bridge

-- Bridge program. By Mitchfizz05

local tArgs = {...}

local function printUsage()
    print("Usage: bridge <length>")
end

if #tArgs ~= 1 then
    -- Bad number of arguments.
    printUsage()
    return
end

local length = tonumber(tArgs[1])

if length == nil then
    -- Argument provided not a number.
    printUsage()
    return
end

function refuel()
    local refuelled = false
    for i = 15,16 do -- attempt refuel from last two slots
        turtle.select(i)
        if turtle.refuel() then
            refuelled = true -- refuelled
        end
    end

    return refuelled
end

local function selectSlot() -- Select next slot with items in it.
    for i = 1,14 do
        if turtle.getItemCount(i) > 0 then
            turtle.select(i)
            return true
        end
    end

    return false
end

local function forward()
    while not turtle.forward() do
        if turtle.getFuelLevel() == 0 then
            -- No fuel! Request fuel.
            print("Out of fuel! Please provide fuel in slot 15 or 16.")
            while (turtle.getFuelLevel() == 0) do
                refuel() -- attempt refuel
                sleep(0.5)
            end
            print("Thank you")
        else
            -- Probably an obstruction blocking the turtle, attempt to destroy it.
            turtle.attack()
            turtle.dig()
            turtle.digUp()
        end

        sleep(0.5)
    end
end

local function build() -- Build bridge segment.
    if not selectSlot() then
        -- Out of items!
        print("Out of building materials! Please provide materials in any slot!")
        while not selectSlot() do
            sleep(0.5)
        end
        print("Thank you")
    end
    turtle.placeDown()
    forward()
end

local function returnToHome() -- Return turtle to home base.
    turtle.turnRight()
    turtle.turnRight()
    i = length
    while i > 0 do
        forward()
        i = i - 1
    end
end

local function fuelRequirement(length) -- Calculate fuel requirement.
    return (length * 2) + 2
    --[[
        Length times two because we gotta build the length of the bridge then return.
        Plus two for good measure, and the initial forwards action.
    ]]
end

local function blockCount() -- Number of blocks in inventory.
    local blocks = 0
    for i = 1,14 do
        blocks = blocks + turtle.getItemCount(i)
    end
    return blocks
end

-- Preform checks.
if blockCount() < length then
    print("Not enough blocks! Are you sure you want to continue? [Y/N]")
    while true do
        local e,key = os.pullEvent("char")
        if key == "y" then
            break -- break loop and continue
        elseif key == "n" then
            return -- exit program
        end
    end
end

if turtle.getFuelLevel() < fuelRequirement(length) then
    print("Not enough fuel! Are you sure you want to continue? [Y/N]")
    while true do
        local e,key = os.pullEvent("char")
        if key == "y" then
            break -- break loop and continue
        elseif key == "n" then
            return -- exit program
        end
    end
end


-- Run program.
forward() -- go forward once first

local i = length
while i > 0 do
    -- Run iteration
    build()

    i = i - 1
end

print("Completed bridge - returning to homebase.")
returnToHome()

print("Job complete.")