Open a
+terminal window and run the following command to install minitest:
+
+    gem install minitest
+
+If you would like color output, you can `require 'minitest/pride'` in
+the test file, or note the alternative instruction, below, for running
+the test file.
+
+Run the tests from the exercise directory using the following command:
+
+    ruby circular_buffer_test.rb
+
+To include color from the command line:
+
+    ruby -r minitest/pride circular_buffer_test.rb
+
+
+## Source
+
+Wikipedia [http://en.wikipedia.org/wiki/Circular_buffer](http://en.wikipedia.org/wiki/Circular_buffer)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

ruby/circular-buffer/circular_buffer.rb

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+# Class CircularBuffer
+class CircularBuffer
+  class BufferEmptyException < RuntimeError
+  end
+
+  class BufferFullException < RuntimeError
+  end
+
+  def initialize(buffer_size)
+    @buffer = Array.new(buffer_size)
+  end
+
+  def read
+    raise BufferEmptyException if @front.nil?
+
+    value = @buffer[@front]
+    @buffer[@front] = nil
+    if @front == @back
+      @back = @front = nil
+    else
+      @front = next_index(@front)
+    end
+    value
+  end
+
+  def write(data, force = false)
+    raise BufferFullException if @buffer[next_index(@back)] && !force
+
+    @back = next_index(@back)
+    @front = 0 if @front.nil?
+    @buffer[@back] = data
+  end
+
+  def write!(data)
+    @front = next_index(@front) if @buffer[next_index(@front)]
+    write(data, true)
+  end
+
+  def clear
+    @buffer = Array.new(@buffer.size)
+    @front = @back = nil
+  end
+
+  private
+
+  def next_index(index)
+    return 0 if index.nil?
+
+    (index + 1) % @buffer.size
+  end
+end

ruby/circular-buffer/circular_buffer_test.rb

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+require 'minitest/autorun'
+require_relative 'circular_buffer'
+
+class CircularBufferTest < Minitest::Test
+  def test_read_empty_buffer_throws_buffer_empty_exception
+    buffer = CircularBuffer.new(1)
+    assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
+  end
+
+  def test_write_and_read_back_one_item
+    # skip
+    buffer = CircularBuffer.new(1)
+    buffer.write '1'
+    assert_equal '1', buffer.read
+    assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
+  end
+
+  def test_write_and_read_back_multiple_items
+    # skip
+    buffer = CircularBuffer.new(2)
+    buffer.write '1'
+    buffer.write '2'
+    assert_equal '1', buffer.read
+    assert_equal '2', buffer.read
+    assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
+  end
+
+  def test_clearing_buffer
+    # skip
+    buffer = CircularBuffer.new(3)
+    ('1'..'3').each { |i| buffer.write i }
+    buffer.clear
+    assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
+    buffer.write '1'
+    buffer.write '2'
+    assert_equal '1', buffer.read
+    buffer.write '3'
+    assert_equal '2', buffer.read
+  end
+
+  def test_alternate_write_and_read
+    # skip
+    buffer = CircularBuffer.new(2)
+    buffer.write '1'
+    assert_equal '1', buffer.read
+    buffer.write '2'
+    assert_equal '2', buffer.read
+  end
+
+  def test_reads_back_oldest_item
+    # skip
+    buffer = CircularBuffer.new(3)
+    buffer.write '1'
+    buffer.write '2'
+    buffer.read
+    buffer.write '3'
+    assert_equal '2', buffer.read
+    assert_equal '3', buffer.read
+  end
+
+  def test_writing_to_a_full_buffer_throws_an_exception
+    # skip
+    buffer = CircularBuffer.new(2)
+    buffer.write '1'
+    buffer.write '2'
+    assert_raises(CircularBuffer::BufferFullException) { buffer.write 'A' }
+  end
+
+  def test_overwriting_oldest_item_in_a_full_buffer
+    # skip
+    buffer = CircularBuffer.new(2)
+    buffer.write '1'
+    buffer.write '2'
+    buffer.write! 'A'
+    assert_equal '2', buffer.read
+    assert_equal 'A', buffer.read
+    assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
+  end
+
+  def test_forced_writes_to_non_full_buffer_should_behave_like_writes
+    # skip
+    buffer = CircularBuffer.new(2)
+    buffer.write '1'
+    buffer.write! '2'
+    assert_equal '1', buffer.read
+    assert_equal '2', buffer.read
+    assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
+  end
+
+  def test_alternate_read_and_write_into_buffer_overflow
+    # skip
+    buffer = CircularBuffer.new(5)
+    ('1'..'3').each { |i| buffer.write i }
+    buffer.read
+    buffer.read
+    buffer.write '4'
+    buffer.read
+    ('5'..'8').each { |i| buffer.write i }
+    buffer.write! 'A'
+    buffer.write! 'B'
+    ('6'..'8').each do |i|
+      assert_equal i, buffer.read
+    end
+    assert_equal 'A', buffer.read
+    assert_equal 'B', buffer.read
+    assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
+  end
+end