Redtracker

local modes = {
    ["regular"] = setmetatable({}, { __call = function( self, side ) return redstone.getInput(side) end, default_value = false }),
    ["bundled"] = setmetatable({}, { __call = function( self, side ) return redstone.getBundledInput(side) end, default_value = 0 })
}

local function actualUpdate( _table )
    for side, sideTable in pairs( _table ) do
        local input = _table(side)
        if sideTable.state ~= input then
            sideTable.state = input
            for _, func in pairs( sideTable.callbacks ) do
                pcall(func, side, sideTable.state)
            end
        end
    end
end

function update()
    for _, mode in pairs( modes ) do
        actualUpdate( mode )
    end
end

function waitRedstoneUpdate()
    os.pullEvent("redstone")
    update()
end

function addCallback(mode, func, side)
    -- Compat check
    if type(mode) == "function" then
        return addCallback("regular", func, side)
    end

    if type(func) ~= "function" then
        error("Function expected, got " .. type(func), 3)
    end
    if side then
        if type(side) ~= "string" then
            error("String expected, got " .. type(side), 4 )
        elseif modes[mode][side] == nil then
            error("Expected valid side", 4)
        end
        modes[mode][side].callbacks[#modes[mode][side].callbacks + 1] = func
        return
    end

    for _, sideTable in pairs( modes[mode] ) do
        sideTable.callbacks[#sideTable.callbacks + 1] = func
    end
end

function addRegularCallback(func, side)
    addCallback("regular", func, side)
end

function addBundledCallback(func, side)
    addCallback("bundled", func, side)
end

-- This is code to initialize the tables (always ran)
do
    local function initialize( _table )
        local mt = getmetatable( _table )
        for _, side in pairs( redstone.getSides() ) do
            _table[side] = {
                ["state"] = mt.default_value,
                ["callbacks"] = {}
            }
        end
    end
    if redstone.getAnalogInput then
        modes["analog"] = setmetatable({}, { __call = function( self, side ) return redstone.getAnalogInput(side) end, default_value = 0 })
        function addAnalogCallback(func, side)
            addCallback("analog", func, side)
        end
    end
    for _, mode in pairs( modes ) do
        initialize( mode )
        actualUpdate( mode )
    end
end