local Observable = require "rx.observable"
local util = require "rx.util"

--- Returns an Observable that omits a specified number of values from the end of the original
-- Observable.
-- @arg {number} count - The number of items to omit from the end.
-- @returns {Observable}
function Observable:skipLast(count)
    if not count or type(count) ~= "number" then
        error("Expected a number")
    end

    local buffer = {}
    return Observable.create(function(observer)
        local function emit()
            if #buffer > count and buffer[1] then
                local values = table.remove(buffer, 1)
                observer:onNext(util.unpack(values))
            end
        end

        local function onNext(...)
            emit()
            table.insert(buffer, util.pack(...))
        end

        local function onError(message)
            return observer:onError(message)
        end

        local function onCompleted()
            emit()
            return observer:onCompleted()
        end

        return self:subscribe(onNext, onError, onCompleted)
    end)
end