Circular buffer

EXERCISES.txt

@@ -13,6 +13,7 @@ proverb
 space-age
 house
 roman-numerals
+circular-buffer
 clock
 prime-factors
 strain

circular-buffer/circular_buffer_test.rb

@@ -0,0 +1,108 @@
+require 'minitest/autorun'
+require_relative 'circular_buffer'
+
+class CircularBufferTest < MiniTest::Unit::TestCase
+
+  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 String(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_writes_of_nil_should_not_occupy_buffer
+    skip    
+    buffer = CircularBuffer.new(5)
+    buffer.write nil
+    (1..3).each { |i| buffer.write String(i) }
+    assert_equal '1', 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_alternate_read_and_write_into_buffer_overflow
+    skip    
+    buffer = CircularBuffer.new(5)
+    (1..3).each { |i| buffer.write String(i) }
+    buffer.read
+    buffer.read
+    buffer.write '4'
+    buffer.read
+    (5..8).each { |i| buffer.write String(i) }
+    buffer.write! 'A'
+    buffer.write! 'B'
+    (6..8).each do |i| 
+      assert_equal String(i), buffer.read
+    end
+    assert_equal 'A', buffer.read
+    assert_equal 'B', buffer.read
+    assert_raises(CircularBuffer::BufferEmptyException) { buffer.read }
+  end
+
+end

circular-buffer/example.rb

@@ -0,0 +1,69 @@
+class CircularBuffer
+
+  def initialize(capacity)
+    @capacity = capacity
+    @write_point = @read_point = 0
+    @buffer = Array.new(capacity, nil)
+  end
+
+  def write data
+    update_buffer(data) do
+      raise BufferFullException if full?
+      @buffer[@write_point] = data
+    end
+  end
+
+  def write! data
+    update_buffer(data) do
+      @buffer[@write_point] = data
+      if overwriting?
+        update_read_point
+      end
+    end
+  end
+
+  def read
+    raise BufferEmptyException if empty?
+    data = @buffer[@read_point]
+    @buffer[@read_point] = nil
+    update_read_point
+    data
+  end
+
+  def clear
+    @buffer = Array.new(@capacity)
+  end
+
+  private
+
+  def update_buffer item
+    return if item.nil?
+    yield if block_given?
+    update_write_point
+  end
+
+  def update_read_point
+    @read_point = (@read_point + 1) % @capacity
+  end
+
+  def update_write_point
+    @write_point = (@write_point + 1) % @capacity
+  end
+
+  def overwriting?
+    (full? && @write_point == @read_point)
+  end
+
+  def empty?
+    @buffer.compact.empty?
+  end
+
+  def full?
+    @buffer.all?
+  end
+
+  class BufferFullException < Exception; end
+
+  class BufferEmptyException < Exception; end
+
+end