--[

--]
local args = { ... }
local top = false
local length = 40
if args[1] ~= nil then
    if args[1] == 'top' then
        top = true
    elseif args[1] == 'bottom' then
        top = false
    else
        print('Wrong argument ' .. args[1])
        print('Usage: bridge [top/bottom]')
        do return end
    end
else
    print('Usage: bridge [top/bottom]')
    print('First 8 slots must be filled with building blocks')
    do return end
end

if args[2] ~= nil then
    arg2 = tonumber(args[2])
    if arg2 ~= nil then
        length = arg2
    end
end


local placeT =
{
    ['up'] = turtle.placeUp,
    ['front'] = turtle.place,
    ['down'] = turtle.placeDown,
}

local digT =
{
    ['up'] = turtle.digUp,
    ['front'] = turtle.dig,
    ['down'] = turtle.digDown,
}

local cur_slot = 1

function ensure_blocks()
    if turtle.getItemCount(cur_slot) < 1 then
        for slot_num = 1, 8, 1 do
            if turtle.getItemCount(slot_num) > 0 then
                turtle.select(slot_num)
                cur_slot = slot_num
                return
            end
        end
        print('No blocks for building!')
        do return end
    end
end


function replace_block(direction)
    ensure_blocks()
    digT[direction]()
    placeT[direction]()
end

function build_one()
    if top then
        replace_block('up')
    else
        replace_block('down')
    end
    turtle.turnLeft()
    replace_block('front')
    turtle.turnRight()
    turtle.turnRight()
    replace_block('front')
    turtle.turnLeft()
end

function forward()
    if turtle.getFuelLevel() < 1 then
        print('Not enough fuel!')
        do return end
    end
    ensure_blocks()
    turtle.dig()
    turtle.forward()
end


function main()
    print('Start building with top=' .. tostring(top) .. ' and length=' .. tostring(length))
    turtle.select(cur_slot)
    for slot_num = 1, length, 1 do
        forward()
        build_one()
    end
end

main()