1 files changed, 113 insertions, 0 deletions
diff --git a/lib/reline/kill_ring.rb b/lib/reline/kill_ring.rb
new file mode 100644
index 0000000000..842fd04697
--- /dev/null
+++ b/lib/reline/kill_ring.rb
@@ -0,0 +1,113 @@
+class Reline::KillRing
+  module State
+    FRESH = :fresh
+    CONTINUED = :continued
+    PROCESSED = :processed
+    YANK = :yank
+  end
+
+  RingPoint = Struct.new(:backward, :forward, :str) do
+    def initialize(str)
+      super(nil, nil, str)
+    end
+
+    def ==(other)
+      object_id == other.object_id
+    end
+  end
+
+  class RingBuffer
+    attr_reader :size
+    attr_reader :head
+
+    def initialize(max = 1024)
+      @max = max
+      @size = 0
+      @head = nil # reading head of ring-shaped tape
+    end
+
+    def <<(point)
+      if @size.zero?
+        @head = point
+        @head.backward = @head
+        @head.forward = @head
+        @size = 1
+      elsif @size >= @max
+        tail = @head.forward
+        new_tail = tail.forward
+        @head.forward = point
+        point.backward = @head
+        new_tail.backward = point
+        point.forward = new_tail
+        @head = point
+      else
+        tail = @head.forward
+        @head.forward = point
+        point.backward = @head
+        tail.backward = point
+        point.forward = tail
+        @head = point
+        @size += 1
+      end
+    end
+
+    def empty?
+      @size.zero?
+    end
+  end
+
+  def initialize(max = 1024)
+    @ring = RingBuffer.new(max)
+    @ring_pointer = nil
+    @buffer = nil
+    @state = State::FRESH
+  end
+
+  def append(string, before_p = false)
+    case @state
+    when State::FRESH, State::YANK
+      @ring << RingPoint.new(string)
+      @state = State::CONTINUED
+    when State::CONTINUED, State::PROCESSED
+      if before_p
+        @ring.head.str.prepend(string)
+      else
+        @ring.head.str.concat(string)
+      end
+      @state = State::CONTINUED
+    end
+  end
+
+  def process
+    case @state
+    when State::FRESH
+      # nothing to do
+    when State::CONTINUED
+      @state = State::PROCESSED
+    when State::PROCESSED
+      @state = State::FRESH
+    when State::YANK
+      # nothing to do
+    end
+  end
+
+  def yank
+    unless @ring.empty?
+      @state = State::YANK
+      @ring_pointer = @ring.head
+      @ring_pointer.str
+    else
+      nil
+    end
+  end
+
+  def yank_pop
+    if @state == State::YANK
+      prev_yank = @ring_pointer.str
+      @ring_pointer = @ring_pointer.backward
+      [@ring_pointer.str, prev_yank]
+    else
+      nil
+    end
+  end
+end