fill

--[[{
  size = {X=x, Y=y},
  forward = function,
  left = function,
  right = function,
  callback = function,
}]]

-- Helper function for looping over a range
function range(limit)
    local function seq(state, x)
        if (x >= limit) then
            return nil
        else
            return x + 1
        end
    end
    return seq, nil, 0
end
-- The magic function
function moveSpiral(w)
    local X,Y = w.size.x,w.size.y

    -- Prepare for first row
    w.forward()
    w.right()

    -- Loop over each row
    for y in range(Y) do
        -- Loop over each column
        for x in range(X) do
            -- Do the callback for each point
            w.callback()

            -- Unless we have completed the row
            if x ~= X then
                -- Move forward
                w.forward()
            end
        end

        -- Unless we have completed all rows
        if y ~= Y then
            -- Move to next row
            if y%2 == 1 then
                w.left()
                w.forward()
                w.left()
            else
                w.right()
                w.forward()
                w.right()
            end
        end
    end

    -- Move back to starting point
    if Y%2 == 1 then
        w.left()
        w.left()
        for x in range(X-1) do w.forward() end
    end
    w.left()
    for y in range(Y) do w.forward() end
    w.right()
    w.right()
end

function forward()
    while not turtle.forward() do
        sleep(0.5)
        turtle.dig()
    end
end

-- Fill hole
function fill()
    -- How far down we have gone
    local depth = 0

    -- Make sure we have an empty slot for picking up junk
    -- This is an attempt to not mess up the convention by
    -- the blocks we dig that are picked up. Not 100%
    -- reliable still...
    turtle.select(9)
    turtle.drop()

    -- Move down to first block we can find
    while not turtle.detectDown() and turtle.down() do
        depth = depth + 1
    end

    -- Remove top block
    turtle.digDown()
    turtle.down()
    depth = depth + 1

    -- Dig down to first non-dirt block we can find
    turtle.select(1)
    while (turtle.compareDown() and turtle.digDown() and turtle.down()) or turtle.down() do
        depth = depth + 1
    end

    -- Start filling
    while depth > 0 do
        -- Until we move up 1 successfully
        while not turtle.up() do
            -- Try dig upwards and wait a bit
            turtle.digUp()
            sleep(0.5)
        end
        depth = depth - 1

        -- As long as we have something to place
        if selectSource(depth) > 0 then
            -- Place it below us
            turtle.placeDown()
        end
    end
end

-- Returns the count of an appropriate slot
function selectSource(depth)
    -- If we're at the top
    if depth==1 then
        -- Select slot 1 and return its count
        turtle.select(1)
        return turtle.getItemCount(1)
    -- Otherwise
    else
        -- Move through the rest of the slots
        for i=2,9 do
            turtle.select(i)
            local count = turtle.getItemCount(i)
            -- Until we find one with something in it
            if count > 0 then
                return count
            end
        end
    end
    return 0
end


local arg = {...}
if #arg == 2 then
    moveSpiral({
        size = {
            x = tonumber(arg[1]),
            y = tonumber(arg[2]),
            },
        forward = forward,
        left = turtle.turnLeft,
        right = turtle.turnRight,
        callback = fill,
    })
else
    print("Usage: fill x y")
end