vein

function refuel()
    if turtle.getFuelLevel() < 10 then
        turtle.select(1)
        turtle.refuel(1)
    end
end

retrace = {}

while true do
    refuel()

    a, b = turtle.inspect()
    if a and b.name == "minecraft:coal_ore" then
        turtle.dig()
        turtle.forward()
        table.insert(retrace, "back")
    else
        a, b = turtle.inspectUp()
        if a and b.name == "minecraft:coal_ore" then
            turtle.digUp()
            turtle.up()
            table.insert(retrace, "down")
        else
            a, b = turtle.inspectDown()
            if a and b.name == "minecraft:coal_ore" then
                turtle.digDown()
                turtle.down()
                table.insert(retrace, "up")
            else
                turtle.turnLeft()

                a, b = turtle.inspect()
                if a and b.name == "minecraft:coal_ore" then
                    turtle.dig()
                    turtle.forward()
                    table.insert(retrace, "right")
                    table.insert(retrace, "back")
                else
                    turtle.turnRight()
                    turtle.turnRight()

                    a, b = turtle.inspect()
                    if a and b.name == "minecraft:coal_ore" then
                        turtle.dig()
                        turtle.forward()
                        table.insert(retrace, "left")
                        table.insert(retrace, "back")
                    else
                        turtle.turnRight()
                        a, b = turtle.inspect()
                        if a and b.name == "minecraft:coal_ore" then
                            turtle.dig()
                            turtle.forward()
                            table.insert(retrace, "right")
                            table.insert(retrace, "back")
                        else
                            turtle.turnRight()
                            break
                        end
                    end
                end
            end
        end
    end
end

for i, command in ipairs(retrace) do
    if command == "forward" then
        turtle.forward()
    end
    if command == "back" then
        turtle.back()
    end
    if command == "right" then
        turtle.turnRight()
    end
    if command == "left" then
        turtle.turnLeft()
    end
    if command == "up" then
        turtle.up()
    end
    if command == "forward" then
        turtle.down()
    end
end