bridgePos = 0

function selectBlock(block)
    currentSelectedBlock = turtle.getItemDetail()
    if currentSelectedBlock ~= block then
        for i = 1, 16 do
            iBlockDetail = turtle.getItemDetail(i)
            if iBlockDetail ~= nil then
                if iBlockDetail.name == block then
                    turtle.select(i)
                    break
                end
            end
            if i == 16 then
                error("oh noes " .. block .. " ran out")
            end
        end
    end
end

function forwardDig()
    blockInFront, blockInspect = turtle.inspect()
    if blockInFront then
        turtle.dig()
    end
    turtle.forward()
end

function downDig()
    blockDown, blockInspect = turtle.inspectDown()
    if blockDown then
        turtle.digDown()
    end
    turtle.down()
end

function upDig()
    blockUp, blockInspect = turtle.inspectUp()
    if blockUp then
        turtle.digUp()
    end
    turtle.up()
end

function placePillar()
    for i = 1, 2 do
        turtle.down()
    end
    turtle.forward()
    selectBlock("minecraft:stone_brick_stairs")
    turtle.placeUp()
    for i = 1, 2 do
        turtle.forward()
    end
    for i = 1, 2 do
        turtle.turnRight()
    end
    turtle.placeUp()
    turtle.forward()
    selectBlock("minecraft:stonebrick")
    turtle.placeUp()
    repeat
        blockBelow, blockInfo = turtle.inspectDown()
        if blockBelow ~= nil then
            if blockInfo.name ~= "minecraft:water" then
                turtle.down()
                turtle.placeUp()
            end
        end
    until blockBelow ~= nil and blockInfo.name ~= "minecraft:water"
    digForward()
    for i = 1, 2 do
        turtle.turnRight()
    end
    turtle.place()
    repeat
        blockAbove = turtle.inspectUp()
        if blockAbove == nil then
            turtle.up()
    until blockAbove ~= nil
    turtle.back()
    for i = 1, 2 do
        turtle.up()
    end
end

function placePillars()
    placePillar()
    turtle.turnRight()
    for i = 1, 4 do
        turtle.forward()
    end
    turtle.turnLeft()
    placePillar()
    turtle.turnLeft()
    for i = 1, 4 do
        turtle.forward()
    end
    turtle.turnRight()
end

function placeTorch()
    turtle.up()
    turtle.turnRight()
    for i = 1, 3 do
        turtle.forward()
    end
    turtle.turnRight()
    selectBlock("minecraft:torch")
    turtle.place()
    turtle.turnRight()
    for i = 1, 3 do
        turtle.forward()
    end
    turtle.turnRight()
    turtle.down()
end

function placeBridgeChunk()
    for i = 1, 2 do
        turtle.turnRight()
    end
    turtle.up()
    selectBlock("minecraft:stonebrick")
    if bridgePos % 2 == 0 then
        turtle.up()
        turtle.place()
        turtle.down()
    end
    turtle.place()
    turtle.down()
    turtle.turnLeft()
    for i = 1, 7 do
        turtle.turnRight()
        turtle.place()
        turtle.turnLeft()
        turtle.forward()
    end
    turtle.down()
    for i = 1, 2 do
        turtle.turnRight()
    end
    turtle.forward()
    for i = 1, 2 do
        turtle.up()
    end
    turtle.turnLeft()
    turtle.place()
    if bridgePos % 2 == 0 then
        turtle.up()
        turtle.place()
        turtle.down()
    end
    for i = 1, 2 do
        turtle.down()
    end
    turtle.turnRight()
    turtle.forward()
    for i = 1, 4 do
        turtle.turnLeft()
        turtle.place()
        turtle.turnRight()
        turtle.forward()
    end
    turtle.place()
    turtle.turnLeft()
    turtle.down()
    turtle.place()
    turtle.turnLeft()
    for i = 1, 4 do
        turtle.forward()
    end
    turtle.turnRight()
    turtle.place()
    if bridgePos % 5 == 0 then
        placePillars()
    end
    turtle.turnRight()
    for i = 1, 2 do
        turtle.up()
    end
    for i = 1, 5 do
        turtle.forward()
    end
    turtle.turnRight()
end

function clearSpace()
    turtle.turnRight()
    for i = 1, 3 do
        upDig()
    end
    for i = 1, 6 do
        for j = 1, 6 do
            forwardDig()
        end
        for j = 1, 2 do
            turtle.turnRight()
        end
        downDig()
    end
    for i = 1, 3 do
        turtle.up()
    end
    turtle.turnLeft()
end

function buildChunkOfBridge()
    forwardDig()
    clearSpace()
    placeBridgeChunk()
    if (bridgePos + 3) % 8 == 0 then
        placeTorch()
    end
    bridgePos = bridgePos + 1
end

function checkFuel()
    fuelLevel = turtle.getFuelLevel()
    if fuelLevel < 50 then
        for i = 1, 16 do
            turtle.select(i)
            turtle.refuel(64)
        end
    end
end

function mainLoop()
   while true do
       checkFuel()
       buildChunkOfBridge()
   end
end

mainLoop()