autosaving tables

local function serializeImpl( t, tTracking, sIndent )
    local sType = type(t)
    if sType == "table" then
        t = getmetatable( t ).origin
        if tTracking[t] ~= nil then
            error( "Cannot serialize table with recursive entries", 0 )
        end
        tTracking[t] = true

        if next(t) == nil then
            -- Empty tables are simple
            return "{}"
        else
            -- Other tables take more work
            local sResult = "{\n"
            local sSubIndent = sIndent .. "  "
            local tSeen = {}
            for k,v in ipairs(t) do
                tSeen[k] = true
                sResult = sResult .. sSubIndent .. serializeImpl( v, tTracking, sSubIndent ) .. ",\n"
            end
            for k,v in pairs(t) do
                if not tSeen[k] then
                    local sEntry
                    if type(k) == "string" and string.match( k, "^[%a_][%a%d_]*$" ) then
                        sEntry = k .. " = " .. serializeImpl( v, tTracking, sSubIndent ) .. ",\n"
                    else
                        sEntry = "[ " .. serializeImpl( k, tTracking, sSubIndent ) .. " ] = " .. serializeImpl( v, tTracking, sSubIndent ) .. ",\n"
                    end
                    sResult = sResult .. sSubIndent .. sEntry
                end
            end
            sResult = sResult .. sIndent .. "}"
            return sResult
        end

    elseif sType == "string" then
        return string.format( "%q", t )

    elseif sType == "number" or sType == "boolean" or sType == "nil" then
        return tostring(t)

    else
        error( "Cannot serialize type "..sType, 0 )

    end
end

local function serialize( t )
    local tTracking = {}
    return serializeImpl( t, tTracking, "" )
end

local function makeInternalSaving( tbl, save )
    for k, v in pairs( tbl ) do
        if type( v ) == "table" then
            tbl[ k ] = makeInternalSaving( v )
        end
    end
    return setmetatable( {}, {
        __index = tbl,
        __newindex = function( self, key, value )
            if type( value ) == "table" then
                tbl[ key ] = makeInternalSaving( value, save )
            else
                tbl[ key ] = value
            end
            save()
        end,
        __len = function() return #tbl end,
        __metatable = { origin = tbl },
        } )
end

function makeAutoSaving( tbl, file )
    for k, v in pairs( tbl ) do
        if type( v ) == "table" then
            tbl[ k ] = makeInternalSaving( v )
        end
    end
    local savable = {}
    local function save()
        local f = fs.open( file, "w" )
        f.write( serialize( savable ) )
        f.close()
    end
    return setmetatable( savable, {
        __index = tbl,
        __newindex = function( self, key, value )
            if type( value ) == "table" then
                tbl[ key ] = makeInternalSaving( value, save )
            else
                tbl[ key ] = value
            end
            save()
        end,
        __len = function( ... ) return #tbl end,
        __metatable = { origin = tbl },
        __call = function() return tbl end,
    } )
end