local record Ringbuffer<T>
    {T}
    push: function(self: Ringbuffer<T>, el: T): boolean
    pop: function(self: Ringbuffer<T>): T | nil
    is_empty: function(self: Ringbuffer<T>): boolean

    head: integer
    n: integer
    size: integer
end

local impl: table = {}

impl.push = function<T>(self: Ringbuffer<T>, el: T): boolean
    if self.n == self.size then return false end
    -- items are at head + 0, head + 1, ..., head + (n-1)
    local tail = (self.head + self.n) % self.size
    self[1 + tail] = el
    self.n = self.n + 1
    return true
end

impl.pop = function<T>(self: Ringbuffer<T>): T | nil
    if self.n == 0 then return nil end
    local res = self[1 + self.head]
    self.head = (self.head + 1) % self.size
    self.n = self.n - 1
    return res
end

impl.is_empty = function<T>(self: Ringbuffer<T>): boolean
    return self.n == 0
end

local function new<T>(size: integer): Ringbuffer<T>
    return setmetatable({ head = 0, n = 0, size = size }, { __index = impl })
end

return {
    new = new,
    Ringbuffer = Ringbuffer
}