deque.lua

-- Deque implementation by Pierre 'catwell' Chapuis

--[[
Source: https://github.com/catwell/cw-lua/tree/master/deque

Copyright (C) 2013-2015 by Pierre Chapuis

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
]]--

local push_right = function(self, x)
  assert(x ~= nil)
  self.tail = self.tail + 1
  self[self.tail] = x
end

local push_left = function(self, x)
  assert(x ~= nil)
  self[self.head] = x
  self.head = self.head - 1
end

local peek_right = function(self)
  return self[self.tail]
end

local peek_left = function(self)
  return self[self.head+1]
end

local pop_right = function(self)
  if self:is_empty() then return nil end
  local r = self[self.tail]
  self[self.tail] = nil
  self.tail = self.tail - 1
  return r
end

local pop_left = function(self)
  if self:is_empty() then return nil end
  local r = self[self.head+1]
  self.head = self.head + 1
  local r = self[self.head]
  self[self.head] = nil
  return r
end

local rotate_right = function(self, n)
  n = n or 1
  if self:is_empty() then return nil end
  for i=1,n do self:push_left(self:pop_right()) end
end

local rotate_left = function(self, n)
  n = n or 1
  if self:is_empty() then return nil end
  for i=1,n do self:push_right(self:pop_left()) end
end

local _remove_at_internal = function(self, idx)
  for i=idx, self.tail do self[i] = self[i+1] end
  self.tail = self.tail - 1
end

local remove_right = function(self, x)
  for i=self.tail,self.head+1,-1 do
    if self[i] == x then
      _remove_at_internal(self, i)
      return true
    end
  end
  return false
end

local remove_left = function(self, x)
  for i=self.head+1,self.tail do
    if self[i] == x then
      _remove_at_internal(self, i)
      return true
    end
  end
  return false
end

local length = function(self)
  return self.tail - self.head
end

local is_empty = function(self)
  return self:length() == 0
end

local contents = function(self)
  local r = {}
  for i=self.head+1,self.tail do
    r[i-self.head] = self[i]
  end
  return r
end

local iter_right = function(self)
  local i = self.tail+1
  return function()
    if i > self.head+1 then
      i = i-1
      return self[i]
    end
  end
end

local iter_left = function(self)
  local i = self.head
  return function()
    if i < self.tail then
      i = i+1
      return self[i]
    end
  end
end

local methods = {
  push_right = push_right,
  push_left = push_left,
  peek_right = peek_right,
  peek_left = peek_left,
  pop_right = pop_right,
  pop_left = pop_left,
  rotate_right = rotate_right,
  rotate_left = rotate_left,
  remove_right = remove_right,
  remove_left = remove_left,
  iter_right = iter_right,
  iter_left = iter_left,
  length = length,
  is_empty = is_empty,
  contents = contents,
}

local new = function()
  local r = {head = 0, tail = 0}
  return setmetatable(r, {__index = methods})
end

return {
  new = new,
}