farmWood

function forward()
    while not turtle.forward() do
        turtle.dig()
        turtle.attack()
    end
end
function downward()
    while not turtle.down() do
        turtle.digDown()
        turtle.attackDown()
    end
end
function upward()
    while not turtle.up() do
        turtle.digUp()
        turtle.attackUp()
    end
end
function selectItem(item)
    for i=1, 16 do
        local d = turtle.getItemDetail(i)
        if d ~= nil then
            if d.name == "minecraft:"..item then
                turtle.select(i)
                return true
            end
        end
    end
    return false
end
function isLog()
    local s,d = turtle.inspect()
    if s then
        if d.name == "minecraft:log" then
            return true
        end
    end
    return false
end
function isLogUp()
    local s,d = turtle.inspectUp()
    if s then
        if d.name == "minecraft:log" then
            return true
        end
    end
    return false
end
function farmWood()
    print(isLog())
    if isLog() then
        forward()
        while isLogUp() do
            upward()
        end
        while turtle.down() do end
        turtle.back()
    end
end
-----------------------------
while true do
    selectItem("sapling")
    turtle.place()
    selectItem("dye")
    while not isLog() do
     selectItem("dye")
     turtle.place()
    end
    farmWood()
end