MiningTurtle = {
    position = {
        x = 0,
        y = 0,
        z = 0
    },
    direction = 0
}

-- Check if the Turtle needs to be refueled ( <= refuelLevel )
-- if yes, try to refuel it taking the contents of the inventory
-- if this is not possible or not enough, go back to base
function MiningTurtle:requiredRefuel( refuelLevel, requiredFuelLevel )

    refuelLevel         = refuelLevel or 25
    requiredFuelLevel   = requiredFuelLevel or 500

    -- should we refuel?
    if turtle.getFuelLevel() <= refuelLevel then

        -- iterate through our inventory
        for slot = 1,16 do

            -- select slot
            turtle.select(slot)

            -- refuel from active slot...
            if turtle.refuel( turtle.getItemCount( slot ) ) then

            end

            -- ...and check again
            if turtle.getFuelLevel() >= requiredFuelLevel then
                return true
            end

        end

        -- check if we did not refueled enough alreay
        if not turtle.getFuelLevel() >= requiredFuelLevel then
            -- if yes, go back to base

            MiningTurtle:toBase()
            -- refuel: to be implemented!!!!
        end
    end

    return false
end

-- Go back to the base of the MiningTurtle
function MiningTurtle:toBase( )

end

-- Go to ground
function MiningTurtle:toGround( )

    while not turtle.detectDown() do
        MiningTurtle:down()
    end

end

-- forward
function MiningTurtle:forward()
    local ret

    ret = turtle.forward()

    if ret then


        if self.direction == 0 then

            self.position.x = self.position.x + 1

        elseif self.direction == 90 then

            self.position.y = self.position.y + 1

        elseif self.direction == 180 then

            self.position.x = self.position.x - 1

        elseif self.direction == 270 then

            self.position.y = self.position.y - 1

        end

    end

    return ret
end

-- back
function MiningTurtle:back()
    local ret

    ret = turtle.back()

    if ret then

        if self.direction == 0 then

            self.position.x = self.position.x - 1

        elseif self.direction == 90 then

            self.position.y = self.position.y - 1

        elseif self.direction == 180 then

            self.position.x = self.position.x + 1

        elseif self.direction == 270 then

            self.position.y = self.position.y + 1

        end

    end

    return ret
end

-- up
function MiningTurtle:up()
    local ret

    ret = turtle.up()

    if ret then
        self.position.z = self.position.z + 1
    end

    return ret
end

-- down
function MiningTurtle:down()
    local ret

    ret = turtle.down()

    if ret then
        self.position.z = self.position.z - 1
    end

    return ret
end

-- turn Left
function MiningTurtle:turnLeft()
    local ret

    ret = turtle.turnLeft()

    if ret then
        self.direction = self.direction + 90

        while self.direction >= 360 do
            self.direction = self.direction - 360
        end
    end

    return ret
end

-- turn Right
function MiningTurtle:turnRight()
    local ret

    ret = turtle.turnRight()

    if ret then
        self.direction = self.direction - 90

        while self.direction < 0 do
            self.direction = self.direction + 360
        end
    end

    return ret
end

-- Save forward
function MiningTurtle:saveForward()

    while not MiningTurtle:forward() do
        turtle.dig()
    end
end

-- Save up
function MiningTurtle:saveUp()

    while not MiningTurtle:up() do
        turtle.digUp()
    end
end

-- Save down
function MiningTurtle:saveDown()

    while not MiningTurtle:down() do
        turtle.digDown()
    end
end

-- 180 degree turn
function MiningTurtle:turn()

    MiningTurtle:turnRight()
    MiningTurtle:turnRight()
end

-- Make a tunnel
function MiningTurtle:tunnel( length, height, width, ret )

    height = height or 2
    width  = width  or 1
    ret    = ret or false

    -- Length loop

    for i = 1,length do

        MiningTurtle:saveForward()

        if i % 2 == 0 then
            -- even

            MiningTurtle:turnLeft()

            for x = 0,width do

                for y = 0,height do

                    if x % 2 == 0 then
                        MiningTurtle:saveUp()
                    else
                        MiningTurtle:saveDown()
                    end

                end

                if x < width then
                    MiningTurtle:saveForward()
                end
            end

            MiningTurtle:turnRight()

        else
            -- odd

            MiningTurtle:turnRight()

            for x = 0,width do

                for y = 0,height do

                    if x % 2 == 0 then
                        MiningTurtle:saveUp()
                    else
                        MiningTurtle:saveDown()
                    end

                end

                if x < width then
                    MiningTurtle:saveForward()
                end
            end

            MiningTurtle:turnLeft()

        end

    end

    if ret then

        MiningTurtle:turn()
    end

end


--
function MiningTurtle:matrix( rows, cols )



end


-- main

while not MiningTurtle:requiredRefuel() do
    print("Waiting for MiningTurtle to have enough fuel")
end

MiningTurtle:toGround()
MiningTurtle:tunnel(10)