-- -----------------------------------------------------------------------
-- dng
-- ------------------------------------------------------------------------
-- Copyright (c) 2022 Steph Enders <steph@senders.io>
--
-- This software is provided 'as-is', without any express or implied
-- warranty. In no event will the authors be held liable for any damages
-- arising from the use of this software.
--
-- Permission is granted to anyone to use this software for any purpose,
-- including commercial applications, and to alter it and redistribute it
-- freely, subject to the following restrictions:
--
-- 1. The origin of this software must not be misrepresented; you must not
--    claim that you wrote the original software. If you use this software
--    in a product, an acknowledgment in the product documentation would
--    be appreciated but is not required.
--
-- 2. Altered source versions must be plainly marked as such, and must not
--    be misrepresented as being the original software.
--
-- 3. This notice may not be removed or altered from any source
--    distribution.
--
-- -----------------------------------------------------------------------

Queue = {}

function Queue:new()
    o = { first = 1, top = 0, data = {} }
    self.__index = self
    return setmetatable(o, self)
end

function Queue:push(val)
    local top = self.top + 1
    self.top = top
    self.data[top] = val
end

function Queue:pop()
    if self:empty() then
        return nil
    end
    local val = self.data[self.first]
    self.data[self.first] = nil
    self.first = self.first + 1
    return val
end

function Queue:empty()
    return self.top < self.first
end

return Queue