-- config
local WALL_WIDTH = 8
local WALL_HEIGHT = 8

-- main program
function createTimer(time)
    return os.startTimer(time)
end

local harvestTimer = createTimer(60)

function dropInventory() 
    for i=1,16 do
    	turtle.select(i)
        turtle.dropDown()
    end
   	turtle.select(1)
end

function harvest()
    term.clear()
    term.setCursorPos(1,1)
    term.write("Start harvesting...")
    for i=0,WALL_WIDTH do
        for j=0,WALL_HEIGHT do
			turtle.dig()
        	turtle.up()
        end
        for j=0,WALL_HEIGHT do
        	turtle.down()
        end
        turtle.turnRight()
        turtle.forward()
        turtle.turnLeft()
    end
    turtle.turnLeft()
    for i=0,WALL_WIDTH do
        turtle.forward()
    end
    turtle.turnRight()
    term.write("Harvesting complete.")
end

while true do
    local event, timerId = os.pullEvent()
    if event == "timer" and timerId == harvestTimer then
        harvest()
        dropInventory()
        harvestTimer = createTimer(60)
    end
end