Track.lua

local distance
local defaultBlockUnderneith

-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------
function refuel()
        -- This beast is designed to run on coal
        if turtle.getFuelLevel() <= 20 then
                turtle.select(1)
                return turtle.refuel(1)
        end
        return true
end

-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------
function findBlockOrWait(name)
        local b=0
        local warn=true
        while ( b == 0 ) do
                b = findBlockOrWaitOrFail(name)

                if (b>0) then
                        return b
                end

                if warn then
                        print("Could not find " .. name .. "!  Please insert to continue.")
                        warn = false
                end
                sleep(2)
        end
end

-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------
function findBlockOrWaitOrFail(name)
        local s = 1
        repeat
                local d = turtle.getItemDetail(s)
                if ( d ) then
                        if (d.name == name) then
                                return s
                        end
                end
                        s = s + 1
        until s > 16
        return 0
end
-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------
function placeBlockDownSafely(item)

        local invSlot = findBlockOrWait(item)
        turtle.select(invSlot)

       local placedOk = turtle.placeDown()
        --print("Placed ok : " .. tostring(placedOk) .. " : " .. item)

        if not placedOk then
                -- If we didn't place a block, try to stick a "default" block underneith where we are
                turtle.down()

                local repSlot  = findBlockOrWait(defaultBlockUnderneith.name)
                turtle.select(repSlot)
                turtle.placeDown()

                turtle.up()

                -- Try to place again.
                turtle.select(invSlot)
                placedOk = turtle.placeDown(invSlot)
                --print("Second try Placed ok : " .. tostring(placedOk) .. " : " .. item)
        end
        return placedOk
end
-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------
function placeBlockMoveForward(item,number)

        local a=number
        while a>0 and distance > 1 do
                a = a - 1
                placeBlockDownSafely(item)
                turtle.forward()
                distance = distance - 1
                print ("Distance remaining : " .. distance)
        end
end

-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------
function placeRedstoneTorch()
        turtle.down()
        turtle.digDown()
        turtle.down()
        turtle.digDown()
        placeBlockDownSafely("minecraft:redstone_torch")
        turtle.up()
        placeBlockDownSafely(defaultBlockUnderneith.name)
        turtle.up()
end

-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------
function beginPlacingTrack()

        repeat
                placeRedstoneTorch()
                placeBlockMoveForward("minecraft:golden_rail",1)
                placeBlockMoveForward("minecraft:rail",6)
       turtle.up()
        placeBlockDownSafely(defaultBlockUnderneith.name)
        turtle.up()
end

-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------
function beginPlacingTrack()

        repeat
                placeRedstoneTorch()
                placeBlockMoveForward("minecraft:golden_rail",1)
                placeBlockMoveForward("minecraft:rail",6)
                refuel()
        until distance <= 1

        turtle.down()
end
-- -------- -------- -------- -------- -------- -------- -------- -------- -------- -------- --------

local tArgs = { ... }
if #tArgs ~= 1 then
        print( "Usage: track <distance>" )
        return
end

distance = tonumber( tArgs[1] )

print("Posi's Trackbuilder ... Use CTRL+T to terminate.")

refuel()

-- Find what block we're sitting on, that's our default for any supports/etc/
local success
local d

success,defaultBlockUnderneith = turtle.inspectDown()

if (not success) then
        print "Must be placed on a block to start."
        return
end

-- We need to be one block up in the air to place track
while (success) do
        turtle.up()
        success,d = turtle.inspectDown()
end

beginPlacingTrack()

-- Done