Lumberjack

FARMX = 5
FARMY = 3
TREE_DISTANCE_X = 3
TREE_DISTANCE_Y = 3
ITER_DELAY = 60

m=peripheral.find('magnet')

function checkblock(r,d)
    t = d.tags
    if type(t)~='table' then return false end
    if t["minecraft:logs"] then return true else return false end
end

function check_front()
    return checkblock(turtle.inspect())
end

function check_up()
    return checkblock(turtle.inspectUp())
end

function check_down()
    return checkblock(turtle.inspectDown())
end



function dfs_mine()
    for i=1,4 do
        if check_front() then
            turtle.dig()
            turtle.forward()
            dfs_mine()
            turtle.back()
        end
        turtle.turnRight()
        if check_up() then
            turtle.digUp()
            turtle.up()
            dfs_mine()
            turtle.down()
        end
        if check_down() then
            turtle.digDown()
            turtle.down()
            dfs_mine()
            turtle.up()
        end
    end
end

function straight_mine()
    i=0
    while check_up() do
        turtle.digUp()
        turtle.up()
        i=i+1
    end
    while i>0 do
        turtle.down()
        i=i-1
    end
end

function check_refuel()
    turtle.select(1)
    while turtle.getFuelLevel()<160 do
        turtle.refuel(1)
    end
end

mine_tree_func = straight_mine --or dfs_mine

function handle_farm(x,y)
    turtle.forward()
    for a=1,x do
        for b=1,y do
            for i=1,TREE_DISTANCE_X do
                turtle.forward()
            end
            turtle.turnLeft()
            if check_front() then
                check_refuel()
                turtle.dig()
                turtle.forward()
                mine_tree_func()
                turtle.back()
                check_refuel()
                os.sleep(5)
                m.magnetize(4)
            end
            turtle.select(2)
            turtle.place()
            turtle.select(1)
            turtle.turnRight()
            check_refuel()
        end
        for b=1,y*TREE_DISTANCE_X do turtle.back() end
        turtle.turnRight()
        for i=1,TREE_DISTANCE_Y do
            turtle.forward()
        end
        turtle.turnLeft()
        check_refuel()
    end
    turtle.turnLeft()
    for a=1,TREE_DISTANCE_Y*x do
        turtle.forward()
        check_refuel()
    end
    turtle.turnRight()
    turtle.back()
    turtle.turnLeft()
    turtle.turnLeft()
    check_refuel()
    for i=3,16 do
        turtle.select(i)
        turtle.drop()
    end
    turtle.select(1)
    turtle.turnLeft()
    turtle.turnLeft()
end

it=1
while true do
    print("Iteration #"..tostring(it))
    handle_farm(FARMX,FARMY)
    print("Done!")
    os.sleep(ITER_DELAY)
    it=it+1
end