StripMiner

local fuelComparisonSlotNumber = 1
local torchComparisonSlotNumber = 2
local freeSpaceSlotNumber = 3
local returnToBase = false
local reachedLimit = false
local limit = 0

local fwdMoves = 0
local maxMoves = 0

function cls()
    term.clear()
    term.setCursorPos(1,1)
end

function hasTorchesLeft()
    for i = freeSpaceSlotNumber, 16 do
        turtle.select(i)
        if turtle.compareTo(torchComparisonSlotNumber) then return true end
    end
    return false
end

function hasFuelLeft()
    for i = freeSpaceSlotNumber, 16 do
        turtle.select(i)
        if turtle.compareTo(fuelComparisonSlotNumber) then return true end
    end
    return false
end

function inventoryFull()
    local result = true
    for i = freeSpaceSlotNumber, 16 do
        if turtle.getItemCount(i) == 0 then
            result = false
        end
    end
    return result
end

function recalculateMaxMoves()
    maxMoves = turtle.getFuelLevel()
end

function refuel()
    for i = freeSpaceSlotNumber, 16 do
        turtle.select(i)
        if turtle.compareTo(fuelComparisonSlotNumber) then turtle.refuel() end
    end
    recalculateMaxMoves()
    turtle.select(freeSpaceSlotNumber)
end

function placeTorch()
    for i = freeSpaceSlotNumber, 16 do
        turtle.select(i)
        if turtle.compareTo(torchComparisonSlotNumber) then break end
    end
    turtle.placeDown()
    turtle.select(freeSpaceSlotNumber)
end

function deposit()
    for i = freeSpaceSlotNumber, 16 do
        turtle.select(i)
        if (turtle.compareTo(fuelComparisonSlotNumber) == false) and (turtle.compareTo(torchComparisonSlotNumber) == false) then
            turtle.dropDown()
        end
    end

    --Indefinite Calls Below!
    if reachedLimit == false then
        if hasTorchesLeft() and hasFuelLeft() then
            returnToBase = false
            mine()
        end
    end
end

function mine()
    refuel()
    --Refuel turtle.

    turtle.turnLeft()
    --Turn left.

    turtle.up()
        recalculateMaxMoves()
    --Move turtle up one and recalculate fuel levels.

    while returnToBase == false do
        if turtle.detect() then turtle.dig() end
        --If there's a block infront then dig it.

        if turtle.forward() then
            recalculateMaxMoves()
            fwdMoves = fwdMoves + 1
        end
        --If the turtle succeeded in moving forward, then add on 1 to fwdMoves and recalculate
        --Fuel consumption.

        if turtle.detectUp() then turtle.digUp() end
        --If there is a block above the turtle, dig up.

        if turtle.detectDown() then turtle.digDown() end
        --If there is a block below the turtle, dig down.

        if fwdMoves % 5 == 0 then placeTorch() end
        --If the turtle has moved 5 places then place a torch.

        if maxMoves <= fwdMoves + 1 then
            cls()
            print("Ran out of fuel!")
            returnToBase = true
        end
        --If the max amount of moves is less than or equal to the amount
        --the turtle has moved forward, then return back.

        if inventoryFull() then
            cls()
            print("Inventory full!")
            returnToBase = true
        end
        --If the inventory is full, return back.

        if hasTorchesLeft() == false then
            cls()
            print("Ran out of torches!")
            returnToBase = true
        end
        --If the turtle has run out of torches, return back.

        if fwdMoves >= limit then
            cls()
            print("Turtle has reached limit!")
            returnToBase = true
            reachedLimit = true
        end

    end

    turtle.turnRight()
    turtle.turnRight()
    --Rotate the turtle 180 degrees.

    for i = 1, fwdMoves do
        local fwdSuccess = false
        while fwdSuccess == false do
            if turtle.detect() then turtle.dig() end
            fwdSuccess = turtle.forward()
        end
    end
    --Go back to base.

    fwdMoves = 0
    --Reset fwdMoves

    turtle.down()
    --Go back down to ground level.

    turtle.turnLeft()
    --Face forward.

    deposit()
    --Deposit all items except coal and torches.

end

function start()
    print("Strip Mining Program")
    print("(Items will drop here!)")
        os.sleep(2)
        cls()
    print("How far would you like the turtle to go?")
        limit = tonumber(read())
        cls()
    print("Beginning mining process...")
        os.sleep(3)
        cls()
    mine()
end

start()
cls()
print("Program end.")