print("Excavator turtle reporting for duty!")
print("How many 6x6 chunks should I excavate?")
local max_excavations =  tonumber(io.read())
local z_pos = 0
local fuel_limit = 20000

local dump_to_chest
local find_fuel
local refuel
local try_down
local move_to_next_layer
local dig_forward
local dig_layer
local try_up
local excavate
local finished

dump_to_chest = function()
    -- dig above to ensure chest placement. Will continue to dig until detectUp() yields false.
    repeat
        turtle.digUp()
        sleep(0.6)
    until not turtle.detectUp()
    -- place Ender Chest
    turtle.select(1)
    turtle.placeUp()
    -- consume all fuel items up to max fuel limit
    refuel()
    -- dump to Ender Chest
    for slot = 2, 16 do
        turtle.select(slot)
        turtle.dropUp()
    end
    -- reclaim Ender Chest
    sleep(0.2)
    turtle.select(1)
    turtle.digUp()
end

-- Look for and consume fuel sources, starting with slot 2
find_fuel = function()
    for slot = 2, 16 do
        turtle.select(slot)
        if turtle.refuel(1) then
            return true
        end
    end
    return false
end

-- Consume all fuel in inventory up to max limit
refuel = function()
    while turtle.getFuelLevel() < fuel_limit do
        if not find_fuel() then
            break
        end
    end
    turtle.select(1)
end

-- handles detecting finished condition (bedrock) and digging, attacking while moving down
-- will return true if movement occurs, will return false if bedrock detected below
try_down = function()
    if not turtle.down() then -- try moving down, if you can't
        if turtle.detectDown() then -- check for a block, if there's a block
            if not turtle.digDown() then -- try digging it, if you can't dig it
                return false
            else
              return try_down() -- try moving down now
            end
        else -- attack until whatever is there is dead or moved
            while turtle.attackDown() do
                sleep(0.5)
            end
            return try_down() -- then move down
        end
    end
    z_pos = z_pos + 1
    return true
end

-- Proceed to mine next layer down
move_to_next_layer = function()
    down_count = 0
    for try = 1, 3 do -- try moving down three times
        if try_down() then
            down_count = down_count + 1
        end
    end
    if down_count == 0 or down_count == 1 then -- if it can't move down enough to dig, call completion function
        finished()
    else
        dig_layer()
    end
end

-- Dig and move forward, attacking and redigging if necessary
dig_forward = function()
    if turtle.detect() then -- dig if there's a block in front
        turtle.dig()
        if turtle.getItemCount(16) > 0 then
            dump_to_chest()
        end
    end
    if turtle.detectUp() then -- dig up if there's a block up
        turtle.digUp()
        if turtle.getItemCount(16) > 0 then
            dump_to_chest()
        end
    end
    if turtle.detectDown() then -- dig down if there's a block down
        turtle.digDown()
        if turtle.getItemCount(16) > 0 then
            dump_to_chest()
        end
    end
    while turtle.detect() do -- keep digging and waiting if there's gravel/sand in front
        turtle.dig()
        sleep(0.6)
    end
    if turtle.getItemCount(16) > 0 then
            dump_to_chest()
    end
    while not turtle.forward() do -- if you can't move forward it's because of mobs (probably)
        turtle.attack()
        turtle.dig()
        sleep(0.5)
    end
end

-- Dig a 6x6x3 layer
dig_layer = function()
    for j = 1, 3 do
        for i = 1, 5 do
            dig_forward()
        end
        turtle.turnRight()
    end
    dig_forward()
    turtle.turnRight()
    for i = 1, 4 do
        dig_forward()
    end
    turtle.turnLeft()
    dig_forward()
    turtle.turnLeft()
    for i = 1, 4 do
        dig_forward()
    end
    turtle.turnRight()
    dig_forward()
    turtle.turnRight()
    for i = 1, 4 do
        dig_forward()
    end
    turtle.turnLeft()
    dig_forward()
    turtle.turnLeft()
    for i = 1, 4 do
        dig_forward()
    end
    turtle.turnRight()
    dig_forward()
    turtle.turnRight()

    move_to_next_layer()
end

try_up = function()
    if not turtle.up() then -- try moving up, if you can't
        if turtle.detectUp() then -- check for a block, if there's a block
            if not turtle.digUp() then -- try digging it, if you can't dig it (shouldn't happen going up)
                return false
            else
              return try_up() -- try moving up now
            end
        else -- attack until whatever is there is dead or moved
            while turtle.attackUp() do
                sleep(0.5)
            end
            return try_up() -- then move up
        end
    end
    return true
end

excavate = function()
    -- move down twice to get below surface for first dig
    try_down()
    try_down()
    -- start digging, will keep moving to next layers
    dig_layer()
end

finished = function()
    --dump to chest
    dump_to_chest()
    -- move back to origin
    for i = 1, z_pos do
        try_up()
    end
    if max_excavations > 1 then
        max_excavations = max_excavations - 1
        -- move forward for next iteration
        for i = 1, 6 do
            dig_forward()
        end
        z_pos = 0
        excavate()
    end
    for i = 1, 6 do -- move forward to be at next starting point
        dig_forward()
    end
end

print("Fueling up!")
refuel()
print("Excavating...")
excavate()