Daemon

--a stateless iterator for use in for loops.
local function fIter (t, i)
    i = not i and #t or (i - 1)
    if i>0 then
        return i, t[i]
    end
end

--[[a table that stores all running daemons
when we add a new value we first create a coroutine using the fFunc passed]]
local tBackground = setmetatable({},{
    __newindex = function(t, k, v)
        v.cRoutine=coroutine.create(v[1])
        rawset(t, k, v)
    end;
})

--[[starts a new daemon

fFunc = function that runs in background
fError = function ran if fFunc ever ends for any reason

returns identifier for new daemon
]]
function add(fFunc, fError)
    tBackground[#tBackground + 1] = {fFunc, fError=fError}
    return tBackground[#tBackground]
end

--[[removes a running daemon
internally this sets a flag telling the system to remove this daemon next time it loops through

cRoutine = daemon to remove
]]
function rem(cRoutine)
    cRoutine.sFilter="Daemon_internal_remove"
end

--returns identifiers for all running daemons
function getBackground()
    return tBackground
end

--[[internal variable
determines what level of depth we are in the daemon]]
local bPullMeta = false


--[[replacing the native os.pullEventRaw to function]]
function os.pullEventRaw(sEvent)
    local tData

    if bPullMeta then
        return coroutine.yield(sEvent)
    else
        repeat
            bPullMeta = true
            tData = {coroutine.yield()}

            for iIndex, cRoutine in fIter, tBackground do --
                if cRoutine.sFilter==tData[1] or not cRoutine.sFilter then
                    local bOk, sInnerEvent = coroutine.resume(cRoutine.cRoutine, unpack(tData))
                    if bOk then
                        cRoutine.sFilter = sInnerEvent
                    else
                        table.remove(tBackground, iIndex)
                        if cRoutine.fError then
                            cRoutine.fError(sInnerEvent, cRoutine)
                        end
                    end
                elseif cRoutine.sFilter=="Daemon_internal_remove" then
                    table.remove(tBackground, iIndex)
                end
            end
            bPullMeta = false
        until tData[1] == sEvent or not sEvent
        return unpack(tData)
    end
end