Smelter

local coal = "minecraft:chest_269"
local input = "minecraft:chest_270"
local output = "minecraft:chest_271"
local self = "turtle_157"
local furnaces = {}
local periphs = {}

for k, v in pairs(peripheral.getNames()) do
  periphs[v] = peripheral.wrap(v)
end

for k,v in pairs(periphs) do
    if k:find("furnace") then
        furnaces[#furnaces + 1] = k
    end
end

print("loading coal")
for k,v in pairs(periphs[coal].list()) do
    periphs[coal].pushItems(self, k, v.count, 1)
    for i = 1, v.count do
        periphs[furnaces[math.random(1, #furnaces)]].pullItems(self, 1, 1, 2)
    end
 sleep(0.1)
 periphs[coal].pullItems(self, 1, 64)
end

print("load input")
for k,v in pairs(periphs[input].list()) do
    local times = math.floor(v.count / 7)
    if times > 0 then
        periphs[input].pushItems(self, k, times * 7, 1)
        for i = 1, times do
            periphs[furnaces[math.random(1, #furnaces)]].pullItems(self, 1, 7, 1)
            sleep(0.1)
        end
        periphs[input].pullItems(self, 1, 64)
    end
end

print("collecting output")
for i = 1, #furnaces do
    local inputper = periphs[furnaces[i]]
    local outputper = periphs[output]
    inputper.pushItems(self, 3, 64, 1)
    outputper.pullItems(self, 1, 64)
    sleep(0.1)
end