stripmine

-- Query unser input

local nTunnels,nDepth,nSpacing,bTorches,nTorchDist,nTorchSlot
while (nTunnels or 0)<1 do
    term.clear()
    term.setCursorPos(1,1)
    write("Number of tunnels: ")
    nTunnels=tonumber(read())
end
while (nDepth or 0)<1 do
    term.clear()
    term.setCursorPos(1,1)
    write("Depth of tunnels: ")
    nDepth=tonumber(read())
end
while (nSpacing or -1)<0 do
    term.clear()
    term.setCursorPos(1,1)
    write("Space between tunnels: ")
    nSpacing=tonumber(read())
end
term.clear()
term.setCursorPos(1,1)
print("Place torches in tunnels? [y | n]")
while true do
    local evts={os.pullEvent("char")}
    if evts[2]=="y" or evts[2]=="Y" then
        bTorches=true
        while (nTorchDist or -1)<0 do
            term.clear()
            term.setCursorPos(1,1)
            write("Distance before a torch is placed: ")
            nTorchDist=tonumber(read())
        end
        while (nTorchSlot or 0)<1 do
            term.clear()
            term.setCursorPos(1,1)
            write("Slot in which torches are kept: ")
            nTorchSlot=tonumber(read())
        end
        break
        elseif evts[2]=="n" or evts[2]=="N" then
            bTorches=false
            break
        end
end

-- Viability calc

local fuelReq=nTunnels*(nDepth*2+nSpacing+1)
local currFuel=turtle.getFuelLevel()
if currFuel<fuelReq then
    term.clear()
    term.setCursorPos(1,1)
    print("Your turtle has insufficient fuel to complete the task. Check inventory for fuel? [y | n]")
    repeat
        local evts={os.pullEvent("char")}
        if evts[2]=="n" or evts[2]=="N" then
            error("cancelled due to lack of fuel")
        end
    until evts[2]=="y" or evts[2]=="Y"
    local tFuels={}
    for nSlot=1,16 do
        turtle.select(nSlot)
        if turtle.refuel(1) then
            tFuels[nSlot]=turtle.getFuelLevel()-currFuel
            currFuel=turtle.getFuelLevel()
        end
    end
    local theoreticalFuelGain=0
    for k,v in pairs(tFuels) do
        theoreticalFuelGain=theoreticalFuelGain+v*turtle.getItemCount(k)
    end
    if currFuel+theoreticalFuelGain>=fuelReq then
        for k,v in pairs(tFuels) do
            turtle.select(k)
            while turtle.getItemCount(k)>0 do
                if turtle.getFuelLevel()>=fuelReq then
                    break
                else
                    turtle.refuel(1)
                end
            end
            if turtle.getFuelLevel()>=fuelReq then
                break
            end
        end
    else
        error("not enough fuel in inventory")
    end
end

-- Exec

turtle.select(nTorchSlot)
for nTunnel=1,nTunnels do
    for nDir=1,2 do
        for nDep=1,nDepth do
            if turtle.detectUp() then turtle.digUp() end
            if turtle.detectDown() and not turtle.compareDown() then turtle.digDown() end
            if bTorches and nDir<2 and (nDep%(nTorchDist+1)==0 or nDep==1) then turtle.placeDown() end
            while not turtle.forward() do turtle.dig() end
        end
        if nDir==1 then
            turtle.turnRight() turtle.turnRight()
        else
            turtle.turnLeft()
        end
    end
    if nTunnel<nTunnels then
        for nSpaced=1,nSpacing+1 do
            while not turtle.forward() do turtle.dig() end
            if turtle.detectUp() then turtle.digUp() end
            if turtle.detectDown() and not turtle.compareDown() then turtle.digDown() end
        end
    else
        for nTravelled=1,(nTunnels-1)*(nSpacing+1) do
            while not turtle.back() do end
        end
    end
    turtle.turnLeft()
end