control

local input = peripheral.wrap("front")
or error("Unable to wrap input chest!",0)
local output = peripheral.wrap("bottom")
or error("Unable to wrap output chest!",0)

local signal = "back"
-- side of the redstone torch

local inputslot = 1
local fuelslot = 2
local outputslot = 3
-- slots inside furnace inv

local fuel = {
  -- {id=number,dmg=number,burn=number}
  -- burn = burntime, how many items
  -- the fuel can burn.
  -- ex: coal/charcoal burns 8
  -- and wood burns 1.5
  {id=263,dmg=0,burn=8},--coal
  {id=263,dmg=1,burn=8},--charcoal
  --{id=5,dmg=-1,burn=1.5},--planks
  --{id=17,dmg=-1,burn=1.5},--wood
  --{id=6,dmg=-1,burn=.5},--sapling
  --{id=280,dmg=0,burn=.5},--stick
}

local furnaceToOutput = "west"
local inputToFurnace = "down"
local inputSlot = 1
local outputSlot = 3

-- returns statement,fuel
-- statement = boolean
-- fuel = table
local function isFuel(item)
  for _,fuel in pairs(fuel) do
    if item.id == fuel.id
    and (item.dmg == fuel.dmg
    or fuel.dmg == -1) then
      return true,fuel
    end
  end
  return false
end

-- returns slot,fuel,item
local function findFuel()
  local items = input.getAllStacks()
  for slot,item in pairs(items) do
    local state,fuel = isFuel(item)
    if state then
      return slot,fuel
    end
  end
end

-- returns slot,item
local function findItem()
  local slot,fuel = findFuel()
  if slot and fuel then
    local items = input.getAllStacks()
    for slot,item in pairs(items) do
      local state = isFuel(item)
      if not state then
        if item.qty >= fuel.burn then
          return slot,item
        end
      end
    end
  end
end

local function emptyFurnace()
  output.pullItem("east",outputslot,64)
end

local function cook()
  -- if furnace is empty
  if rs.getInput(signal) == false then
    -- get fuel and item
    local fuelslot,fuel,fueli = findFuel()
    local itemslot,item = findItem()

    -- no fuel/item found: cancel out
    if not fuel then return end
    if not item then return end

    -- # items to move
    local fuelmove = math.floor(item.qty/fuel.burn)
    local itemmove = item.qty-(item.qty%fuel.burn)

    -- move items
    input.pushItemIntoSlot("down",fuelslot,fuelmove,fuelslot)
    input.pushItemIntoSlot("down",itemslot,itemmove,inputslot)
  end
end

cook()